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@c %**start of header
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@settitle GNU Guix Reference Manual
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@dircategory System administration
@direntry
* Guix: (guix).       Manage installed software and system configuration.
* guix package: (guix)Invoking guix package.  Installing, removing, and upgrading packages.
* guix gc: (guix)Invoking guix gc.            Reclaiming unused disk space.
* guix pull: (guix)Invoking guix pull.        Update the list of available packages.
* guix system: (guix)Invoking guix system.    Manage the operating system configuration.
* guix deploy: (guix)Invoking guix deploy.    Manage operating system configurations for remote hosts.
@end direntry

@dircategory Software development
@direntry
* guix shell: (guix)Invoking guix shell.      Creating software environments.
* guix environment: (guix)Invoking guix environment.  Building development environments with Guix.
* guix build: (guix)Invoking guix build.      Building packages.
* guix pack: (guix)Invoking guix pack.        Creating binary bundles.
@end direntry

@titlepage
@title GNU Guix Reference Manual
@subtitle Using the GNU Guix Functional Package Manager
@author The GNU Guix Developers

@page
@vskip 0pt plus 1filll
Edition @value{EDITION} @*
@value{UPDATED} @*

@insertcopying
@end titlepage

@contents

@c *********************************************************************
@node Top
@top GNU Guix

This document describes GNU Guix version @value{VERSION}, a functional
package management tool written for the GNU system.

@c TRANSLATORS: You can replace the following paragraph with information on
@c how to join your own translation team and how to report issues with the
@c translation.
This manual is also available in Simplified Chinese (@pxref{Top,,, guix.zh_CN,
GNU Guix参考手册}), French (@pxref{Top,,, guix.fr, Manuel de référence de GNU
Guix}), German (@pxref{Top,,, guix.de, Referenzhandbuch zu GNU Guix}),
Spanish (@pxref{Top,,, guix.es, Manual de referencia de GNU Guix}),
Brazilian Portuguese (@pxref{Top,,, guix.pt_BR, Manual de referência do
GNU Guix}), and Russian (@pxref{Top,,, guix.ru, Руководство GNU Guix}).  If you
would like to translate it in your native language, consider joining
@uref{https://translate.fedoraproject.org/projects/guix/documentation-manual,
Weblate} (@pxref{Translating Guix}).

@menu
* Introduction::                What is Guix about?
* Installation::                Installing Guix.
* System Installation::         Installing the whole operating system.
* Getting Started::             Your first steps.
* Package Management::          Package installation, upgrade, etc.
* Channels::                    Customizing the package collection.
* Development::                 Guix-aided software development.
* Programming Interface::       Using Guix in Scheme.
* Utilities::                   Package management commands.
* Foreign Architectures::       Build for foreign architectures.
* System Configuration::        Configuring the operating system.
* System Troubleshooting Tips::  When things don't go as planned.
* Home Configuration::          Configuring the home environment.
* Documentation::               Browsing software user manuals.
* Platforms::                   Defining platforms.
* System Images::               Creating system images.
* Installing Debugging Files::  Feeding the debugger.
* Using TeX and LaTeX::         Typesetting.
* Security Updates::            Deploying security fixes quickly.
* Bootstrapping::               GNU/Linux built from scratch.
* Porting::                     Targeting another platform or kernel.
* Contributing::                Your help needed!

* Acknowledgments::             Thanks!
* GNU Free Documentation License::  The license of this manual.
* Concept Index::               Concepts.
* Programming Index::           Data types, functions, and variables.

@detailmenu
 --- The Detailed Node Listing ---

Introduction

* Managing Software the Guix Way::  What's special.
* GNU Distribution::            The packages and tools.

Installation

* Binary Installation::         Getting Guix running in no time!
* Setting Up the Daemon::       Preparing the build daemon's environment.
* Invoking guix-daemon::        Running the build daemon.
* Application Setup::           Application-specific setup.
* Upgrading Guix::              Upgrading Guix and its build daemon.

Setting Up the Daemon

* Build Environment Setup::     Preparing the isolated build environment.
* Daemon Offload Setup::        Offloading builds to remote machines.
* SELinux Support::             Using an SELinux policy for the daemon.

System Installation

* Limitations::                 What you can expect.
* Hardware Considerations::     Supported hardware.
* USB Stick and DVD Installation::  Preparing the installation medium.
* Preparing for Installation::  Networking, partitioning, etc.
* Guided Graphical Installation::  Easy graphical installation.
* Manual Installation::         Manual installation for wizards.
* After System Installation::   When installation succeeded.
* Installing Guix in a VM::     Guix System playground.
* Building the Installation Image::  How this comes to be.

Manual Installation

* Keyboard Layout and Networking and Partitioning::  Initial setup.
* Proceeding with the Installation::  Installing.

Package Management

* Features::                    How Guix will make your life brighter.
* Invoking guix package::       Package installation, removal, etc.
* Substitutes::                 Downloading pre-built binaries.
* Packages with Multiple Outputs::  Single source package, multiple outputs.
* Invoking guix locate::        Locating packages that provide a file.
* Invoking guix gc::            Running the garbage collector.
* Invoking guix pull::          Fetching the latest Guix and distribution.
* Invoking guix time-machine::  Running an older revision of Guix.
* Inferiors::                   Interacting with another revision of Guix.
* Invoking guix describe::      Display information about your Guix revision.
* Invoking guix archive::       Exporting and importing store files.

Substitutes

* Official Substitute Servers::  One particular source of substitutes.
* Substitute Server Authorization::  How to enable or disable substitutes.
* Getting Substitutes from Other Servers::  Substitute diversity.
* Substitute Authentication::   How Guix verifies substitutes.
* Proxy Settings::              How to get substitutes via proxy.
* Substitution Failure::        What happens when substitution fails.
* On Trusting Binaries::        How can you trust that binary blob?

Channels

* Specifying Additional Channels::  Extending the package collection.
* Using a Custom Guix Channel::  Using a customized Guix.
* Replicating Guix::            Running the @emph{exact same} Guix.
* Channel Authentication::      How Guix verifies what it fetches.
* Channels with Substitutes::   Using channels with available substitutes.
* Creating a Channel::          How to write your custom channel.
* Package Modules in a Sub-directory::  Specifying the channel's package modules location.
* Declaring Channel Dependencies::  How to depend on other channels.
* Specifying Channel Authorizations::  Defining channel authors authorizations.
* Primary URL::                 Distinguishing mirror to original.
* Writing Channel News::        Communicating information to channel's users.

Development

* Invoking guix shell::         Spawning one-off software environments.
* Invoking guix environment::   Setting up development environments.
* Invoking guix pack::          Creating software bundles.
* The GCC toolchain::           Working with languages supported by GCC.
* Invoking guix git authenticate::  Authenticating Git repositories.

Programming Interface

* Package Modules::             Packages from the programmer's viewpoint.
* Defining Packages::           Defining new packages.
* Defining Package Variants::   Customizing packages.
* Writing Manifests::           The bill of materials of your environment.
* Build Systems::               Specifying how packages are built.
* Build Phases::                Phases of the build process of a package.
* Build Utilities::             Helpers for your package definitions and more.
* Search Paths::                Declaring search path environment variables.
* The Store::                   Manipulating the package store.
* Derivations::                 Low-level interface to package derivations.
* The Store Monad::             Purely functional interface to the store.
* G-Expressions::               Manipulating build expressions.
* Invoking guix repl::          Programming Guix in Guile
* Using Guix Interactively::    Fine-grain interaction at the REPL.

Defining Packages

* package Reference::           The package data type.
* origin Reference::            The origin data type.

Utilities

* Invoking guix build::         Building packages from the command line.
* Invoking guix edit::          Editing package definitions.
* Invoking guix download::      Downloading a file and printing its hash.
* Invoking guix hash::          Computing the cryptographic hash of a file.
* Invoking guix import::        Importing package definitions.
* Invoking guix refresh::       Updating package definitions.
* Invoking guix style::         Styling package definitions.
* Invoking guix lint::          Finding errors in package definitions.
* Invoking guix size::          Profiling disk usage.
* Invoking guix graph::         Visualizing the graph of packages.
* Invoking guix publish::       Sharing substitutes.
* Invoking guix challenge::     Challenging substitute servers.
* Invoking guix copy::          Copying to and from a remote store.
* Invoking guix container::     Process isolation.
* Invoking guix weather::       Assessing substitute availability.
* Invoking guix processes::     Listing client processes.

Invoking @command{guix build}

* Common Build Options::        Build options for most commands.
* Package Transformation Options::  Creating variants of packages.
* Additional Build Options::    Options specific to 'guix build'.
* Debugging Build Failures::    Real life packaging experience.

Foreign Architectures

* Cross-Compilation::           Cross-compiling for another architecture.
* Native Builds::               Targeting another architecture through native builds.

System Configuration

* Getting Started with the System::  Your first steps.
* Using the Configuration System::  Customizing your GNU system.
* operating-system Reference::  Detail of operating-system declarations.
* File Systems::                Configuring file system mounts.
* Mapped Devices::              Block device extra processing.
* Swap Space::                  Backing RAM with disk space.
* User Accounts::               Specifying user accounts.
* Keyboard Layout::             How the system interprets key strokes.
* Locales::                     Language and cultural convention settings.
* Services::                    Specifying system services.
* Privileged Programs::         Programs running with elevated privileges.
* X.509 Certificates::          Authenticating HTTPS servers.
* Name Service Switch::         Configuring libc's name service switch.
* Initial RAM Disk::            Linux-Libre bootstrapping.
* Bootloader Configuration::    Configuring the boot loader.
* Invoking guix system::        Instantiating a system configuration.
* Invoking guix deploy::        Deploying a system configuration to a remote host.
* Running Guix in a VM::        How to run Guix System in a virtual machine.
* Defining Services::           Adding new service definitions.

File Systems

* Btrfs file system::

Services

* Base Services::               Essential system services.
* Scheduled Job Execution::     The mcron service.
* Log Rotation::                The rottlog service.
* Networking Setup::            Setting up network interfaces.
* Networking Services::         Firewall, SSH daemon, etc.
* Unattended Upgrades::         Automated system upgrades.
* X Window::                    Graphical display.
* Printing Services::           Local and remote printer support.
* Desktop Services::            D-Bus and desktop services.
* Sound Services::              ALSA and Pulseaudio services.
* File Search Services::        Tools to search for files.
* Database Services::           SQL databases, key-value stores, etc.
* Mail Services::               IMAP, POP3, SMTP, and all that.
* Messaging Services::          Messaging services.
* Telephony Services::          Telephony services.
* File-Sharing Services::       File-sharing services.
* Monitoring Services::         Monitoring services.
* Kerberos Services::           Kerberos services.
* LDAP Services::               LDAP services.
* Web Services::                Web servers.
* Certificate Services::        TLS certificates via Let's Encrypt.
* DNS Services::                DNS daemons.
* VNC Services::                VNC daemons.
* VPN Services::                VPN daemons.
* Network File System::         NFS related services.
* Samba Services::              Samba services.
* Continuous Integration::      Cuirass and Laminar services.
* Power Management Services::   Extending battery life.
* Audio Services::              The MPD.
* Virtualization Services::     Virtualization services.
* Version Control Services::    Providing remote access to Git repositories.
* Game Services::               Game servers.
* PAM Mount Service::           Service to mount volumes when logging in.
* Guix Services::               Services relating specifically to Guix.
* Linux Services::              Services tied to the Linux kernel.
* Hurd Services::               Services specific for a Hurd System.
* Miscellaneous Services::      Other services.

Defining Services

* Service Composition::         The model for composing services.
* Service Types and Services::  Types and services.
* Service Reference::           API reference.
* Shepherd Services::           A particular type of service.
* Complex Configurations::      Defining bindings for complex configurations.

System Troubleshooting Tips

* Chrooting into an existing system::

Home Configuration

* Declaring the Home Environment::  Customizing your Home.
* Configuring the Shell::       Enabling home environment.
* Home Services::               Specifying home services.
* Invoking guix home::          Instantiating a home configuration.

Home Services

* Essential Home Services::     Environment variables, packages, on-* scripts.
* Shells: Shells Home Services.  POSIX shells, Bash, Zsh.
* Mcron: Mcron Home Service.    Scheduled User's Job Execution.
* Power Management: Power Management Home Services.  Services for battery power.
* Shepherd: Shepherd Home Service.  Managing User's Daemons.
* SSH: Secure Shell.            Setting up the secure shell client.
* GPG: GNU Privacy Guard.       Setting up GPG and related tools.
* Desktop: Desktop Home Services.  Services for graphical environments.
* Guix: Guix Home Services.     Services for Guix.
* Fonts: Fonts Home Services.   Services for managing User's fonts.
* Sound: Sound Home Services.   Dealing with audio.
* Mail: Mail Home Services.     Services for managing mail.
* Messaging: Messaging Home Services.  Services for managing messaging.
* Media: Media Home Services.   Services for managing media.
* Networking: Networking Home Services.  Networking services.
* Miscellaneous: Miscellaneous Home Services.  More services.

Platforms

* platform Reference::          Detail of platform declarations.
* Supported Platforms::         Description of the supported platforms.

Creating System Images

* image Reference::             Detail of image declarations.
* Instantiate an Image::        How to instantiate an image record.
* image-type Reference::        Detail of image types declaration.
* Image Modules::               Definition of image modules.

@code{image} Reference

* partition Reference::

Installing Debugging Files

* Separate Debug Info::         Installing 'debug' outputs.
* Rebuilding Debug Info::       Building missing debug info.

Bootstrapping

* Full-Source Bootstrap::       A Bootstrap worthy of GNU.
* Preparing to Use the Bootstrap Binaries::  Building that what matters most.

@end detailmenu
@end menu

@c *********************************************************************
@node Introduction
@chapter Introduction

@cindex purpose
GNU Guix@footnote{``Guix'' is pronounced like ``geeks'', or ``ɡiːks''
using the international phonetic alphabet (IPA).} is a package
management tool for and distribution of the GNU system.
Guix makes it easy for unprivileged
users to install, upgrade, or remove software packages, to roll back to a
previous package set, to build packages from source, and generally
assists with the creation and maintenance of software environments.

@cindex Guix System
@cindex GuixSD, now Guix System
@cindex Guix System Distribution, now Guix System
You can install GNU@tie{}Guix on top of an existing GNU/Linux system where it
complements the available tools without interference (@pxref{Installation}),
or you can use it as a standalone operating system distribution,
@dfn{Guix@tie{}System}@footnote{We used to refer to Guix System as ``Guix
System Distribution'' or ``GuixSD''.  We now consider it makes more sense to
group everything under the ``Guix'' banner since, after all, Guix System is
readily available through the @command{guix system} command, even if you're
using a different distro underneath!}.  @xref{GNU Distribution}.

@menu
* Managing Software the Guix Way::  What's special.
* GNU Distribution::            The packages and tools.
@end menu

@node Managing Software the Guix Way
@section Managing Software the Guix Way

@cindex user interfaces
Guix provides a command-line package management interface
(@pxref{Package Management}), tools to help with software development
(@pxref{Development}), command-line utilities for more advanced usage
(@pxref{Utilities}), as well as Scheme programming interfaces
(@pxref{Programming Interface}).
@cindex build daemon
Its @dfn{build daemon} is responsible for building packages on behalf of
users (@pxref{Setting Up the Daemon}) and for downloading pre-built
binaries from authorized sources (@pxref{Substitutes}).

@cindex extensibility of the distribution
@cindex customization, of packages
Guix includes package definitions for many GNU and non-GNU packages, all
of which @uref{https://www.gnu.org/philosophy/free-sw.html, respect the
user's computing freedom}.  It is @emph{extensible}: users can write
their own package definitions (@pxref{Defining Packages}) and make them
available as independent package modules (@pxref{Package Modules}).  It
is also @emph{customizable}: users can @emph{derive} specialized package
definitions from existing ones, including from the command line
(@pxref{Package Transformation Options}).

@cindex functional package management
@cindex isolation
Under the hood, Guix implements the @dfn{functional package management}
discipline pioneered by Nix (@pxref{Acknowledgments}).
In Guix, the package build and installation process is seen
as a @emph{function}, in the mathematical sense.  That function takes inputs,
such as build scripts, a compiler, and libraries, and
returns an installed package.  As a pure function, its result depends
solely on its inputs---for instance, it cannot refer to software or
scripts that were not explicitly passed as inputs.  A build function
always produces the same result when passed a given set of inputs.  It
cannot alter the environment of the running system in
any way; for instance, it cannot create, modify, or delete files outside
of its build and installation directories.  This is achieved by running
build processes in isolated environments (or @dfn{containers}), where only their
explicit inputs are visible.

@cindex store
The result of package build functions is @dfn{cached} in the file
system, in a special directory called @dfn{the store} (@pxref{The
Store}).  Each package is installed in a directory of its own in the
store---by default under @file{/gnu/store}.  The directory name contains
a hash of all the inputs used to build that package; thus, changing an
input yields a different directory name.

This approach is the foundation for the salient features of Guix: support
for transactional package upgrade and rollback, per-user installation, and
garbage collection of packages (@pxref{Features}).


@node GNU Distribution
@section GNU Distribution

@cindex Guix System
Guix comes with a distribution of the GNU system consisting entirely of
free software@footnote{The term ``free'' here refers to the
@url{https://www.gnu.org/philosophy/free-sw.html,freedom provided to
users of that software}.}.  The
distribution can be installed on its own (@pxref{System Installation}),
but it is also possible to install Guix as a package manager on top of
an installed GNU/Linux system (@pxref{Installation}).  When we need to
distinguish between the two, we refer to the standalone distribution as
Guix@tie{}System.

The distribution provides core GNU packages such as GNU libc, GCC, and
Binutils, as well as many GNU and non-GNU applications.  The complete
list of available packages can be browsed
@url{https://www.gnu.org/software/guix/packages,on-line} or by
running @command{guix package} (@pxref{Invoking guix package}):

@example
guix package --list-available
@end example

Our goal is to provide a practical 100% free software distribution of
Linux-based and other variants of GNU, with a focus on the promotion and
tight integration of GNU components, and an emphasis on programs and
tools that help users exert that freedom.

Packages are currently available on the following platforms:

@table @code

@item x86_64-linux
Intel/AMD @code{x86_64} architecture, Linux-Libre kernel.

@item i686-linux
Intel 32-bit architecture (IA32), Linux-Libre kernel.

@item armhf-linux
ARMv7-A architecture with hard float, Thumb-2 and NEON,
using the EABI hard-float application binary interface (ABI),
and Linux-Libre kernel.

@item aarch64-linux
little-endian 64-bit ARMv8-A processors, Linux-Libre kernel.

@item i586-gnu
@uref{https://hurd.gnu.org, GNU/Hurd} on the Intel 32-bit architecture
(IA32).

This configuration is experimental and under development.  The easiest
way for you to give it a try is by setting up an instance of
@code{hurd-vm-service-type} on your GNU/Linux machine
(@pxref{transparent-emulation-qemu, @code{hurd-vm-service-type}}).
@xref{Contributing}, on how to help!

@item mips64el-linux (unsupported)
little-endian 64-bit MIPS processors, specifically the Loongson series,
n32 ABI, and Linux-Libre kernel.  This configuration is no longer fully
supported; in particular, there is no ongoing work to ensure that this
architecture still works.  Should someone decide they wish to revive this
architecture then the code is still available.

@item powerpc-linux (unsupported)
big-endian 32-bit PowerPC processors, specifically the PowerPC G4 with
AltiVec support, and Linux-Libre kernel.  This configuration is not
fully supported and there is no ongoing work to ensure this architecture
works.

@item powerpc64le-linux
little-endian 64-bit Power ISA processors, Linux-Libre kernel.  This
includes POWER9 systems such as the
@uref{https://www.fsf.org/news/talos-ii-mainboard-and-talos-ii-lite-mainboard-now-fsf-certified-to-respect-your-freedom,
RYF Talos II mainboard}. This platform is available as a "technology
preview": although it is supported, substitutes are not yet available
from the build farm (@pxref{Substitutes}), and some packages may fail to
build (@pxref{Tracking Bugs and Changes}).  That said, the Guix
community is actively working on improving this support, and now is a
great time to try it and get involved!

@item riscv64-linux
little-endian 64-bit RISC-V processors, specifically RV64GC, and
Linux-Libre kernel. This platform is available as a "technology
preview": although it is supported, substitutes are not yet available
from the build farm (@pxref{Substitutes}), and some packages may fail to
build (@pxref{Tracking Bugs and Changes}).  That said, the Guix
community is actively working on improving this support, and now is a
great time to try it and get involved!

@end table

With Guix@tie{}System, you @emph{declare} all aspects of the operating system
configuration and Guix takes care of instantiating the configuration in a
transactional, reproducible, and stateless fashion (@pxref{System
Configuration}).  Guix System uses the Linux-libre kernel, the Shepherd
initialization system (@pxref{Introduction,,, shepherd, The GNU Shepherd
Manual}), the well-known GNU utilities and tool chain, as well as the
graphical environment or system services of your choice.

Guix System is available on all the above platforms except
@code{mips64el-linux}, @code{powerpc-linux}, @code{powerpc64le-linux} and
@code{riscv64-linux}.

@noindent
For information on porting to other architectures or kernels,
@pxref{Porting}.

Building this distribution is a cooperative effort, and you are invited
to join!  @xref{Contributing}, for information about how you can help.


@c *********************************************************************
@node Installation
@chapter Installation

@cindex installing Guix
@cindex foreign distro
@cindex Guix System
You can install the package management tool Guix on top of an existing
GNU/Linux or GNU/Hurd system@footnote{Hurd support is currently
limited.}, referred to as a @dfn{foreign distro}.  If, instead, you want
to install the complete, standalone GNU system distribution,
@dfn{Guix@tie{}System}, @pxref{System Installation}.  This section is
concerned only with the installation of Guix on a foreign distro.

@quotation Important
This section only applies to systems without Guix.  Following it for
existing Guix installations will overwrite important system files.
@end quotation

@cindex directories related to foreign distro
When installed on a foreign distro, GNU@tie{}Guix complements the available
tools without interference.  Its data lives exclusively in two directories,
usually @file{/gnu/store} and @file{/var/guix}; other files on your system,
such as @file{/etc}, are left untouched.

Once installed, Guix can be updated by running @command{guix pull}
(@pxref{Invoking guix pull}).

@menu
* Binary Installation::         Getting Guix running in no time!
* Setting Up the Daemon::       Preparing the build daemon's environment.
* Invoking guix-daemon::        Running the build daemon.
* Application Setup::           Application-specific setup.
* Upgrading Guix::              Upgrading Guix and its build daemon.
@end menu

@node Binary Installation
@section Binary Installation

@cindex installing Guix from binaries
@cindex installer script
This section describes how to install Guix from a self-contained tarball
providing binaries for Guix and for all its dependencies.  This is often
quicker than installing from source, described later (@pxref{Building
from Git}).

@quotation Important
This section only applies to systems without Guix.  Following it for
existing Guix installations will overwrite important system files.
@end quotation

Some GNU/Linux distributions, such as Debian, Ubuntu, and openSUSE
provide Guix through their own package managers.  The version of Guix
may be older than @value{VERSION} but you can update it afterwards by
running @samp{guix pull}.

We advise system administrators who install Guix, both from the
installation script or @i{via} the native package manager of their
foreign distribution, to also regularly read and follow security
notices, as shown by @command{guix pull}.

For Debian or derivatives such as Ubuntu or Trisquel, call:

@example
sudo apt install guix
@end example

Likewise, on openSUSE:

@example
sudo zypper install guix
@end example

If you are running Parabola, after enabling the pcr (Parabola
Community Repo) repository, you can install Guix with:
@example
sudo pacman -S guix
@end example

The Guix project also provides a shell script, @file{guix-install.sh},
which automates the binary installation process without use of a foreign
distro package
manager@footnote{@uref{https://git.savannah.gnu.org/cgit/guix.git/plain/etc/guix-install.sh}}.
Use of @file{guix-install.sh} requires Bash, GnuPG, GNU@tie{}tar, wget,
and Xz.

The script guides you through the following:

@itemize
@item Downloading and extracting the binary tarball
@item Setting up the build daemon
@item Making the ‘guix’ command available to non-root users
@item Configuring substitute servers
@end itemize

As root, run:

@example
# cd /tmp
# wget https://git.savannah.gnu.org/cgit/guix.git/plain/etc/guix-install.sh
# chmod +x guix-install.sh
# ./guix-install.sh
@end example

The script to install Guix is also packaged in Parabola (in the pcr
repository). You can install and run it with:
@example
sudo pacman -S guix-installer
sudo guix-install.sh
@end example

@quotation Note
By default, @file{guix-install.sh} will configure Guix to download
pre-built package binaries, called @dfn{substitutes}
(@pxref{Substitutes}), from the project's build farms.  If you choose
not to permit this, Guix will build @emph{everything} from source,
making each installation and upgrade very expensive.  @xref{On Trusting
Binaries} for a discussion of why you may want to build packages from
source.

@cindex substitutes, authorization thereof
To use substitutes from @code{@value{SUBSTITUTE-SERVER-1}},
@code{@value{SUBSTITUTE-SERVER-2}} or a mirror, you must authorize them.
For example,

@example
# guix archive --authorize < \
     ~root/.config/guix/current/share/guix/@value{SUBSTITUTE-SERVER-1}.pub
# guix archive --authorize < \
     ~root/.config/guix/current/share/guix/@value{SUBSTITUTE-SERVER-2}.pub
@end example
@end quotation

When you're done installing Guix, @pxref{Application Setup} for extra
configuration you might need, and @ref{Getting Started} for your first
steps!

@quotation Note
The binary installation tarball can be (re)produced and verified simply
by running the following command in the Guix source tree:

@example
make guix-binary.@var{system}.tar.xz
@end example

@noindent
...@: which, in turn, runs:

@example
guix pack -s @var{system} --localstatedir \
  --profile-name=current-guix guix
@end example

@xref{Invoking guix pack}, for more info on this handy tool.
@end quotation

@cindex uninstalling Guix
@cindex uninstallation, of Guix
Should you eventually want to uninstall Guix, run the same script with
the @option{--uninstall} flag:

@example
./guix-install.sh --uninstall
@end example

With @option{--uninstall}, the script irreversibly deletes all the Guix
files, configuration, and services.

@node Setting Up the Daemon
@section Setting Up the Daemon

@cindex daemon
During installation, the @dfn{build daemon} that must be running
to use Guix has already been set up and you can run @command{guix}
commands in your terminal program, @pxref{Getting Started}:

@example
guix build hello
@end example

If this runs through without error, feel free to skip this section.
You should continue with the following section, @ref{Application
Setup}.

However, now would be a good time to replace outdated daemon versions,
tweak it, perform builds on other machines (@pxref{Daemon Offload
Setup}), or start it manually in special environments like ``chroots''
(@pxref{Chrooting into an existing system}) or WSL (not needed for WSL
images created with Guix, @pxref{System Images,
@code{wsl2-image-type}}).  If you want to know more or optimize your
system, this section is worth reading.

Operations such as building a package or running the garbage collector
are all performed by a specialized process, the build daemon, on
behalf of clients.  Only the daemon may access the store and its
associated database.  Thus, any operation that manipulates the store
goes through the daemon.  For instance, command-line tools such as
@command{guix package} and @command{guix build} communicate with the
daemon (@i{via} remote procedure calls) to instruct it what to do.

The following sections explain how to prepare the build daemon's
environment.  @xref{Substitutes} for how to allow the daemon to download
pre-built binaries.

@menu
* Build Environment Setup::     Preparing the isolated build environment.
* Daemon Offload Setup::        Offloading builds to remote machines.
* SELinux Support::             Using an SELinux policy for the daemon.
@end menu

@node Build Environment Setup
@subsection Build Environment Setup

@cindex build environment
In a standard multi-user setup, Guix and its daemon---the
@command{guix-daemon} program---are installed by the system
administrator; @file{/gnu/store} is owned by @code{root} and
@command{guix-daemon} runs as @code{root}.  Unprivileged users may use
Guix tools to build packages or otherwise access the store, and the
daemon will do it on their behalf, ensuring that the store is kept in a
consistent state, and allowing built packages to be shared among users.

@cindex build users
When @command{guix-daemon} runs as @code{root}, you may not want package
build processes themselves to run as @code{root} too, for obvious
security reasons.  To avoid that, a special pool of @dfn{build users}
should be created for use by build processes started by the daemon.
These build users need not have a shell and a home directory: they will
just be used when the daemon drops @code{root} privileges in build
processes.  Having several such users allows the daemon to launch
distinct build processes under separate UIDs, which guarantees that they
do not interfere with each other---an essential feature since builds are
regarded as pure functions (@pxref{Introduction}).

On a GNU/Linux system, a build user pool may be created like this (using
Bash syntax and the @code{shadow} commands):

@c See https://lists.gnu.org/archive/html/bug-guix/2013-01/msg00239.html
@c for why `-G' is needed.
@example
# groupadd --system guixbuild
# for i in $(seq -w 1 10);
  do
    useradd -g guixbuild -G guixbuild           \
            -d /var/empty -s $(which nologin)   \
            -c "Guix build user $i" --system    \
            guixbuilder$i;
  done
@end example

@noindent
The number of build users determines how many build jobs may run in
parallel, as specified by the @option{--max-jobs} option
(@pxref{Invoking guix-daemon, @option{--max-jobs}}).  To use
@command{guix system vm} and related commands, you may need to add the
build users to the @code{kvm} group so they can access @file{/dev/kvm},
using @code{-G guixbuild,kvm} instead of @code{-G guixbuild}
(@pxref{Invoking guix system}).

The @code{guix-daemon} program may then be run as @code{root} with the
following command@footnote{If your machine uses the systemd init system,
copying the @file{@var{prefix}/lib/systemd/system/guix-daemon.service}
file to @file{/etc/systemd/system} will ensure that
@command{guix-daemon} is automatically started.  Similarly, if your
machine uses the Upstart init system, copy the
@file{@var{prefix}/lib/upstart/system/guix-daemon.conf}
file to @file{/etc/init}.}:

@example
# guix-daemon --build-users-group=guixbuild
@end example

@cindex chroot
@noindent
This way, the daemon starts build processes in a chroot, under one of
the @code{guixbuilder} users.  On GNU/Linux, by default, the chroot
environment contains nothing but:

@c Keep this list in sync with libstore/build.cc! -----------------------
@itemize
@item
a minimal @code{/dev} directory, created mostly independently from the
host @code{/dev}@footnote{``Mostly'', because while the set of files
that appear in the chroot's @code{/dev} is fixed, most of these files
can only be created if the host has them.};

@item
the @code{/proc} directory; it only shows the processes of the container
since a separate PID name space is used;

@item
@file{/etc/passwd} with an entry for the current user and an entry for
user @file{nobody};

@item
@file{/etc/group} with an entry for the user's group;

@item
@file{/etc/hosts} with an entry that maps @code{localhost} to
@code{127.0.0.1};

@item
a writable @file{/tmp} directory.
@end itemize

The chroot does not contain a @file{/home} directory, and the @env{HOME}
environment variable is set to the non-existent
@file{/homeless-shelter}.  This helps to highlight inappropriate uses of
@env{HOME} in the build scripts of packages.

All this usually enough to ensure details of the environment do not
influence build processes.  In some exceptional cases where more control
is needed---typically over the date, kernel, or CPU---you can resort to
a virtual build machine (@pxref{build-vm, virtual build machines}).

You can influence the directory where the daemon stores build trees
@i{via} the @env{TMPDIR} environment variable.  However, the build tree
within the chroot is always called @file{/tmp/guix-build-@var{name}.drv-0},
where @var{name} is the derivation name---e.g., @code{coreutils-8.24}.
This way, the value of @env{TMPDIR} does not leak inside build
environments, which avoids discrepancies in cases where build processes
capture the name of their build tree.

@vindex http_proxy
@vindex https_proxy
The daemon also honors the @env{http_proxy} and @env{https_proxy}
environment variables for HTTP and HTTPS downloads it performs, be it
for fixed-output derivations (@pxref{Derivations}) or for substitutes
(@pxref{Substitutes}).

If you are installing Guix as an unprivileged user, it is still possible
to run @command{guix-daemon} provided you pass @option{--disable-chroot}.
However, build processes will not be isolated from one another, and not
from the rest of the system.  Thus, build processes may interfere with
each other, and may access programs, libraries, and other files
available on the system---making it much harder to view them as
@emph{pure} functions.


@node Daemon Offload Setup
@subsection Using the Offload Facility

@cindex offloading
@cindex build hook
When desired, the build daemon can @dfn{offload} derivation builds to
other machines running Guix, using the @code{offload} @dfn{build
hook}@footnote{This feature is available only when
@uref{https://github.com/artyom-poptsov/guile-ssh, Guile-SSH} is
present.}.  When that feature is enabled, a list of user-specified build
machines is read from @file{/etc/guix/machines.scm}; every time a build
is requested, for instance via @code{guix build}, the daemon attempts to
offload it to one of the machines that satisfy the constraints of the
derivation, in particular its system types---e.g., @code{x86_64-linux}.
A single machine can have multiple system types, either because its
architecture natively supports it, via emulation
(@pxref{transparent-emulation-qemu, Transparent Emulation with QEMU}),
or both.  Missing prerequisites for the build are
copied over SSH to the target machine, which then proceeds with the
build; upon success the output(s) of the build are copied back to the
initial machine.  The offload facility comes with a basic scheduler that
attempts to select the best machine.  The best machine is chosen among
the available machines based on criteria such as:

@enumerate
@item
The availability of a build slot.  A build machine can have as many
build slots (connections) as the value of the @code{parallel-builds}
field of its @code{build-machine} object.

@item
Its relative speed, as defined via the @code{speed} field of its
@code{build-machine} object.

@item
Its load.  The normalized machine load must be lower than a threshold
value, configurable via the @code{overload-threshold} field of its
@code{build-machine} object.

@item
Disk space availability.  More than a 100 MiB must be available.
@end enumerate

The @file{/etc/guix/machines.scm} file typically looks like this:

@lisp
(list (build-machine
        (name "eightysix.example.org")
        (systems (list "x86_64-linux" "i686-linux"))
        (host-key "ssh-ed25519 AAAAC3Nza@dots{}")
        (user "bob")
        (speed 2.))     ;incredibly fast!

      (build-machine
        (name "armeight.example.org")
        (systems (list "aarch64-linux"))
        (host-key "ssh-rsa AAAAB3Nza@dots{}")
        (user "alice")

        ;; Remember 'guix offload' is spawned by
        ;; 'guix-daemon' as root.
        (private-key "/root/.ssh/identity-for-guix")))
@end lisp

@noindent
In the example above we specify a list of two build machines, one for
the @code{x86_64} and @code{i686} architectures and one for the
@code{aarch64} architecture.

In fact, this file is---not surprisingly!---a Scheme file that is
evaluated when the @code{offload} hook is started.  Its return value
must be a list of @code{build-machine} objects.  While this example
shows a fixed list of build machines, one could imagine, say, using
DNS-SD to return a list of potential build machines discovered in the
local network (@pxref{Introduction, Guile-Avahi,, guile-avahi, Using
Avahi in Guile Scheme Programs}).  The @code{build-machine} data type is
detailed below.

@deftp {Data Type} build-machine
This data type represents build machines to which the daemon may offload
builds.  The important fields are:

@table @code

@item name
The host name of the remote machine.

@item systems
The system types the remote machine supports---e.g., @code{(list
"x86_64-linux" "i686-linux")}.

@item user
The user account on the remote machine to use when connecting over SSH.
Note that the SSH key pair must @emph{not} be passphrase-protected, to
allow non-interactive logins.

@item host-key
This must be the machine's SSH @dfn{public host key} in OpenSSH format.
This is used to authenticate the machine when we connect to it.  It is a
long string that looks like this:

@example
ssh-ed25519 AAAAC3NzaC@dots{}mde+UhL hint@@example.org
@end example

If the machine is running the OpenSSH daemon, @command{sshd}, the host
key can be found in a file such as
@file{/etc/ssh/ssh_host_ed25519_key.pub}.

If the machine is running the SSH daemon of GNU@tie{}lsh,
@command{lshd}, the host key is in @file{/etc/lsh/host-key.pub} or a
similar file.  It can be converted to the OpenSSH format using
@command{lsh-export-key} (@pxref{Converting keys,,, lsh, LSH Manual}):

@example
$ lsh-export-key --openssh < /etc/lsh/host-key.pub
ssh-rsa AAAAB3NzaC1yc2EAAAAEOp8FoQAAAQEAs1eB46LV@dots{}
@end example

@end table

A number of optional fields may be specified:

@table @asis

@item @code{port} (default: @code{22})
Port number of SSH server on the machine.

@item @code{private-key} (default: @file{~root/.ssh/id_rsa})
The SSH private key file to use when connecting to the machine, in
OpenSSH format.  This key must not be protected with a passphrase.

Note that the default value is the private key @emph{of the root
account}.  Make sure it exists if you use the default.

@item @code{compression} (default: @code{"zlib@@openssh.com,zlib"})
@itemx @code{compression-level} (default: @code{3})
The SSH-level compression methods and compression level requested.

Note that offloading relies on SSH compression to reduce bandwidth usage
when transferring files to and from build machines.

@item @code{daemon-socket} (default: @code{"/var/guix/daemon-socket/socket"})
File name of the Unix-domain socket @command{guix-daemon} is listening
to on that machine.

@item @code{overload-threshold} (default: @code{0.8})
The load threshold above which a potential offload machine is
disregarded by the offload scheduler.  The value roughly translates to
the total processor usage of the build machine, ranging from 0.0 (0%) to
1.0 (100%).  It can also be disabled by setting
@code{overload-threshold} to @code{#f}.

@item @code{parallel-builds} (default: @code{1})
The number of builds that may run in parallel on the machine.

@item @code{speed} (default: @code{1.0})
A ``relative speed factor''.  The offload scheduler will tend to prefer
machines with a higher speed factor.

@item @code{features} (default: @code{'()})
A list of strings denoting specific features supported by the machine.
An example is @code{"kvm"} for machines that have the KVM Linux modules
and corresponding hardware support.  Derivations can request features by
name, and they will be scheduled on matching build machines.

@end table
@end deftp

@quotation Note
On Guix System, instead of managing @file{/etc/guix/machines.scm}
independently, you can choose to specify build machines directly in the
@code{operating-system} declaration, in the @code{build-machines} field
of @code{guix-configuration}.  @xref{guix-configuration-build-machines,
@code{build-machines} field of @code{guix-configuration}}.
@end quotation

The @command{guix} command must be in the search path on the build
machines.  You can check whether this is the case by running:

@example
ssh build-machine guix repl --version
@end example

There is one last thing to do once @file{machines.scm} is in place.  As
explained above, when offloading, files are transferred back and forth
between the machine stores.  For this to work, you first need to
generate a key pair on each machine to allow the daemon to export signed
archives of files from the store (@pxref{Invoking guix archive}):

@example
# guix archive --generate-key
@end example

@quotation Note
This key pair is not related to the SSH key pair that was previously
mentioned in the description of the @code{build-machine} data type.
@end quotation

@noindent
Each build machine must authorize the key of the master machine so that
it accepts store items it receives from the master:

@example
# guix archive --authorize < master-public-key.txt
@end example

@noindent
Likewise, the master machine must authorize the key of each build machine.

All the fuss with keys is here to express pairwise mutual trust
relations between the master and the build machines.  Concretely, when
the master receives files from a build machine (and @i{vice versa}), its
build daemon can make sure they are genuine, have not been tampered
with, and that they are signed by an authorized key.

@cindex offload test
To test whether your setup is operational, run this command on the
master node:

@example
# guix offload test
@end example

This will attempt to connect to each of the build machines specified in
@file{/etc/guix/machines.scm}, make sure Guix is
available on each machine, attempt to export to the machine and import
from it, and report any error in the process.

If you want to test a different machine file, just specify it on the
command line:

@example
# guix offload test machines-qualif.scm
@end example

Last, you can test the subset of the machines whose name matches a
regular expression like this:

@example
# guix offload test machines.scm '\.gnu\.org$'
@end example

@cindex offload status
To display the current load of all build hosts, run this command on the
main node:

@example
# guix offload status
@end example


@node SELinux Support
@subsection SELinux Support

@cindex SELinux, daemon policy
@cindex mandatory access control, SELinux
@cindex security, guix-daemon
Guix includes an SELinux policy file at @file{etc/guix-daemon.cil} that
can be installed on a system where SELinux is enabled, in order to label
Guix files and to specify the expected behavior of the daemon.  Since
Guix System does not provide an SELinux base policy, the daemon policy cannot
be used on Guix System.

@subsubsection Installing the SELinux policy
@cindex SELinux, policy installation

@quotation Note
The @code{guix-install.sh} binary installation script offers to perform
the steps below for you (@pxref{Binary Installation}).
@end quotation

To install the policy run this command as root:

@example
semodule -i /var/guix/profiles/per-user/root/current-guix/share/selinux/guix-daemon.cil
@end example

Then, as root, relabel the file system, possibly after making it
writable:

@example
mount -o remount,rw /gnu/store
restorecon -R /gnu /var/guix
@end example

At this point you can start or restart @command{guix-daemon}; on a
distribution that uses systemd as its service manager, you can do that
with:

@example
systemctl restart guix-daemon
@end example

Once the policy is installed, the file system has been relabeled, and
the daemon has been restarted, it should be running in the
@code{guix_daemon_t} context.  You can confirm this with the following
command:

@example
ps -Zax | grep guix-daemon
@end example

Monitor the SELinux log files as you run a command like @code{guix build
hello} to convince yourself that SELinux permits all necessary
operations.

@subsubsection Limitations
@cindex SELinux, limitations

This policy is not perfect.  Here is a list of limitations or quirks
that should be considered when deploying the provided SELinux policy for
the Guix daemon.

@enumerate
@item
@code{guix_daemon_socket_t} isn’t actually used.  None of the socket
operations involve contexts that have anything to do with
@code{guix_daemon_socket_t}.  It doesn’t hurt to have this unused label,
but it would be preferable to define socket rules for only this label.

@item
@code{guix gc} cannot access arbitrary links to profiles.  By design,
the file label of the destination of a symlink is independent of the
file label of the link itself.  Although all profiles under
@file{$localstatedir} are labelled, the links to these profiles inherit the
label of the directory they are in.  For links in the user’s home
directory this will be @code{user_home_t}.  But for links from the root
user’s home directory, or @file{/tmp}, or the HTTP server’s working
directory, etc, this won’t work.  @code{guix gc} would be prevented from
reading and following these links.

@item
The daemon’s feature to listen for TCP connections might no longer work.
This might require extra rules, because SELinux treats network sockets
differently from files.

@item
Currently all files with a name matching the regular expression
@code{/gnu/store/.+-(guix-.+|profile)/bin/guix-daemon} are assigned the
label @code{guix_daemon_exec_t}; this means that @emph{any} file with
that name in any profile would be permitted to run in the
@code{guix_daemon_t} domain.  This is not ideal.  An attacker could
build a package that provides this executable and convince a user to
install and run it, which lifts it into the @code{guix_daemon_t} domain.
At that point SELinux could not prevent it from accessing files that are
allowed for processes in that domain.

You will need to relabel the store directory after all upgrades to
@file{guix-daemon}, such as after running @code{guix pull}.  Assuming the
store is in @file{/gnu}, you can do this with @code{restorecon -vR /gnu},
or by other means provided by your operating system.

We could generate a much more restrictive policy at installation time,
so that only the @emph{exact} file name of the currently installed
@code{guix-daemon} executable would be labelled with
@code{guix_daemon_exec_t}, instead of using a broad regular expression.
The downside is that root would have to install or upgrade the policy at
installation time whenever the Guix package that provides the
effectively running @code{guix-daemon} executable is upgraded.
@end enumerate

@node Invoking guix-daemon
@section Invoking @command{guix-daemon}
@cindex @command{guix-daemon}
The @command{guix-daemon} program implements all the functionality to
access the store.  This includes launching build processes, running the
garbage collector, querying the availability of a build result, etc.  It
is normally run as @code{root} like this:

@example
# guix-daemon --build-users-group=guixbuild
@end example

@cindex socket activation, for @command{guix-daemon}
This daemon can also be started following the systemd ``socket
activation'' protocol (@pxref{Service De- and Constructors,
@code{make-systemd-constructor},, shepherd, The GNU Shepherd Manual}).

For details on how to set it up, @pxref{Setting Up the Daemon}.

@cindex chroot
@cindex container, build environment
@cindex build environment
@cindex reproducible builds
By default, @command{guix-daemon} launches build processes under
different UIDs, taken from the build group specified with
@option{--build-users-group}.  In addition, each build process is run in a
chroot environment that only contains the subset of the store that the
build process depends on, as specified by its derivation
(@pxref{Programming Interface, derivation}), plus a set of specific
system directories.  By default, the latter contains @file{/dev} and
@file{/dev/pts}.  Furthermore, on GNU/Linux, the build environment is a
@dfn{container}: in addition to having its own file system tree, it has
a separate mount name space, its own PID name space, network name space,
etc.  This helps achieve reproducible builds (@pxref{Features}).

When the daemon performs a build on behalf of the user, it creates a
build directory under @file{/tmp} or under the directory specified by
its @env{TMPDIR} environment variable.  This directory is shared with
the container for the duration of the build, though within the container,
the build tree is always called @file{/tmp/guix-build-@var{name}.drv-0}.

The build directory is automatically deleted upon completion, unless the
build failed and the client specified @option{--keep-failed}
(@pxref{Common Build Options, @option{--keep-failed}}).

The daemon listens for connections and spawns one sub-process for each session
started by a client (one of the @command{guix} sub-commands).  The
@command{guix processes} command allows you to get an overview of the activity
on your system by viewing each of the active sessions and clients.
@xref{Invoking guix processes}, for more information.

The following command-line options are supported:

@table @code
@item --build-users-group=@var{group}
Take users from @var{group} to run build processes (@pxref{Setting Up
the Daemon, build users}).

@item --no-substitutes
@cindex substitutes
Do not use substitutes for build products.  That is, always build things
locally instead of allowing downloads of pre-built binaries
(@pxref{Substitutes}).

When the daemon runs with @option{--no-substitutes}, clients can still
explicitly enable substitution @i{via} the @code{set-build-options}
remote procedure call (@pxref{The Store}).

@anchor{daemon-substitute-urls}
@item --substitute-urls=@var{urls}
Consider @var{urls} the default whitespace-separated list of substitute
source URLs.  When this option is omitted,
@indicateurl{@value{SUBSTITUTE-URLS}} is used.

This means that substitutes may be downloaded from @var{urls}, as long
as they are signed by a trusted signature (@pxref{Substitutes}).

@xref{Getting Substitutes from Other Servers}, for more information on
how to configure the daemon to get substitutes from other servers.

@cindex offloading
@item --no-offload
Do not use offload builds to other machines (@pxref{Daemon Offload
Setup}).  That is, always build things locally instead of offloading
builds to remote machines.

@item --cache-failures
Cache build failures.  By default, only successful builds are cached.

When this option is used, @command{guix gc --list-failures} can be used
to query the set of store items marked as failed; @command{guix gc
--clear-failures} removes store items from the set of cached failures.
@xref{Invoking guix gc}.

@item --cores=@var{n}
@itemx -c @var{n}
Use @var{n} CPU cores to build each derivation; @code{0} means as many
as available.

The default value is @code{0}, but it may be overridden by clients, such
as the @option{--cores} option of @command{guix build} (@pxref{Invoking
guix build}).

The effect is to define the @env{NIX_BUILD_CORES} environment variable
in the build process, which can then use it to exploit internal
parallelism---for instance, by running @code{make -j$NIX_BUILD_CORES}.

@item --max-jobs=@var{n}
@itemx -M @var{n}
Allow at most @var{n} build jobs in parallel.  The default value is
@code{1}.  Setting it to @code{0} means that no builds will be performed
locally; instead, the daemon will offload builds (@pxref{Daemon Offload
Setup}), or simply fail.

@item --max-silent-time=@var{seconds}
When the build or substitution process remains silent for more than
@var{seconds}, terminate it and report a build failure.

The default value is @code{3600} (one hour).

The value specified here can be overridden by clients (@pxref{Common
Build Options, @option{--max-silent-time}}).

@item --timeout=@var{seconds}
Likewise, when the build or substitution process lasts for more than
@var{seconds}, terminate it and report a build failure.

The default value is 24 hours.

The value specified here can be overridden by clients (@pxref{Common
Build Options, @option{--timeout}}).

@item --rounds=@var{N}
Build each derivation @var{n} times in a row, and raise an error if
consecutive build results are not bit-for-bit identical.  Note that this
setting can be overridden by clients such as @command{guix build}
(@pxref{Invoking guix build}).

When used in conjunction with @option{--keep-failed}, the differing
output is kept in the store, under @file{/gnu/store/@dots{}-check}.
This makes it easy to look for differences between the two results.

@item --debug
Produce debugging output.

This is useful to debug daemon start-up issues, but then it may be
overridden by clients, for example the @option{--verbosity} option of
@command{guix build} (@pxref{Invoking guix build}).

@item --chroot-directory=@var{dir}
Add @var{dir} to the build chroot.

Doing this may change the result of build processes---for instance if
they use optional dependencies found in @var{dir} when it is available,
and not otherwise.  For that reason, it is not recommended to do so.
Instead, make sure that each derivation declares all the inputs that it
needs.

@item --disable-chroot
Disable chroot builds.

Using this option is not recommended since, again, it would allow build
processes to gain access to undeclared dependencies.  It is necessary,
though, when @command{guix-daemon} is running under an unprivileged user
account.

@item --log-compression=@var{type}
Compress build logs according to @var{type}, one of @code{gzip},
@code{bzip2}, or @code{none}.

Unless @option{--lose-logs} is used, all the build logs are kept in the
@var{localstatedir}.  To save space, the daemon automatically compresses
them with gzip by default.

@item --discover[=yes|no]
Whether to discover substitute servers on the local network using mDNS
and DNS-SD.

This feature is still experimental.  However, here are a few
considerations.

@enumerate
@item
It might be faster/less expensive than fetching from remote servers;
@item
There are no security risks, only genuine substitutes will be used
(@pxref{Substitute Authentication});
@item
An attacker advertising @command{guix publish} on your LAN cannot serve
you malicious binaries, but they can learn what software you’re
installing;
@item
Servers may serve substitute over HTTP, unencrypted, so anyone on the
LAN can see what software you’re installing.
@end enumerate

It is also possible to enable or disable substitute server discovery at
run-time by running:

@example
herd discover guix-daemon on
herd discover guix-daemon off
@end example

@item --disable-deduplication
@cindex deduplication
Disable automatic file ``deduplication'' in the store.

By default, files added to the store are automatically ``deduplicated'':
if a newly added file is identical to another one found in the store,
the daemon makes the new file a hard link to the other file.  This can
noticeably reduce disk usage, at the expense of slightly increased
input/output load at the end of a build process.  This option disables
this optimization.

@item --gc-keep-outputs[=yes|no]
Tell whether the garbage collector (GC) must keep outputs of live
derivations.

@cindex GC roots
@cindex garbage collector roots
When set to @code{yes}, the GC will keep the outputs of any live
derivation available in the store---the @file{.drv} files.  The default
is @code{no}, meaning that derivation outputs are kept only if they are
reachable from a GC root.  @xref{Invoking guix gc}, for more on GC
roots.

@item --gc-keep-derivations[=yes|no]
Tell whether the garbage collector (GC) must keep derivations
corresponding to live outputs.

When set to @code{yes}, as is the case by default, the GC keeps
derivations---i.e., @file{.drv} files---as long as at least one of their
outputs is live.  This allows users to keep track of the origins of
items in their store.  Setting it to @code{no} saves a bit of disk
space.

In this way, setting @option{--gc-keep-derivations} to @code{yes} causes
liveness to flow from outputs to derivations, and setting
@option{--gc-keep-outputs} to @code{yes} causes liveness to flow from
derivations to outputs.  When both are set to @code{yes}, the effect is
to keep all the build prerequisites (the sources, compiler, libraries,
and other build-time tools) of live objects in the store, regardless of
whether these prerequisites are reachable from a GC root.  This is
convenient for developers since it saves rebuilds or downloads.

@item --impersonate-linux-2.6
On Linux-based systems, impersonate Linux 2.6.  This means that the
kernel's @command{uname} system call will report 2.6 as the release number.

This might be helpful to build programs that (usually wrongfully) depend
on the kernel version number.

@item --lose-logs
Do not keep build logs.  By default they are kept under
@file{@var{localstatedir}/guix/log}.

@item --system=@var{system}
Assume @var{system} as the current system type.  By default it is the
architecture/kernel pair found at configure time, such as
@code{x86_64-linux}.

@item --listen=@var{endpoint}
Listen for connections on @var{endpoint}.  @var{endpoint} is interpreted
as the file name of a Unix-domain socket if it starts with
@code{/} (slash sign).  Otherwise, @var{endpoint} is interpreted as a
host name or host name and port to listen to.  Here are a few examples:

@table @code
@item --listen=/gnu/var/daemon
Listen for connections on the @file{/gnu/var/daemon} Unix-domain socket,
creating it if needed.

@item --listen=localhost
@cindex daemon, remote access
@cindex remote access to the daemon
@cindex daemon, cluster setup
@cindex clusters, daemon setup
Listen for TCP connections on the network interface corresponding to
@code{localhost}, on port 44146.

@item --listen=128.0.0.42:1234
Listen for TCP connections on the network interface corresponding to
@code{128.0.0.42}, on port 1234.
@end table

This option can be repeated multiple times, in which case
@command{guix-daemon} accepts connections on all the specified
endpoints.  Users can tell client commands what endpoint to connect to
by setting the @env{GUIX_DAEMON_SOCKET} environment variable
(@pxref{The Store, @env{GUIX_DAEMON_SOCKET}}).

@quotation Note
The daemon protocol is @emph{unauthenticated and unencrypted}.  Using
@option{--listen=@var{host}} is suitable on local networks, such as
clusters, where only trusted nodes may connect to the build daemon.  In
other cases where remote access to the daemon is needed, we recommend
using Unix-domain sockets along with SSH.
@end quotation

When @option{--listen} is omitted, @command{guix-daemon} listens for
connections on the Unix-domain socket located at
@file{@var{localstatedir}/guix/daemon-socket/socket}.
@end table


@node Application Setup
@section Application Setup

@cindex foreign distro
When using Guix on top of GNU/Linux distribution other than Guix System---a
so-called @dfn{foreign distro}---a few additional steps are needed to
get everything in place.  Here are some of them.

@subsection Locales

@anchor{locales-and-locpath}
@cindex locales, when not on Guix System
@vindex LOCPATH
@vindex GUIX_LOCPATH
Packages installed @i{via} Guix will not use the locale data of the
host system.  Instead, you must first install one of the locale packages
available with Guix and then define the @env{GUIX_LOCPATH} environment
variable:

@example
$ guix install glibc-locales
$ export GUIX_LOCPATH=$HOME/.guix-profile/lib/locale
@end example

Note that the @code{glibc-locales} package contains data for all the
locales supported by the GNU@tie{}libc and weighs in at around
930@tie{}MiB@footnote{The size of the @code{glibc-locales} package is
reduced down to about 213@tie{}MiB with store deduplication and further
down to about 67@tie{}MiB when using a zstd-compressed Btrfs file
system.}.  If you only need a few locales, you can define your custom
locales package via the @code{make-glibc-utf8-locales} procedure from
the @code{(gnu packages base)} module.  The following example defines a
package containing the various Canadian UTF-8 locales known to the
GNU@tie{}libc, that weighs around 14@tie{}MiB:

@lisp
(use-modules (gnu packages base))

(define my-glibc-locales
  (make-glibc-utf8-locales
   glibc
   #:locales (list "en_CA" "fr_CA" "ik_CA" "iu_CA" "shs_CA")
   #:name "glibc-canadian-utf8-locales"))
@end lisp

The @env{GUIX_LOCPATH} variable plays a role similar to @env{LOCPATH}
(@pxref{Locale Names, @env{LOCPATH},, libc, The GNU C Library Reference
Manual}).  There are two important differences though:

@enumerate
@item
@env{GUIX_LOCPATH} is honored only by the libc in Guix, and not by the libc
provided by foreign distros.  Thus, using @env{GUIX_LOCPATH} allows you
to make sure the programs of the foreign distro will not end up loading
incompatible locale data.

@item
libc suffixes each entry of @env{GUIX_LOCPATH} with @code{/X.Y}, where
@code{X.Y} is the libc version---e.g., @code{2.22}.  This means that,
should your Guix profile contain a mixture of programs linked against
different libc version, each libc version will only try to load locale
data in the right format.
@end enumerate

This is important because the locale data format used by different libc
versions may be incompatible.

@subsection Name Service Switch

@cindex name service switch, glibc
@cindex NSS (name service switch), glibc
@cindex @abbr{nscd, name service cache daemon}
When using Guix on a foreign distro, we @emph{strongly recommend} that
the system run the GNU C library's @dfn{name service cache daemon},
@command{nscd}, which should be listening on the
@file{/var/run/nscd/socket} socket.  Failing to do that, applications
installed with Guix may fail to look up host names or user accounts, or
may even crash.  The next paragraphs explain why.

@cindex @file{nsswitch.conf}
The GNU C library implements a @dfn{name service switch} (NSS), which is
an extensible mechanism for ``name lookups'' in general: host name
resolution, user accounts, and more (@pxref{Name Service Switch,,, libc,
The GNU C Library Reference Manual}).

@cindex Network information service (NIS)
@cindex NIS (Network information service)
Being extensible, the NSS supports @dfn{plugins}, which provide new name
lookup implementations: for example, the @code{nss-mdns} plugin allow
resolution of @code{.local} host names, the @code{nis} plugin allows
user account lookup using the Network information service (NIS), and so
on.  These extra ``lookup services'' are configured system-wide in
@file{/etc/nsswitch.conf}, and all the programs running on the system
honor those settings (@pxref{NSS Configuration File,,, libc, The GNU C
Reference Manual}).

When they perform a name lookup---for instance by calling the
@code{getaddrinfo} function in C---applications first try to connect to
the nscd; on success, nscd performs name lookups on their behalf.  If
the nscd is not running, then they perform the name lookup by
themselves, by loading the name lookup services into their own address
space and running it.  These name lookup services---the
@file{libnss_*.so} files---are @code{dlopen}'d, but they may come from
the host system's C library, rather than from the C library the
application is linked against (the C library coming from Guix).

And this is where the problem is: if your application is linked against
Guix's C library (say, glibc 2.24) and tries to load NSS plugins from
another C library (say, @code{libnss_mdns.so} for glibc 2.22), it will
likely crash or have its name lookups fail unexpectedly.

Running @command{nscd} on the system, among other advantages, eliminates
this binary incompatibility problem because those @code{libnss_*.so}
files are loaded in the @command{nscd} process, not in applications
themselves.

@subsection X11 Fonts

@cindex fonts
The majority of graphical applications use Fontconfig to locate and load
fonts and perform X11-client-side rendering.  The @code{fontconfig}
package in Guix looks for fonts in @file{$HOME/.guix-profile} by
default.  Thus, to allow graphical applications installed with Guix to
display fonts, you have to install fonts with Guix as well.  Essential
font packages include @code{font-ghostscript}, @code{font-dejavu}, and
@code{font-gnu-freefont}.

@cindex @code{fc-cache}
@cindex font cache
Once you have installed or removed fonts, or when you notice an
application that does not find fonts, you may need to install Fontconfig
and to force an update of its font cache by running:

@example
guix install fontconfig
fc-cache -rv
@end example

To display text written in Chinese languages, Japanese, or Korean in
graphical applications, consider installing
@code{font-adobe-source-han-sans} or @code{font-wqy-zenhei}.  The former
has multiple outputs, one per language family (@pxref{Packages with
Multiple Outputs}).  For instance, the following command installs fonts
for Chinese languages:

@example
guix install font-adobe-source-han-sans:cn
@end example

@cindex @code{xterm}
Older programs such as @command{xterm} do not use Fontconfig and instead
rely on server-side font rendering.  Such programs require to specify a
full name of a font using XLFD (X Logical Font Description), like this:

@example
-*-dejavu sans-medium-r-normal-*-*-100-*-*-*-*-*-1
@end example

To be able to use such full names for the TrueType fonts installed in
your Guix profile, you need to extend the font path of the X server:

@c Note: 'xset' does not accept symlinks so the trick below arranges to
@c get at the real directory.  See <https://bugs.gnu.org/30655>.
@example
xset +fp $(dirname $(readlink -f ~/.guix-profile/share/fonts/truetype/fonts.dir))
@end example

@cindex @code{xlsfonts}
After that, you can run @code{xlsfonts} (from @code{xlsfonts} package)
to make sure your TrueType fonts are listed there.


@subsection X.509 Certificates

@cindex @code{nss-certs}
The @code{nss-certs} package provides X.509 certificates, which allow
programs to authenticate Web servers accessed over HTTPS.

When using Guix on a foreign distro, you can install this package and
define the relevant environment variables so that packages know where to
look for certificates.  @xref{X.509 Certificates}, for detailed
information.

@subsection Emacs Packages

@cindex @code{emacs}
When you install Emacs packages with Guix, the Elisp files are placed
under the @file{share/emacs/site-lisp/} directory of the profile in
which they are installed.  The Elisp libraries are made available to
Emacs through the @env{EMACSLOADPATH} environment variable, which is
set when installing Emacs itself.

@cindex guix-emacs-autoload-packages, refreshing Emacs packages
Additionally, autoload definitions are automatically evaluated at the
initialization of Emacs, by the Guix-specific
@code{guix-emacs-autoload-packages} procedure.  This procedure can be
interactively invoked to have newly installed Emacs packages discovered,
without having to restart Emacs.  If, for some reason, you want to avoid
auto-loading the Emacs packages installed with Guix, you can do so by
running Emacs with the @option{--no-site-file} option (@pxref{Init
File,,, emacs, The GNU Emacs Manual}).

@quotation Note
Most Emacs variants are now capable of doing native compilation.
The approach taken by Guix Emacs however differs greatly
from the approach taken upstream.

Upstream Emacs compiles packages just-in-time and typically places
shared object files  in a special folder within your
@code{user-emacs-directory}.
These shared objects within said folder are organized in a
flat hierarchy, and their file names contain two hashes to
verify the original file name and contents of the source code.

Guix Emacs on the other hand prefers to compile packages ahead-of-time.
Shared objects retain much of the original file name and no hashes
are added to verify the original file name or the contents of the file.
Crucially, this allows Guix Emacs and packages built against it
to be grafted (@pxref{Security Updates, grafts}), but at the same time,
Guix Emacs lacks the hash-based verification of source code baked
into upstream Emacs.  As this naming schema is trivial to exploit,
we disable just-in-time compilation.

Further note, that @code{emacs-minimal}---the default Emacs
for building packages---has been configured without native compilation.
To natively compile your emacs packages ahead of time, use a
transformation like @option{--with-input=emacs-minimal=emacs}.
@end quotation

@node Upgrading Guix
@section Upgrading Guix

@cindex Upgrading Guix, on a foreign distro

To upgrade Guix, run:

@example
guix pull
@end example

@xref{Invoking guix pull}, for more information.

@cindex upgrading Guix for the root user, on a foreign distro
@cindex upgrading the Guix daemon, on a foreign distro
@cindex @command{guix pull} for the root user, on a foreign distro

On a foreign distro, you can upgrade the build daemon by running:

@example
sudo -i guix pull
@end example

@noindent
followed by (assuming your distro uses the systemd service management
tool):

@example
systemctl restart guix-daemon.service
@end example

On Guix System, upgrading the daemon is achieved by reconfiguring the
system (@pxref{Invoking guix system, @code{guix system reconfigure}}).

@c TODO What else?

@c *********************************************************************
@node System Installation
@chapter System Installation

@cindex installing Guix System
@cindex Guix System, installation
This section explains how to install Guix System
on a machine.  Guix, as a package manager, can
also be installed on top of a running GNU/Linux system,
@pxref{Installation}.

@ifinfo
@quotation Note
@c This paragraph is for people reading this from tty2 of the
@c installation image.
You are reading this documentation with an Info reader.  For details on
how to use it, hit the @key{RET} key (``return'' or ``enter'') on the
link that follows: @pxref{Top, Info reader,, info-stnd, Stand-alone GNU
Info}.  Hit @kbd{l} afterwards to come back here.

Alternatively, run @command{info info} in another tty to keep the manual
available.
@end quotation
@end ifinfo

@menu
* Limitations::                 What you can expect.
* Hardware Considerations::     Supported hardware.
* USB Stick and DVD Installation::  Preparing the installation medium.
* Preparing for Installation::  Networking, partitioning, etc.
* Guided Graphical Installation::  Easy graphical installation.
* Manual Installation::         Manual installation for wizards.
* After System Installation::   When installation succeeded.
* Installing Guix in a VM::     Guix System playground.
* Building the Installation Image::  How this comes to be.
@end menu

@node Limitations
@section Limitations

We consider Guix System to be ready for a wide range of ``desktop'' and server
use cases.  The reliability guarantees it provides---transactional upgrades
and rollbacks, reproducibility---make it a solid foundation.

More and more system services are provided (@pxref{Services}).

Nevertheless, before you proceed with the installation, be aware that some
services you rely on may still be missing from version @value{VERSION}.

More than a disclaimer, this is an invitation to report issues (and success
stories!), and to join us in improving it.  @xref{Contributing}, for more
info.


@node Hardware Considerations
@section Hardware Considerations

@cindex hardware support on Guix System
GNU@tie{}Guix focuses on respecting the user's computing freedom.  It
builds around the kernel Linux-libre, which means that only hardware for
which free software drivers and firmware exist is supported.  Nowadays,
a wide range of off-the-shelf hardware is supported on
GNU/Linux-libre---from keyboards to graphics cards to scanners and
Ethernet controllers.  Unfortunately, there are still areas where
hardware vendors deny users control over their own computing, and such
hardware is not supported on Guix System.

@cindex WiFi, hardware support
One of the main areas where free drivers or firmware are lacking is WiFi
devices.  WiFi devices known to work include those using Atheros chips
(AR9271 and AR7010), which corresponds to the @code{ath9k} Linux-libre
driver, and those using Broadcom/AirForce chips (BCM43xx with
Wireless-Core Revision 5), which corresponds to the @code{b43-open}
Linux-libre driver.  Free firmware exists for both and is available
out-of-the-box on Guix System, as part of @code{%base-firmware}
(@pxref{operating-system Reference, @code{firmware}}).

The installer warns you early on if it detects devices that are known
@emph{not} to work due to the lack of free firmware or free drivers.

@cindex RYF, Respects Your Freedom
The @uref{https://www.fsf.org/, Free Software Foundation} runs
@uref{https://www.fsf.org/ryf, @dfn{Respects Your Freedom}} (RYF), a
certification program for hardware products that respect your freedom
and your privacy and ensure that you have control over your device.  We
encourage you to check the list of RYF-certified devices.

Another useful resource is the @uref{https://www.h-node.org/, H-Node}
web site.  It contains a catalog of hardware devices with information
about their support in GNU/Linux.


@node USB Stick and DVD Installation
@section USB Stick and DVD Installation

An ISO-9660 installation image that can be written to a USB stick or
burnt to a DVD can be downloaded from
@indicateurl{@value{BASE-URL}/guix-system-install-@value{VERSION}.x86_64-linux.iso},
where you can replace @code{x86_64-linux} with one of:

@table @code
@item x86_64-linux
for a GNU/Linux system on Intel/AMD-compatible 64-bit CPUs;

@item i686-linux
for a 32-bit GNU/Linux system on Intel-compatible CPUs.
@end table

@c start duplication of authentication part from ``Binary Installation''
Make sure to download the associated @file{.sig} file and to verify the
authenticity of the image against it, along these lines:

@example
$ wget @value{BASE-URL}/guix-system-install-@value{VERSION}.x86_64-linux.iso.sig
$ gpg --verify guix-system-install-@value{VERSION}.x86_64-linux.iso.sig
@end example

If that command fails because you do not have the required public key,
then run this command to import it:

@example
$ wget @value{OPENPGP-SIGNING-KEY-URL} \
      -qO - | gpg --import -
@end example

@noindent
and rerun the @code{gpg --verify} command.

Take note that a warning like ``This key is not certified with a trusted
signature!'' is normal.

@c end duplication

This image contains the tools necessary for an installation.
It is meant to be copied @emph{as is} to a large-enough USB stick or DVD.

@unnumberedsubsec Copying to a USB Stick

Insert a USB stick of 1@tie{}GiB or more into your machine, and determine
its device name.  Assuming that the USB stick is known as @file{/dev/sdX},
copy the image with:

@example
dd if=guix-system-install-@value{VERSION}.x86_64-linux.iso of=/dev/sdX status=progress
sync
@end example

Access to @file{/dev/sdX} usually requires root privileges.

@unnumberedsubsec Burning on a DVD

Insert a blank DVD into your machine, and determine
its device name.  Assuming that the DVD drive is known as @file{/dev/srX},
copy the image with:

@example
growisofs -dvd-compat -Z /dev/srX=guix-system-install-@value{VERSION}.x86_64-linux.iso
@end example

Access to @file{/dev/srX} usually requires root privileges.

@unnumberedsubsec Booting

Once this is done, you should be able to reboot the system and boot from
the USB stick or DVD@.  The latter usually requires you to get in the
BIOS or UEFI boot menu, where you can choose to boot from the USB stick.
In order to boot from Libreboot, switch to the command mode by pressing
the @kbd{c} key and type @command{search_grub usb}.

Sadly, on some machines, the installation medium cannot be properly
booted and you only see a black screen after booting even after you
waited for ten minutes.  This may indicate that your machine cannot run
Guix System; perhaps you instead want to install Guix on a foreign
distro (@pxref{Binary Installation}).  But don't give up just yet; a
possible workaround is pressing the @kbd{e} key in the GRUB boot menu
and appending @option{nomodeset} to the Linux bootline.
Sometimes the black screen issue can also be resolved by connecting a
different display.

@xref{Installing Guix in a VM}, if, instead, you would like to install
Guix System in a virtual machine (VM).


@node Preparing for Installation
@section Preparing for Installation

Once you have booted, you can use the guided graphical installer, which makes
it easy to get started (@pxref{Guided Graphical Installation}).  Alternatively,
if you are already familiar with GNU/Linux and if you want more control than
what the graphical installer provides, you can choose the ``manual''
installation process (@pxref{Manual Installation}).

The graphical installer is available on TTY1.  You can obtain root shells on
TTYs 3 to 6 by hitting @kbd{ctrl-alt-f3}, @kbd{ctrl-alt-f4}, etc.  TTY2 shows
this documentation and you can reach it with @kbd{ctrl-alt-f2}.  Documentation
is browsable using the Info reader commands (@pxref{Top,,, info-stnd,
Stand-alone GNU Info}).  The installation system runs the GPM mouse daemon,
which allows you to select text with the left mouse button and to paste it
with the middle button.

@quotation Note
Installation requires access to the Internet so that any missing
dependencies of your system configuration can be downloaded.  See the
``Networking'' section below.
@end quotation

@node Guided Graphical Installation
@section Guided Graphical Installation

The graphical installer is a text-based user interface.  It will guide you,
with dialog boxes, through the steps needed to install GNU@tie{}Guix System.

The first dialog boxes allow you to set up the system as you use it during the
installation: you can choose the language, keyboard layout, and set up
networking, which will be used during the installation.  The image below shows
the networking dialog.

@image{images/installer-network,5in,, networking setup with the graphical installer}

Later steps allow you to partition your hard disk, as shown in the image
below, to choose whether or not to use encrypted file systems, to enter the
host name and root password, and to create an additional account, among other
things.

@image{images/installer-partitions,5in,, partitioning with the graphical installer}

Note that, at any time, the installer allows you to exit the current
installation step and resume at a previous step, as show in the image below.

@image{images/installer-resume,5in,, resuming the installation process}

Once you're done, the installer produces an operating system configuration and
displays it (@pxref{Using the Configuration System}).  At that point you can
hit ``OK'' and installation will proceed.  On success, you can reboot into the
new system and enjoy.  @xref{After System Installation}, for what's next!


@node Manual Installation
@section Manual Installation

This section describes how you would ``manually'' install GNU@tie{}Guix System
on your machine.  This option requires familiarity with GNU/Linux, with the
shell, and with common administration tools.  If you think this is not for
you, consider using the guided graphical installer (@pxref{Guided Graphical
Installation}).

The installation system provides root shells on TTYs 3 to 6; press
@kbd{ctrl-alt-f3}, @kbd{ctrl-alt-f4}, and so on to reach them.  It includes
many common tools needed to install the system, but is also a full-blown
Guix System.  This means that you can install additional packages, should you
need it, using @command{guix package} (@pxref{Invoking guix package}).

@menu
* Keyboard Layout and Networking and Partitioning::  Initial setup.
* Proceeding with the Installation::  Installing.
@end menu

@node Keyboard Layout and Networking and Partitioning
@subsection Keyboard Layout, Networking, and Partitioning

Before you can install the system, you may want to adjust the keyboard layout,
set up networking, and partition your target hard disk.  This section will
guide you through this.

@subsubsection Keyboard Layout

@cindex keyboard layout
The installation image uses the US qwerty keyboard layout.  If you want
to change it, you can use the @command{loadkeys} command.  For example,
the following command selects the Dvorak keyboard layout:

@example
loadkeys dvorak
@end example

See the files under @file{/run/current-system/profile/share/keymaps} for
a list of available keyboard layouts.  Run @command{man loadkeys} for
more information.

@anchor{manual-installation-networking}
@subsubsection Networking

Run the following command to see what your network interfaces are called:

@example
ifconfig -a
@end example

@noindent
@dots{} or, using the GNU/Linux-specific @command{ip} command:

@example
ip address
@end example

@c https://cgit.freedesktop.org/systemd/systemd/tree/src/udev/udev-builtin-net_id.c#n20
Wired interfaces have a name starting with @samp{e}; for example, the
interface corresponding to the first on-board Ethernet controller is
called @samp{eno1}.  Wireless interfaces have a name starting with
@samp{w}, like @samp{w1p2s0}.

@table @asis
@item Wired connection
To configure a wired network run the following command, substituting
@var{interface} with the name of the wired interface you want to use.

@example
ifconfig @var{interface} up
@end example

@noindent
@dots{} or, using the GNU/Linux-specific @command{ip} command:

@example
ip link set @var{interface} up
@end example

@item Wireless connection
@cindex wireless
@cindex WiFi
To configure wireless networking, you can create a configuration file
for the @command{wpa_supplicant} configuration tool (its location is not
important) using one of the available text editors such as
@command{nano}:

@example
nano wpa_supplicant.conf
@end example

As an example, the following stanza can go to this file and will work
for many wireless networks, provided you give the actual SSID and
passphrase for the network you are connecting to:

@example
network=@{
  ssid="@var{my-ssid}"
  key_mgmt=WPA-PSK
  psk="the network's secret passphrase"
@}
@end example

Start the wireless service and run it in the background with the
following command (substitute @var{interface} with the name of the
network interface you want to use):

@example
wpa_supplicant -c wpa_supplicant.conf -i @var{interface} -B
@end example

Run @command{man wpa_supplicant} for more information.
@end table

@cindex DHCP
At this point, you need to acquire an IP address.  On a network where IP
addresses are automatically assigned @i{via} DHCP, you can run:

@example
dhclient -v @var{interface}
@end example

Try to ping a server to see if networking is up and running:

@example
ping -c 3 gnu.org
@end example

Setting up network access is almost always a requirement because the
image does not contain all the software and tools that may be needed.

@cindex proxy, during system installation
If you need HTTP and HTTPS access to go through a proxy, run the
following command:

@example
herd set-http-proxy guix-daemon @var{URL}
@end example

@noindent
where @var{URL} is the proxy URL, for example
@code{http://example.org:8118}.

@cindex installing over SSH
If you want to, you can continue the installation remotely by starting
an SSH server:

@example
herd start ssh-daemon
@end example

Make sure to either set a password with @command{passwd}, or configure
OpenSSH public key authentication before logging in.

@subsubsection Disk Partitioning

Unless this has already been done, the next step is to partition, and
then format the target partition(s).

The installation image includes several partitioning tools, including
Parted (@pxref{Overview,,, parted, GNU Parted User Manual}),
@command{fdisk}, and @command{cfdisk}.  Run it and set up your disk with
the partition layout you want:

@example
cfdisk
@end example

If your disk uses the GUID Partition Table (GPT) format and you plan to
install BIOS-based GRUB (which is the default), make sure a BIOS Boot
Partition is available (@pxref{BIOS installation,,, grub, GNU GRUB
manual}).

@cindex EFI, installation
@cindex UEFI, installation
@cindex ESP, EFI system partition
If you instead wish to use EFI-based GRUB, a FAT32 @dfn{EFI System Partition}
(ESP) is required.  This partition can be mounted at @file{/boot/efi} for
instance and must have the @code{esp} flag set.  E.g., for @command{parted}:

@example
parted /dev/sda set 1 esp on
@end example

@quotation Note
@vindex grub-bootloader
@vindex grub-efi-bootloader
Unsure whether to use EFI- or BIOS-based GRUB?  If the directory
@file{/sys/firmware/efi} exists in the installation image, then you should
probably perform an EFI installation, using @code{grub-efi-bootloader}.
Otherwise you should use the BIOS-based GRUB, known as
@code{grub-bootloader}.  @xref{Bootloader Configuration}, for more info on
bootloaders.
@end quotation

Once you are done partitioning the target hard disk drive, you have to
create a file system on the relevant partition(s)@footnote{Currently
Guix System only supports ext4, btrfs, JFS, F2FS, and XFS file systems.  In
particular, code that reads file system UUIDs and labels only works for these
file system types.}.  For the ESP, if you have one and assuming it is
@file{/dev/sda1}, run:

@example
mkfs.fat -F32 /dev/sda1
@end example

For the root file system, ext4 is the most widely used format.  Other
file systems, such as Btrfs, support compression, which is reported to
nicely complement file deduplication that the daemon performs
independently of the file system (@pxref{Invoking guix-daemon,
deduplication}).

Preferably, assign file systems a label so that you can easily and
reliably refer to them in @code{file-system} declarations (@pxref{File
Systems}).  This is typically done using the @code{-L} option of
@command{mkfs.ext4} and related commands.  So, assuming the target root
partition lives at @file{/dev/sda2}, a file system with the label
@code{my-root} can be created with:

@example
mkfs.ext4 -L my-root /dev/sda2
@end example

@cindex encrypted disk
If you are instead planning to encrypt the root partition, you can use
the Cryptsetup/LUKS utilities to do that (see @inlinefmtifelse{html,
@uref{https://linux.die.net/man/8/cryptsetup, @code{man cryptsetup}},
@code{man cryptsetup}} for more information).

Assuming you want to store the root partition on @file{/dev/sda2}, the
command sequence to format it as a LUKS partition would be along these
lines:

@example
cryptsetup luksFormat /dev/sda2
cryptsetup open /dev/sda2 my-partition
mkfs.ext4 -L my-root /dev/mapper/my-partition
@end example

Once that is done, mount the target file system under @file{/mnt}
with a command like (again, assuming @code{my-root} is the label of the
root file system):

@example
mount LABEL=my-root /mnt
@end example

Also mount any other file systems you would like to use on the target
system relative to this path.  If you have opted for @file{/boot/efi} as an
EFI mount point for example, mount it at @file{/mnt/boot/efi} now so it is
found by @code{guix system init} afterwards.

Finally, if you plan to use one or more swap partitions (@pxref{Swap
Space}), make sure to initialize them with @command{mkswap}.  Assuming
you have one swap partition on @file{/dev/sda3}, you would run:

@example
mkswap /dev/sda3
swapon /dev/sda3
@end example

Alternatively, you may use a swap file.  For example, assuming that in
the new system you want to use the file @file{/swapfile} as a swap file,
you would run@footnote{This example will work for many types of file
systems (e.g., ext4).  However, for copy-on-write file systems (e.g.,
btrfs), the required steps may be different.  For details, see the
manual pages for @command{mkswap} and @command{swapon}.}:

@example
# This is 10 GiB of swap space.  Adjust "count" to change the size.
dd if=/dev/zero of=/mnt/swapfile bs=1MiB count=10240
# For security, make the file readable and writable only by root.
chmod 600 /mnt/swapfile
mkswap /mnt/swapfile
swapon /mnt/swapfile
@end example

Note that if you have encrypted the root partition and created a swap
file in its file system as described above, then the encryption also
protects the swap file, just like any other file in that file system.

@node Proceeding with the Installation
@subsection Proceeding with the Installation

With the target partitions ready and the target root mounted on
@file{/mnt}, we're ready to go.  First, run:

@example
herd start cow-store /mnt
@end example

This makes @file{/gnu/store} copy-on-write, such that packages added to it
during the installation phase are written to the target disk on @file{/mnt}
rather than kept in memory.  This is necessary because the first phase of
the @command{guix system init} command (see below) entails downloads or
builds to @file{/gnu/store} which, initially, is an in-memory file system.

Next, you have to edit a file and
provide the declaration of the operating system to be installed.  To
that end, the installation system comes with three text editors.  We
recommend GNU nano (@pxref{Top,,, nano, GNU nano Manual}), which
supports syntax highlighting and parentheses matching; other editors
include mg (an Emacs clone), and
nvi (a clone of the original BSD @command{vi} editor).
We strongly recommend storing that file on the target root file system, say,
as @file{/mnt/etc/config.scm}.  Failing to do that, you will have lost your
configuration file once you have rebooted into the newly-installed system.

@xref{Using the Configuration System}, for an overview of the
configuration file.  The example configurations discussed in that
section are available under @file{/etc/configuration} in the
installation image.  Thus, to get started with a system configuration
providing a graphical display server (a ``desktop'' system), you can run
something along these lines:

@example
# mkdir /mnt/etc
# cp /etc/configuration/desktop.scm /mnt/etc/config.scm
# nano /mnt/etc/config.scm
@end example

You should pay attention to what your configuration file contains, and
in particular:

@itemize
@item
Make sure the @code{bootloader-configuration} form refers to the targets
you want to install GRUB on.  It should mention @code{grub-bootloader}
if you are installing GRUB in the legacy way, or
@code{grub-efi-bootloader} for newer UEFI systems.  For legacy systems,
the @code{targets} field contain the names of the devices, like
@code{(list "/dev/sda")}; for UEFI systems it names the paths to mounted
EFI partitions, like @code{(list "/boot/efi")}; do make sure the paths
are currently mounted and a @code{file-system} entry is specified in
your configuration.

@item
Be sure that your file system labels match the value of their respective
@code{device} fields in your @code{file-system} configuration, assuming
your @code{file-system} configuration uses the @code{file-system-label}
procedure in its @code{device} field.

@item
If there are encrypted or RAID partitions, make sure to add a
@code{mapped-devices} field to describe them (@pxref{Mapped Devices}).
@end itemize

Once you are done preparing the configuration file, the new system must
be initialized (remember that the target root file system is mounted
under @file{/mnt}):

@example
guix system init /mnt/etc/config.scm /mnt
@end example

@noindent
This copies all the necessary files and installs GRUB on
@file{/dev/sdX}, unless you pass the @option{--no-bootloader} option.  For
more information, @pxref{Invoking guix system}.  This command may trigger
downloads or builds of missing packages, which can take some time.

Once that command has completed---and hopefully succeeded!---you can run
@command{reboot} and boot into the new system.  The @code{root} password
in the new system is initially empty; other users' passwords need to be
initialized by running the @command{passwd} command as @code{root},
unless your configuration specifies otherwise
(@pxref{user-account-password, user account passwords}).
@xref{After System Installation}, for what's next!


@node After System Installation
@section After System Installation

Success, you've now booted into Guix System!  You can upgrade the system
whenever you want by running:

@example
guix pull
sudo guix system reconfigure /etc/config.scm
@end example

@noindent
This builds a new system @dfn{generation} with the latest packages and
services.

Now, @pxref{Getting Started with the System}, and
join us on @code{#guix} on the Libera.Chat IRC network or on
@email{guix-devel@@gnu.org} to share your experience!


@node Installing Guix in a VM
@section Installing Guix in a Virtual Machine

@cindex virtual machine, Guix System installation
@cindex virtual private server (VPS)
@cindex VPS (virtual private server)
If you'd like to install Guix System in a virtual machine (VM) or on a
virtual private server (VPS) rather than on your beloved machine, this
section is for you.

To boot a @uref{https://qemu.org/,QEMU} VM for installing Guix System in a
disk image, follow these steps:

@enumerate
@item
First, retrieve and decompress the Guix system installation image as
described previously (@pxref{USB Stick and DVD Installation}).

@item
Create a disk image that will hold the installed system.  To make a
qcow2-formatted disk image, use the @command{qemu-img} command:

@example
qemu-img create -f qcow2 guix-system.img 50G
@end example

The resulting file will be much smaller than 50 GB (typically less than
1 MB), but it will grow as the virtualized storage device is filled up.

@item
Boot the USB installation image in a VM:

@example
qemu-system-x86_64 -m 1024 -smp 1 -enable-kvm \
  -nic user,model=virtio-net-pci -boot menu=on,order=d \
  -drive file=guix-system.img \
  -drive media=cdrom,readonly=on,file=guix-system-install-@value{VERSION}.@var{system}.iso
@end example

@code{-enable-kvm} is optional, but significantly improves performance,
@pxref{Running Guix in a VM}.

@item
You're now root in the VM, proceed with the installation process.
@xref{Preparing for Installation}, and follow the instructions.
@end enumerate

Once installation is complete, you can boot the system that's on your
@file{guix-system.img} image.  @xref{Running Guix in a VM}, for how to do
that.

@node Building the Installation Image
@section Building the Installation Image

@cindex installation image
The installation image described above was built using the @command{guix
system} command, specifically:

@example
guix system image -t iso9660 gnu/system/install.scm
@end example

Have a look at @file{gnu/system/install.scm} in the source tree,
and see also @ref{Invoking guix system} for more information
about the installation image.

@section Building the Installation Image for ARM Boards

Many ARM boards require a specific variant of the
@uref{https://www.denx.de/wiki/U-Boot/, U-Boot} bootloader.

If you build a disk image and the bootloader is not available otherwise
(on another boot drive etc), it's advisable to build an image that
includes the bootloader, specifically:

@example
guix system image --system=armhf-linux -e '((@@ (gnu system install) os-with-u-boot) (@@ (gnu system install) installation-os) "A20-OLinuXino-Lime2")'
@end example

@code{A20-OLinuXino-Lime2} is the name of the board.  If you specify an invalid
board, a list of possible boards will be printed.


@c *********************************************************************
@node Getting Started
@chapter Getting Started

Presumably, you've reached this section because either you have
installed Guix on top of another distribution (@pxref{Installation}), or
you've installed the standalone Guix System (@pxref{System
Installation}).  It's time for you to get started using Guix and this
section aims to help you do that and give you a feel of what it's like.

Guix is about installing software, so probably the first thing you'll
want to do is to actually look for software.  Let's say you're looking
for a text editor, you can run:

@example
guix search text editor
@end example

This command shows you a number of matching @dfn{packages}, each time
showing the package's name, version, a description, and additional info.
Once you've found out the one you want to use, let's say Emacs (ah ha!),
you can go ahead and install it (run this command as a regular user,
@emph{no need for root privileges}!):

@example
guix install emacs
@end example

@cindex profile
You've installed your first package, congrats!  The package is now
visible in your default @dfn{profile}, @file{$HOME/.guix-profile}---a
profile is a directory containing installed packages.
In the process, you've
probably noticed that Guix downloaded pre-built binaries; or, if you
explicitly chose to @emph{not} use pre-built binaries, then probably
Guix is still building software (@pxref{Substitutes}, for more info).

Unless you're using Guix System, the @command{guix install} command must
have printed this hint:

@example
hint: Consider setting the necessary environment variables by running:

     GUIX_PROFILE="$HOME/.guix-profile"
     . "$GUIX_PROFILE/etc/profile"

Alternately, see `guix package --search-paths -p "$HOME/.guix-profile"'.
@end example

Indeed, you must now tell your shell where @command{emacs} and other
programs installed with Guix are to be found.  Pasting the two lines
above will do just that: it will add
@code{$HOME/.guix-profile/bin}---which is where the installed package
is---to the @code{PATH} environment variable.  You can paste these two
lines in your shell so they take effect right away, but more importantly
you should add them to @file{~/.bash_profile} (or equivalent file if you
do not use Bash) so that environment variables are set next time you
spawn a shell.  You only need to do this once and other search paths
environment variables will be taken care of similarly---e.g., if you
eventually install @code{python} and Python libraries,
@env{GUIX_PYTHONPATH} will be defined.

You can go on installing packages at your will.  To list installed
packages, run:

@example
guix package --list-installed
@end example

To remove a package, you would unsurprisingly run @command{guix remove}.
A distinguishing feature is the ability to @dfn{roll back} any operation
you made---installation, removal, upgrade---by simply typing:

@example
guix package --roll-back
@end example

This is because each operation is in fact a @dfn{transaction} that
creates a new @dfn{generation}.  These generations and the difference
between them can be displayed by running:

@example
guix package --list-generations
@end example

Now you know the basics of package management!

@quotation Going further
@xref{Package Management}, for more about package management.  You may
like @dfn{declarative} package management with @command{guix package
--manifest}, managing separate @dfn{profiles} with @option{--profile},
deleting old generations, collecting garbage, and other nifty features
that will come in handy as you become more familiar with Guix.  If you
are a developer, @pxref{Development} for additional tools.  And if
you're curious, @pxref{Features}, to peek under the hood.

You can also manage the configuration of your entire @dfn{home
environment}---your user ``dot files'', services, and packages---using
Guix Home.  @xref{Home Configuration}, to learn more about it!
@end quotation

Once you've installed a set of packages, you will want to periodically
@emph{upgrade} them to the latest and greatest version.  To do that, you
will first pull the latest revision of Guix and its package collection:

@example
guix pull
@end example

The end result is a new @command{guix} command, under
@file{~/.config/guix/current/bin}.  Unless you're on Guix System, the
first time you run @command{guix pull}, be sure to follow the hint that
the command prints and, similar to what we saw above, paste these two
lines in your terminal and @file{.bash_profile}:

@example
GUIX_PROFILE="$HOME/.config/guix/current"
. "$GUIX_PROFILE/etc/profile"
@end example

@noindent
You must also instruct your shell to point to this new @command{guix}:

@example
hash guix
@end example

At this point, you're running a brand new Guix.  You can thus go ahead
and actually upgrade all the packages you previously installed:

@example
guix upgrade
@end example

As you run this command, you will see that binaries are downloaded (or
perhaps some packages are built), and eventually you end up with the
upgraded packages.  Should one of these upgraded packages not be to your
liking, remember you can always roll back!

You can display the exact revision of Guix you're currently using by
running:

@example
guix describe
@end example

The information it displays is @emph{all it takes to reproduce the exact
same Guix}, be it at a different point in time or on a different
machine.

@quotation Going further
@xref{Invoking guix pull}, for more information.  @xref{Channels}, on
how to specify additional @dfn{channels} to pull packages from, how to
replicate Guix, and more.  You may also find @command{time-machine}
handy (@pxref{Invoking guix time-machine}).
@end quotation

If you installed Guix System, one of the first things you'll want to do
is to upgrade your system.  Once you've run @command{guix pull} to get
the latest Guix, you can upgrade the system like this:

@example
sudo guix system reconfigure /etc/config.scm
@end example

Upon completion, the system runs the latest versions of its software
packages.  Just like for packages, you can always @emph{roll back} to a
previous generation @emph{of the whole system}.  @xref{Getting Started
with the System}, to learn how to manage your system.

Now you know enough to get started!

@quotation Resources
The rest of this manual provides a reference for all things Guix.  Here
are some additional resources you may find useful:

@itemize
@item
@xref{Top,,, guix-cookbook, The GNU Guix Cookbook}, for a list of
``how-to'' style of recipes for a variety of applications.

@item
The @uref{https://guix.gnu.org/guix-refcard.pdf, GNU Guix Reference
Card} lists in two pages most of the commands and options you'll ever
need.

@item
The web site contains @uref{https://guix.gnu.org/en/videos/,
instructional videos} covering topics such as everyday use of Guix, how
to get help, and how to become a contributor.

@item
@xref{Documentation}, to learn how to access documentation on your
computer.
@end itemize

We hope you will enjoy Guix as much as the community enjoys building it!
@end quotation

@c *********************************************************************
@node Package Management
@chapter Package Management

@cindex packages
The purpose of GNU Guix is to allow users to easily install, upgrade, and
remove software packages, without having to know about their build
procedures or dependencies.  Guix also goes beyond this obvious set of
features.

This chapter describes the main features of Guix, as well as the
package management tools it provides.  Along with the command-line
interface described below (@pxref{Invoking guix package, @code{guix
package}}), you may also use the Emacs-Guix interface (@pxref{Top,,,
emacs-guix, The Emacs-Guix Reference Manual}), after installing
@code{emacs-guix} package (run @kbd{M-x guix-help} command to start
with it):

@example
guix install emacs-guix
@end example

@menu
* Features::                    How Guix will make your life brighter.
* Invoking guix package::       Package installation, removal, etc.
* Substitutes::                 Downloading pre-built binaries.
* Packages with Multiple Outputs::  Single source package, multiple outputs.
* Invoking guix locate::        Locating packages that provide a file.
* Invoking guix gc::            Running the garbage collector.
* Invoking guix pull::          Fetching the latest Guix and distribution.
* Invoking guix time-machine::  Running an older revision of Guix.
* Inferiors::                   Interacting with another revision of Guix.
* Invoking guix describe::      Display information about your Guix revision.
* Invoking guix archive::       Exporting and importing store files.
@end menu

@node Features
@section Features

Here we assume you've already made your first steps with Guix
(@pxref{Getting Started}) and would like to get an overview about what's
going on under the hood.

When using Guix, each package ends up in the @dfn{package store}, in its
own directory---something that resembles
@file{/gnu/store/xxx-package-1.2}, where @code{xxx} is a base32 string.

Instead of referring to these directories, users have their own
@dfn{profile}, which points to the packages that they actually want to
use.  These profiles are stored within each user's home directory, at
@code{$HOME/.guix-profile}.

For example, @code{alice} installs GCC 4.7.2.  As a result,
@file{/home/alice/.guix-profile/bin/gcc} points to
@file{/gnu/store/@dots{}-gcc-4.7.2/bin/gcc}.  Now, on the same machine,
@code{bob} had already installed GCC 4.8.0.  The profile of @code{bob}
simply continues to point to
@file{/gnu/store/@dots{}-gcc-4.8.0/bin/gcc}---i.e., both versions of GCC
coexist on the same system without any interference.

The @command{guix package} command is the central tool to manage
packages (@pxref{Invoking guix package}).  It operates on the per-user
profiles, and can be used @emph{with normal user privileges}.

@cindex transactions
The command provides the obvious install, remove, and upgrade
operations.  Each invocation is actually a @emph{transaction}: either
the specified operation succeeds, or nothing happens.  Thus, if the
@command{guix package} process is terminated during the transaction,
or if a power outage occurs during the transaction, then the user's
profile remains in its previous state, and remains usable.

In addition, any package transaction may be @emph{rolled back}.  So, if,
for example, an upgrade installs a new version of a package that turns
out to have a serious bug, users may roll back to the previous instance
of their profile, which was known to work well.  Similarly, the global
system configuration on Guix is subject to
transactional upgrades and roll-back
(@pxref{Getting Started with the System}).

All packages in the package store may be @emph{garbage-collected}.
Guix can determine which packages are still referenced by user
profiles, and remove those that are provably no longer referenced
(@pxref{Invoking guix gc}).  Users may also explicitly remove old
generations of their profile so that the packages they refer to can be
collected.

@cindex reproducibility
@cindex reproducible builds
Guix takes a @dfn{purely functional} approach to package
management, as described in the introduction (@pxref{Introduction}).
Each @file{/gnu/store} package directory name contains a hash of all the
inputs that were used to build that package---compiler, libraries, build
scripts, etc.  This direct correspondence allows users to make sure a
given package installation matches the current state of their
distribution.  It also helps maximize @dfn{build reproducibility}:
thanks to the isolated build environments that are used, a given build
is likely to yield bit-identical files when performed on different
machines (@pxref{Invoking guix-daemon, container}).

@cindex substitutes
This foundation allows Guix to support @dfn{transparent binary/source
deployment}.  When a pre-built binary for a @file{/gnu/store} item is
available from an external source---a @dfn{substitute}, Guix just
downloads it and unpacks it;
otherwise, it builds the package from source, locally
(@pxref{Substitutes}).  Because build results are usually bit-for-bit
reproducible, users do not have to trust servers that provide
substitutes: they can force a local build and @emph{challenge} providers
(@pxref{Invoking guix challenge}).

Control over the build environment is a feature that is also useful for
developers.  The @command{guix shell} command allows developers of
a package to quickly set up the right development environment for their
package, without having to manually install the dependencies of the
package into their profile (@pxref{Invoking guix shell}).

@cindex replication, of software environments
@cindex provenance tracking, of software artifacts
All of Guix and its package definitions is version-controlled, and
@command{guix pull} allows you to ``travel in time'' on the history of Guix
itself (@pxref{Invoking guix pull}).  This makes it possible to replicate a
Guix instance on a different machine or at a later point in time, which in
turn allows you to @emph{replicate complete software environments}, while
retaining precise @dfn{provenance tracking} of the software.

@node Invoking guix package
@section Invoking @command{guix package}

@cindex installing packages
@cindex removing packages
@cindex package installation
@cindex package removal
@cindex profile
@cindex @command{guix package}
The @command{guix package} command is the tool that allows users to
install, upgrade, and remove packages, as well as rolling back to
previous configurations.  These operations work on a user
@dfn{profile}---a directory of installed packages.  Each user has a
default profile in @file{$HOME/.guix-profile}.
The command operates only on the user's own profile,
and works with normal user privileges (@pxref{Features}).  Its syntax
is:

@example
guix package @var{options}
@end example

@cindex transactions
Primarily, @var{options} specifies the operations to be performed during
the transaction.  Upon completion, a new profile is created, but
previous @dfn{generations} of the profile remain available, should the user
want to roll back.

For example, to remove @code{lua} and install @code{guile} and
@code{guile-cairo} in a single transaction:

@example
guix package -r lua -i guile guile-cairo
@end example

@cindex aliases, for @command{guix package}
For your convenience, we also provide the following aliases:

@itemize
@item
@command{guix search} is an alias for @command{guix package -s},
@item
@command{guix install} is an alias for @command{guix package -i},
@item
@command{guix remove} is an alias for @command{guix package -r},
@item
@command{guix upgrade} is an alias for @command{guix package -u},
@item
and @command{guix show} is an alias for @command{guix package --show=}.
@end itemize

These aliases are less expressive than @command{guix package} and provide
fewer options, so in some cases you'll probably want to use @command{guix
package} directly.

@command{guix package} also supports a @dfn{declarative approach}
whereby the user specifies the exact set of packages to be available and
passes it @i{via} the @option{--manifest} option
(@pxref{profile-manifest, @option{--manifest}}).

@cindex profile
For each user, a symlink to the user's default profile is automatically
created in @file{$HOME/.guix-profile}.  This symlink always points to the
current generation of the user's default profile.  Thus, users can add
@file{$HOME/.guix-profile/bin} to their @env{PATH} environment
variable, and so on.
@cindex search paths
If you are not using Guix System, consider adding the
following lines to your @file{~/.bash_profile} (@pxref{Bash Startup
Files,,, bash, The GNU Bash Reference Manual}) so that newly-spawned
shells get all the right environment variable definitions:

@example
GUIX_PROFILE="$HOME/.guix-profile" ; \
source "$GUIX_PROFILE/etc/profile"
@end example

In a multi-user setup, user profiles are stored in a place registered as
a @dfn{garbage-collector root}, which @file{$HOME/.guix-profile} points
to (@pxref{Invoking guix gc}).  That directory is normally
@code{@var{localstatedir}/guix/profiles/per-user/@var{user}}, where
@var{localstatedir} is the value passed to @code{configure} as
@option{--localstatedir}, and @var{user} is the user name.  The
@file{per-user} directory is created when @command{guix-daemon} is
started, and the @var{user} sub-directory is created by @command{guix
package}.

The @var{options} can be among the following:

@table @code

@item --install=@var{package} @dots{}
@itemx -i @var{package} @dots{}
Install the specified @var{package}s.

Each @var{package} may specify a simple package name, such as
@code{guile}, optionally followed by an at-sign and version number,
such as @code{guile@@3.0.7} or simply @code{guile@@3.0}.  In the latter
case, the newest version prefixed by @code{3.0} is selected.

If no version number is specified, the newest available version will be
selected.  In addition, such a @var{package} specification
may contain a colon, followed by the name of one of the outputs of the
package, as in @code{gcc:doc} or @code{binutils@@2.22:lib}
(@pxref{Packages with Multiple Outputs}).

Packages with a corresponding
name (and optionally version) are searched for among the GNU
distribution modules (@pxref{Package Modules}).

Alternatively, a @var{package} can directly specify a store file name
such as @file{/gnu/store/...-guile-3.0.7}, as produced by, e.g.,
@code{guix build}.

@cindex propagated inputs
Sometimes packages have @dfn{propagated inputs}: these are dependencies
that automatically get installed along with the required package
(@pxref{package-propagated-inputs, @code{propagated-inputs} in
@code{package} objects}, for information about propagated inputs in
package definitions).

@anchor{package-cmd-propagated-inputs}
An example is the GNU MPC library: its C header files refer to those of
the GNU MPFR library, which in turn refer to those of the GMP library.
Thus, when installing MPC, the MPFR and GMP libraries also get installed
in the profile; removing MPC also removes MPFR and GMP---unless they had
also been explicitly installed by the user.

Besides, packages sometimes rely on the definition of environment
variables for their search paths (see explanation of
@option{--search-paths} below).  Any missing or possibly incorrect
environment variable definitions are reported here.

@item --install-from-expression=@var{exp}
@itemx -e @var{exp}
Install the package @var{exp} evaluates to.

@var{exp} must be a Scheme expression that evaluates to a
@code{<package>} object.  This option is notably useful to disambiguate
between same-named variants of a package, with expressions such as
@code{(@@ (gnu packages commencement) guile-final)}.

Note that this option installs the first output of the specified
package, which may be insufficient when needing a specific output of a
multiple-output package.

@item --install-from-file=@var{file}
@itemx -f @var{file}
Install the package that the code within @var{file} evaluates to.

As an example, @var{file} might contain a definition like this
(@pxref{Defining Packages}):

@lisp
@include package-hello.scm
@end lisp

Developers may find it useful to include such a @file{guix.scm} file
in the root of their project source tree that can be used to test
development snapshots and create reproducible development environments
(@pxref{Invoking guix shell}).

The @var{file} may also contain a JSON representation of one or more
package definitions.  Running @code{guix package -f} on
@file{hello.json} with the following contents would result in installing
the package @code{greeter} after building @code{myhello}:

@example
@verbatiminclude package-hello.json
@end example

@item --remove=@var{package} @dots{}
@itemx -r @var{package} @dots{}
Remove the specified @var{package}s.

As for @option{--install}, each @var{package} may specify a version number
and/or output name in addition to the package name.  For instance,
@samp{-r glibc:debug} would remove the @code{debug} output of
@code{glibc}.

@item --upgrade[=@var{regexp} @dots{}]
@itemx -u [@var{regexp} @dots{}]
@cindex upgrading packages
Upgrade all the installed packages.  If one or more @var{regexp}s are
specified, upgrade only installed packages whose name matches a
@var{regexp}.  Also see the @option{--do-not-upgrade} option below.

Note that this upgrades package to the latest version of packages found
in the distribution currently installed.  To update your distribution,
you should regularly run @command{guix pull} (@pxref{Invoking guix
pull}).

@cindex package transformations, upgrades
When upgrading, package transformations that were originally applied
when creating the profile are automatically re-applied (@pxref{Package
Transformation Options}).  For example, assume you first installed Emacs
from the tip of its development branch with:

@example
guix install emacs-next --with-branch=emacs-next=master
@end example

Next time you run @command{guix upgrade}, Guix will again pull the tip
of the Emacs development branch and build @code{emacs-next} from that
checkout.

Note that transformation options such as @option{--with-branch} and
@option{--with-source} depend on external state; it is up to you to
ensure that they work as expected.  You can also discard a
transformations that apply to a package by running:

@example
guix install @var{package}
@end example

@item --do-not-upgrade[=@var{regexp} @dots{}]
When used together with the @option{--upgrade} option, do @emph{not}
upgrade any packages whose name matches a @var{regexp}.  For example, to
upgrade all packages in the current profile except those containing the
substring ``emacs'':

@example
$ guix package --upgrade . --do-not-upgrade emacs
@end example

@item @anchor{profile-manifest}--manifest=@var{file}
@itemx -m @var{file}
@cindex profile declaration
@cindex profile manifest
Create a new generation of the profile from the manifest object
returned by the Scheme code in @var{file}.  This option can be repeated
several times, in which case the manifests are concatenated.

This allows you to @emph{declare} the profile's contents rather than
constructing it through a sequence of @option{--install} and similar
commands.  The advantage is that @var{file} can be put under version
control, copied to different machines to reproduce the same profile, and
so on.

@var{file} must return a @dfn{manifest} object, which is roughly a list
of packages:

@findex packages->manifest
@lisp
(use-package-modules guile emacs)

(packages->manifest
 (list emacs
       guile-2.0
       ;; Use a specific package output.
       (list guile-2.0 "debug")))
@end lisp

@xref{Writing Manifests}, for information on how to write a manifest.
@xref{export-manifest, @option{--export-manifest}}, to learn how to
obtain a manifest file from an existing profile.

@item --roll-back
@cindex rolling back
@cindex undoing transactions
@cindex transactions, undoing
Roll back to the previous @dfn{generation} of the profile---i.e., undo
the last transaction.

When combined with options such as @option{--install}, roll back occurs
before any other actions.

When rolling back from the first generation that actually contains
installed packages, the profile is made to point to the @dfn{zeroth
generation}, which contains no files apart from its own metadata.

After having rolled back, installing, removing, or upgrading packages
overwrites previous future generations.  Thus, the history of the
generations in a profile is always linear.

@item --switch-generation=@var{pattern}
@itemx -S @var{pattern}
@cindex generations
Switch to a particular generation defined by @var{pattern}.

@var{pattern} may be either a generation number or a number prefixed
with ``+'' or ``-''.  The latter means: move forward/backward by a
specified number of generations.  For example, if you want to return to
the latest generation after @option{--roll-back}, use
@option{--switch-generation=+1}.

The difference between @option{--roll-back} and
@option{--switch-generation=-1} is that @option{--switch-generation} will
not make a zeroth generation, so if a specified generation does not
exist, the current generation will not be changed.

@item --search-paths[=@var{kind}]
@cindex search paths
Report environment variable definitions, in Bash syntax, that may be
needed in order to use the set of installed packages.  These environment
variables are used to specify @dfn{search paths} for files used by some
of the installed packages.

For example, GCC needs the @env{CPATH} and @env{LIBRARY_PATH}
environment variables to be defined so it can look for headers and
libraries in the user's profile (@pxref{Environment Variables,,, gcc,
Using the GNU Compiler Collection (GCC)}).  If GCC and, say, the C
library are installed in the profile, then @option{--search-paths} will
suggest setting these variables to @file{@var{profile}/include} and
@file{@var{profile}/lib}, respectively (@pxref{Search Paths}, for info
on search path specifications associated with packages.)

The typical use case is to define these environment variables in the
shell:

@example
$ eval $(guix package --search-paths)
@end example

@var{kind} may be one of @code{exact}, @code{prefix}, or @code{suffix},
meaning that the returned environment variable definitions will either
be exact settings, or prefixes or suffixes of the current value of these
variables.  When omitted, @var{kind} defaults to @code{exact}.

This option can also be used to compute the @emph{combined} search paths
of several profiles.  Consider this example:

@example
$ guix package -p foo -i guile
$ guix package -p bar -i guile-json
$ guix package -p foo -p bar --search-paths
@end example

The last command above reports about the @env{GUILE_LOAD_PATH}
variable, even though, taken individually, neither @file{foo} nor
@file{bar} would lead to that recommendation.


@cindex profile, choosing
@item --profile=@var{profile}
@itemx -p @var{profile}
Use @var{profile} instead of the user's default profile.

@var{profile} must be the name of a file that will be created upon
completion.  Concretely, @var{profile} will be a mere symbolic link
(``symlink'') pointing to the actual profile where packages are
installed:

@example
$ guix install hello -p ~/code/my-profile
@dots{}
$ ~/code/my-profile/bin/hello
Hello, world!
@end example

All it takes to get rid of the profile is to remove this symlink and its
siblings that point to specific generations:

@example
$ rm ~/code/my-profile ~/code/my-profile-*-link
@end example

@item --list-profiles
List all the user's profiles:

@example
$ guix package --list-profiles
/home/charlie/.guix-profile
/home/charlie/code/my-profile
/home/charlie/code/devel-profile
/home/charlie/tmp/test
@end example

When running as root, list all the profiles of all the users.

@cindex collisions, in a profile
@cindex colliding packages in profiles
@cindex profile collisions
@item --allow-collisions
Allow colliding packages in the new profile.  Use at your own risk!

By default, @command{guix package} reports as an error @dfn{collisions}
in the profile.  Collisions happen when two or more different versions
or variants of a given package end up in the profile.

@item --bootstrap
Use the bootstrap Guile to build the profile.  This option is only
useful to distribution developers.

@end table

In addition to these actions, @command{guix package} supports the
following options to query the current state of a profile, or the
availability of packages:

@table @option

@item --search=@var{regexp}
@itemx -s @var{regexp}
@anchor{guix-search}
@cindex searching for packages
List the available packages whose name, synopsis, or description matches
@var{regexp} (in a case-insensitive fashion), sorted by relevance.
Print all the metadata of matching packages in
@code{recutils} format (@pxref{Top, GNU recutils databases,, recutils,
GNU recutils manual}).

This allows specific fields to be extracted using the @command{recsel}
command, for instance:

@example
$ guix package -s malloc | recsel -p name,version,relevance
name: jemalloc
version: 4.5.0
relevance: 6

name: glibc
version: 2.25
relevance: 1

name: libgc
version: 7.6.0
relevance: 1
@end example

Similarly, to show the name of all the packages available under the
terms of the GNU@tie{}LGPL version 3:

@example
$ guix package -s "" | recsel -p name -e 'license ~ "LGPL 3"'
name: elfutils

name: gmp
@dots{}
@end example

It is also possible to refine search results using several @code{-s} flags to
@command{guix package}, or several arguments to @command{guix search}.  For
example, the following command returns a list of board games (this time using
the @command{guix search} alias):

@example
$ guix search '\<board\>' game | recsel -p name
name: gnubg
@dots{}
@end example

If we were to omit @code{-s game}, we would also get software packages
that deal with printed circuit boards; removing the angle brackets
around @code{board} would further add packages that have to do with
keyboards.

And now for a more elaborate example.  The following command searches
for cryptographic libraries, filters out Haskell, Perl, Python, and Ruby
libraries, and prints the name and synopsis of the matching packages:

@example
$ guix search crypto library | \
    recsel -e '! (name ~ "^(ghc|perl|python|ruby)")' -p name,synopsis
@end example

@noindent
@xref{Selection Expressions,,, recutils, GNU recutils manual}, for more
information on @dfn{selection expressions} for @code{recsel -e}.

@item --show=@var{package}
Show details about @var{package}, taken from the list of available packages, in
@code{recutils} format (@pxref{Top, GNU recutils databases,, recutils, GNU
recutils manual}).

@example
$ guix package --show=guile | recsel -p name,version
name: guile
version: 3.0.5

name: guile
version: 3.0.2

name: guile
version: 2.2.7
@dots{}
@end example

You may also specify the full name of a package to only get details about a
specific version of it (this time using the @command{guix show} alias):
@example
$ guix show guile@@3.0.5 | recsel -p name,version
name: guile
version: 3.0.5
@end example

@item --list-installed[=@var{regexp}]
@itemx -I [@var{regexp}]
List the currently installed packages in the specified profile, with the
most recently installed packages shown last.  When @var{regexp} is
specified, list only installed packages whose name matches @var{regexp}.

For each installed package, print the following items, separated by
tabs: the package name, its version string, the part of the package that
is installed (for instance, @code{out} for the default output,
@code{include} for its headers, etc.), and the path of this package in
the store.

@item --list-available[=@var{regexp}]
@itemx -A [@var{regexp}]
List packages currently available in the distribution for this system
(@pxref{GNU Distribution}).  When @var{regexp} is specified, list only
available packages whose name matches @var{regexp}.

For each package, print the following items separated by tabs: its name,
its version string, the parts of the package (@pxref{Packages with
Multiple Outputs}), and the source location of its definition.

@item --list-generations[=@var{pattern}]
@itemx -l [@var{pattern}]
@cindex generations
Return a list of generations along with their creation dates; for each
generation, show the installed packages, with the most recently
installed packages shown last.  Note that the zeroth generation is never
shown.

For each installed package, print the following items, separated by
tabs: the name of a package, its version string, the part of the package
that is installed (@pxref{Packages with Multiple Outputs}), and the
location of this package in the store.

When @var{pattern} is used, the command returns only matching
generations.  Valid patterns include:

@itemize
@item @emph{Integers and comma-separated integers}.  Both patterns denote
generation numbers.  For instance, @option{--list-generations=1} returns
the first one.

And @option{--list-generations=1,8,2} outputs three generations in the
specified order.  Neither spaces nor trailing commas are allowed.

@item @emph{Ranges}.  @option{--list-generations=2..9} prints the
specified generations and everything in between.  Note that the start of
a range must be smaller than its end.

It is also possible to omit the endpoint.  For example,
@option{--list-generations=2..}, returns all generations starting from the
second one.

@item @emph{Durations}.  You can also get the last @emph{N}@tie{}days, weeks,
or months by passing an integer along with the first letter of the
duration.  For example, @option{--list-generations=20d} lists generations
that are up to 20 days old.
@end itemize

@item --delete-generations[=@var{pattern}]
@itemx -d [@var{pattern}]
When @var{pattern} is omitted, delete all generations except the current
one.

This command accepts the same patterns as @option{--list-generations}.
When @var{pattern} is specified, delete the matching generations.  When
@var{pattern} specifies a duration, generations @emph{older} than the
specified duration match.  For instance, @option{--delete-generations=1m}
deletes generations that are more than one month old.

If the current generation matches, it is @emph{not} deleted.  Also, the
zeroth generation is never deleted.

Note that deleting generations prevents rolling back to them.
Consequently, this command must be used with care.

@cindex manifest, exporting
@anchor{export-manifest}
@item --export-manifest
Write to standard output a manifest suitable for @option{--manifest}
corresponding to the chosen profile(s).

This option is meant to help you migrate from the ``imperative''
operating mode---running @command{guix install}, @command{guix upgrade},
etc.---to the declarative mode that @option{--manifest} offers.

Be aware that the resulting manifest @emph{approximates} what your
profile actually contains; for instance, depending on how your profile
was created, it can refer to packages or package versions that are not
exactly what you specified.

Keep in mind that a manifest is purely symbolic: it only contains
package names and possibly versions, and their meaning varies over time.
If you wish to ``pin'' channels to the revisions that were used to build
the profile(s), see @option{--export-channels} below.

@cindex pinning, channel revisions of a profile
@item --export-channels
Write to standard output the list of channels used by the chosen
profile(s), in a format suitable for @command{guix pull --channels} or
@command{guix time-machine --channels} (@pxref{Channels}).

Together with @option{--export-manifest}, this option provides
information allowing you to replicate the current profile
(@pxref{Replicating Guix}).

However, note that the output of this command @emph{approximates} what
was actually used to build this profile.  In particular, a single
profile might have been built from several different revisions of the
same channel.  In that case, @option{--export-manifest} chooses the last
one and writes the list of other revisions in a comment.  If you really
need to pick packages from different channel revisions, you can use
inferiors in your manifest to do so (@pxref{Inferiors}).

Together with @option{--export-manifest}, this is a good starting point
if you are willing to migrate from the ``imperative'' model to the fully
declarative model consisting of a manifest file along with a channels
file pinning the exact channel revision(s) you want.
@end table

Finally, since @command{guix package} may actually start build
processes, it supports all the common build options (@pxref{Common Build
Options}).  It also supports package transformation options, such as
@option{--with-source}, and preserves them across upgrades
(@pxref{Package Transformation Options}).

@node Substitutes
@section Substitutes

@cindex substitutes
@cindex pre-built binaries
Guix supports transparent source/binary deployment, which means that it
can either build things locally, or download pre-built items from a
server, or both.  We call these pre-built items @dfn{substitutes}---they
are substitutes for local build results.  In many cases, downloading a
substitute is much faster than building things locally.

Substitutes can be anything resulting from a derivation build
(@pxref{Derivations}).  Of course, in the common case, they are
pre-built package binaries, but source tarballs, for instance, which
also result from derivation builds, can be available as substitutes.

@menu
* Official Substitute Servers::  One particular source of substitutes.
* Substitute Server Authorization::  How to enable or disable substitutes.
* Getting Substitutes from Other Servers::  Substitute diversity.
* Substitute Authentication::   How Guix verifies substitutes.
* Proxy Settings::              How to get substitutes via proxy.
* Substitution Failure::        What happens when substitution fails.
* On Trusting Binaries::        How can you trust that binary blob?
@end menu

@node Official Substitute Servers
@subsection Official Substitute Servers

@cindex build farm
@code{@value{SUBSTITUTE-SERVER-1}} and
@code{@value{SUBSTITUTE-SERVER-2}} are both front-ends to official build
farms that build packages from Guix continuously for some architectures,
and make them available as substitutes.  These are the default source of
substitutes; which can be overridden by passing the
@option{--substitute-urls} option either to @command{guix-daemon}
(@pxref{daemon-substitute-urls,, @code{guix-daemon --substitute-urls}})
or to client tools such as @command{guix package}
(@pxref{client-substitute-urls,, client @option{--substitute-urls}
option}).

Substitute URLs can be either HTTP or HTTPS.
HTTPS is recommended because communications are encrypted; conversely,
using HTTP makes all communications visible to an eavesdropper, who
could use the information gathered to determine, for instance, whether
your system has unpatched security vulnerabilities.

Substitutes from the official build farms are enabled by default when
using Guix System (@pxref{GNU Distribution}).  However,
they are disabled by default when using Guix on a foreign distribution,
unless you have explicitly enabled them via one of the recommended
installation steps (@pxref{Installation}).  The following paragraphs
describe how to enable or disable substitutes for the official build
farm; the same procedure can also be used to enable substitutes for any
other substitute server.

@node Substitute Server Authorization
@subsection Substitute Server Authorization

@cindex security
@cindex substitutes, authorization thereof
@cindex access control list (ACL), for substitutes
@cindex ACL (access control list), for substitutes
To allow Guix to download substitutes from @code{@value{SUBSTITUTE-SERVER-1}}, @code{@value{SUBSTITUTE-SERVER-2}} or a mirror, you
must add the relevant public key to the access control list (ACL) of archive
imports, using the @command{guix archive} command (@pxref{Invoking guix
archive}).  Doing so implies that you trust the substitute server to not
be compromised and to serve genuine substitutes.

@quotation Note
If you are using Guix System, you can skip this section: Guix System
authorizes substitutes from @code{@value{SUBSTITUTE-SERVER-1}} and
@code{@value{SUBSTITUTE-SERVER-2}} by default.
@end quotation

The public keys for each of the project maintained substitute servers
are installed along with Guix, in @code{@var{prefix}/share/guix/}, where
@var{prefix} is the installation prefix of Guix.  If you installed Guix
from source, make sure you checked the GPG signature of
@file{guix-@value{VERSION}.tar.gz}, which contains this public key file.
Then, you can run something like this:

@example
# guix archive --authorize < @var{prefix}/share/guix/@value{SUBSTITUTE-SERVER-1}.pub
# guix archive --authorize < @var{prefix}/share/guix/@value{SUBSTITUTE-SERVER-2}.pub
@end example

Once this is in place, the output of a command like @code{guix build}
should change from something like:

@example
$ guix build emacs --dry-run
The following derivations would be built:
   /gnu/store/yr7bnx8xwcayd6j95r2clmkdl1qh688w-emacs-24.3.drv
   /gnu/store/x8qsh1hlhgjx6cwsjyvybnfv2i37z23w-dbus-1.6.4.tar.gz.drv
   /gnu/store/1ixwp12fl950d15h2cj11c73733jay0z-alsa-lib-1.0.27.1.tar.bz2.drv
   /gnu/store/nlma1pw0p603fpfiqy7kn4zm105r5dmw-util-linux-2.21.drv
@dots{}
@end example

@noindent
to something like:

@example
$ guix build emacs --dry-run
112.3 MB would be downloaded:
   /gnu/store/pk3n22lbq6ydamyymqkkz7i69wiwjiwi-emacs-24.3
   /gnu/store/2ygn4ncnhrpr61rssa6z0d9x22si0va3-libjpeg-8d
   /gnu/store/71yz6lgx4dazma9dwn2mcjxaah9w77jq-cairo-1.12.16
   /gnu/store/7zdhgp0n1518lvfn8mb96sxqfmvqrl7v-libxrender-0.9.7
@dots{}
@end example

@noindent
The text changed from ``The following derivations would be built'' to
``112.3 MB would be downloaded''.  This indicates that substitutes from
the configured substitute servers are usable and will be downloaded,
when possible, for future builds.

@cindex substitutes, how to disable
The substitute mechanism can be disabled globally by running
@code{guix-daemon} with @option{--no-substitutes} (@pxref{Invoking
guix-daemon}).  It can also be disabled temporarily by passing the
@option{--no-substitutes} option to @command{guix package},
@command{guix build}, and other command-line tools.

@node Getting Substitutes from Other Servers
@subsection Getting Substitutes from Other Servers
@c Note: This section name appears in a hint printed by 'guix weather'.

@cindex substitute servers, adding more
Guix can look up and fetch substitutes from several servers.  This is
useful when you are using packages from additional channels for which
the official server does not have substitutes but another server
provides them.  Another situation where this is useful is when you would
prefer to download from your organization's substitute server, resorting
to the official server only as a fallback or dismissing it altogether.

You can give Guix a list of substitute server URLs and it will check
them in the specified order.  You also need to explicitly authorize the
public keys of substitute servers to instruct Guix to accept the
substitutes they sign.

On Guix System, this is achieved by modifying the configuration of the
@code{guix} service.  Since the @code{guix} service is part of the
default lists of services, @code{%base-services} and
@code{%desktop-services}, you can use @code{modify-services} to change
its configuration and add the URLs and substitute keys that you want
(@pxref{Service Reference, @code{modify-services}}).

As an example, suppose you want to fetch substitutes from
@code{guix.example.org} and to authorize the signing key of that server,
in addition to the default @code{@value{SUBSTITUTE-SERVER-1}} and
@code{@value{SUBSTITUTE-SERVER-2}}.  The resulting operating system
configuration will look something like:

@lisp
(operating-system
  ;; @dots{}
  (services
    ;; Assume we're starting from '%desktop-services'.  Replace it
    ;; with the list of services you're actually using.
    (modify-services %desktop-services
      (guix-service-type config =>
                        (guix-configuration
                          (inherit config)
                          (substitute-urls
                            (append (list "https://guix.example.org")
                                    %default-substitute-urls))
                          (authorized-keys
                            (append (list (local-file "./key.pub"))
                                    %default-authorized-guix-keys)))))))
@end lisp

This assumes that the file @file{key.pub} contains the signing key of
@code{guix.example.org}.  With this change in place in your operating
system configuration file (say @file{/etc/config.scm}), you can
reconfigure and restart the @code{guix-daemon} service or reboot so the
changes take effect:

@example
$ sudo guix system reconfigure /etc/config.scm
$ sudo herd restart guix-daemon
@end example

If you're running Guix on a ``foreign distro'', you would instead take
the following steps to get substitutes from additional servers:

@enumerate
@item
Edit the service configuration file for @code{guix-daemon}; when using
systemd, this is normally
@file{/etc/systemd/system/guix-daemon.service}.  Add the
@option{--substitute-urls} option on the @command{guix-daemon} command
line and list the URLs of interest (@pxref{daemon-substitute-urls,
@code{guix-daemon --substitute-urls}}):

@example
@dots{} --substitute-urls='https://guix.example.org @value{SUBSTITUTE-URLS}'
@end example

@item
Restart the daemon.  For systemd, it goes like this:

@example
systemctl daemon-reload
systemctl restart guix-daemon.service
@end example

@item
Authorize the key of the new server (@pxref{Invoking guix archive}):

@example
guix archive --authorize < key.pub
@end example

Again this assumes @file{key.pub} contains the public key that
@code{guix.example.org} uses to sign substitutes.
@end enumerate

Now you're all set!  Substitutes will be preferably taken from
@code{https://guix.example.org}, using
@code{@value{SUBSTITUTE-SERVER-1}} then
@code{@value{SUBSTITUTE-SERVER-2}} as fallback options.  Of course you
can list as many substitute servers as you like, with the caveat that
substitute lookup can be slowed down if too many servers need to be
contacted.

@quotation Troubleshooting
To diagnose problems, you can run @command{guix weather}.  For example,
running:

@example
guix weather coreutils
@end example

@noindent
not only tells you which of the currently-configured servers has
substitutes for the @code{coreutils} package, it also reports whether
one of these servers is unauthorized.  @xref{Invoking guix weather}, for
more information.
@end quotation

Note that there are also situations where one may want to add the URL of
a substitute server @emph{without} authorizing its key.
@xref{Substitute Authentication}, to understand this fine point.

@node Substitute Authentication
@subsection Substitute Authentication

@cindex digital signatures
Guix detects and raises an error when attempting to use a substitute
that has been tampered with.  Likewise, it ignores substitutes that are
not signed, or that are not signed by one of the keys listed in the ACL.

There is one exception though: if an unauthorized server provides
substitutes that are @emph{bit-for-bit identical} to those provided by
an authorized server, then the unauthorized server becomes eligible for
downloads.  For example, assume we have chosen two substitute servers
with this option:

@example
--substitute-urls="https://a.example.org https://b.example.org"
@end example

@noindent
@cindex reproducible builds
If the ACL contains only the key for @samp{b.example.org}, and if
@samp{a.example.org} happens to serve the @emph{exact same} substitutes,
then Guix will download substitutes from @samp{a.example.org} because it
comes first in the list and can be considered a mirror of
@samp{b.example.org}.  In practice, independent build machines usually
produce the same binaries, thanks to bit-reproducible builds (see
below).

When using HTTPS, the server's X.509 certificate is @emph{not} validated
(in other words, the server is not authenticated), contrary to what
HTTPS clients such as Web browsers usually do.  This is because Guix
authenticates substitute information itself, as explained above, which
is what we care about (whereas X.509 certificates are about
authenticating bindings between domain names and public keys).

@node Proxy Settings
@subsection Proxy Settings

@vindex http_proxy
@vindex https_proxy
Substitutes are downloaded over HTTP or HTTPS@.  The @env{http_proxy} and
@env{https_proxy} environment variables can be set in the environment of
@command{guix-daemon} and are honored for downloads of substitutes.
Note that the value of those environment variables in the environment
where @command{guix build}, @command{guix package}, and other client
commands are run has @emph{absolutely no effect}.

@node Substitution Failure
@subsection Substitution Failure

Even when a substitute for a derivation is available, sometimes the
substitution attempt will fail.  This can happen for a variety of
reasons: the substitute server might be offline, the substitute may
recently have been deleted, the connection might have been interrupted,
etc.

When substitutes are enabled and a substitute for a derivation is
available, but the substitution attempt fails, Guix will attempt to
build the derivation locally depending on whether or not
@option{--fallback} was given (@pxref{fallback-option,, common build
option @option{--fallback}}).  Specifically, if @option{--fallback} was
omitted, then no local build will be performed, and the derivation is
considered to have failed.  However, if @option{--fallback} was given,
then Guix will attempt to build the derivation locally, and the success
or failure of the derivation depends on the success or failure of the
local build.  Note that when substitutes are disabled or no substitute
is available for the derivation in question, a local build will
@emph{always} be performed, regardless of whether or not
@option{--fallback} was given.

To get an idea of how many substitutes are available right now, you can
try running the @command{guix weather} command (@pxref{Invoking guix
weather}).  This command provides statistics on the substitutes provided
by a server.

@node On Trusting Binaries
@subsection On Trusting Binaries

@cindex trust, of pre-built binaries
Today, each individual's control over their own computing is at the
mercy of institutions, corporations, and groups with enough power and
determination to subvert the computing infrastructure and exploit its
weaknesses.  While using substitutes can be convenient, we encourage
users to also build on their own, or even run their own build farm, such
that the project run substitute servers are less of an interesting
target.  One way to help is by publishing the software you build using
@command{guix publish} so that others have one more choice of server to
download substitutes from (@pxref{Invoking guix publish}).

Guix has the foundations to maximize build reproducibility
(@pxref{Features}).  In most cases, independent builds of a given
package or derivation should yield bit-identical results.  Thus, through
a diverse set of independent package builds, we can strengthen the
integrity of our systems.  The @command{guix challenge} command aims to
help users assess substitute servers, and to assist developers in
finding out about non-deterministic package builds (@pxref{Invoking guix
challenge}).  Similarly, the @option{--check} option of @command{guix
build} allows users to check whether previously-installed substitutes
are genuine by rebuilding them locally (@pxref{build-check,
@command{guix build --check}}).

In the future, we want Guix to have support to publish and retrieve
binaries to/from other users, in a peer-to-peer fashion.  If you would
like to discuss this project, join us on @email{guix-devel@@gnu.org}.

@node Packages with Multiple Outputs
@section Packages with Multiple Outputs

@cindex multiple-output packages
@cindex package outputs
@cindex outputs

Often, packages defined in Guix have a single @dfn{output}---i.e., the
source package leads to exactly one directory in the store.  When running
@command{guix install glibc}, one installs the default output of the
GNU libc package; the default output is called @code{out}, but its name
can be omitted as shown in this command.  In this particular case, the
default output of @code{glibc} contains all the C header files, shared
libraries, static libraries, Info documentation, and other supporting
files.

Sometimes it is more appropriate to separate the various types of files
produced from a single source package into separate outputs.  For
instance, the GLib C library (used by GTK+ and related packages)
installs more than 20 MiB of reference documentation as HTML pages.
To save space for users who do not need it, the documentation goes to a
separate output, called @code{doc}.  To install the main GLib output,
which contains everything but the documentation, one would run:

@example
guix install glib
@end example

@cindex documentation
The command to install its documentation is:

@example
guix install glib:doc
@end example

While the colon syntax works for command-line specification of package
outputs, it will not work when using a package @emph{variable} in Scheme
code.  For example, to add the documentation of @code{glib} to the
globally installed packages of an @code{operating-system} (see
@ref{operating-system Reference}), a list of two items, the first one
being the package @emph{variable} and the second one the name of the
output to select (a string), must be used instead:

@lisp
(use-modules (gnu packages glib))
;; glib-with-documentation is the Guile symbol for the glib package
(operating-system
 ...
 (packages
  (append
   (list (list glib-with-documentation "doc"))
         %base-packages)))
@end lisp

Some packages install programs with different ``dependency footprints''.
For instance, the WordNet package installs both command-line tools and
graphical user interfaces (GUIs).  The former depend solely on the C
library, whereas the latter depend on Tcl/Tk and the underlying X
libraries.  In this case, we leave the command-line tools in the default
output, whereas the GUIs are in a separate output.  This allows users
who do not need the GUIs to save space.  The @command{guix size} command
can help find out about such situations (@pxref{Invoking guix size}).
@command{guix graph} can also be helpful (@pxref{Invoking guix graph}).

There are several such multiple-output packages in the GNU distribution.
Other conventional output names include @code{lib} for libraries and
possibly header files, @code{bin} for stand-alone programs, and
@code{debug} for debugging information (@pxref{Installing Debugging
Files}).  The outputs of a package are listed in the third column of
the output of @command{guix package --list-available} (@pxref{Invoking
guix package}).


@node Invoking guix locate
@section Invoking @command{guix locate}

@cindex file, searching in packages
@cindex file search
@cindex searching for packages
There's so much free software out there that sooner or later, you will
need to search for packages.  The @command{guix search} command that
we've seen before (@pxref{Invoking guix package}) lets you search by
keywords:

@example
guix search video editor
@end example

@cindex searching for packages, by file name
Sometimes, you instead want to find which package provides a given file,
and this is where @command{guix locate} comes in.  Here is how you can
find which package provides the @command{ls} command:

@example
$ guix locate ls
coreutils@@9.1       /gnu/store/@dots{}-coreutils-9.1/bin/ls
@end example

Of course the command works for any file, not just commands:

@example
$ guix locate unistr.h
icu4c@@71.1          /gnu/store/@dots{}/include/unicode/unistr.h
libunistring@@1.0    /gnu/store/@dots{}/include/unistr.h
@end example

You may also specify @dfn{glob patterns} with wildcards.  For example,
here is how you would search for packages providing @file{.service}
files:

@example
$ guix locate -g '*.service'
man-db@@2.11.1        @dots{}/lib/systemd/system/man-db.service
wpa-supplicant@@2.10  @dots{}/system-services/fi.w1.wpa_supplicant1.service
@end example

The @command{guix locate} command relies on a database that maps file
names to package names.  By default, it automatically creates that
database if it does not exist yet by traversing packages available
@emph{locally}, which can take a few minutes (depending on the size of
your store and the speed of your storage device).

@quotation Note
For now, @command{guix locate} builds its database based on purely local
knowledge---meaning that you will not find packages that never reached
your store.  Eventually it will support downloading a pre-built database
so you can potentially find more packages.
@end quotation

By default, @command{guix locate} first tries to look for a system-wide
database, usually under @file{/var/cache/guix/locate}; if it does not
exist or is too old, it falls back to the per-user database, by default
under @file{~/.cache/guix/locate}.  On a multi-user system,
administrators may want to periodically update the system-wide database
so that all users can benefit from it, for instance by setting up
@code{package-database-service-type} (@pxref{File Search Services,
@code{package-database-service-type}}).

The general syntax is:

@example
guix locate [@var{options}@dots{}] @var{file}@dots{}
@end example

@noindent
... where @var{file} is the name of a file to search for (specifically,
the ``base name'' of the file: files whose parent directories are called
@var{file} are not matched).

The available options are as follows:

@table @code
@item --glob
@item -g
Interpret @var{file}@dots{} as @dfn{glob patterns}---patterns that may
include wildcards, such as @samp{*.scm} to denote all files ending in
@samp{.scm}.

@item --stats
Display database statistics.

@item --update
@itemx -u
Update the file database.

By default, the database is automatically updated when it is too old.

@item --clear
Clear the database and re-populate it.

This option lets you start anew, ensuring old data is removed from the
database, which also avoids having an endlessly growing database.  By
default @command{guix locate} automatically does that periodically,
though infrequently.

@item --database=@var{file}
Use @var{file} as the database, creating it if necessary.

By default, @command{guix locate} picks the database under
@file{~/.cache/guix} or @file{/var/cache/guix}, whichever is the most
recent one.

@item --method=@var{method}
@itemx -m @var{method}
Use @var{method} to select the set of packages to index.  Possible
values are:

@table @code
@item manifests
This is the default method: it works by traversing profiles on the
machine and recording packages it encounters---packages you or other
users of the machine installed, directly or indirectly.  It is fast but
it can miss other packages available in the store but not referred to by
any profile.

@item store
This is a slower but more exhaustive method: it checks among all the
existing packages those that are available in the store and records
them.
@end table
@end table


@node Invoking guix gc
@section Invoking @command{guix gc}

@cindex garbage collector
@cindex disk space
@cindex @command{guix gc}
Packages that are installed, but not used, may be @dfn{garbage-collected}.
The @command{guix gc} command allows users to explicitly run the garbage
collector to reclaim space from the @file{/gnu/store} directory.  It is
the @emph{only} way to remove files from @file{/gnu/store}---removing
files or directories manually may break it beyond repair!

@cindex GC roots
@cindex garbage collector roots
The garbage collector has a set of known @dfn{roots}: any file under
@file{/gnu/store} reachable from a root is considered @dfn{live} and
cannot be deleted; any other file is considered @dfn{dead} and may be
deleted.  The set of garbage collector roots (``GC roots'' for short)
includes default user profiles; by default, the symlinks under
@file{/var/guix/gcroots} represent these GC roots.  New GC roots can be
added with @command{guix build --root}, for example (@pxref{Invoking
guix build}).  The @command{guix gc --list-roots} command lists them.

Prior to running @code{guix gc --collect-garbage} to make space, it is
often useful to remove old generations from user profiles; that way, old
package builds referenced by those generations can be reclaimed.  This
is achieved by running @code{guix package --delete-generations}
(@pxref{Invoking guix package}).

Our recommendation is to run a garbage collection periodically, or when
you are short on disk space.  For instance, to guarantee that at least
5@tie{}GB are available on your disk, simply run:

@example
guix gc -F 5G
@end example

It is perfectly safe to run as a non-interactive periodic job
(@pxref{Scheduled Job Execution}, for how to set up such a job).
Running @command{guix gc} with no arguments will collect as
much garbage as it can, but that is often inconvenient: you may find
yourself having to rebuild or re-download software that is ``dead'' from
the GC viewpoint but that is necessary to build other pieces of
software---e.g., the compiler tool chain.

The @command{guix gc} command has three modes of operation: it can be
used to garbage-collect any dead files (the default), to delete specific
files (the @option{--delete} option), to print garbage-collector
information, or for more advanced queries.  The garbage collection
options are as follows:

@table @code
@item --collect-garbage[=@var{min}]
@itemx -C [@var{min}]
Collect garbage---i.e., unreachable @file{/gnu/store} files and
sub-directories.  This is the default operation when no option is
specified.

When @var{min} is given, stop once @var{min} bytes have been collected.
@var{min} may be a number of bytes, or it may include a unit as a
suffix, such as @code{MiB} for mebibytes and @code{GB} for gigabytes
(@pxref{Block size, size specifications,, coreutils, GNU Coreutils}).

When @var{min} is omitted, collect all the garbage.

@item --free-space=@var{free}
@itemx -F @var{free}
Collect garbage until @var{free} space is available under
@file{/gnu/store}, if possible; @var{free} denotes storage space, such
as @code{500MiB}, as described above.

When @var{free} or more is already available in @file{/gnu/store}, do
nothing and exit immediately.

@item --delete-generations[=@var{duration}]
@itemx -d [@var{duration}]
Before starting the garbage collection process, delete all the generations
older than @var{duration}, for all the user profiles and home environment
generations; when run as root, this
applies to all the profiles @emph{of all the users}.

For example, this command deletes all the generations of all your profiles
that are older than 2 months (except generations that are current), and then
proceeds to free space until at least 10 GiB are available:

@example
guix gc -d 2m -F 10G
@end example

@item --delete
@itemx -D
Attempt to delete all the store files and directories specified as
arguments.  This fails if some of the files are not in the store, or if
they are still live.

@item --list-failures
List store items corresponding to cached build failures.

This prints nothing unless the daemon was started with
@option{--cache-failures} (@pxref{Invoking guix-daemon,
@option{--cache-failures}}).

@item --list-roots
List the GC roots owned by the user; when run as root, list @emph{all} the GC
roots.

@item --list-busy
List store items in use by currently running processes.  These store
items are effectively considered GC roots: they cannot be deleted.

@item --clear-failures
Remove the specified store items from the failed-build cache.

Again, this option only makes sense when the daemon is started with
@option{--cache-failures}.  Otherwise, it does nothing.

@item --list-dead
Show the list of dead files and directories still present in the
store---i.e., files and directories no longer reachable from any root.

@item --list-live
Show the list of live store files and directories.

@end table

In addition, the references among existing store files can be queried:

@table @code

@item --references
@itemx --referrers
@cindex package dependencies
List the references (respectively, the referrers) of store files given
as arguments.

@item --requisites
@itemx -R
@cindex closure
List the requisites of the store files passed as arguments.  Requisites
include the store files themselves, their references, and the references
of these, recursively.  In other words, the returned list is the
@dfn{transitive closure} of the store files.

@xref{Invoking guix size}, for a tool to profile the size of the closure
of an element.  @xref{Invoking guix graph}, for a tool to visualize
the graph of references.

@item --derivers
@cindex derivation
Return the derivation(s) leading to the given store items
(@pxref{Derivations}).

For example, this command:

@example
guix gc --derivers $(guix package -I ^emacs$ | cut -f4)
@end example

@noindent
returns the @file{.drv} file(s) leading to the @code{emacs} package
installed in your profile.

Note that there may be zero matching @file{.drv} files, for instance
because these files have been garbage-collected.  There can also be more
than one matching @file{.drv} due to fixed-output derivations.
@end table

Lastly, the following options allow you to check the integrity of the
store and to control disk usage.

@table @option

@item --verify[=@var{options}]
@cindex integrity, of the store
@cindex integrity checking
Verify the integrity of the store.

By default, make sure that all the store items marked as valid in the
database of the daemon actually exist in @file{/gnu/store}.

When provided, @var{options} must be a comma-separated list containing one
or more of @code{contents} and @code{repair}.

When passing @option{--verify=contents}, the daemon computes the
content hash of each store item and compares it against its hash in the
database.  Hash mismatches are reported as data corruptions.  Because it
traverses @emph{all the files in the store}, this command can take a
long time, especially on systems with a slow disk drive.

@cindex repairing the store
@cindex corruption, recovering from
Using @option{--verify=repair} or @option{--verify=contents,repair}
causes the daemon to try to repair corrupt store items by fetching
substitutes for them (@pxref{Substitutes}).  Because repairing is not
atomic, and thus potentially dangerous, it is available only to the
system administrator.  A lightweight alternative, when you know exactly
which items in the store are corrupt, is @command{guix build --repair}
(@pxref{Invoking guix build}).

@item --optimize
@cindex deduplication
Optimize the store by hard-linking identical files---this is
@dfn{deduplication}.

The daemon performs deduplication after each successful build or archive
import, unless it was started with @option{--disable-deduplication}
(@pxref{Invoking guix-daemon, @option{--disable-deduplication}}).  Thus,
this option is primarily useful when the daemon was running with
@option{--disable-deduplication}.

@item --vacuum-database
@cindex vacuum the store database
@comment Avoid words like 'repair,' 'compress,' and 'optimize.'
Guix uses an sqlite database to keep track of the items in (@pxref{The Store}).
Over time it is possible that the database may grow to a large size and become
fragmented.  As a result, one may wish to clear the freed space and join the
partially used pages in the database left behind from removed packages or after
running the garbage collector.  Running @command{sudo guix gc
--vacuum-database} will lock the database and @code{VACUUM} the store,
defragmenting the database and purging freed pages, unlocking the database when
it finishes.

@end table

@node Invoking guix pull
@section Invoking @command{guix pull}

@cindex upgrading Guix
@cindex updating Guix
@cindex @command{guix pull}
@cindex pull
@cindex security, @command{guix pull}
@cindex authenticity, of code obtained with @command{guix pull}
Packages are installed or upgraded to the latest version available in
the distribution currently available on your local machine.  To update
that distribution, along with the Guix tools, you must run @command{guix
pull}: the command downloads the latest Guix source code and package
descriptions, and deploys it.  Source code is downloaded from a
@uref{https://git-scm.com/book/en/, Git} repository, by default the official
GNU@tie{}Guix repository, though this can be customized.  @command{guix
pull} ensures that the code it downloads is @emph{authentic} by
verifying that commits are signed by Guix developers.

Specifically, @command{guix pull} downloads code from the @dfn{channels}
(@pxref{Channels}) specified by one of the following, in this order:

@enumerate
@item
the @option{--channels} option;
@item
the user's @file{~/.config/guix/channels.scm} file, unless @option{-q}
is passed;
@item
the system-wide @file{/etc/guix/channels.scm} file, unless @option{-q}
is passed (on Guix System, this file can be declared in the operating
system configuration, @pxref{guix-configuration-channels,
@code{channels} field of @code{guix-configuration}});
@item
the built-in default channels specified in the @code{%default-channels}
variable.
@end enumerate

On completion, @command{guix package} will use packages and package
versions from this just-retrieved copy of Guix.  Not only that, but all
the Guix commands and Scheme modules will also be taken from that latest
version.  New @command{guix} sub-commands added by the update also
become available.

Any user can update their Guix copy using @command{guix pull}, and the
effect is limited to the user who ran @command{guix pull}.  For
instance, when user @code{root} runs @command{guix pull}, this has no
effect on the version of Guix that user @code{alice} sees, and vice
versa.

The result of running @command{guix pull} is a @dfn{profile} available
under @file{~/.config/guix/current} containing the latest Guix.

The @option{--list-generations} or @option{-l} option lists past generations
produced by @command{guix pull}, along with details about their provenance:

@example
$ guix pull -l
Generation 1	Jun 10 2018 00:18:18
  guix 65956ad
    repository URL: https://git.savannah.gnu.org/git/guix.git
    branch: origin/master
    commit: 65956ad3526ba09e1f7a40722c96c6ef7c0936fe

Generation 2	Jun 11 2018 11:02:49
  guix e0cc7f6
    repository URL: https://git.savannah.gnu.org/git/guix.git
    branch: origin/master
    commit: e0cc7f669bec22c37481dd03a7941c7d11a64f1d

Generation 3	Jun 13 2018 23:31:07	(current)
  guix 844cc1c
    repository URL: https://git.savannah.gnu.org/git/guix.git
    branch: origin/master
    commit: 844cc1c8f394f03b404c5bb3aee086922373490c
@end example

@xref{Invoking guix describe, @command{guix describe}}, for other ways to
describe the current status of Guix.

This @code{~/.config/guix/current} profile works exactly like the profiles
created by @command{guix package} (@pxref{Invoking guix package}).  That
is, you can list generations, roll back to the previous
generation---i.e., the previous Guix---and so on:

@example
$ guix pull --roll-back
switched from generation 3 to 2
$ guix pull --delete-generations=1
deleting /var/guix/profiles/per-user/charlie/current-guix-1-link
@end example

You can also use @command{guix package} (@pxref{Invoking guix package})
to manage the profile by naming it explicitly:
@example
$ guix package -p ~/.config/guix/current --roll-back
switched from generation 3 to 2
$ guix package -p ~/.config/guix/current --delete-generations=1
deleting /var/guix/profiles/per-user/charlie/current-guix-1-link
@end example

The @command{guix pull} command is usually invoked with no arguments,
but it supports the following options:

@table @code
@item --url=@var{url}
@itemx --commit=@var{commit}
@itemx --branch=@var{branch}
Download code for the @code{guix} channel from the specified @var{url}, at the
given @var{commit} (a valid Git commit ID represented as a hexadecimal
string or the name of a tag), or @var{branch}.

@cindex @file{channels.scm}, configuration file
@cindex configuration file for channels
These options are provided for convenience, but you can also specify your
configuration in the @file{~/.config/guix/channels.scm} file or using the
@option{--channels} option (see below).

@item --channels=@var{file}
@itemx -C @var{file}
Read the list of channels from @var{file} instead of
@file{~/.config/guix/channels.scm} or @file{/etc/guix/channels.scm}.
@var{file} must contain Scheme code that
evaluates to a list of channel objects.  @xref{Channels}, for more
information.

@item --no-channel-files
@itemx -q
Inhibit loading of the user and system channel files,
@file{~/.config/guix/channels.scm} and @file{/etc/guix/channels.scm}.

@cindex channel news
@item --news
@itemx -N
Display news written by channel authors for their users for changes made
since the previous generation (@pxref{Channels, Writing Channel News}).
When @option{--details} is passed, additionally display new and upgraded
packages.

You can view that information for previous generations with
@command{guix pull -l}.

@item --list-generations[=@var{pattern}]
@itemx -l [@var{pattern}]
List all the generations of @file{~/.config/guix/current} or, if @var{pattern}
is provided, the subset of generations that match @var{pattern}.
The syntax of @var{pattern} is the same as with @code{guix package
--list-generations} (@pxref{Invoking guix package}).

By default, this prints information about the channels used in each
revision as well as the corresponding news entries.  If you pass
@option{--details}, it will also print the list of packages added and
upgraded in each generation compared to the previous one.

@item --details
Instruct @option{--list-generations} or @option{--news} to display more
information about the differences between subsequent generations---see
above.

@item --roll-back
@cindex rolling back
@cindex undoing transactions
@cindex transactions, undoing
Roll back to the previous @dfn{generation} of @file{~/.config/guix/current}---i.e.,
undo the last transaction.

@item --switch-generation=@var{pattern}
@itemx -S @var{pattern}
@cindex generations
Switch to a particular generation defined by @var{pattern}.

@var{pattern} may be either a generation number or a number prefixed
with ``+'' or ``-''.  The latter means: move forward/backward by a
specified number of generations.  For example, if you want to return to
the latest generation after @option{--roll-back}, use
@option{--switch-generation=+1}.

@item --delete-generations[=@var{pattern}]
@itemx -d [@var{pattern}]
When @var{pattern} is omitted, delete all generations except the current
one.

This command accepts the same patterns as @option{--list-generations}.
When @var{pattern} is specified, delete the matching generations.  When
@var{pattern} specifies a duration, generations @emph{older} than the
specified duration match.  For instance, @option{--delete-generations=1m}
deletes generations that are more than one month old.

If the current generation matches, it is @emph{not} deleted.

Note that deleting generations prevents rolling back to them.
Consequently, this command must be used with care.

@xref{Invoking guix describe}, for a way to display information about the
current generation only.

@item --profile=@var{profile}
@itemx -p @var{profile}
Use @var{profile} instead of @file{~/.config/guix/current}.

@item --dry-run
@itemx -n
Show which channel commit(s) would be used and what would be built or
substituted but do not actually do it.

@item --allow-downgrades
Allow pulling older or unrelated revisions of channels than those
currently in use.

@cindex downgrade attacks, protection against
By default, @command{guix pull} protects against so-called ``downgrade
attacks'' whereby the Git repository of a channel would be reset to an
earlier or unrelated revision of itself, potentially leading you to
install older, known-vulnerable versions of software packages.

@quotation Note
Make sure you understand its security implications before using
@option{--allow-downgrades}.
@end quotation

@item --disable-authentication
Allow pulling channel code without authenticating it.

@cindex authentication, of channel code
By default, @command{guix pull} authenticates code downloaded from
channels by verifying that its commits are signed by authorized
developers, and raises an error if this is not the case.  This option
instructs it to not perform any such verification.

@quotation Note
Make sure you understand its security implications before using
@option{--disable-authentication}.
@end quotation

@item --system=@var{system}
@itemx -s @var{system}
Attempt to build for @var{system}---e.g., @code{i686-linux}---instead of
the system type of the build host.

@item --bootstrap
Use the bootstrap Guile to build the latest Guix.  This option is only
useful to Guix developers.
@end table

The @dfn{channel} mechanism allows you to instruct @command{guix pull} which
repository and branch to pull from, as well as @emph{additional} repositories
containing package modules that should be deployed.  @xref{Channels}, for more
information.

In addition, @command{guix pull} supports all the common build options
(@pxref{Common Build Options}).

@node Invoking guix time-machine
@section Invoking @command{guix time-machine}

@cindex @command{guix time-machine}
@cindex pinning, channels
@cindex replicating Guix
@cindex reproducibility, of Guix

The @command{guix time-machine} command provides access to other
revisions of Guix, for example to install older versions of packages,
or to reproduce a computation in an identical environment.  The revision
of Guix to be used is defined by a commit or by a channel
description file created by @command{guix describe}
(@pxref{Invoking guix describe}).

Let's assume that you want to travel to those days of November 2020 when
version 1.2.0 of Guix was released and, once you're there, run the
@command{guile} of that time:

@example
guix time-machine --commit=v1.2.0 -- \
  environment -C --ad-hoc guile -- guile
@end example

The command above fetches Guix@tie{}1.2.0 (and possibly other channels
specified by your @file{channels.scm} configuration files---see
below) and runs its @command{guix
environment} command to spawn an environment in a container running
@command{guile} (@command{guix environment} has since been subsumed by
@command{guix shell}; @pxref{Invoking guix shell}).  It's like driving a
DeLorean@footnote{If you don't know what a DeLorean is, consider
traveling back to the 1980's. (@uref{https://www.imdb.com/title/tt0088763/,
Back to the Future (1985)})}!  The first @command{guix time-machine}
invocation can be expensive: it may have to download or even build a
large number of packages; the result is cached though and subsequent
commands targeting the same commit are almost instantaneous.

As for @command{guix pull}, in the absence of any options,
@command{time-machine} fetches the latest commits of the channels
specified in @file{~/.config/guix/channels.scm},
@file{/etc/guix/channels.scm}, or the default channels; the @option{-q}
option lets you ignore these configuration files.  The command:

@example
guix time-machine -q -- build hello
@end example

will thus build the package @code{hello} as defined in the main branch
of Guix, without any additional channel, which is in general a newer
revision of Guix than you have installed.  Time travel works in both
directions!

@quotation Note
The history of Guix is immutable and @command{guix time-machine}
provides the exact same software as they are in a specific Guix
revision.  Naturally, no security fixes are provided for old versions
of Guix or its channels.  A careless use of @command{guix time-machine}
opens the door to security vulnerabilities.  @xref{Invoking guix pull,
@option{--allow-downgrades}}.
@end quotation

@c Keep this paragraph in sync with 'time-machine.scm'.
@command{guix time-machine} raises an error when attempting to travel to
commits older than ``v0.16.0'' (commit @samp{4a0b87f0}), dated
Dec.@: 2018.  This is one of the oldest commits supporting the channel
mechanism that makes ``time travel'' possible.

@quotation Note
Although it should technically be possible to travel to such an old
commit, the ease to do so will largely depend on the availability of
binary substitutes.  When traveling to a distant past, some packages may
not easily build from source anymore.  One such example are old versions
of OpenSSL whose tests would fail after a certain date.  This particular
problem can be worked around by running a @dfn{virtual build machine}
with its clock set to the right time (@pxref{build-vm, Virtual Build
Machines}).
@end quotation

The general syntax is:

@example
guix time-machine @var{options}@dots{} -- @var{command} @var {arg}@dots{}
@end example

where @var{command} and @var{arg}@dots{} are passed unmodified to the
@command{guix} command of the specified revision.  The @var{options} that define
this revision are the same as for @command{guix pull} (@pxref{Invoking guix pull}):

@table @code
@item --url=@var{url}
@itemx --commit=@var{commit}
@itemx --branch=@var{branch}
Use the @code{guix} channel from the specified @var{url}, at the
given @var{commit} (a valid Git commit ID represented as a hexadecimal
string or the name of a tag), or @var{branch}.

@item --channels=@var{file}
@itemx -C @var{file}
Read the list of channels from @var{file}.  @var{file} must contain
Scheme code that evaluates to a list of channel objects.
@xref{Channels} for more information.

@item --no-channel-files
@itemx -q
Inhibit loading of the user and system channel files,
@file{~/.config/guix/channels.scm} and @file{/etc/guix/channels.scm}.

Thus, @command{guix time-machine -q} is equivalent to the following Bash
command, using the ``process substitution'' syntax (@pxref{Process
Substitution,,, bash, The GNU Bash Reference Manual}):

@example
guix time-machine -C <(echo %default-channels) @dots{}
@end example

@end table

Note that @command{guix time-machine} can trigger builds of channels and
their dependencies, and these are controlled by the standard build
options (@pxref{Common Build Options}).

@node Inferiors
@section Inferiors

@c TODO: Remove this once we're more confident about API stability.
@quotation Note
The functionality described here is a ``technology preview'' as of version
@value{VERSION}.  As such, the interface is subject to change.
@end quotation

@cindex inferiors
@cindex composition of Guix revisions
Sometimes you might need to mix packages from the revision of Guix you're
currently running with packages available in a different revision of Guix.
Guix @dfn{inferiors} allow you to achieve that by composing different Guix
revisions in arbitrary ways.

@cindex inferior packages
Technically, an ``inferior'' is essentially a separate Guix process connected
to your main Guix process through a REPL (@pxref{Invoking guix repl}).  The
@code{(guix inferior)} module allows you to create inferiors and to
communicate with them.  It also provides a high-level interface to browse and
manipulate the packages that an inferior provides---@dfn{inferior packages}.

When combined with channels (@pxref{Channels}), inferiors provide a simple way
to interact with a separate revision of Guix.  For example, let's assume you
want to install in your profile the current @code{guile} package, along with
the @code{guile-json} as it existed in an older revision of Guix---perhaps
because the newer @code{guile-json} has an incompatible API and you want to
run your code against the old API@.  To do that, you could write a manifest for
use by @code{guix package --manifest} (@pxref{Writing Manifests}); in that
manifest, you would create an inferior for that old Guix revision you care
about, and you would look up the @code{guile-json} package in the inferior:

@lisp
(use-modules (guix inferior) (guix channels)
             (srfi srfi-1))   ;for 'first'

(define channels
  ;; This is the old revision from which we want to
  ;; extract guile-json.
  (list (channel
         (name 'guix)
         (url "https://git.savannah.gnu.org/git/guix.git")
         (commit
          "65956ad3526ba09e1f7a40722c96c6ef7c0936fe"))))

(define inferior
  ;; An inferior representing the above revision.
  (inferior-for-channels channels))

;; Now create a manifest with the current "guile" package
;; and the old "guile-json" package.
(packages->manifest
 (list (first (lookup-inferior-packages inferior "guile-json"))
       (specification->package "guile")))
@end lisp

On its first run, @command{guix package --manifest} might have to build the
channel you specified before it can create the inferior; subsequent runs will
be much faster because the Guix revision will be cached.

The @code{(guix inferior)} module provides the following procedures to open an
inferior:

@deffn {Procedure} inferior-for-channels channels [#:cache-directory] [#:ttl]
Return an inferior for @var{channels}, a list of channels.  Use the cache at
@var{cache-directory}, where entries can be reclaimed after @var{ttl} seconds.
This procedure opens a new connection to the build daemon.

As a side effect, this procedure may build or substitute binaries for
@var{channels}, which can take time.
@end deffn

@deffn {Procedure} open-inferior directory [#:command "bin/guix"]
Open the inferior Guix in @var{directory}, running
@code{@var{directory}/@var{command} repl} or equivalent.  Return @code{#f} if
the inferior could not be launched.
@end deffn

@cindex inferior packages
The procedures listed below allow you to obtain and manipulate inferior
packages.

@deffn {Procedure} inferior-packages inferior
Return the list of packages known to @var{inferior}.
@end deffn

@deffn {Procedure} lookup-inferior-packages inferior name [version]
Return the sorted list of inferior packages matching @var{name} in
@var{inferior}, with highest version numbers first.  If @var{version} is true,
return only packages with a version number prefixed by @var{version}.
@end deffn

@deffn {Procedure} inferior-package? obj
Return true if @var{obj} is an inferior package.
@end deffn

@deffn {Procedure} inferior-package-name package
@deffnx {Procedure} inferior-package-version package
@deffnx {Procedure} inferior-package-synopsis package
@deffnx {Procedure} inferior-package-description package
@deffnx {Procedure} inferior-package-home-page package
@deffnx {Procedure} inferior-package-location package
@deffnx {Procedure} inferior-package-inputs package
@deffnx {Procedure} inferior-package-native-inputs package
@deffnx {Procedure} inferior-package-propagated-inputs package
@deffnx {Procedure} inferior-package-transitive-propagated-inputs package
@deffnx {Procedure} inferior-package-native-search-paths package
@deffnx {Procedure} inferior-package-transitive-native-search-paths package
@deffnx {Procedure} inferior-package-search-paths package
These procedures are the counterpart of package record accessors
(@pxref{package Reference}).  Most of them work by querying the inferior
@var{package} comes from, so the inferior must still be live when you call
these procedures.
@end deffn

Inferior packages can be used transparently like any other package or
file-like object in G-expressions (@pxref{G-Expressions}).  They are also
transparently handled by the @code{packages->manifest} procedure, which is
commonly used in manifests (@pxref{Invoking guix package, the
@option{--manifest} option of @command{guix package}}).  Thus you can insert
an inferior package pretty much anywhere you would insert a regular package:
in manifests, in the @code{packages} field of your @code{operating-system}
declaration, and so on.

@node Invoking guix describe
@section Invoking @command{guix describe}

@cindex reproducibility
@cindex replicating Guix
@cindex @command{guix describe}
Often you may want to answer questions like: ``Which revision of Guix am I
using?'' or ``Which channels am I using?''  This is useful information in many
situations: if you want to @emph{replicate} an environment on a different
machine or user account, if you want to report a bug or to determine what
change in the channels you are using caused it, or if you want to record your
system state for reproducibility purposes.  The @command{guix describe}
command answers these questions.

When run from a @command{guix pull}ed @command{guix}, @command{guix describe}
displays the channel(s) that it was built from, including their repository URL
and commit IDs (@pxref{Channels}):

@example
$ guix describe
Generation 10	Sep 03 2018 17:32:44	(current)
  guix e0fa68c
    repository URL: https://git.savannah.gnu.org/git/guix.git
    branch: master
    commit: e0fa68c7718fffd33d81af415279d6ddb518f727
@end example

If you're familiar with the Git version control system, this is similar in
spirit to @command{git describe}; the output is also similar to that of
@command{guix pull --list-generations}, but limited to the current generation
(@pxref{Invoking guix pull, the @option{--list-generations} option}).  Because
the Git commit ID shown above unambiguously refers to a snapshot of Guix, this
information is all it takes to describe the revision of Guix you're using, and
also to replicate it.

To make it easier to replicate Guix, @command{guix describe} can also be asked
to return a list of channels instead of the human-readable description above:

@example
$ guix describe -f channels
(list (channel
        (name 'guix)
        (url "https://git.savannah.gnu.org/git/guix.git")
        (commit
          "e0fa68c7718fffd33d81af415279d6ddb518f727")
        (introduction
          (make-channel-introduction
            "9edb3f66fd807b096b48283debdcddccfea34bad"
            (openpgp-fingerprint
              "BBB0 2DDF 2CEA F6A8 0D1D  E643 A2A0 6DF2 A33A 54FA")))))
@end example

@noindent
You can save this to a file and feed it to @command{guix pull -C} on some
other machine or at a later point in time, which will instantiate @emph{this
exact Guix revision} (@pxref{Invoking guix pull, the @option{-C} option}).
From there on, since you're able to deploy the same revision of Guix, you can
just as well @emph{replicate a complete software environment}.  We humbly
think that this is @emph{awesome}, and we hope you'll like it too!

The details of the options supported by @command{guix describe} are as
follows:

@table @code
@item --format=@var{format}
@itemx -f @var{format}
Produce output in the specified @var{format}, one of:

@table @code
@item human
produce human-readable output;
@item channels
produce a list of channel specifications that can be passed to @command{guix
pull -C} or installed as @file{~/.config/guix/channels.scm} (@pxref{Invoking
guix pull});
@item channels-sans-intro
like @code{channels}, but omit the @code{introduction} field; use it to
produce a channel specification suitable for Guix version 1.1.0 or
earlier---the @code{introduction} field has to do with channel
authentication (@pxref{Channels, Channel Authentication}) and is not
supported by these older versions;
@item json
@cindex JSON
produce a list of channel specifications in JSON format;
@item recutils
produce a list of channel specifications in Recutils format.
@end table

@item --list-formats
Display available formats for @option{--format} option.

@item --profile=@var{profile}
@itemx -p @var{profile}
Display information about @var{profile}.
@end table

@node Invoking guix archive
@section Invoking @command{guix archive}

@cindex @command{guix archive}
@cindex archive
@cindex exporting files from the store
@cindex importing files to the store
The @command{guix archive} command allows users to @dfn{export} files
from the store into a single archive, and to later @dfn{import} them on
a machine that runs Guix.
In particular, it allows store files to be transferred from one machine
to the store on another machine.

@quotation Note
If you're looking for a way to produce archives in a format suitable for
tools other than Guix, @pxref{Invoking guix pack}.
@end quotation

@cindex exporting store items
To export store files as an archive to standard output, run:

@example
guix archive --export @var{options} @var{specifications}...
@end example

@var{specifications} may be either store file names or package
specifications, as for @command{guix package} (@pxref{Invoking guix
package}).  For instance, the following command creates an archive
containing the @code{gui} output of the @code{git} package and the main
output of @code{emacs}:

@example
guix archive --export git:gui /gnu/store/...-emacs-24.3 > great.nar
@end example

If the specified packages are not built yet, @command{guix archive}
automatically builds them.  The build process may be controlled with the
common build options (@pxref{Common Build Options}).

To transfer the @code{emacs} package to a machine connected over SSH,
one would run:

@example
guix archive --export -r emacs | ssh the-machine guix archive --import
@end example

@noindent
Similarly, a complete user profile may be transferred from one machine
to another like this:

@example
guix archive --export -r $(readlink -f ~/.guix-profile) | \
  ssh the-machine guix archive --import
@end example

@noindent
However, note that, in both examples, all of @code{emacs} and the
profile as well as all of their dependencies are transferred (due to
@option{-r}), regardless of what is already available in the store on
the target machine.  The @option{--missing} option can help figure out
which items are missing from the target store.  The @command{guix copy}
command simplifies and optimizes this whole process, so this is probably
what you should use in this case (@pxref{Invoking guix copy}).

@cindex nar, archive format
@cindex normalized archive (nar)
@cindex nar bundle, archive format
Each store item is written in the @dfn{normalized archive} or @dfn{nar}
format (described below), and the output of @command{guix archive
--export} (and input of @command{guix archive --import}) is a @dfn{nar
bundle}.

The nar format is
comparable in spirit to `tar', but with differences
that make it more appropriate for our purposes.  First, rather than
recording all Unix metadata for each file, the nar format only mentions
the file type (regular, directory, or symbolic link); Unix permissions
and owner/group are dismissed.  Second, the order in which directory
entries are stored always follows the order of file names according to
the C locale collation order.  This makes archive production fully
deterministic.

That nar bundle format is essentially the concatenation of zero or more
nars along with metadata for each store item it contains: its file name,
references, corresponding derivation, and a digital signature.

When exporting, the daemon digitally signs the contents of the archive,
and that digital signature is appended.  When importing, the daemon
verifies the signature and rejects the import in case of an invalid
signature or if the signing key is not authorized.
@c FIXME: Add xref to daemon doc about signatures.

The main options are:

@table @code
@item --export
Export the specified store files or packages (see below).  Write the
resulting archive to the standard output.

Dependencies are @emph{not} included in the output, unless
@option{--recursive} is passed.

@item -r
@itemx --recursive
When combined with @option{--export}, this instructs @command{guix archive}
to include dependencies of the given items in the archive.  Thus, the
resulting archive is self-contained: it contains the closure of the
exported store items.

@item --import
Read an archive from the standard input, and import the files listed
therein into the store.  Abort if the archive has an invalid digital
signature, or if it is signed by a public key not among the authorized
keys (see @option{--authorize} below).

@item --missing
Read a list of store file names from the standard input, one per line,
and write on the standard output the subset of these files missing from
the store.

@item --generate-key[=@var{parameters}]
@cindex signing, archives
Generate a new key pair for the daemon.  This is a prerequisite before
archives can be exported with @option{--export}.  This
operation is usually instantaneous but it can take time if the system's
entropy pool needs to be refilled.  On Guix System,
@code{guix-service-type} takes care of generating this key pair the
first boot.

The generated key pair is typically stored under @file{/etc/guix}, in
@file{signing-key.pub} (public key) and @file{signing-key.sec} (private
key, which must be kept secret).  When @var{parameters} is omitted,
an ECDSA key using the Ed25519 curve is generated, or, for Libgcrypt
versions before 1.6.0, it is a 4096-bit RSA key.
Alternatively, @var{parameters} can specify
@code{genkey} parameters suitable for Libgcrypt (@pxref{General
public-key related Functions, @code{gcry_pk_genkey},, gcrypt, The
Libgcrypt Reference Manual}).

@item --authorize
@cindex authorizing, archives
Authorize imports signed by the public key passed on standard input.
The public key must be in ``s-expression advanced format''---i.e., the
same format as the @file{signing-key.pub} file.

The list of authorized keys is kept in the human-editable file
@file{/etc/guix/acl}.  The file contains
@url{https://people.csail.mit.edu/rivest/Sexp.txt, ``advanced-format
s-expressions''} and is structured as an access-control list in the
@url{https://theworld.com/~cme/spki.txt, Simple Public-Key Infrastructure
(SPKI)}.

@item --extract=@var{directory}
@itemx -x @var{directory}
Read a single-item archive as served by substitute servers
(@pxref{Substitutes}) and extract it to @var{directory}.  This is a
low-level operation needed in only very narrow use cases; see below.

For example, the following command extracts the substitute for Emacs
served by @code{@value{SUBSTITUTE-SERVER-1}} to @file{/tmp/emacs}:

@example
$ wget -O - \
  https://@value{SUBSTITUTE-SERVER-1}/nar/gzip/@dots{}-emacs-24.5 \
  | gunzip | guix archive -x /tmp/emacs
@end example

Single-item archives are different from multiple-item archives produced
by @command{guix archive --export}; they contain a single store item,
and they do @emph{not} embed a signature.  Thus this operation does
@emph{no} signature verification and its output should be considered
unsafe.

The primary purpose of this operation is to facilitate inspection of
archive contents coming from possibly untrusted substitute servers
(@pxref{Invoking guix challenge}).

@item --list
@itemx -t
Read a single-item archive as served by substitute servers
(@pxref{Substitutes}) and print the list of files it contains, as in
this example:

@example
$ wget -O - \
  https://@value{SUBSTITUTE-SERVER-1}/nar/lzip/@dots{}-emacs-26.3 \
  | lzip -d | guix archive -t
@end example

@end table

@c *********************************************************************
@node Channels
@chapter Channels

@cindex channels
@cindex @file{channels.scm}, configuration file
@cindex configuration file for channels
@cindex @command{guix pull}, configuration file
@cindex configuration of @command{guix pull}
Guix and its package collection are updated by running @command{guix
pull}.  By default @command{guix pull} downloads and deploys Guix itself
from the official GNU@tie{}Guix repository.  This can be customized by
providing a file specifying the set of @dfn{channels} to pull from
(@pxref{Invoking guix pull}).  A channel
specifies the URL and branch of a Git repository to be deployed, and
@command{guix pull} can be instructed to pull from one or more channels.
In other words, channels can be used to @emph{customize} and to
@emph{extend} Guix, as we will see below.  Guix is able to take into
account security concerns and deal with authenticated updates.

@menu
* Specifying Additional Channels::  Extending the package collection.
* Using a Custom Guix Channel::  Using a customized Guix.
* Replicating Guix::            Running the @emph{exact same} Guix.
* Customizing the System-Wide Guix:: Default channels on Guix System.
* Channel Authentication::      How Guix verifies what it fetches.
* Channels with Substitutes::   Using channels with available substitutes.
* Creating a Channel::          How to write your custom channel.
* Package Modules in a Sub-directory::  Specifying the channel's package modules location.
* Declaring Channel Dependencies::  How to depend on other channels.
* Specifying Channel Authorizations::  Defining channel authors authorizations.
* Primary URL::                 Distinguishing mirror to original.
* Writing Channel News::        Communicating information to channel's users.
@end menu

@node Specifying Additional Channels
@section Specifying Additional Channels

@cindex extending the package collection (channels)
@cindex variant packages (channels)
You can specify @emph{additional channels} to pull from.  To use a channel, write
@code{~/.config/guix/channels.scm} to instruct @command{guix pull} to pull from it
@emph{in addition} to the default Guix channel(s):

@vindex %default-channels
@lisp
;; Add variant packages to those Guix provides.
(cons (channel
        (name 'variant-packages)
        (url "https://example.org/variant-packages.git"))
      %default-channels)
@end lisp

@noindent
Note that the snippet above is (as always!)@: Scheme code; we use @code{cons} to
add a channel the list of channels that the variable @code{%default-channels}
is bound to (@pxref{Pairs, @code{cons} and lists,, guile, GNU Guile Reference
Manual}).  With this file in place, @command{guix pull} builds not only Guix
but also the package modules from your own repository.  The result in
@file{~/.config/guix/current} is the union of Guix with your own package
modules:

@example
$ guix describe
Generation 19	Aug 27 2018 16:20:48
  guix d894ab8
    repository URL: https://git.savannah.gnu.org/git/guix.git
    branch: master
    commit: d894ab8e9bfabcefa6c49d9ba2e834dd5a73a300
  variant-packages dd3df5e
    repository URL: https://example.org/variant-packages.git
    branch: master
    commit: dd3df5e2c8818760a8fc0bd699e55d3b69fef2bb
@end example

@noindent
The output of @command{guix describe} above shows that we're now running
Generation@tie{}19 and that it includes
both Guix and packages from the @code{variant-packages} channel
(@pxref{Invoking guix describe}).

@node Using a Custom Guix Channel
@section Using a Custom Guix Channel

The channel called @code{guix} specifies where Guix itself---its command-line
tools as well as its package collection---should be downloaded.  For instance,
suppose you want to update from another copy of the Guix repository at
@code{example.org}, and specifically the @code{super-hacks} branch, you can
write in @code{~/.config/guix/channels.scm} this specification:

@lisp
;; Tell 'guix pull' to use another repo.
(list (channel
        (name 'guix)
        (url "https://example.org/another-guix.git")
        (branch "super-hacks")))
@end lisp

@noindent
From there on, @command{guix pull} will fetch code from the @code{super-hacks}
branch of the repository at @code{example.org}.  The authentication concern is
addressed below (@pxref{Channel Authentication}).

Note that you can specify a local directory on the @code{url} field above if
the channel that you intend to use resides on a local file system.  However,
in this case @command{guix} checks said directory for ownership before any
further processing.  This means that if the user is not the directory owner,
but wants to use it as their default, they will then need to set it as a safe
directory in their global git configuration file.  Otherwise, @command{guix}
will refuse to even read it.  Supposing your system-wide local directory is at
@code{/src/guix.git}, you would then create a git configuration file at
@code{~/.gitconfig} with the following contents:

@example
[safe]
        directory = /src/guix.git
@end example

@noindent
This also applies to the root user unless when called with @command{sudo} by
the directory owner.

@node Replicating Guix
@section Replicating Guix

@cindex pinning, channels
@cindex replicating Guix
@cindex reproducibility, of Guix
The @command{guix describe} command shows precisely which commits were
used to build the instance of Guix we're using (@pxref{Invoking guix
describe}).  We can replicate this instance on another machine or at a
different point in time by providing a channel specification ``pinned''
to these commits that looks like this:

@lisp
;; Deploy specific commits of my channels of interest.
(list (channel
       (name 'guix)
       (url "https://git.savannah.gnu.org/git/guix.git")
       (commit "6298c3ffd9654d3231a6f25390b056483e8f407c"))
      (channel
       (name 'variant-packages)
       (url "https://example.org/variant-packages.git")
       (commit "dd3df5e2c8818760a8fc0bd699e55d3b69fef2bb")))
@end lisp

To obtain this pinned channel specification, the easiest way is to run
@command{guix describe} and to save its output in the @code{channels}
format in a file, like so:

@example
guix describe -f channels > channels.scm
@end example

The resulting @file{channels.scm} file can be passed to the @option{-C}
option of @command{guix pull} (@pxref{Invoking guix pull}) or
@command{guix time-machine} (@pxref{Invoking guix time-machine}), as in
this example:

@example
guix time-machine -C channels.scm -- shell python -- python3
@end example

Given the @file{channels.scm} file, the command above will always fetch
the @emph{exact same Guix instance}, then use that instance to run the
exact same Python (@pxref{Invoking guix shell}).  On any machine, at any
time, it ends up running the exact same binaries, bit for bit.

@cindex lock files
Pinned channels address a problem similar to ``lock files'' as
implemented by some deployment tools---they let you pin and reproduce a
set of packages.  In the case of Guix though, you are effectively
pinning the entire package set as defined at the given channel commits;
in fact, you are pinning all of Guix, including its core modules and
command-line tools.  You're also getting strong guarantees that you are,
indeed, obtaining the exact same software.

This gives you super powers, allowing you to track the provenance of binary
artifacts with very fine grain, and to reproduce software environments at
will---some sort of ``meta reproducibility'' capabilities, if you will.
@xref{Inferiors}, for another way to take advantage of these super powers.

@node Customizing the System-Wide Guix
@section Customizing the System-Wide Guix

@cindex system-wide Guix, customization
@cindex channels, for the default Guix
If you're running Guix System or building system images with it, maybe
you will want to customize the system-wide @command{guix} it
provides---specifically, @file{/run/current-system/profile/bin/guix}.
For example, you might want to provide additional channels or to pin its
revision.

This can be done using the @code{guix-for-channels} procedure, which
returns a package for the given channels, and using it as part of your
operating system configuration, as in this example:

@lisp
(use-modules (gnu packages package-management)
             (guix channels))

(define my-channels
  ;; Channels that should be available to
  ;; /run/current-system/profile/bin/guix.
  (append
   (list (channel
          (name 'guix-science)
          (url "https://github.com/guix-science/guix-science")
          (branch "master")))
   %default-channels))

(operating-system
  ;; @dots{}
  (services
    ;; Change the package used by 'guix-service-type'.
    (modify-services %base-services
      (guix-service-type
       config => (guix-configuration
                  (inherit config)
                  (channels my-channels)
                  (guix (guix-for-channels my-channels)))))))
@end lisp

The resulting operating system will have both the @code{guix} and the
@code{guix-science} channels visible by default.  The @code{channels}
field of @code{guix-configuration} above further ensures that
@file{/etc/guix/channels.scm}, which is used by @command{guix pull},
specifies the same set of channels (@pxref{guix-configuration-channels,
@code{channels} field of @code{guix-configuration}}).

The @code{(gnu packages package-management)} module exports the
@code{guix-for-channels} procedure, described below.

@deffn {Procedure} guix-for-channels @var{channels}
Return a package corresponding to @var{channels}.

The result is a ``regular'' package, which can be used in
@code{guix-configuration} as shown above or in any other place that
expects a package.
@end deffn

@node Channel Authentication
@section Channel Authentication

@anchor{channel-authentication}
@cindex authentication, of channel code
The @command{guix pull} and @command{guix time-machine} commands
@dfn{authenticate} the code retrieved from channels: they make sure each
commit that is fetched is signed by an authorized developer.  The goal
is to protect from unauthorized modifications to the channel that would
lead users to run malicious code.

As a user, you must provide a @dfn{channel introduction} in your
channels file so that Guix knows how to authenticate its first commit.
A channel specification, including its introduction, looks something
along these lines:

@lisp
(channel
  (name 'some-channel)
  (url "https://example.org/some-channel.git")
  (introduction
   (make-channel-introduction
    "6f0d8cc0d88abb59c324b2990bfee2876016bb86"
    (openpgp-fingerprint
     "CABB A931 C0FF EEC6 900D  0CFB 090B 1199 3D9A EBB5"))))
@end lisp

The specification above shows the name and URL of the channel.  The call
to @code{make-channel-introduction} above specifies that authentication
of this channel starts at commit @code{6f0d8cc@dots{}}, which is signed
by the OpenPGP key with fingerprint @code{CABB A931@dots{}}.

For the main channel, called @code{guix}, you automatically get that
information from your Guix installation.  For other channels, include
the channel introduction provided by the channel authors in your
@file{channels.scm} file.  Make sure you retrieve the channel
introduction from a trusted source since that is the root of your trust.

If you're curious about the authentication mechanics, read on!

@node Channels with Substitutes
@section Channels with Substitutes

When running @command{guix pull}, Guix will first compile the
definitions of every available package.  This is an expensive operation
for which substitutes (@pxref{Substitutes}) may be available.  The
following snippet in @file{channels.scm} will ensure that @command{guix
pull} uses the latest commit with available substitutes for the package
definitions: this is done by querying the continuous integration
server at @url{https://ci.guix.gnu.org}.

@lisp
(use-modules (guix ci))

(list (channel-with-substitutes-available
       %default-guix-channel
       "https://ci.guix.gnu.org"))
@end lisp

Note that this does not mean that all the packages that you will
install after running @command{guix pull} will have available
substitutes.  It only ensures that @command{guix pull} will not try to
compile package definitions.  This is particularly useful when using
machines with limited resources.

@node Creating a Channel
@section Creating a Channel

@cindex personal packages (channels)
@cindex channels, for personal packages
Let's say you have a bunch of custom package variants or personal packages
that you think would make little sense to contribute to the Guix project, but
would like to have these packages transparently available to you at the
command line.  By creating a @dfn{channel}, you can use and publish such
a package collection.  This involves the following steps:

@enumerate
@item
A channel lives in a Git repository so the first step, when creating a
channel, is to create its repository:

@example
mkdir my-channel
cd my-channel
git init
@end example

@item
The next step is to create files containing package modules
(@pxref{Package Modules}), each of which will contain one or more
package definitions (@pxref{Defining Packages}).  A channel can provide
things other than packages, such as build systems or services; we're
using packages as it's the most common use case.

For example, Alice might want to provide a module called @code{(alice
packages greetings)} that will provide her favorite ``hello world''
implementations.  To do that Alice will create a directory corresponding
to that module name.

@example
mkdir -p alice/packages
$EDITOR alice/packages/greetings.scm
git add alice/packages/greetings.scm
@end example

You can name your package modules however you like; the main constraint
to keep in mind is to avoid name clashes with other package collections,
which is why our hypothetical Alice wisely chose the @code{(alice
packages @dots{})} name space.

Note that you can also place modules in a sub-directory of the
repository; @pxref{Package Modules in a Sub-directory}, for more info on
that.

@item
With this first module in place, the next step is to test the packages
it provides.  This can be done with @command{guix build}, which needs to
be told to look for modules in the Git checkout.  For example, assuming
@code{(alice packages greetings)} provides a package called
@code{hi-from-alice}, Alice will run this command from the Git checkout:

@example
guix build -L. hi-from-alice
@end example

@noindent
... where @code{-L.} adds the current directory to Guile's load path
(@pxref{Load Paths,,, guile, GNU Guile Reference Manual}).

@item
It might take Alice a few iterations to obtain satisfying package
definitions.  Eventually Alice will commit this file:

@example
git commit
@end example

As a channel author, consider bundling authentication material with your
channel so that users can authenticate it.  @xref{Channel
Authentication}, and @ref{Specifying Channel Authorizations}, for info
on how to do it.

@item
To use Alice's channel, anyone can now add it to their channel file
(@pxref{Specifying Additional Channels}) and run @command{guix pull}
(@pxref{Invoking guix pull}):

@example
$EDITOR ~/.config/guix/channels.scm
guix pull
@end example

Guix will now behave as if the root directory of that channel's Git
repository had been permanently added to the Guile load path.  In this
example, @code{(alice packages greetings)} will automatically be found
by the @command{guix} command.
@end enumerate

Voilà!

@c What follows stems from discussions at
@c <https://debbugs.gnu.org/cgi/bugreport.cgi?bug=22629#134> as well as
@c earlier discussions on guix-devel@gnu.org.
@quotation Warning
Before you publish your channel, we would like to share a few words of
caution:

@itemize
@item
Before publishing a channel, please consider contributing your package
definitions to Guix proper (@pxref{Contributing}).  Guix as a project is open
to free software of all sorts, and packages in Guix proper are readily
available to all Guix users and benefit from the project's quality assurance
process.

@item
Package modules and package definitions are Scheme code that uses
various programming interfaces (APIs).  We, Guix developers, never
change APIs gratuitously, but we do @emph{not} commit to freezing APIs
either.  When you maintain package definitions outside Guix, we consider
that @emph{the compatibility burden is on you}.

@item
Corollary: if you're using an external channel and that channel breaks, please
@emph{report the issue to the channel authors}, not to the Guix project.
@end itemize

You've been warned!  Having said this, we believe external channels are a
practical way to exert your freedom to augment Guix' package collection and to
share your improvements, which are basic tenets of
@uref{https://www.gnu.org/philosophy/free-sw.html, free software}.  Please
email us at @email{guix-devel@@gnu.org} if you'd like to discuss this.
@end quotation



@node Package Modules in a Sub-directory
@section Package Modules in a Sub-directory

@cindex subdirectory, channels
As a channel author, you may want to keep your channel modules in a
sub-directory.  If your modules are in the sub-directory @file{guix}, you must
add a meta-data file @file{.guix-channel} that contains:

@lisp
(channel
  (version 0)
  (directory "guix"))
@end lisp

The modules must be @b{underneath} the specified directory, as the
@code{directory} changes Guile's @code{load-path}.  For example, if
@file{.guix-channel} has @code{(directory "base")}, then a module
defined as @code{(define-module (gnu packages fun))} must be located at
@code{base/gnu/packages/fun.scm}.

Doing this allows for only parts of a repository to be used as a
channel, as Guix expects valid Guile modules when pulling.  For
instance, @command{guix deploy} machine configuration files are not
valid Guile modules, and treating them as such would make @command{guix
pull} fail.

@node Declaring Channel Dependencies
@section Declaring Channel Dependencies

@cindex dependencies, channels
@cindex meta-data, channels
Channel authors may decide to augment a package collection provided by other
channels.  They can declare their channel to be dependent on other channels in
a meta-data file @file{.guix-channel}, which is to be placed in the root of
the channel repository.

The meta-data file should contain a simple S-expression like this:

@lisp
(channel
 (version 0)
 (dependencies
  (channel
   (name some-collection)
   (url "https://example.org/first-collection.git")

   ;; The 'introduction' bit below is optional: you would
   ;; provide it for dependencies that can be authenticated.
   (introduction
    (channel-introduction
      (version 0)
      (commit "a8883b58dc82e167c96506cf05095f37c2c2c6cd")
      (signer "CABB A931 C0FF EEC6 900D  0CFB 090B 1199 3D9A EBB5"))))
  (channel
   (name some-other-collection)
   (url "https://example.org/second-collection.git")
   (branch "testing"))))
@end lisp

In the above example this channel is declared to depend on two other channels,
which will both be fetched automatically.  The modules provided by the channel
will be compiled in an environment where the modules of all these declared
channels are available.

For the sake of reliability and maintainability, you should avoid dependencies
on channels that you don't control, and you should aim to keep the number of
dependencies to a minimum.

@node Specifying Channel Authorizations
@section Specifying Channel Authorizations

@cindex channel authorizations
@anchor{channel-authorizations}
As we saw above, Guix ensures the source code it pulls from channels
comes from authorized developers.  As a channel author, you need to
specify the list of authorized developers in the
@file{.guix-authorizations} file in the channel's Git repository.  The
authentication rule is simple: each commit must be signed by a key
listed in the @file{.guix-authorizations} file of its parent
commit(s)@footnote{Git commits form a @dfn{directed acyclic graph}
(DAG).  Each commit can have zero or more parents; ``regular'' commits
have one parent and merge commits have two parent commits.  Read
@uref{https://eagain.net/articles/git-for-computer-scientists/, @i{Git
for Computer Scientists}} for a great overview.}  The
@file{.guix-authorizations} file looks like this:

@lisp
;; Example '.guix-authorizations' file.

(authorizations
 (version 0)               ;current file format version

 (("AD17 A21E F8AE D8F1 CC02  DBD9 F8AE D8F1 765C 61E3"
   (name "alice"))
  ("2A39 3FFF 68F4 EF7A 3D29  12AF 68F4 EF7A 22FB B2D5"
   (name "bob"))
  ("CABB A931 C0FF EEC6 900D  0CFB 090B 1199 3D9A EBB5"
   (name "charlie"))))
@end lisp

Each fingerprint is followed by optional key/value pairs, as in the
example above.  Currently these key/value pairs are ignored.

This authentication rule creates a chicken-and-egg issue: how do we
authenticate the first commit?  Related to that: how do we deal with
channels whose repository history contains unsigned commits and lack
@file{.guix-authorizations}?  And how do we fork existing channels?

@cindex channel introduction
Channel introductions answer these questions by describing the first
commit of a channel that should be authenticated.  The first time a
channel is fetched with @command{guix pull} or @command{guix
time-machine}, the command looks up the introductory commit and verifies
that it is signed by the specified OpenPGP key.  From then on, it
authenticates commits according to the rule above.  Authentication fails
if the target commit is neither a descendant nor an ancestor of the
introductory commit.

Additionally, your channel must provide all the OpenPGP keys that were
ever mentioned in @file{.guix-authorizations}, stored as @file{.key}
files, which can be either binary or ``ASCII-armored''.  By default,
those @file{.key} files are searched for in the branch named
@code{keyring} but you can specify a different branch name in
@code{.guix-channel} like so:

@lisp
(channel
  (version 0)
  (keyring-reference "my-keyring-branch"))
@end lisp

To summarize, as the author of a channel, there are three things you have
to do to allow users to authenticate your code:

@enumerate
@item
Export the OpenPGP keys of past and present committers with @command{gpg
--export} and store them in @file{.key} files, by default in a branch
named @code{keyring} (we recommend making it an @dfn{orphan branch}).

@item
Introduce an initial @file{.guix-authorizations} in the channel's
repository.  Do that in a signed commit (@pxref{Commit Access}, for
information on how to sign Git commits.)

@item
Advertise the channel introduction, for instance on your channel's web
page.  The channel introduction, as we saw above, is the commit/key
pair---i.e., the commit that introduced @file{.guix-authorizations}, and
the fingerprint of the OpenPGP used to sign it.
@end enumerate

Before pushing to your public Git repository, you can run @command{guix
git authenticate} to verify that you did sign all the commits you are
about to push with an authorized key:

@example
guix git authenticate @var{commit} @var{signer}
@end example

@noindent
where @var{commit} and @var{signer} are your channel introduction.
@xref{Invoking guix git authenticate}, for details.

Publishing a signed channel requires discipline: any mistake, such as an
unsigned commit or a commit signed by an unauthorized key, will prevent
users from pulling from your channel---well, that's the whole point of
authentication!  Pay attention to merges in particular: merge commits
are considered authentic if and only if they are signed by a key present
in the @file{.guix-authorizations} file of @emph{both} branches.

@node Primary URL
@section Primary URL

@cindex primary URL, channels
Channel authors can indicate the primary URL of their channel's Git
repository in the @file{.guix-channel} file, like so:

@lisp
(channel
  (version 0)
  (url "https://example.org/guix.git"))
@end lisp

This allows @command{guix pull} to determine whether it is pulling code
from a mirror of the channel; when that is the case, it warns the user
that the mirror might be stale and displays the primary URL@.  That way,
users cannot be tricked into fetching code from a stale mirror that does
not receive security updates.

This feature only makes sense for authenticated repositories, such as
the official @code{guix} channel, for which @command{guix pull} ensures
the code it fetches is authentic.

@node Writing Channel News
@section Writing Channel News

@cindex news, for channels
Channel authors may occasionally want to communicate to their users
information about important changes in the channel.  You'd send them all
an email, but that's not convenient.

Instead, channels can provide a @dfn{news file}; when the channel users
run @command{guix pull}, that news file is automatically read and
@command{guix pull --news} can display the announcements that correspond
to the new commits that have been pulled, if any.

To do that, channel authors must first declare the name of the news file
in their @file{.guix-channel} file:

@lisp
(channel
  (version 0)
  (news-file "etc/news.txt"))
@end lisp

The news file itself, @file{etc/news.txt} in this example, must look
something like this:

@lisp
(channel-news
  (version 0)
  (entry (tag "the-bug-fix")
         (title (en "Fixed terrible bug")
                (fr "Oh la la"))
         (body (en "@@emph@{Good news@}!  It's fixed!")
               (eo "Certe ĝi pli bone funkcias nun!")))
  (entry (commit "bdcabe815cd28144a2d2b4bc3c5057b051fa9906")
         (title (en "Added a great package")
                (ca "Què vol dir guix?"))
         (body (en "Don't miss the @@code@{hello@} package!"))))
@end lisp

While the news file is using the Scheme syntax, avoid naming it with a
@file{.scm} extension or else it will get picked up when building the
channel and yield an error since it is not a valid module.
Alternatively, you can move the channel module to a subdirectory and
store the news file in another directory.

The file consists of a list of @dfn{news entries}.  Each entry is
associated with a commit or tag: it describes changes made in this
commit, possibly in preceding commits as well.  Users see entries only
the first time they obtain the commit the entry refers to.

The @code{title} field should be a one-line summary while @code{body}
can be arbitrarily long, and both can contain Texinfo markup
(@pxref{Overview,,, texinfo, GNU Texinfo}).  Both the title and body are
a list of language tag/message tuples, which allows @command{guix pull}
to display news in the language that corresponds to the user's locale.

If you want to translate news using a gettext-based workflow, you can
extract translatable strings with @command{xgettext} (@pxref{xgettext
Invocation,,, gettext, GNU Gettext Utilities}).  For example, assuming
you write news entries in English first, the command below creates a PO
file containing the strings to translate:

@example
xgettext -o news.po -l scheme -ken etc/news.txt
@end example

To sum up, yes, you could use your channel as a blog.  But beware, this
is @emph{not quite} what your users might expect.

@c *********************************************************************
@node Development
@chapter Development

@cindex software development
If you are a software developer, Guix provides tools that you should find
helpful---independently of the language you're developing in.  This is what
this chapter is about.

The @command{guix shell} command provides a convenient way to set up
one-off software environments, be it for development purposes or to run
a command without installing it in your profile.  The @command{guix
pack} command allows you to create @dfn{application bundles} that can be
easily distributed to users who do not run Guix.

@menu
* Invoking guix shell::         Spawning one-off software environments.
* Invoking guix environment::   Setting up development environments.
* Invoking guix pack::          Creating software bundles.
* The GCC toolchain::           Working with languages supported by GCC.
* Invoking guix git authenticate::  Authenticating Git repositories.
@end menu

@node Invoking guix shell
@section Invoking @command{guix shell}

@cindex reproducible build environments
@cindex development environments
@cindex @command{guix environment}
@cindex @command{guix shell}
@cindex environment, package build environment
The purpose of @command{guix shell} is to make it easy to create one-off
software environments, without changing one's profile.  It is typically
used to create development environments; it is also a convenient way to
run applications without ``polluting'' your profile.

@quotation Note
The @command{guix shell} command was recently introduced to supersede
@command{guix environment} (@pxref{Invoking guix environment}).  If you
are familiar with @command{guix environment}, you will notice that it is
similar but also---we hope!---more convenient.
@end quotation

The general syntax is:

@example
guix shell [@var{options}] [@var{package}@dots{}]
@end example

The following example creates an environment containing Python and NumPy,
building or downloading any missing package, and runs the
@command{python3} command in that environment:

@example
guix shell python python-numpy -- python3
@end example

Note that it is necessary to include the main @code{python} package in
this command even if it is already installed into your environment.
This is so that the shell environment knows to set @env{PYTHONPATH} and
other related variables.  The shell environment cannot check the
previously installed environment, because then it would be
non-deterministic.  This is true for most libraries: their corresponding
language package should be included in the shell invocation.

@quotation Note
@cindex shebang, for @command{guix shell}
@command{guix shell} can be also be used as a script interpreter, also
known as @dfn{shebang}.  Here is an example self-contained Python script
making use of this feature:

@example
#!/usr/bin/env -S guix shell python python-numpy -- python3
import numpy
print("This is numpy", numpy.version.version)
@end example

You may pass any @command{guix shell} option, but there's one caveat:
the Linux kernel has a limit of 127 bytes on shebang length.
@end quotation

Development environments can be created as in the example below, which
spawns an interactive shell containing all the dependencies and
environment variables needed to work on Inkscape:

@example
guix shell --development inkscape
@end example

Exiting the shell places the user back in the original environment
before @command{guix shell} was invoked.  The next garbage collection
(@pxref{Invoking guix gc}) may clean up packages that were installed in
the environment and that are no longer used outside of it.

As an added convenience, @command{guix shell} will try to do what you
mean when it is invoked interactively without any other arguments
as in:

@example
guix shell
@end example

If it finds a @file{manifest.scm} in the current working directory or
any of its parents, it uses this manifest as though it was given via @code{--manifest}.
Likewise, if it finds a @file{guix.scm} in the same directories, it uses
it to build a development profile as though both @code{--development}
and @code{--file} were present.
In either case, the file will only be loaded if the directory it
resides in is listed in
@file{~/.config/guix/shell-authorized-directories}.
This provides an easy way to define, share, and enter development
environments.

By default, the shell session or command runs in an @emph{augmented}
environment, where the new packages are added to search path environment
variables such as @code{PATH}.  You can, instead, choose to create an
@emph{isolated} environment containing nothing but the packages you
asked for.  Passing the @option{--pure} option clears environment
variable definitions found in the parent environment@footnote{Be sure to
use the @option{--check} option the first time you use @command{guix
shell} interactively to make sure the shell does not undo the effect of
@option{--pure}.}; passing @option{--container} goes one step further by
spawning a @dfn{container} isolated from the rest of the system:

@example
guix shell --container emacs gcc-toolchain
@end example

The command above spawns an interactive shell in a container where
nothing but @code{emacs}, @code{gcc-toolchain}, and their dependencies
is available.  The container lacks network access and shares no files
other than the current working directory with the surrounding
environment.  This is useful to prevent access to system-wide resources
such as @file{/usr/bin} on foreign distros.

This @option{--container} option can also prove useful if you wish to
run a security-sensitive application, such as a web browser, in an
isolated environment.  For example, the command below launches
Ungoogled-Chromium in an isolated environment, which:
@itemize
@item shares network access with the host
@item inherits host's environment variables @code{DISPLAY} and @code{XAUTHORITY}
@item has access to host's authentication records from the @code{XAUTHORITY}
file
@item has no information about host's current directory
@end itemize

@example
guix shell --container --network --no-cwd ungoogled-chromium \
  --preserve='^XAUTHORITY$' --expose="$@{XAUTHORITY@}" \
  --preserve='^DISPLAY$' -- chromium
@end example

@vindex GUIX_ENVIRONMENT
@command{guix shell} defines the @env{GUIX_ENVIRONMENT}
variable in the shell it spawns; its value is the file name of the
profile of this environment.  This allows users to, say, define a
specific prompt for development environments in their @file{.bashrc}
(@pxref{Bash Startup Files,,, bash, The GNU Bash Reference Manual}):

@example
if [ -n "$GUIX_ENVIRONMENT" ]
then
    export PS1="\u@@\h \w [dev]\$ "
fi
@end example

@noindent
...@: or to browse the profile:

@example
$ ls "$GUIX_ENVIRONMENT/bin"
@end example

The available options are summarized below.

@table @code
@item --check
Set up the environment and check whether the shell would clobber
environment variables.  It's a good idea to use this option the first
time you run @command{guix shell} for an interactive session to make
sure your setup is correct.

For example, if the shell modifies the @env{PATH} environment variable,
report it since you would get a different environment than what you
asked for.

Such problems usually indicate that the shell startup files are
unexpectedly modifying those environment variables.  For example, if you
are using Bash, make sure that environment variables are set or modified
in @file{~/.bash_profile} and @emph{not} in @file{~/.bashrc}---the
former is sourced only by log-in shells.  @xref{Bash Startup Files,,,
bash, The GNU Bash Reference Manual}, for details on Bash start-up
files.

@anchor{shell-development-option}
@item --development
@itemx -D
Cause @command{guix shell} to include in the environment the
dependencies of the following package rather than the package itself.
This can be combined with other packages.  For instance, the command
below starts an interactive shell containing the build-time dependencies
of GNU@tie{}Guile, plus Autoconf, Automake, and Libtool:

@example
guix shell -D guile autoconf automake libtool
@end example

@item --expression=@var{expr}
@itemx -e @var{expr}
Create an environment for the package or list of packages that
@var{expr} evaluates to.

For example, running:

@example
guix shell -D -e '(@@ (gnu packages maths) petsc-openmpi)'
@end example

starts a shell with the environment for this specific variant of the
PETSc package.

Running:

@example
guix shell -e '(@@ (gnu) %base-packages)'
@end example

starts a shell with all the base system packages available.

The above commands only use the default output of the given packages.
To select other outputs, two element tuples can be specified:

@example
guix shell -e '(list (@@ (gnu packages bash) bash) "include")'
@end example

@xref{package-development-manifest,
@code{package->development-manifest}}, for information on how to write a
manifest for the development environment of a package.

@item --file=@var{file}
@itemx -f @var{file}
Create an environment containing the package or list of packages that
the code within @var{file} evaluates to.

As an example, @var{file} might contain a definition like this
(@pxref{Defining Packages}):

@lisp
@verbatiminclude environment-gdb.scm
@end lisp

With the file above, you can enter a development environment for GDB by
running:

@example
guix shell -D -f gdb-devel.scm
@end example

@anchor{shell-manifest}
@item --manifest=@var{file}
@itemx -m @var{file}
Create an environment for the packages contained in the manifest object
returned by the Scheme code in @var{file}.  This option can be repeated
several times, in which case the manifests are concatenated.

This is similar to the same-named option in @command{guix package}
(@pxref{profile-manifest, @option{--manifest}}) and uses the same
manifest files.

@xref{Writing Manifests}, for information on how to write a manifest.
See @option{--export-manifest} below on how to obtain a first manifest.

@cindex manifest, exporting
@anchor{shell-export-manifest}
@item --export-manifest
Write to standard output a manifest suitable for @option{--manifest}
corresponding to given command-line options.

This is a way to ``convert'' command-line arguments into a manifest.
For example, imagine you are tired of typing long lines and would like
to get a manifest equivalent to this command line:

@example
guix shell -D guile git emacs emacs-geiser emacs-geiser-guile
@end example

Just add @option{--export-manifest} to the command line above:

@example
guix shell --export-manifest \
  -D guile git emacs emacs-geiser emacs-geiser-guile
@end example

@noindent
... and you get a manifest along these lines:

@lisp
(concatenate-manifests
  (list (specifications->manifest
          (list "git"
                "emacs"
                "emacs-geiser"
                "emacs-geiser-guile"))
        (package->development-manifest
          (specification->package "guile"))))
@end lisp

You can store it into a file, say @file{manifest.scm}, and from there
pass it to @command{guix shell} or indeed pretty much any @command{guix}
command:

@example
guix shell -m manifest.scm
@end example

Voilà, you've converted a long command line into a manifest!  That
conversion process honors package transformation options (@pxref{Package
Transformation Options}) so it should be lossless.

@item --profile=@var{profile}
@itemx -p @var{profile}
Create an environment containing the packages installed in @var{profile}.
Use @command{guix package} (@pxref{Invoking guix package}) to create
and manage profiles.

@item --pure
Unset existing environment variables when building the new environment, except
those specified with @option{--preserve} (see below).  This has the effect of
creating an environment in which search paths only contain package inputs.

@item --preserve=@var{regexp}
@itemx -E @var{regexp}
When used alongside @option{--pure}, preserve the environment variables
matching @var{regexp}---in other words, put them on a ``white list'' of
environment variables that must be preserved.  This option can be repeated
several times.

@example
guix shell --pure --preserve=^SLURM openmpi @dots{} \
  -- mpirun @dots{}
@end example

This example runs @command{mpirun} in a context where the only environment
variables defined are @env{PATH}, environment variables whose name starts
with @samp{SLURM}, as well as the usual ``precious'' variables (@env{HOME},
@env{USER}, etc.).

@item --search-paths
Display the environment variable definitions that make up the
environment.

@item --system=@var{system}
@itemx -s @var{system}
Attempt to build for @var{system}---e.g., @code{i686-linux}.

@item --container
@itemx -C
@cindex container
Run @var{command} within an isolated container.  The current working
directory outside the container is mapped inside the container.
Additionally, unless overridden with @option{--user}, a dummy home
directory is created that matches the current user's home directory, and
@file{/etc/passwd} is configured accordingly.

The spawned process runs as the current user outside the container.  Inside
the container, it has the same UID and GID as the current user, unless
@option{--user} is passed (see below).

@item --network
@itemx -N
For containers, share the network namespace with the host system.
Containers created without this flag only have access to the loopback
device.

@item --link-profile
@itemx -P
For containers, link the environment profile to @file{~/.guix-profile}
within the container and set @code{GUIX_ENVIRONMENT} to that.
This is equivalent to making @file{~/.guix-profile} a symlink to the
actual profile within the container.
Linking will fail and abort the environment if the directory already
exists, which will certainly be the case if @command{guix shell}
was invoked in the user's home directory.

Certain packages are configured to look in @file{~/.guix-profile} for
configuration files and data;@footnote{For example, the
@code{fontconfig} package inspects @file{~/.guix-profile/share/fonts}
for additional fonts.}  @option{--link-profile} allows these programs to
behave as expected within the environment.

@item --user=@var{user}
@itemx -u @var{user}
For containers, use the username @var{user} in place of the current
user.  The generated @file{/etc/passwd} entry within the container will
contain the name @var{user}, the home directory will be
@file{/home/@var{user}}, and no user GECOS data will be copied.  Furthermore,
the UID and GID inside the container are 1000.  @var{user}
need not exist on the system.

Additionally, any shared or exposed path (see @option{--share} and
@option{--expose} respectively) whose target is within the current user's
home directory will be remapped relative to @file{/home/USER}; this
includes the automatic mapping of the current working directory.

@example
# will expose paths as /home/foo/wd, /home/foo/test, and /home/foo/target
cd $HOME/wd
guix shell --container --user=foo \
     --expose=$HOME/test \
     --expose=/tmp/target=$HOME/target
@end example

While this will limit the leaking of user identity through home paths
and each of the user fields, this is only one useful component of a
broader privacy/anonymity solution---not one in and of itself.

@item --no-cwd
For containers, the default behavior is to share the current working
directory with the isolated container and immediately change to that
directory within the container.  If this is undesirable,
@option{--no-cwd} will cause the current working directory to @emph{not}
be automatically shared and will change to the user's home directory
within the container instead.  See also @option{--user}.

@item --expose=@var{source}[=@var{target}]
@itemx --share=@var{source}[=@var{target}]
For containers, @option{--expose} (resp. @option{--share}) exposes the
file system @var{source} from the host system as the read-only
(resp. writable) file system @var{target} within the container.  If
@var{target} is not specified, @var{source} is used as the target mount
point in the container.

The example below spawns a Guile REPL in a container in which the user's
home directory is accessible read-only via the @file{/exchange}
directory:

@example
guix shell --container --expose=$HOME=/exchange guile -- guile
@end example

@cindex symbolic links, guix shell
@item --symlink=@var{spec}
@itemx -S @var{spec}
For containers, create the symbolic links specified by @var{spec}, as
documented in @ref{pack-symlink-option}.

@cindex file system hierarchy standard (FHS)
@cindex FHS (file system hierarchy standard)
@item --emulate-fhs
@itemx -F
When used with @option{--container}, emulate a
@uref{https://refspecs.linuxfoundation.org/fhs.shtml, Filesystem
Hierarchy Standard (FHS)} configuration within the container, providing
@file{/bin}, @file{/lib}, and other directories and files specified by
the FHS.

As Guix deviates from the FHS specification, this
option sets up the container to more closely mimic that of other
GNU/Linux distributions.  This is useful for reproducing other
development environments, testing, and using programs which expect the
FHS specification to be followed.  With this option, the container will
include a version of glibc that will read
@file{/etc/ld.so.cache} within the container for the shared library
cache (contrary to glibc in regular Guix usage) and set up the
expected FHS directories: @file{/bin}, @file{/etc}, @file{/lib}, and
@file{/usr} from the container's profile.

@cindex nested containers, for @command{guix shell}
@cindex container nesting, for @command{guix shell}
@item --nesting
@itemx -W
When used with @option{--container}, provide Guix @emph{inside} the
container and arrange so that it can interact with the build daemon that
runs outside the container.  This is useful if you want, within your
isolated container, to create other containers, as in this sample
session:

@example
$ guix shell -CW coreutils
[env]$ guix shell -C guile -- guile -c '(display "hello!\n")'
hello!
[env]$ exit
@end example

The session above starts a container with @code{coreutils} programs
available in @env{PATH}.  From there, we spawn @command{guix shell} to
create a @emph{nested} container that provides nothing but Guile.

Another example is evaluating a @file{guix.scm} file that is untrusted,
as shown here:

@example
guix shell -CW -- guix build -f guix.scm
@end example

The @command{guix build} command as executed above can only access the
current directory.

Under the hood, the @option{-W} option does several things:

@itemize
@item
map the daemon's socket (by default
@file{/var/guix/daemon-socket/socket}) inside the container;
@item
map the whole store (by default @file{/gnu/store}) inside the container
such that store items made available by nested @command{guix}
invocations are visible;
@item
add the currently-used @command{guix} command to the profile in the
container, such that @command{guix describe} returns the same state
inside and outside the container;
@item
share the cache (by default @file{~/.cache/guix}) with the host, to
speed up operations such as @command{guix time-machine} and
@command{guix shell}.
@end itemize

@item --rebuild-cache
@cindex caching, of profiles
@cindex caching, in @command{guix shell}
In most cases, @command{guix shell} caches the environment so that
subsequent uses are instantaneous.  Least-recently used cache entries
are periodically removed.  The cache is also invalidated, when using
@option{--file} or @option{--manifest}, anytime the corresponding file
is modified.

The @option{--rebuild-cache} forces the cached environment to be
refreshed.  This is useful when using @option{--file} or
@option{--manifest} and the @command{guix.scm} or @command{manifest.scm}
file has external dependencies, or if its behavior depends, say, on
environment variables.

@item --root=@var{file}
@itemx -r @var{file}
@cindex persistent environment
@cindex garbage collector root, for environments
Make @var{file} a symlink to the profile for this environment, and
register it as a garbage collector root.

This is useful if you want to protect your environment from garbage
collection, to make it ``persistent''.

When this option is omitted, @command{guix shell} caches profiles so
that subsequent uses of the same environment are instantaneous---this is
comparable to using @option{--root} except that @command{guix shell}
takes care of periodically removing the least-recently used garbage
collector roots.

In some cases, @command{guix shell} does not cache profiles---e.g., if
transformation options such as @option{--with-latest} are used.  In
those cases, the environment is protected from garbage collection only
for the duration of the @command{guix shell} session.  This means that
next time you recreate the same environment, you could have to rebuild
or re-download packages.

@xref{Invoking guix gc}, for more on GC roots.
@end table

@command{guix shell} also supports all of the common build options that
@command{guix build} supports (@pxref{Common Build Options}) as well as
package transformation options (@pxref{Package Transformation Options}).

@node Invoking guix environment
@section Invoking @command{guix environment}

@cindex @command{guix environment}

The purpose of @command{guix environment} is to assist in creating
development environments.

@quotation Deprecation warning
The @command{guix environment} command is deprecated in favor of
@command{guix shell}, which performs similar functions but is more
convenient to use.  @xref{Invoking guix shell}.

Being deprecated, @command{guix environment} is slated for eventual
removal, but the Guix project is committed to keeping it until May 1st,
2023.  Please get in touch with us at @email{guix-devel@@gnu.org} if you
would like to discuss it.
@end quotation

The general syntax is:

@example
guix environment @var{options} @var{package}@dots{}
@end example

The following example spawns a new shell set up for the development of
GNU@tie{}Guile:

@example
guix environment guile
@end example

If the needed dependencies are not built yet, @command{guix environment}
automatically builds them.  The environment of the new shell is an
augmented version of the environment that @command{guix environment} was
run in.  It contains the necessary search paths for building the given
package added to the existing environment variables.  To create
a ``pure'' environment, in which the original environment variables have
been unset, use the @option{--pure} option@footnote{Users sometimes
wrongfully augment environment variables such as @env{PATH} in their
@file{~/.bashrc} file.  As a consequence, when @command{guix
environment} launches it, Bash may read @file{~/.bashrc}, thereby
introducing ``impurities'' in these environment variables.  It is an
error to define such environment variables in @file{.bashrc}; instead,
they should be defined in @file{.bash_profile}, which is sourced only by
log-in shells.  @xref{Bash Startup Files,,, bash, The GNU Bash Reference
Manual}, for details on Bash start-up files.}.

Exiting from a Guix environment is the same as exiting from the shell,
and will place the user back in the old environment before @command{guix
environment} was invoked.  The next garbage collection (@pxref{Invoking
guix gc}) will clean up packages that were installed from within the
environment and are no longer used outside of it.

@vindex GUIX_ENVIRONMENT
@command{guix environment} defines the @env{GUIX_ENVIRONMENT}
variable in the shell it spawns; its value is the file name of the
profile of this environment.  This allows users to, say, define a
specific prompt for development environments in their @file{.bashrc}
(@pxref{Bash Startup Files,,, bash, The GNU Bash Reference Manual}):

@example
if [ -n "$GUIX_ENVIRONMENT" ]
then
    export PS1="\u@@\h \w [dev]\$ "
fi
@end example

@noindent
...@: or to browse the profile:

@example
$ ls "$GUIX_ENVIRONMENT/bin"
@end example

Additionally, more than one package may be specified, in which case the
union of the inputs for the given packages are used.  For example, the
command below spawns a shell where all of the dependencies of both Guile
and Emacs are available:

@example
guix environment guile emacs
@end example

Sometimes an interactive shell session is not desired.  An arbitrary
command may be invoked by placing the @code{--} token to separate the
command from the rest of the arguments:

@example
guix environment guile -- make -j4
@end example

In other situations, it is more convenient to specify the list of
packages needed in the environment.  For example, the following command
runs @command{python} from an environment containing Python@tie{}3 and
NumPy:

@example
guix environment --ad-hoc python-numpy python -- python3
@end example

Furthermore, one might want the dependencies of a package and also some
additional packages that are not build-time or runtime dependencies, but
are useful when developing nonetheless.  Because of this, the
@option{--ad-hoc} flag is positional.  Packages appearing before
@option{--ad-hoc} are interpreted as packages whose dependencies will be
added to the environment.  Packages appearing after are interpreted as
packages that will be added to the environment directly.  For example,
the following command creates a Guix development environment that
additionally includes Git and strace:

@example
guix environment --pure guix --ad-hoc git strace
@end example

@cindex container
Sometimes it is desirable to isolate the environment as much as
possible, for maximal purity and reproducibility.  In particular, when
using Guix on a host distro that is not Guix System, it is desirable to
prevent access to @file{/usr/bin} and other system-wide resources from
the development environment.  For example, the following command spawns
a Guile REPL in a ``container'' where only the store and the current
working directory are mounted:

@example
guix environment --ad-hoc --container guile -- guile
@end example

@quotation Note
The @option{--container} option requires Linux-libre 3.19 or newer.
@end quotation

@cindex certificates
Another typical use case for containers is to run security-sensitive
applications such as a web browser.  To run Eolie, we must expose and
share some files and directories; we include @code{nss-certs} and expose
@file{/etc/ssl/certs/} for HTTPS authentication; finally we preserve the
@env{DISPLAY} environment variable since containerized graphical
applications won't display without it.

@example
guix environment --preserve='^DISPLAY$' --container --network \
  --expose=/etc/machine-id \
  --expose=/etc/ssl/certs/ \
  --share=$HOME/.local/share/eolie/=$HOME/.local/share/eolie/ \
  --ad-hoc eolie nss-certs dbus --  eolie
@end example

The available options are summarized below.

@table @code
@item --check
Set up the environment and check whether the shell would clobber
environment variables.  @xref{Invoking guix shell, @option{--check}},
for more info.

@item --root=@var{file}
@itemx -r @var{file}
@cindex persistent environment
@cindex garbage collector root, for environments
Make @var{file} a symlink to the profile for this environment, and
register it as a garbage collector root.

This is useful if you want to protect your environment from garbage
collection, to make it ``persistent''.

When this option is omitted, the environment is protected from garbage
collection only for the duration of the @command{guix environment}
session.  This means that next time you recreate the same environment,
you could have to rebuild or re-download packages.  @xref{Invoking guix
gc}, for more on GC roots.

@item --expression=@var{expr}
@itemx -e @var{expr}
Create an environment for the package or list of packages that
@var{expr} evaluates to.

For example, running:

@example
guix environment -e '(@@ (gnu packages maths) petsc-openmpi)'
@end example

starts a shell with the environment for this specific variant of the
PETSc package.

Running:

@example
guix environment --ad-hoc -e '(@@ (gnu) %base-packages)'
@end example

starts a shell with all the base system packages available.

The above commands only use the default output of the given packages.
To select other outputs, two element tuples can be specified:

@example
guix environment --ad-hoc -e '(list (@@ (gnu packages bash) bash) "include")'
@end example

@item --load=@var{file}
@itemx -l @var{file}
Create an environment for the package or list of packages that the code
within @var{file} evaluates to.

As an example, @var{file} might contain a definition like this
(@pxref{Defining Packages}):

@lisp
@verbatiminclude environment-gdb.scm
@end lisp

@item --manifest=@var{file}
@itemx -m @var{file}
Create an environment for the packages contained in the manifest object
returned by the Scheme code in @var{file}.  This option can be repeated
several times, in which case the manifests are concatenated.

This is similar to the same-named option in @command{guix package}
(@pxref{profile-manifest, @option{--manifest}}) and uses the same
manifest files.

@xref{shell-export-manifest, @command{guix shell --export-manifest}},
for information on how to ``convert'' command-line options into a
manifest.

@item --ad-hoc
Include all specified packages in the resulting environment, as if an
@i{ad hoc} package were defined with them as inputs.  This option is
useful for quickly creating an environment without having to write a
package expression to contain the desired inputs.

For instance, the command:

@example
guix environment --ad-hoc guile guile-sdl -- guile
@end example

runs @command{guile} in an environment where Guile and Guile-SDL are
available.

Note that this example implicitly asks for the default output of
@code{guile} and @code{guile-sdl}, but it is possible to ask for a
specific output---e.g., @code{glib:bin} asks for the @code{bin} output
of @code{glib} (@pxref{Packages with Multiple Outputs}).

This option may be composed with the default behavior of @command{guix
environment}.  Packages appearing before @option{--ad-hoc} are
interpreted as packages whose dependencies will be added to the
environment, the default behavior.  Packages appearing after are
interpreted as packages that will be added to the environment directly.

@item --profile=@var{profile}
@itemx -p @var{profile}
Create an environment containing the packages installed in @var{profile}.
Use @command{guix package} (@pxref{Invoking guix package}) to create
and manage profiles.

@item --pure
Unset existing environment variables when building the new environment, except
those specified with @option{--preserve} (see below).  This has the effect of
creating an environment in which search paths only contain package inputs.

@item --preserve=@var{regexp}
@itemx -E @var{regexp}
When used alongside @option{--pure}, preserve the environment variables
matching @var{regexp}---in other words, put them on a ``white list'' of
environment variables that must be preserved.  This option can be repeated
several times.

@example
guix environment --pure --preserve=^SLURM --ad-hoc openmpi @dots{} \
  -- mpirun @dots{}
@end example

This example runs @command{mpirun} in a context where the only environment
variables defined are @env{PATH}, environment variables whose name starts
with @samp{SLURM}, as well as the usual ``precious'' variables (@env{HOME},
@env{USER}, etc.).

@item --search-paths
Display the environment variable definitions that make up the
environment.

@item --system=@var{system}
@itemx -s @var{system}
Attempt to build for @var{system}---e.g., @code{i686-linux}.

@item --container
@itemx -C
@cindex container
Run @var{command} within an isolated container.  The current working
directory outside the container is mapped inside the container.
Additionally, unless overridden with @option{--user}, a dummy home
directory is created that matches the current user's home directory, and
@file{/etc/passwd} is configured accordingly.

The spawned process runs as the current user outside the container.  Inside
the container, it has the same UID and GID as the current user, unless
@option{--user} is passed (see below).

@item --network
@itemx -N
For containers, share the network namespace with the host system.
Containers created without this flag only have access to the loopback
device.

@item --link-profile
@itemx -P
For containers, link the environment profile to @file{~/.guix-profile}
within the container and set @code{GUIX_ENVIRONMENT} to that.
This is equivalent to making @file{~/.guix-profile} a symlink to the
actual profile within the container.
Linking will fail and abort the environment if the directory already
exists, which will certainly be the case if @command{guix environment}
was invoked in the user's home directory.

Certain packages are configured to look in @file{~/.guix-profile} for
configuration files and data;@footnote{For example, the
@code{fontconfig} package inspects @file{~/.guix-profile/share/fonts}
for additional fonts.}  @option{--link-profile} allows these programs to
behave as expected within the environment.

@item --user=@var{user}
@itemx -u @var{user}
For containers, use the username @var{user} in place of the current
user.  The generated @file{/etc/passwd} entry within the container will
contain the name @var{user}, the home directory will be
@file{/home/@var{user}}, and no user GECOS data will be copied.  Furthermore,
the UID and GID inside the container are 1000.  @var{user}
need not exist on the system.

Additionally, any shared or exposed path (see @option{--share} and
@option{--expose} respectively) whose target is within the current user's
home directory will be remapped relative to @file{/home/USER}; this
includes the automatic mapping of the current working directory.

@example
# will expose paths as /home/foo/wd, /home/foo/test, and /home/foo/target
cd $HOME/wd
guix environment --container --user=foo \
     --expose=$HOME/test \
     --expose=/tmp/target=$HOME/target
@end example

While this will limit the leaking of user identity through home paths
and each of the user fields, this is only one useful component of a
broader privacy/anonymity solution---not one in and of itself.

@item --no-cwd
For containers, the default behavior is to share the current working
directory with the isolated container and immediately change to that
directory within the container.  If this is undesirable,
@option{--no-cwd} will cause the current working directory to @emph{not}
be automatically shared and will change to the user's home directory
within the container instead.  See also @option{--user}.

@item --expose=@var{source}[=@var{target}]
@itemx --share=@var{source}[=@var{target}]
For containers, @option{--expose} (resp. @option{--share}) exposes the
file system @var{source} from the host system as the read-only
(resp. writable) file system @var{target} within the container.  If
@var{target} is not specified, @var{source} is used as the target mount
point in the container.

The example below spawns a Guile REPL in a container in which the user's
home directory is accessible read-only via the @file{/exchange}
directory:

@example
guix environment --container --expose=$HOME=/exchange --ad-hoc guile -- guile
@end example

@item --emulate-fhs
@item -F
For containers, emulate a Filesystem Hierarchy Standard (FHS)
configuration within the container, see
@uref{https://refspecs.linuxfoundation.org/fhs.shtml, the official
specification}.  As Guix deviates from the FHS specification, this
option sets up the container to more closely mimic that of other
GNU/Linux distributions.  This is useful for reproducing other
development environments, testing, and using programs which expect the
FHS specification to be followed.  With this option, the container will
include a version of @code{glibc} which will read
@code{/etc/ld.so.cache} within the container for the shared library
cache (contrary to @code{glibc} in regular Guix usage) and set up the
expected FHS directories: @code{/bin}, @code{/etc}, @code{/lib}, and
@code{/usr} from the container's profile.

@end table

@command{guix environment}
also supports all of the common build options that @command{guix
build} supports (@pxref{Common Build Options}) as well as package
transformation options (@pxref{Package Transformation Options}).

@node Invoking guix pack
@section Invoking @command{guix pack}

@cindex @command{guix pack}

Occasionally you want to pass software to people who are not (yet!)
lucky enough to be using Guix.  You'd tell them to run @command{guix
package -i @var{something}}, but that's not possible in this case.  This
is where @command{guix pack} comes in.

@quotation Note
If you are looking for ways to exchange binaries among machines that
already run Guix, @pxref{Invoking guix copy}, @ref{Invoking guix
publish}, and @ref{Invoking guix archive}.
@end quotation

@cindex pack
@cindex bundle
@cindex application bundle
@cindex software bundle
The @command{guix pack} command creates a shrink-wrapped @dfn{pack} or
@dfn{software bundle}: it creates a tarball or some other archive
containing the binaries of the software you're interested in, and all
its dependencies.  The resulting archive can be used on any machine that
does not have Guix, and people can run the exact same binaries as those
you have with Guix.  The pack itself is created in a bit-reproducible
fashion, so anyone can verify that it really contains the build results
that you pretend to be shipping.

For example, to create a bundle containing Guile, Emacs, Geiser, and all
their dependencies, you can run:

@example
$ guix pack guile emacs emacs-geiser
@dots{}
/gnu/store/@dots{}-pack.tar.gz
@end example

The result here is a tarball containing a @file{/gnu/store} directory
with all the relevant packages.  The resulting tarball contains a
@dfn{profile} with the three packages of interest; the profile is the
same as would be created by @command{guix package -i}.  It is this
mechanism that is used to create Guix's own standalone binary tarball
(@pxref{Binary Installation}).

Users of this pack would have to run
@file{/gnu/store/@dots{}-profile/bin/guile} to run Guile, which you may
find inconvenient.  To work around it, you can create, say, a
@file{/opt/gnu/bin} symlink to the profile:

@example
guix pack -S /opt/gnu/bin=bin guile emacs emacs-geiser
@end example

@noindent
That way, users can happily type @file{/opt/gnu/bin/guile} and enjoy.

@cindex relocatable binaries, with @command{guix pack}
What if the recipient of your pack does not have root privileges on
their machine, and thus cannot unpack it in the root file system?  In
that case, you will want to use the @option{--relocatable} option (see
below).  This option produces @dfn{relocatable binaries}, meaning they
can be placed anywhere in the file system hierarchy: in the example
above, users can unpack your tarball in their home directory and
directly run @file{./opt/gnu/bin/guile}.

@cindex Docker, build an image with guix pack
Alternatively, you can produce a pack in the Docker image format using
the following command:

@example
guix pack -f docker -S /bin=bin guile guile-readline
@end example

@noindent
The result is a tarball that can be passed to the @command{docker load}
command, followed by @code{docker run}:

@example
docker load < @var{file}
docker run -ti guile-guile-readline /bin/guile
@end example

@noindent
where @var{file} is the image returned by @command{guix pack}, and
@code{guile-guile-readline} is its ``image tag''.  See the
@uref{https://docs.docker.com/engine/reference/commandline/load/, Docker
documentation} for more information.

@cindex Singularity, build an image with guix pack
@cindex SquashFS, build an image with guix pack
Yet another option is to produce a SquashFS image with the following
command:

@example
guix pack -f squashfs bash guile emacs emacs-geiser
@end example

@noindent
The result is a SquashFS file system image that can either be mounted or
directly be used as a file system container image with the
@uref{https://www.sylabs.io/docs/, Singularity container execution
environment}, using commands like @command{singularity shell} or
@command{singularity exec}.

Several command-line options allow you to customize your pack:

@table @code
@item --format=@var{format}
@itemx -f @var{format}
Produce a pack in the given @var{format}.

The available formats are:

@table @code
@item tarball
This is the default format.  It produces a tarball containing all the
specified binaries and symlinks.

@item docker
This produces a tarball that follows the
@uref{https://github.com/docker/docker/blob/master/image/spec/v1.2.md,
Docker Image Specification}.  By default, the ``repository name'' as it
appears in the output of the @command{docker images} command is computed
from package names passed on the command line or in the manifest file.
Alternatively, the ``repository name'' can also be configured via the
@option{--image-tag} option.  Refer to @option{--help-docker-format} for
more information on such advanced options.

@item squashfs
This produces a SquashFS image containing all the specified binaries and
symlinks, as well as empty mount points for virtual file systems like
procfs.

@quotation Note
Singularity @emph{requires} you to provide @file{/bin/sh} in the image.
For that reason, @command{guix pack -f squashfs} always implies @code{-S
/bin=bin}.  Thus, your @command{guix pack} invocation must always start
with something like:

@example
guix pack -f squashfs bash @dots{}
@end example

If you forget the @code{bash} (or similar) package, @command{singularity
run} and @command{singularity exec} will fail with an unhelpful ``no
such file or directory'' message.
@end quotation

@item deb
@cindex Debian, build a .deb package with guix pack
This produces a Debian archive (a package with the @samp{.deb} file
extension) containing all the specified binaries and symbolic links,
that can be installed on top of any dpkg-based GNU(/Linux) distribution.
Advanced options can be revealed via the @option{--help-deb-format}
option.  They allow embedding control files for more fine-grained
control, such as activating specific triggers or providing a maintainer
configure script to run arbitrary setup code upon installation.

@example
guix pack -f deb -C xz -S /usr/bin/hello=bin/hello hello
@end example

@quotation Note
Because archives produced with @command{guix pack} contain a collection
of store items and because each @command{dpkg} package must not have
conflicting files, in practice that means you likely won't be able to
install more than one such archive on a given system.  You can
nonetheless pack as many Guix packages as you want in one such archive.
@end quotation

@quotation Warning
@command{dpkg} will assume ownership of any files contained in the pack
that it does @emph{not} know about.  It is unwise to install
Guix-produced @samp{.deb} files on a system where @file{/gnu/store} is
shared by other software, such as a Guix installation or other, non-deb
packs.
@end quotation

@item rpm
@cindex RPM, build an RPM archive with guix pack
This produces an RPM archive (a package with the @samp{.rpm} file
extension) containing all the specified binaries and symbolic links,
that can be installed on top of any RPM-based GNU/Linux distribution.
The RPM format embeds checksums for every file it contains, which the
@command{rpm} command uses to validate the integrity of the archive.

Advanced RPM-related options are revealed via the
@option{--help-rpm-format} option.  These options allow embedding
maintainer scripts that can run before or after the installation of the
RPM archive, for example.

The RPM format supports relocatable packages via the @option{--prefix}
option of the @command{rpm} command, which can be handy to install an
RPM package to a specific prefix.

@example
guix pack -f rpm -R -C xz -S /usr/bin/hello=bin/hello hello
@end example

@example
sudo rpm --install --prefix=/opt /gnu/store/...-hello.rpm
@end example

@quotation Note
Contrary to Debian packages, conflicting but @emph{identical} files in
RPM packages can be installed simultaneously, which means multiple
@command{guix pack}-produced RPM packages can usually be installed side
by side without any problem.
@end quotation

@quotation Warning
@command{rpm} assumes ownership of any files contained in the pack,
which means it will remove @file{/gnu/store} upon uninstalling a
Guix-generated RPM package, unless the RPM package was installed with
the @option{--prefix} option of the @command{rpm} command.  It is unwise
to install Guix-produced @samp{.rpm} packages on a system where
@file{/gnu/store} is shared by other software, such as a Guix
installation or other, non-rpm packs.
@end quotation

@end table

@cindex relocatable binaries
@item --relocatable
@itemx -R
Produce @dfn{relocatable binaries}---i.e., binaries that can be placed
anywhere in the file system hierarchy and run from there.

When this option is passed once, the resulting binaries require support for
@dfn{user namespaces} in the kernel Linux; when passed
@emph{twice}@footnote{Here's a trick to memorize it: @code{-RR}, which adds
PRoot support, can be thought of as the abbreviation of ``Really
Relocatable''.  Neat, isn't it?}, relocatable binaries fall to back to
other techniques if user namespaces are unavailable, and essentially
work anywhere---see below for the implications.

For example, if you create a pack containing Bash with:

@example
guix pack -RR -S /mybin=bin bash
@end example

@noindent
...@: you can copy that pack to a machine that lacks Guix, and from your
home directory as a normal user, run:

@example
tar xf pack.tar.gz
./mybin/sh
@end example

@noindent
In that shell, if you type @code{ls /gnu/store}, you'll notice that
@file{/gnu/store} shows up and contains all the dependencies of
@code{bash}, even though the machine actually lacks @file{/gnu/store}
altogether!  That is probably the simplest way to deploy Guix-built
software on a non-Guix machine.

@quotation Note
By default, relocatable binaries rely on the @dfn{user namespace} feature of
the kernel Linux, which allows unprivileged users to mount or change root.
Old versions of Linux did not support it, and some GNU/Linux distributions
turn it off.

To produce relocatable binaries that work even in the absence of user
namespaces, pass @option{--relocatable} or @option{-R} @emph{twice}.  In that
case, binaries will try user namespace support and fall back to another
@dfn{execution engine} if user namespaces are not supported.  The
following execution engines are supported:

@table @code
@item default
Try user namespaces and fall back to PRoot if user namespaces are not
supported (see below).

@item performance
Try user namespaces and fall back to Fakechroot if user namespaces are
not supported (see below).

@item userns
Run the program through user namespaces and abort if they are not
supported.

@item proot
Run through PRoot.  The @uref{https://proot-me.github.io/, PRoot} program
provides the necessary
support for file system virtualization.  It achieves that by using the
@code{ptrace} system call on the running program.  This approach has the
advantage to work without requiring special kernel support, but it incurs
run-time overhead every time a system call is made.

@item fakechroot
Run through Fakechroot.  @uref{https://github.com/dex4er/fakechroot/,
Fakechroot} virtualizes file system accesses by intercepting calls to C
library functions such as @code{open}, @code{stat}, @code{exec}, and so
on.  Unlike PRoot, it incurs very little overhead.  However, it does not
always work: for example, some file system accesses made from within the
C library are not intercepted, and file system accesses made @i{via}
direct syscalls are not intercepted either, leading to erratic behavior.
@end table

@vindex GUIX_EXECUTION_ENGINE
When running a wrapped program, you can explicitly request one of the
execution engines listed above by setting the
@env{GUIX_EXECUTION_ENGINE} environment variable accordingly.
@end quotation

@cindex entry point, for Docker and Singularity images
@item --entry-point=@var{command}
Use @var{command} as the @dfn{entry point} of the resulting pack, if the pack
format supports it---currently @code{docker} and @code{squashfs} (Singularity)
support it.  @var{command} must be relative to the profile contained in the
pack.

The entry point specifies the command that tools like @code{docker run} or
@code{singularity run} automatically start by default.  For example, you can
do:

@example
guix pack -f docker --entry-point=bin/guile guile
@end example

The resulting pack can easily be loaded and @code{docker run} with no extra
arguments will spawn @code{bin/guile}:

@example
docker load -i pack.tar.gz
docker run @var{image-id}
@end example

@cindex entry point arguments, for docker images
@item --entry-point-argument=@var{command}
@itemx -A @var{command}
Use @var{command} as an argument to @dfn{entry point} of the resulting pack.
This option is only valid in conjunction with @code{--entry-point} and can
appear multiple times on the command line.

@example
guix pack -f docker --entry-point=bin/guile --entry-point-argument="--help" guile
@end example

@cindex maximum layers argument, for docker images
@item --max-layers=@code{n}
Specifies the maximum number of Docker image layers allowed when
building an image.

@example
guix pack -f docker --max-layers=100 guile
@end example

This option allows you to limit the number of layers in a Docker image.
Docker images are comprised of multiple layers, and each layer adds to
the overall size and complexity of the image.  By setting a maximum
number of layers, you can control the following effects:

@itemize
@item Disk Usage:
Increasing the number of layers can help optimize the disk space
required to store multiple images built with a similar package graph.

@item Pulling:
When transferring images between different nodes or systems, having more
layers can reduce the time required to pull the image.
@end itemize

@item --expression=@var{expr}
@itemx -e @var{expr}
Consider the package @var{expr} evaluates to.

This has the same purpose as the same-named option in @command{guix
build} (@pxref{Additional Build Options, @option{--expression} in
@command{guix build}}).

@anchor{pack-manifest}
@item --manifest=@var{file}
@itemx -m @var{file}
Use the packages contained in the manifest object returned by the Scheme
code in @var{file}.  This option can be repeated several times, in which
case the manifests are concatenated.

This has a similar purpose as the same-named option in @command{guix
package} (@pxref{profile-manifest, @option{--manifest}}) and uses the
same manifest files.  It allows you to define a collection of packages
once and use it both for creating profiles and for creating archives
for use on machines that do not have Guix installed.  Note that you can
specify @emph{either} a manifest file @emph{or} a list of packages,
but not both.

@xref{Writing Manifests}, for information on how to write a manifest.
@xref{shell-export-manifest, @command{guix shell --export-manifest}},
for information on how to ``convert'' command-line options into a
manifest.

@item --system=@var{system}
@itemx -s @var{system}
Attempt to build for @var{system}---e.g., @code{i686-linux}---instead of
the system type of the build host.

@item --target=@var{triplet}
@cindex cross-compilation
Cross-build for @var{triplet}, which must be a valid GNU triplet, such
as @code{"aarch64-linux-gnu"} (@pxref{Specifying target triplets, GNU
configuration triplets,, autoconf, Autoconf}).

@item --compression=@var{tool}
@itemx -C @var{tool}
Compress the resulting tarball using @var{tool}---one of @code{gzip},
@code{zstd}, @code{bzip2}, @code{xz}, @code{lzip}, or @code{none} for no
compression.

@anchor{pack-symlink-option}
@item --symlink=@var{spec}
@itemx -S @var{spec}
Add the symlinks specified by @var{spec} to the pack.  This option can
appear several times.

@var{spec} has the form @code{@var{source}=@var{target}}, where
@var{source} is the symlink that will be created and @var{target} is the
symlink target.

For instance, @code{-S /opt/gnu/bin=bin} creates a @file{/opt/gnu/bin}
symlink pointing to the @file{bin} sub-directory of the profile.

@item --save-provenance
Save provenance information for the packages passed on the command line.
Provenance information includes the URL and commit of the channels in use
(@pxref{Channels}).

Provenance information is saved in the
@file{/gnu/store/@dots{}-profile/manifest} file in the pack, along with the
usual package metadata---the name and version of each package, their
propagated inputs, and so on.  It is useful information to the recipient of
the pack, who then knows how the pack was (supposedly) obtained.

This option is not enabled by default because, like timestamps, provenance
information contributes nothing to the build process.  In other words, there
is an infinity of channel URLs and commit IDs that can lead to the same pack.
Recording such ``silent'' metadata in the output thus potentially breaks the
source-to-binary bitwise reproducibility property.

@item --root=@var{file}
@itemx -r @var{file}
@cindex garbage collector root, for packs
Make @var{file} a symlink to the resulting pack, and register it as a garbage
collector root.

@item --localstatedir
@itemx --profile-name=@var{name}
Include the ``local state directory'', @file{/var/guix}, in the resulting
pack, and notably the @file{/var/guix/profiles/per-user/root/@var{name}}
profile---by default @var{name} is @code{guix-profile}, which corresponds to
@file{~root/.guix-profile}.

@file{/var/guix} contains the store database (@pxref{The Store}) as well
as garbage-collector roots (@pxref{Invoking guix gc}).  Providing it in
the pack means that the store is ``complete'' and manageable by Guix;
not providing it pack means that the store is ``dead'': items cannot be
added to it or removed from it after extraction of the pack.

One use case for this is the Guix self-contained binary tarball
(@pxref{Binary Installation}).

@item --derivation
@itemx -d
Print the name of the derivation that builds the pack.

@item --bootstrap
Use the bootstrap binaries to build the pack.  This option is only
useful to Guix developers.
@end table

In addition, @command{guix pack} supports all the common build options
(@pxref{Common Build Options}) and all the package transformation
options (@pxref{Package Transformation Options}).


@node The GCC toolchain
@section The GCC toolchain

@cindex GCC
@cindex ld-wrapper
@cindex linker wrapper
@cindex toolchain, for C development
@cindex toolchain, for Fortran development

If you need a complete toolchain for compiling and linking C or C++
source code, use the @code{gcc-toolchain} package.  This package
provides a complete GCC toolchain for C/C++ development, including GCC
itself, the GNU C Library (headers and binaries, plus debugging symbols
in the @code{debug} output), Binutils, and a linker wrapper.

The wrapper's purpose is to inspect the @code{-L} and @code{-l} switches
passed to the linker, add corresponding @code{-rpath} arguments, and
invoke the actual linker with this new set of arguments.  You can instruct the
wrapper to refuse to link against libraries not in the store by setting the
@env{GUIX_LD_WRAPPER_ALLOW_IMPURITIES} environment variable to @code{no}.

The package @code{gfortran-toolchain} provides a complete GCC toolchain
for Fortran development.  For other languages, please use
@samp{guix search gcc toolchain} (@pxref{guix-search,, Invoking guix package}).


@node Invoking guix git authenticate
@section Invoking @command{guix git authenticate}

@cindex @command{guix git authenticate}
@cindex authentication, of Git checkouts
@cindex Git checkout authentication

The @command{guix git authenticate} command authenticates a Git checkout
following the same rule as for channels (@pxref{channel-authentication,
channel authentication}).  That is, starting from a given commit, it
ensures that all subsequent commits are signed by an OpenPGP key whose
fingerprint appears in the @file{.guix-authorizations} file of its
parent commit(s).

You will find this command useful if you maintain a channel.  But in
fact, this authentication mechanism is useful in a broader context, so
you might want to use it for Git repositories that have nothing to do
with Guix.

The general syntax is:

@example
guix git authenticate @var{commit} @var{signer} [@var{options}@dots{}]
@end example

@cindex introduction, for Git authentication
By default, this command authenticates the Git checkout in the current
directory; it outputs nothing and exits with exit code zero on success
and non-zero on failure.  @var{commit} above denotes the first commit
where authentication takes place, and @var{signer} is the OpenPGP
fingerprint of public key used to sign @var{commit}.  Together, they
form a @dfn{channel introduction} (@pxref{channel-authentication, channel
introduction}).  On your first successful run, the introduction is
recorded in the @file{.git/config} file of your checkout, allowing you
to omit them from subsequent invocations:

@example
guix git authenticate [@var{options}@dots{}]
@end example

Should you have branches that require different introductions, you can
specify them directly in @file{.git/config}.  For example, if the branch
called @code{personal-fork} has a different introduction than other
branches, you can extend @file{.git/config} along these lines:

@smallexample
[guix "authentication-personal-fork"]
	introduction-commit = cabba936fd807b096b48283debdcddccfea3900d
	introduction-signer = C0FF EECA BBA9 E6A8 0D1D  E643 A2A0 6DF2 A33A 54FA
	keyring = keyring
@end smallexample

The first run also attempts to install pre-push and post-merge hooks,
such that @command{guix git authenticate} is invoked as soon as you run
@command{git push}, @command{git pull}, and related commands; it does
not overwrite preexisting hooks though.

The command-line options described below allow you to fine-tune the
process.

@table @code
@item --repository=@var{directory}
@itemx -r @var{directory}
Open the Git repository in @var{directory} instead of the current
directory.

@item --keyring=@var{reference}
@itemx -k @var{reference}
Load OpenPGP keyring from @var{reference}, the reference of a branch
such as @code{origin/keyring} or @code{my-keyring}.  The branch must
contain OpenPGP public keys in @file{.key} files, either in binary form
or ``ASCII-armored''.  By default the keyring is loaded from the branch
named @code{keyring}.

@item --end=@var{commit}
Authenticate revisions up to @var{commit}.

@item --stats
Display commit signing statistics upon completion.

@item --cache-key=@var{key}
Previously-authenticated commits are cached in a file under
@file{~/.cache/guix/authentication}.  This option forces the cache to be
stored in file @var{key} in that directory.

@item --historical-authorizations=@var{file}
By default, any commit whose parent commit(s) lack the
@file{.guix-authorizations} file is considered inauthentic.  In
contrast, this option considers the authorizations in @var{file} for any
commit that lacks @file{.guix-authorizations}.  The format of @var{file}
is the same as that of @file{.guix-authorizations}
(@pxref{channel-authorizations, @file{.guix-authorizations} format}).
@end table


@c *********************************************************************
@node Programming Interface
@chapter Programming Interface

GNU Guix provides several Scheme programming interfaces (APIs) to
define, build, and query packages.  The first interface allows users to
write high-level package definitions.  These definitions refer to
familiar packaging concepts, such as the name and version of a package,
its build system, and its dependencies.  These definitions can then be
turned into concrete build actions.

Build actions are performed by the Guix daemon, on behalf of users.  In a
standard setup, the daemon has write access to the store---the
@file{/gnu/store} directory---whereas users do not.  The recommended
setup also has the daemon perform builds in chroots, under specific
build users, to minimize interference with the rest of the system.

@cindex derivation
Lower-level APIs are available to interact with the daemon and the
store.  To instruct the daemon to perform a build action, users actually
provide it with a @dfn{derivation}.  A derivation is a low-level
representation of the build actions to be taken, and the environment in
which they should occur---derivations are to package definitions what
assembly is to C programs.  The term ``derivation'' comes from the fact
that build results @emph{derive} from them.

This chapter describes all these APIs in turn, starting from high-level
package definitions.  @xref{Source Tree Structure}, for a more general
overview of the source code.

@menu
* Package Modules::             Packages from the programmer's viewpoint.
* Defining Packages::           Defining new packages.
* Defining Package Variants::   Customizing packages.
* Writing Manifests::           The bill of materials of your environment.
* Build Systems::               Specifying how packages are built.
* Build Phases::                Phases of the build process of a package.
* Build Utilities::             Helpers for your package definitions and more.
* Search Paths::                Declaring search path environment variables.
* The Store::                   Manipulating the package store.
* Derivations::                 Low-level interface to package derivations.
* The Store Monad::             Purely functional interface to the store.
* G-Expressions::               Manipulating build expressions.
* Invoking guix repl::          Programming Guix in Guile
* Using Guix Interactively::    Fine-grain interaction at the REPL.
@end menu

@node Package Modules
@section Package Modules

From a programming viewpoint, the package definitions of the
GNU distribution are provided by Guile modules in the @code{(gnu packages
@dots{})} name space@footnote{Note that packages under the @code{(gnu
packages @dots{})} module name space are not necessarily ``GNU
packages''.  This module naming scheme follows the usual Guile module
naming convention: @code{gnu} means that these modules are distributed
as part of the GNU system, and @code{packages} identifies modules that
define packages.}  (@pxref{Modules, Guile modules,, guile, GNU Guile
Reference Manual}).  For instance, the @code{(gnu packages emacs)}
module exports a variable named @code{emacs}, which is bound to a
@code{<package>} object (@pxref{Defining Packages}).

The @code{(gnu packages @dots{})} module name space is
automatically scanned for packages by the command-line tools.  For
instance, when running @code{guix install emacs}, all the @code{(gnu
packages @dots{})} modules are scanned until one that exports a package
object whose name is @code{emacs} is found.  This package search
facility is implemented in the @code{(gnu packages)} module.

@cindex customization, of packages
@cindex package module search path
Users can store package definitions in modules with different
names---e.g., @code{(my-packages emacs)}@footnote{Note that the file
name and module name must match.  For instance, the @code{(my-packages
emacs)} module must be stored in a @file{my-packages/emacs.scm} file
relative to the load path specified with @option{--load-path} or
@env{GUIX_PACKAGE_PATH}.  @xref{Modules and the File System,,,
guile, GNU Guile Reference Manual}, for details.}.  There are two ways to make
these package definitions visible to the user interfaces:

@enumerate
@item
By adding the directory containing your package modules to the search path
with the @code{-L} flag of @command{guix package} and other commands
(@pxref{Common Build Options}), or by setting the @env{GUIX_PACKAGE_PATH}
environment variable described below.

@item
By defining a @dfn{channel} and configuring @command{guix pull} so that it
pulls from it.  A channel is essentially a Git repository containing package
modules.  @xref{Channels}, for more information on how to define and use
channels.
@end enumerate

@env{GUIX_PACKAGE_PATH} works similarly to other search path variables:

@defvr {Environment Variable} GUIX_PACKAGE_PATH
This is a colon-separated list of directories to search for additional
package modules.  Directories listed in this variable take precedence
over the own modules of the distribution.
@end defvr

The distribution is fully @dfn{bootstrapped} and @dfn{self-contained}:
each package is built based solely on other packages in the
distribution.  The root of this dependency graph is a small set of
@dfn{bootstrap binaries}, provided by the @code{(gnu packages
bootstrap)} module.  For more information on bootstrapping,
@pxref{Bootstrapping}.

@node Defining Packages
@section Defining Packages

The high-level interface to package definitions is implemented in the
@code{(guix packages)} and @code{(guix build-system)} modules.  As an
example, the package definition, or @dfn{recipe}, for the GNU Hello
package looks like this:

@lisp
(define-module (gnu packages hello)
  #:use-module (guix packages)
  #:use-module (guix download)
  #:use-module (guix build-system gnu)
  #:use-module (guix licenses)
  #:use-module (gnu packages gawk))

(define-public hello
  (package
    (name "hello")
    (version "2.10")
    (source (origin
              (method url-fetch)
              (uri (string-append "mirror://gnu/hello/hello-" version
                                  ".tar.gz"))
              (sha256
               (base32
                "0ssi1wpaf7plaswqqjwigppsg5fyh99vdlb9kzl7c9lng89ndq1i"))))
    (build-system gnu-build-system)
    (arguments '(#:configure-flags '("--enable-silent-rules")))
    (inputs (list gawk))
    (synopsis "Hello, GNU world: An example GNU package")
    (description "Guess what GNU Hello prints!")
    (home-page "https://www.gnu.org/software/hello/")
    (license gpl3+)))
@end lisp

@noindent
Without being a Scheme expert, the reader may have guessed the meaning
of the various fields here.  This expression binds the variable
@code{hello} to a @code{<package>} object, which is essentially a record
(@pxref{SRFI-9, Scheme records,, guile, GNU Guile Reference Manual}).
This package object can be inspected using procedures found in the
@code{(guix packages)} module; for instance, @code{(package-name hello)}
returns---surprise!---@code{"hello"}.

With luck, you may be able to import part or all of the definition of
the package you are interested in from another repository, using the
@code{guix import} command (@pxref{Invoking guix import}).

In the example above, @code{hello} is defined in a module of its own,
@code{(gnu packages hello)}.  Technically, this is not strictly
necessary, but it is convenient to do so: all the packages defined in
modules under @code{(gnu packages @dots{})} are automatically known to
the command-line tools (@pxref{Package Modules}).

There are a few points worth noting in the above package definition:

@itemize
@item
The @code{source} field of the package is an @code{<origin>} object
(@pxref{origin Reference}, for the complete reference).
Here, the @code{url-fetch} method from @code{(guix download)} is used,
meaning that the source is a file to be downloaded over FTP or HTTP.

The @code{mirror://gnu} prefix instructs @code{url-fetch} to use one of
the GNU mirrors defined in @code{(guix download)}.

The @code{sha256} field specifies the expected SHA256 hash of the file
being downloaded.  It is mandatory, and allows Guix to check the
integrity of the file.  The @code{(base32 @dots{})} form introduces the
base32 representation of the hash.  You can obtain this information with
@code{guix download} (@pxref{Invoking guix download}) and @code{guix
hash} (@pxref{Invoking guix hash}).

@cindex patches
When needed, the @code{origin} form can also have a @code{patches} field
listing patches to be applied, and a @code{snippet} field giving a
Scheme expression to modify the source code.

@item
@cindex GNU Build System
The @code{build-system} field specifies the procedure to build the
package (@pxref{Build Systems}).  Here, @code{gnu-build-system}
represents the familiar GNU Build System, where packages may be
configured, built, and installed with the usual @code{./configure &&
make && make check && make install} command sequence.

When you start packaging non-trivial software, you may need tools to
manipulate those build phases, manipulate files, and so on.  @xref{Build
Utilities}, for more on this.

@item
The @code{arguments} field specifies options for the build system
(@pxref{Build Systems}).  Here it is interpreted by
@code{gnu-build-system} as a request run @file{configure} with the
@option{--enable-silent-rules} flag.

@cindex quote
@cindex quoting
@findex '
@findex quote
@cindex backquote (quasiquote)
@findex `
@findex quasiquote
@cindex comma (unquote)
@findex ,
@findex unquote
What about these quote (@code{'}) characters?  They are Scheme syntax to
introduce a literal list; @code{'} is synonymous with @code{quote}.
Sometimes you'll also see @code{`} (a backquote, synonymous with
@code{quasiquote}) and @code{,} (a comma, synonymous with @code{unquote}).
@xref{Expression Syntax, quoting,, guile, GNU Guile Reference Manual},
for details.  Here the value of the @code{arguments} field is a list of
arguments passed to the build system down the road, as with @code{apply}
(@pxref{Fly Evaluation, @code{apply},, guile, GNU Guile Reference
Manual}).

The hash-colon (@code{#:}) sequence defines a Scheme @dfn{keyword}
(@pxref{Keywords,,, guile, GNU Guile Reference Manual}), and
@code{#:configure-flags} is a keyword used to pass a keyword argument
to the build system (@pxref{Coding With Keywords,,, guile, GNU Guile
Reference Manual}).

@item
The @code{inputs} field specifies inputs to the build process---i.e.,
build-time or run-time dependencies of the package.  Here, we add
an input, a reference to the @code{gawk}
variable; @code{gawk} is itself bound to a @code{<package>} object.

Note that GCC, Coreutils, Bash, and other essential tools do not need to
be specified as inputs here.  Instead, @code{gnu-build-system} takes care
of ensuring that they are present (@pxref{Build Systems}).

However, any other dependencies need to be specified in the
@code{inputs} field.  Any dependency not specified here will simply be
unavailable to the build process, possibly leading to a build failure.
@end itemize

@xref{package Reference}, for a full description of possible fields.

@quotation Going further
@cindex Scheme programming language, getting started
Intimidated by the Scheme language or curious about it?  The Cookbook
has a short section to get started that recaps some of the things shown
above and explains the fundamentals.  @xref{A Scheme Crash Course,,,
guix-cookbook, GNU Guix Cookbook}, for more information.
@end quotation

Once a package definition is in place, the
package may actually be built using the @code{guix build} command-line
tool (@pxref{Invoking guix build}), troubleshooting any build failures
you encounter (@pxref{Debugging Build Failures}).  You can easily jump back to the
package definition using the @command{guix edit} command
(@pxref{Invoking guix edit}).
@xref{Packaging Guidelines}, for
more information on how to test package definitions, and
@ref{Invoking guix lint}, for information on how to check a definition
for style conformance.
@vindex GUIX_PACKAGE_PATH
Lastly, @pxref{Channels}, for information
on how to extend the distribution by adding your own package definitions
in a ``channel''.

Finally, updating the package definition to a new upstream version
can be partly automated by the @command{guix refresh} command
(@pxref{Invoking guix refresh}).

Behind the scenes, a derivation corresponding to the @code{<package>}
object is first computed by the @code{package-derivation} procedure.
That derivation is stored in a @file{.drv} file under @file{/gnu/store}.
The build actions it prescribes may then be realized by using the
@code{build-derivations} procedure (@pxref{The Store}).

@deffn {Procedure} package-derivation store package [system]
Return the @code{<derivation>} object of @var{package} for @var{system}
(@pxref{Derivations}).

@var{package} must be a valid @code{<package>} object, and @var{system}
must be a string denoting the target system type---e.g.,
@code{"x86_64-linux"} for an x86_64 Linux-based GNU system.  @var{store}
must be a connection to the daemon, which operates on the store
(@pxref{The Store}).
@end deffn

@noindent
@cindex cross-compilation
Similarly, it is possible to compute a derivation that cross-builds a
package for some other system:

@deffn {Procedure} package-cross-derivation store package target [system]
Return the @code{<derivation>} object of @var{package} cross-built from
@var{system} to @var{target}.

@var{target} must be a valid GNU triplet denoting the target hardware
and operating system, such as @code{"aarch64-linux-gnu"}
(@pxref{Specifying Target Triplets,,, autoconf, Autoconf}).
@end deffn

Once you have package definitions, you can easily define @emph{variants}
of those packages.  @xref{Defining Package Variants}, for more on that.

@menu
* package Reference::           The package data type.
* origin Reference::            The origin data type.
@end menu


@node package Reference
@subsection @code{package} Reference

This section summarizes all the options available in @code{package}
declarations (@pxref{Defining Packages}).

@deftp {Data Type} package
This is the data type representing a package recipe.

@table @asis
@item @code{name}
The name of the package, as a string.

@item @code{version}
The version of the package, as a string.  @xref{Version Numbers}, for
guidelines.

@item @code{source}
An object telling how the source code for the package should be
acquired.  Most of the time, this is an @code{origin} object, which
denotes a file fetched from the Internet (@pxref{origin Reference}).  It
can also be any other ``file-like'' object such as a @code{local-file},
which denotes a file from the local file system (@pxref{G-Expressions,
@code{local-file}}).

@item @code{build-system}
The build system that should be used to build the package (@pxref{Build
Systems}).

@item @code{arguments} (default: @code{'()})
The arguments that should be passed to the build system (@pxref{Build
Systems}).  This is a list, typically containing sequential
keyword-value pairs, as in this example:

@lisp
(package
  (name "example")
  ;; several fields omitted
  (arguments
    (list #:tests? #f                     ;skip tests
          #:make-flags #~'("VERBOSE=1")   ;pass flags to 'make'
          #:configure-flags #~'("--enable-frobbing"))))
@end lisp

The exact set of supported keywords depends on the build system
(@pxref{Build Systems}), but you will find that almost all of them honor
@code{#:configure-flags}, @code{#:make-flags}, @code{#:tests?}, and
@code{#:phases}.  The @code{#:phases} keyword in particular lets you
modify the set of build phases for your package (@pxref{Build Phases}).

The REPL has dedicated commands to interactively inspect values of some
of these arguments, as a convenient debugging aid (@pxref{Using Guix
Interactively}).

@quotation Compatibility Note
Until version 1.3.0, the @code{arguments} field would typically use
@code{quote} (@code{'}) or @code{quasiquote} (@code{`}) and no
G-expressions, like so:

@lisp
(package
  ;; several fields omitted
  (arguments   ;old-style quoted arguments
   '(#:tests? #f
     #:configure-flags '("--enable-frobbing"))))
@end lisp

To convert from that style to the one shown above, you can run
@code{guix style -S arguments @var{package}} (@pxref{Invoking guix
style}).
@end quotation

@item @code{inputs} (default: @code{'()})
@itemx @code{native-inputs} (default: @code{'()})
@itemx @code{propagated-inputs} (default: @code{'()})
@cindex inputs, of packages
These fields list dependencies of the package.  Each element of these
lists is either a package, origin, or other ``file-like object''
(@pxref{G-Expressions}); to specify the output of that file-like object
that should be used, pass a two-element list where the second element is
the output (@pxref{Packages with Multiple Outputs}, for more on package
outputs).  For example, the list below specifies three inputs:

@lisp
(list libffi libunistring
      `(,glib "bin"))      ;the "bin" output of GLib
@end lisp

In the example above, the @code{"out"} output of @code{libffi} and
@code{libunistring} is used.

@quotation Compatibility Note
Until version 1.3.0, input lists were a list of tuples,
where each tuple has a label for the input (a string) as its
first element, a package, origin, or derivation as its second element,
and optionally the name of the output thereof that should be used, which
defaults to @code{"out"}.  For example, the list below is equivalent to
the one above, but using the @dfn{old input style}:

@lisp
;; Old input style (deprecated).
`(("libffi" ,libffi)
  ("libunistring" ,libunistring)
  ("glib:bin" ,glib "bin"))  ;the "bin" output of GLib
@end lisp

This style is now deprecated; it is still supported but support will be
removed in a future version.  It should not be used for new package
definitions.  @xref{Invoking guix style}, on how to migrate to the new
style.
@end quotation

@cindex cross compilation, package dependencies
The distinction between @code{native-inputs} and @code{inputs} is
necessary when considering cross-compilation.  When cross-compiling,
dependencies listed in @code{inputs} are built for the @emph{target}
architecture; conversely, dependencies listed in @code{native-inputs}
are built for the architecture of the @emph{build} machine.

@code{native-inputs} is typically used to list tools needed at
build time, but not at run time, such as Autoconf, Automake, pkg-config,
Gettext, or Bison.  @command{guix lint} can report likely mistakes in
this area (@pxref{Invoking guix lint}).

@anchor{package-propagated-inputs}
Lastly, @code{propagated-inputs} is similar to @code{inputs}, but the
specified packages will be automatically installed to profiles
(@pxref{Features, the role of profiles in Guix}) alongside the package
they belong to (@pxref{package-cmd-propagated-inputs, @command{guix
package}}, for information on how @command{guix package} deals with
propagated inputs).

For example this is necessary when packaging a C/C++ library that needs
headers of another library to compile, or when a pkg-config file refers
to another one @i{via} its @code{Requires} field.

Another example where @code{propagated-inputs} is useful is for languages
that lack a facility to record the run-time search path akin to the
@code{RUNPATH} of ELF files; this includes Guile, Python, Perl, and
more.  When packaging libraries written in those languages, ensure they
can find library code they depend on at run time by listing run-time
dependencies in @code{propagated-inputs} rather than @code{inputs}.

@item @code{outputs} (default: @code{'("out")})
The list of output names of the package.  @xref{Packages with Multiple
Outputs}, for typical uses of additional outputs.

@item @code{native-search-paths} (default: @code{'()})
@itemx @code{search-paths} (default: @code{'()})
A list of @code{search-path-specification} objects describing
search-path environment variables honored by the package.  @xref{Search
Paths}, for more on search path specifications.

As for inputs, the distinction between @code{native-search-paths} and
@code{search-paths} only matters when cross-compiling.  In a
cross-compilation context, @code{native-search-paths} applies
exclusively to native inputs whereas @code{search-paths} applies only to
host inputs.

Packages such as cross-compilers care about target inputs---for
instance, our (modified) GCC cross-compiler has
@env{CROSS_C_INCLUDE_PATH} in @code{search-paths}, which allows it to
pick @file{.h} files for the target system and @emph{not} those of
native inputs.  For the majority of packages though, only
@code{native-search-paths} makes sense.

@item @code{replacement} (default: @code{#f})
This must be either @code{#f} or a package object that will be used as a
@dfn{replacement} for this package.  @xref{Security Updates, grafts},
for details.

@item @code{synopsis}
A one-line description of the package.

@item @code{description}
A more elaborate description of the package, as a string in Texinfo
syntax.

@item @code{license}
@cindex license, of packages
The license of the package; a value from @code{(guix licenses)},
or a list of such values.

@item @code{home-page}
The URL to the home-page of the package, as a string.

@item @code{supported-systems} (default: @code{%supported-systems})
The list of systems supported by the package, as strings of the form
@code{architecture-kernel}, for example @code{"x86_64-linux"}.

@item @code{location} (default: source location of the @code{package} form)
The source location of the package.  It is useful to override this when
inheriting from another package, in which case this field is not
automatically corrected.
@end table
@end deftp

@defmac this-package
When used in the @emph{lexical scope} of a package field definition, this
identifier resolves to the package being defined.

The example below shows how to add a package as a native input of itself when
cross-compiling:

@lisp
(package
  (name "guile")
  ;; ...

  ;; When cross-compiled, Guile, for example, depends on
  ;; a native version of itself.  Add it here.
  (native-inputs (if (%current-target-system)
                     (list this-package)
                     '())))
@end lisp

It is an error to refer to @code{this-package} outside a package definition.
@end defmac

The following helper procedures are provided to help deal with package
inputs.

@deffn {Procedure} lookup-package-input package name
@deffnx {Procedure} lookup-package-native-input package name
@deffnx {Procedure} lookup-package-propagated-input package name
@deffnx {Procedure} lookup-package-direct-input package name
Look up @var{name} among @var{package}'s inputs (or native, propagated,
or direct inputs).  Return it if found, @code{#f} otherwise.

@var{name} is the name of a package depended on.  Here's how you might
use it:

@lisp
(use-modules (guix packages) (gnu packages base))

(lookup-package-direct-input coreutils "gmp")
@result{} #<package gmp@@6.2.1 @dots{}>
@end lisp

In this example we obtain the @code{gmp} package that is among the
direct inputs of @code{coreutils}.
@end deffn

@cindex development inputs, of a package
@cindex implicit inputs, of a package
Sometimes you will want to obtain the list of inputs needed to
@emph{develop} a package---all the inputs that are visible when the
package is compiled.  This is what the @code{package-development-inputs}
procedure returns.

@deffn {Procedure} package-development-inputs package [system] [#:target #f]
Return the list of inputs required by @var{package} for development
purposes on @var{system}.  When @var{target} is true, return the inputs
needed to cross-compile @var{package} from @var{system} to
@var{target}, where @var{target} is a triplet such as
@code{"aarch64-linux-gnu"}.

Note that the result includes both explicit inputs and implicit
inputs---inputs automatically added by the build system (@pxref{Build
Systems}).  Let us take the @code{hello} package to illustrate that:

@lisp
(use-modules (gnu packages base) (guix packages))

hello
@result{} #<package hello@@2.10 gnu/packages/base.scm:79 7f585d4f6790>

(package-direct-inputs hello)
@result{} ()

(package-development-inputs hello)
@result{} (("source" @dots{}) ("tar" #<package tar@@1.32 @dots{}>) @dots{})
@end lisp

In this example, @code{package-direct-inputs} returns the empty list,
because @code{hello} has zero explicit dependencies.  Conversely,
@code{package-development-inputs} includes inputs implicitly added by
@code{gnu-build-system} that are required to build @code{hello}: tar,
gzip, GCC, libc, Bash, and more.  To visualize it, @command{guix graph
hello} would show you explicit inputs, whereas @command{guix graph -t
bag hello} would include implicit inputs (@pxref{Invoking guix graph}).
@end deffn

Because packages are regular Scheme objects that capture a complete
dependency graph and associated build procedures, it is often useful to
write procedures that take a package and return a modified version
thereof according to some parameters.  Below are a few examples.

@cindex tool chain, choosing a package's tool chain
@deffn {Procedure} package-with-c-toolchain package toolchain
Return a variant of @var{package} that uses @var{toolchain} instead of
the default GNU C/C++ toolchain.  @var{toolchain} must be a list of
inputs (label/package tuples) providing equivalent functionality, such
as the @code{gcc-toolchain} package.

The example below returns a variant of the @code{hello} package built
with GCC@tie{}10.x and the rest of the GNU tool chain (Binutils and the
GNU C Library) instead of the default tool chain:

@lisp
(let ((toolchain (specification->package "gcc-toolchain@@10")))
  (package-with-c-toolchain hello `(("toolchain" ,toolchain))))
@end lisp

The build tool chain is part of the @dfn{implicit inputs} of
packages---it's usually not listed as part of the various ``inputs''
fields and is instead pulled in by the build system.  Consequently, this
procedure works by changing the build system of @var{package} so that it
pulls in @var{toolchain} instead of the defaults.  @ref{Build Systems},
for more on build systems.
@end deffn

@node origin Reference
@subsection @code{origin} Reference

This section documents @dfn{origins}.  An @code{origin} declaration
specifies data that must be ``produced''---downloaded, usually---and
whose content hash is known in advance.  Origins are primarily used to
represent the source code of packages (@pxref{Defining Packages}).  For
that reason, the @code{origin} form allows you to declare patches to
apply to the original source code as well as code snippets to modify it.

@deftp {Data Type} origin
This is the data type representing a source code origin.

@table @asis
@item @code{uri}
An object containing the URI of the source.  The object type depends on
the @code{method} (see below).  For example, when using the
@var{url-fetch} method of @code{(guix download)}, the valid @code{uri}
values are: a URL represented as a string, or a list thereof.

@cindex fixed-output derivations, for download
@item @code{method}
A monadic procedure that handles the given URI@.  The procedure must
accept at least three arguments: the value of the @code{uri} field and
the hash algorithm and hash value specified by the @code{hash} field.
It must return a store item or a derivation in the store monad
(@pxref{The Store Monad}); most methods return a fixed-output derivation
(@pxref{Derivations}).

Commonly used methods include @code{url-fetch}, which fetches data from
a URL, and @code{git-fetch}, which fetches data from a Git repository
(see below).

@item @code{sha256}
A bytevector containing the SHA-256 hash of the source.  This is
equivalent to providing a @code{content-hash} SHA256 object in the
@code{hash} field described below.

@item @code{hash}
The @code{content-hash} object of the source---see below for how to use
@code{content-hash}.

You can obtain this information using @code{guix download}
(@pxref{Invoking guix download}) or @code{guix hash} (@pxref{Invoking
guix hash}).

@item @code{file-name} (default: @code{#f})
The file name under which the source code should be saved.  When this is
@code{#f}, a sensible default value will be used in most cases.  In case
the source is fetched from a URL, the file name from the URL will be
used.  For version control checkouts, it is recommended to provide the
file name explicitly because the default is not very descriptive.

@item @code{patches} (default: @code{'()})
A list of file names, origins, or file-like objects (@pxref{G-Expressions,
file-like objects}) pointing to patches to be applied to the source.

This list of patches must be unconditional.  In particular, it cannot
depend on the value of @code{%current-system} or
@code{%current-target-system}.

@item @code{snippet} (default: @code{#f})
A G-expression (@pxref{G-Expressions}) or S-expression that will be run
in the source directory.  This is a convenient way to modify the source,
sometimes more convenient than a patch.

@item @code{patch-flags} (default: @code{'("-p1")})
A list of command-line flags that should be passed to the @code{patch}
command.

@item @code{patch-inputs} (default: @code{#f})
Input packages or derivations to the patching process.  When this is
@code{#f}, the usual set of inputs necessary for patching are provided,
such as GNU@tie{}Patch.

@item @code{modules} (default: @code{'()})
A list of Guile modules that should be loaded during the patching
process and while running the code in the @code{snippet} field.

@item @code{patch-guile} (default: @code{#f})
The Guile package that should be used in the patching process.  When
this is @code{#f}, a sensible default is used.
@end table
@end deftp

@deftp {Data Type} content-hash @var{value} [@var{algorithm}]
Construct a content hash object for the given @var{algorithm}, and with
@var{value} as its hash value.  When @var{algorithm} is omitted, assume
it is @code{sha256}.

@var{value} can be a literal string, in which case it is base32-decoded,
or it can be a bytevector.

The following forms are all equivalent:

@lisp
(content-hash "05zxkyz9bv3j9h0xyid1rhvh3klhsmrpkf3bcs6frvlgyr2gwilj")
(content-hash "05zxkyz9bv3j9h0xyid1rhvh3klhsmrpkf3bcs6frvlgyr2gwilj"
              sha256)
(content-hash (base32
               "05zxkyz9bv3j9h0xyid1rhvh3klhsmrpkf3bcs6frvlgyr2gwilj"))
(content-hash (base64 "kkb+RPaP7uyMZmu4eXPVkM4BN8yhRd8BTHLslb6f/Rc=")
              sha256)
@end lisp

Technically, @code{content-hash} is currently implemented as a macro.
It performs sanity checks at macro-expansion time, when possible, such
as ensuring that @var{value} has the right size for @var{algorithm}.
@end deftp

As we have seen above, how exactly the data an origin refers to is
retrieved is determined by its @code{method} field.  The @code{(guix
download)} module provides the most common method, @code{url-fetch},
described below.

@deffn {Procedure} url-fetch url hash-algo hash [name] [#:executable? #f]
Return a fixed-output derivation that fetches data from @var{url} (a
string, or a list of strings denoting alternate URLs), which is expected
to have hash @var{hash} of type @var{hash-algo} (a symbol).  By default,
the file name is the base name of URL; optionally, @var{name} can
specify a different file name.  When @var{executable?} is true, make the
downloaded file executable.

When one of the URL starts with @code{mirror://}, then its host part is
interpreted as the name of a mirror scheme, taken from @file{%mirror-file}.

Alternatively, when URL starts with @code{file://}, return the
corresponding file name in the store.
@end deffn

Likewise, the @code{(guix git-download)} module defines the
@code{git-fetch} origin method, which fetches data from a Git version
control repository, and the @code{git-reference} data type to describe
the repository and revision to fetch.

@deffn {Procedure} git-fetch ref hash-algo hash
Return a fixed-output derivation that fetches @var{ref}, a
@code{<git-reference>} object.  The output is expected to have recursive
hash @var{hash} of type @var{hash-algo} (a symbol).  Use @var{name} as
the file name, or a generic name if @code{#f}.
@end deffn

@deffn {Procedure} git-fetch/lfs ref hash-algo hash
This is a variant of the @code{git-fetch} procedure that supports the
Git @acronym{LFS, Large File Storage} extension.  This may be useful to
pull some binary test data to run the test suite of a package, for
example.
@end deffn

@deftp {Data Type} git-reference
This data type represents a Git reference for @code{git-fetch} to
retrieve.

@table @asis
@item @code{url}
The URL of the Git repository to clone.

@item @code{commit}
This string denotes either the commit to fetch (a hexadecimal string),
or the tag to fetch.  You can also use a ``short'' commit ID or a
@command{git describe} style identifier such as
@code{v1.0.1-10-g58d7909c97}.

@item @code{recursive?} (default: @code{#f})
This Boolean indicates whether to recursively fetch Git sub-modules.
@end table

The example below denotes the @code{v2.10} tag of the GNU@tie{}Hello
repository:

@lisp
(git-reference
  (url "https://git.savannah.gnu.org/git/hello.git")
  (commit "v2.10"))
@end lisp

This is equivalent to the reference below, which explicitly names the
commit:

@lisp
(git-reference
  (url "https://git.savannah.gnu.org/git/hello.git")
  (commit "dc7dc56a00e48fe6f231a58f6537139fe2908fb9"))
@end lisp
@end deftp

For Mercurial repositories, the module @code{(guix hg-download)} defines
the @code{hg-fetch} origin method and @code{hg-reference} data type for
support of the Mercurial version control system.

@deffn {Procedure} hg-fetch ref hash-algo hash [name]
Return a fixed-output derivation that fetches @var{ref}, a
@code{<hg-reference>} object.  The output is expected to have recursive
hash @var{hash} of type @var{hash-algo} (a symbol).  Use @var{name} as
the file name, or a generic name if @code{#f}.
@end deffn

@deftp {Data Type} hg-reference
This data type represents a Mercurial reference for @code{hg-fetch} to
retrieve.

@table @asis
@item @code{url}
The URL of the Mercurial repository to clone.

@item @code{changeset}
This string denotes changeset to fetch.
@end table
@end deftp

For Subversion repositories, the module @code{(guix svn-download)}
defines the @code{svn-fetch} origin method and @code{svn-reference} data
type for support of the Subversion version control system.

@deffn {Procedure} svn-fetch ref hash-algo hash [name]
Return a fixed-output derivation that fetches @var{ref}, a
@code{<svn-reference>} object.  The output is expected to have recursive
hash @var{hash} of type @var{hash-algo} (a symbol).  Use @var{name} as
the file name, or a generic name if @code{#f}.
@end deffn

@deftp {Data Type} svn-reference
This data type represents a Subversion reference for @code{svn-fetch} to
retrieve.

@table @asis
@item @code{url}
The URL of the Subversion repository to clone.

@item @code{revision}
This string denotes revision to fetch specified as a number.

@item @code{recursive?} (default: @code{#f})
This Boolean indicates whether to recursively fetch Subversion
``externals''.

@item @code{user-name} (default: @code{#f})
The name of an account that has read-access to the repository, if the
repository isn't public.

@item @code{password} (default: @code{#f})
Password to access the Subversion repository, if required.
@end table
@end deftp

For Bazaar repositories, the module @code{(guix bzr-download)}
defines the @code{bzr-fetch} origin method and @code{bzr-reference} data
type for support of the Bazaar version control system.

@deffn {Procedure} bzr-fetch ref hash-algo hash [name]
Return a fixed-output derivation that fetches @var{ref}, a
@code{<bzr-reference>} object.  The output is expected to have recursive
hash @var{hash} of type @var{hash-algo} (a symbol).  Use @var{name} as
the file name, or a generic name if @code{#f}.
@end deffn

@deftp {Data Type} bzr-reference
This data type represents a Bazaar reference for @code{bzr-fetch} to
retrieve.

@table @asis
@item @code{url}
The URL of the Bazaar repository to clone.

@item @code{revision}
This string denotes revision to fetch specified as a number.
@end table
@end deftp

For CVS repositories, the module @code{(guix cvs-download)} defines the
@code{cvs-fetch} origin method and @code{cvs-reference} data type for
support of the Concurrent Versions System (CVS).

@deffn {Procedure} cvs-fetch ref hash-algo hash [name]
Return a fixed-output derivation that fetches @var{ref}, a
@code{<cvs-reference>} object.  The output is expected to have recursive
hash @var{hash} of type @var{hash-algo} (a symbol).  Use @var{name} as
the file name, or a generic name if @code{#f}.
@end deffn

@deftp {Data Type} cvs-reference
This data type represents a CVS reference for @code{cvs-fetch} to
retrieve.

@table @asis
@item @code{root-directory}
The CVS root directory.

@item @code{module}
Module to fetch.

@item @code{revision}
Revision to fetch.
@end table

The example below denotes a version of gnu-standards to fetch:

@lisp
(cvs-reference
  (root-directory ":pserver:anonymous@@cvs.savannah.gnu.org:/sources/gnustandards")
  (module "gnustandards")
  (revision "2020-11-25"))
@end lisp

@end deftp

@node Defining Package Variants
@section Defining Package Variants

@cindex customizing packages
@cindex variants, of packages
One of the nice things with Guix is that, given a package definition,
you can easily @emph{derive} variants of that package---for a different
upstream version, with different dependencies, different compilation
options, and so on.  Some of these custom packages can be defined
straight from the command line (@pxref{Package Transformation Options}).
This section describes how to define package variants in code.  This can
be useful in ``manifests'' (@pxref{Writing Manifests})
and in your own package collection
(@pxref{Creating a Channel}), among others!

@cindex inherit, for package definitions
As discussed earlier, packages are first-class objects in the Scheme
language.  The @code{(guix packages)} module provides the @code{package}
construct to define new package objects (@pxref{package Reference}).
The easiest way to define a package variant is using the @code{inherit}
keyword together with @code{package}.  This allows you to inherit from a
package definition while overriding the fields you want.

For example, given the @code{hello} variable, which contains a
definition for the current version of GNU@tie{}Hello, here's how you
would define a variant for version 2.2 (released in 2006, it's
vintage!):

@lisp
(use-modules (gnu packages base))    ;for 'hello'

(define hello-2.2
  (package
    (inherit hello)
    (version "2.2")
    (source (origin
              (method url-fetch)
              (uri (string-append "mirror://gnu/hello/hello-" version
                                  ".tar.gz"))
              (sha256
               (base32
                "0lappv4slgb5spyqbh6yl5r013zv72yqg2pcl30mginf3wdqd8k9"))))))
@end lisp

The example above corresponds to what the @option{--with-version}
or @option{--with-source} package transformations option do.
Essentially @code{hello-2.2} preserves all
the fields of @code{hello}, except @code{version} and @code{source},
which it overrides.  Note that the original @code{hello} variable is
still there, in the @code{(gnu packages base)} module, unchanged.  When
you define a custom package like this, you are really @emph{adding} a
new package definition; the original one remains available.

You can just as well define variants with a different set of
dependencies than the original package.  For example, the default
@code{gdb} package depends on @code{guile}, but since that is an
optional dependency, you can define a variant that removes that
dependency like so:

@lisp
(use-modules (gnu packages gdb))   ;for 'gdb'

(define gdb-sans-guile
  (package
    (inherit gdb)
    (inputs (modify-inputs (package-inputs gdb)
              (delete "guile")))))
@end lisp

The @code{modify-inputs} form above removes the @code{"guile"} package
from the @code{inputs} field of @code{gdb}.  The @code{modify-inputs}
macro is a helper that can prove useful anytime you want to remove, add,
or replace package inputs.

@defmac modify-inputs inputs clauses
Modify the given package inputs, as returned by @code{package-inputs} & co.,
according to the given clauses.  Each clause must have one of the
following forms:

@table @code
@item (delete @var{name}@dots{})
Delete from the inputs packages with the given @var{name}s (strings).

@item (prepend @var{package}@dots{})
Add @var{package}s to the front of the input list.

@item (append @var{package}@dots{})
Add @var{package}s to the end of the input list.

@item (replace @var{name} @var{replacement})
Replace the package called @var{name} with @var{replacement}.
@end table

The example below removes the GMP and ACL inputs of Coreutils and adds
libcap to the front of the input list:

@lisp
(modify-inputs (package-inputs coreutils)
  (delete "gmp" "acl")
  (prepend libcap))
@end lisp

The example below replaces the @code{guile} package from the inputs of
@code{guile-redis} with @code{guile-2.2}:

@lisp
(modify-inputs (package-inputs guile-redis)
  (replace "guile" guile-2.2))
@end lisp

The last type of clause is @code{append}, to add inputs at the back of
the list.
@end defmac

In some cases, you may find it useful to write functions
(``procedures'', in Scheme parlance) that return a package based on some
parameters.  For example, consider the @code{luasocket} library for the
Lua programming language.  We want to create @code{luasocket} packages
for major versions of Lua.  One way to do that is to define a procedure
that takes a Lua package and returns a @code{luasocket} package that
depends on it:

@lisp
(define (make-lua-socket name lua)
  ;; Return a luasocket package built with LUA.
  (package
    (name name)
    (version "3.0")
    ;; several fields omitted
    (inputs (list lua))
    (synopsis "Socket library for Lua")))

(define-public lua5.1-socket
  (make-lua-socket "lua5.1-socket" lua-5.1))

(define-public lua5.2-socket
  (make-lua-socket "lua5.2-socket" lua-5.2))
@end lisp

Here we have defined packages @code{lua5.1-socket} and
@code{lua5.2-socket} by calling @code{make-lua-socket} with different
arguments.  @xref{Procedures,,, guile, GNU Guile Reference Manual}, for
more info on procedures.  Having top-level public definitions for these
two packages means that they can be referred to from the command line
(@pxref{Package Modules}).

@cindex package transformations
These are pretty simple package variants.  As a convenience, the
@code{(guix transformations)} module provides a high-level interface
that directly maps to the more sophisticated package transformation
options (@pxref{Package Transformation Options}):

@deffn {Procedure} options->transformation opts
Return a procedure that, when passed an object to build (package,
derivation, etc.), applies the transformations specified by @var{opts} and returns
the resulting objects.  @var{opts} must be a list of symbol/string pairs such as:

@lisp
((with-branch . "guile-gcrypt=master")
 (without-tests . "libgcrypt"))
@end lisp

Each symbol names a transformation and the corresponding string is an argument
to that transformation.
@end deffn

For instance, a manifest equivalent to this command:

@example
guix build guix \
  --with-branch=guile-gcrypt=master \
  --with-debug-info=zlib
@end example

@noindent
... would look like this:

@lisp
(use-modules (guix transformations))

(define transform
  ;; The package transformation procedure.
  (options->transformation
   '((with-branch . "guile-gcrypt=master")
     (with-debug-info . "zlib"))))

(packages->manifest
 (list (transform (specification->package "guix"))))
@end lisp

@cindex input rewriting
@cindex dependency graph rewriting
The @code{options->transformation} procedure is convenient, but it's
perhaps also not as flexible as you may like.  How is it implemented?
The astute reader probably noticed that most package transformation
options go beyond the superficial changes shown in the first examples of
this section: they involve @dfn{input rewriting}, whereby the dependency
graph of a package is rewritten by replacing specific inputs by others.

Dependency graph rewriting, for the purposes of swapping packages in the
graph, is what the @code{package-input-rewriting} procedure in
@code{(guix packages)} implements.

@deffn {Procedure} package-input-rewriting replacements [rewrite-name] [#:deep? #t]
Return a procedure that, when passed a package, replaces its direct and
indirect dependencies, including implicit inputs when @var{deep?} is
true, according to @var{replacements}.  @var{replacements} is a list of
package pairs; the first element of each pair is the package to replace,
and the second one is the replacement.

Optionally, @var{rewrite-name} is a one-argument procedure that takes
the name of a package and returns its new name after rewrite.
@end deffn

@noindent
Consider this example:

@lisp
(define libressl-instead-of-openssl
  ;; This is a procedure to replace OPENSSL by LIBRESSL,
  ;; recursively.
  (package-input-rewriting `((,openssl . ,libressl))))

(define git-with-libressl
  (libressl-instead-of-openssl git))
@end lisp

@noindent
Here we first define a rewriting procedure that replaces @var{openssl}
with @var{libressl}.  Then we use it to define a @dfn{variant} of the
@var{git} package that uses @var{libressl} instead of @var{openssl}.
This is exactly what the @option{--with-input} command-line option does
(@pxref{Package Transformation Options, @option{--with-input}}).

The following variant of @code{package-input-rewriting} can match packages to
be replaced by name rather than by identity.

@deffn {Procedure} package-input-rewriting/spec @var{replacements} [#:deep? #t]
Return a procedure that, given a package, applies the given
@var{replacements} to all the package graph, including implicit inputs
unless @var{deep?} is false.

@var{replacements} is a list of spec/procedures pair; each spec is a
package specification such as @code{"gcc"} or @code{"guile@@2"}, and
each procedure takes a matching package and returns a replacement for
that package.  Matching packages that have the @code{hidden?} property
set are not replaced.
@end deffn

The example above could be rewritten this way:

@lisp
(define libressl-instead-of-openssl
  ;; Replace all the packages called "openssl" with LibreSSL.
  (package-input-rewriting/spec `(("openssl" . ,(const libressl)))))
@end lisp

The key difference here is that, this time, packages are matched by spec and
not by identity.  In other words, any package in the graph that is called
@code{openssl} will be replaced.

A more generic procedure to rewrite a package dependency graph is
@code{package-mapping}: it supports arbitrary changes to nodes in the
graph.

@deffn {Procedure} package-mapping proc [cut?] [#:deep? #f]
Return a procedure that, given a package, applies @var{proc} to all the packages
depended on and returns the resulting package.  The procedure stops recursion
when @var{cut?} returns true for a given package.  When @var{deep?} is true, @var{proc} is
applied to implicit inputs as well.
@end deffn

@quotation Tips
Understanding what a variant really looks like can be difficult as one
starts combining the tools shown above.  There are several ways to
inspect a package before attempting to build it that can prove handy:

@itemize
@item
You can inspect the package interactively at the REPL, for instance to
view its inputs, the code of its build phases, or its configure flags
(@pxref{Using Guix Interactively}).

@item
When rewriting dependencies, @command{guix graph} can often help
visualize the changes that are made (@pxref{Invoking guix graph}).
@end itemize
@end quotation

@node Writing Manifests
@section Writing Manifests

@cindex manifest
@cindex bill of materials (manifests)
@command{guix} commands let you specify package lists on the command
line.  This is convenient, but as the command line becomes longer and
less trivial, it quickly becomes more convenient to have that package
list in what we call a @dfn{manifest}.  A manifest is some sort of a
``bill of materials'' that defines a package set.  You would typically
come up with a code snippet that builds the manifest, store it in a
file, say @file{manifest.scm}, and then pass that file to the
@option{-m} (or @option{--manifest}) option that many @command{guix}
commands support.  For example, here's what a manifest for a simple
package set might look like:

@lisp
;; Manifest for three packages.
(specifications->manifest '("gcc-toolchain" "make" "git"))
@end lisp

Once you have that manifest, you can pass it, for example, to
@command{guix package} to install just those three packages to your
profile (@pxref{profile-manifest, @option{-m} option of @command{guix
package}}):

@example
guix package -m manifest.scm
@end example

@noindent
... or you can pass it to @command{guix shell} (@pxref{shell-manifest,
@command{-m} option of @command{guix shell}}) to spawn an ephemeral
environment:

@example
guix shell -m manifest.scm
@end example

@noindent
... or you can pass it to @command{guix pack} in pretty much the same
way (@pxref{pack-manifest, @option{-m} option of @command{guix pack}}).
You can store the manifest under version control, share it with others
so they can easily get set up, etc.

But how do you write your first manifest?  To get started, maybe you'll
want to write a manifest that mirrors what you already have in a
profile.  Rather than start from a blank page, @command{guix package}
can generate a manifest for you (@pxref{export-manifest, @command{guix
package --export-manifest}}):

@example
# Write to 'manifest.scm' a manifest corresponding to the
# default profile, ~/.guix-profile.
guix package --export-manifest > manifest.scm
@end example

Or maybe you'll want to ``translate'' command-line arguments into a
manifest.  In that case, @command{guix shell} can help
(@pxref{shell-export-manifest, @command{guix shell --export-manifest}}):

@example
# Write a manifest for the packages specified on the command line.
guix shell --export-manifest gcc-toolchain make git > manifest.scm
@end example

In both cases, the @option{--export-manifest} option tries hard to
generate a faithful manifest; in particular, it takes package
transformation options into account (@pxref{Package Transformation
Options}).

@quotation Note
Manifests are @emph{symbolic}: they refer to packages of the channels
@emph{currently in use} (@pxref{Channels}).  In the example above,
@code{gcc-toolchain} might refer to version 11 today, but it might refer
to version 13 two years from now.

If you want to ``pin'' your software environment to specific package
versions and variants, you need an additional piece of information: the
list of channel revisions in use, as returned by @command{guix
describe}.  @xref{Replicating Guix}, for more information.
@end quotation

Once you've obtained your first manifest, perhaps you'll want to
customize it.  Since your manifest is code, you now have access to all
the Guix programming interfaces!

Let's assume you want a manifest to deploy a custom variant of GDB, the
GNU Debugger, that does not depend on Guile, together with another
package.  Building on the example seen in the previous section
(@pxref{Defining Package Variants}), you can write a manifest along
these lines:

@lisp
(use-modules (guix packages)
             (gnu packages gdb)               ;for 'gdb'
             (gnu packages version-control))  ;for 'git'

;; Define a variant of GDB without a dependency on Guile.
(define gdb-sans-guile
  (package
    (inherit gdb)
    (inputs (modify-inputs (package-inputs gdb)
              (delete "guile")))))

;; Return a manifest containing that one package plus Git.
(packages->manifest (list gdb-sans-guile git))
@end lisp

Note that in this example, the manifest directly refers to the
@code{gdb} and @code{git} variables, which are bound to a @code{package}
object (@pxref{package Reference}), instead of calling
@code{specifications->manifest} to look up packages by name as we did
before.  The @code{use-modules} form at the top lets us access the core
package interface (@pxref{Defining Packages}) and the modules that
define @code{gdb} and @code{git} (@pxref{Package Modules}).  Seamlessly,
we're weaving all this together---the possibilities are endless, unleash
your creativity!

The data type for manifests as well as supporting procedures are defined
in the @code{(guix profiles)} module, which is automatically available
to code passed to @option{-m}.  The reference follows.

@deftp {Data Type} manifest
Data type representing a manifest.

It currently has one field:

@table @code
@item entries
This must be a list of @code{manifest-entry} records---see below.
@end table
@end deftp

@deftp {Data Type} manifest-entry
Data type representing a manifest entry.  A manifest entry contains
essential metadata: a name and version string, the object (usually a
package) for that entry, the desired output (@pxref{Packages with
Multiple Outputs}), and a number of optional pieces of information
detailed below.

Most of the time, you won't build a manifest entry directly; instead,
you will pass a package to @code{package->manifest-entry}, described
below.  In some unusual cases though, you might want to create manifest
entries for things that are @emph{not} packages, as in this example:

@lisp
;; Manually build a single manifest entry for a non-package object.
(let ((hello (program-file "hello" #~(display "Hi!"))))
  (manifest-entry
    (name "foo")
    (version "42")
    (item
     (computed-file "hello-directory"
                     #~(let ((bin (string-append #$output "/bin")))
                         (mkdir #$output) (mkdir bin)
                          (symlink #$hello
                                   (string-append bin "/hello")))))))
@end lisp

The available fields are the following:

@table @asis
@item @code{name}
@itemx @code{version}
Name and version string for this entry.

@item @code{item}
A package or other file-like object (@pxref{G-Expressions, file-like
objects}).

@item @code{output} (default: @code{"out"})
Output of @code{item} to use, in case @code{item} has multiple outputs
(@pxref{Packages with Multiple Outputs}).

@item @code{dependencies} (default: @code{'()})
List of manifest entries this entry depends on.  When building a
profile, dependencies are added to the profile.

Typically, the propagated inputs of a package (@pxref{package Reference,
@code{propagated-inputs}}) end up having a corresponding manifest entry
in among the dependencies of the package's own manifest entry.

@item @code{search-paths} (default: @code{'()})
The list of search path specifications honored by this entry
(@pxref{Search Paths}).

@item @code{properties} (default: @code{'()})
List of symbol/value pairs.  When building a profile, those properties
get serialized.

This can be used to piggyback additional metadata---e.g., the
transformations applied to a package (@pxref{Package Transformation
Options}).

@item @code{parent} (default: @code{(delay #f)})
A promise pointing to the ``parent'' manifest entry.

This is used as a hint to provide context when reporting an error
related to a manifest entry coming from a @code{dependencies} field.
@end table
@end deftp

@deffn {Procedure} concatenate-manifests lst
Concatenate the manifests listed in @var{lst} and return the resulting
manifest.
@end deffn

@c TODO: <manifest-pattern>, manifest-lookup, manifest-remove, etc.

@deffn {Procedure} package->manifest-entry package [output] [#:properties]
Return a manifest entry for the @var{output} of package @var{package},
where @var{output} defaults to @code{"out"}, and with the given
@var{properties}.  By default @var{properties} is the empty list or, if
one or more package transformations were applied to @var{package}, it is
an association list representing those transformations, suitable as an
argument to @code{options->transformation} (@pxref{Defining Package
Variants, @code{options->transformation}}).

The code snippet below builds a manifest with an entry for the default
output and the @code{send-email} output of the @code{git} package:

@lisp
(use-modules (gnu packages version-control))

(manifest (list (package->manifest-entry git)
                (package->manifest-entry git "send-email")))
@end lisp
@end deffn

@deffn {Procedure} packages->manifest packages
Return a list of manifest entries, one for each item listed in
@var{packages}.  Elements of @var{packages} can be either package
objects or package/string tuples denoting a specific output of a
package.

Using this procedure, the manifest above may be rewritten more
concisely:

@lisp
(use-modules (gnu packages version-control))

(packages->manifest (list git `(,git "send-email")))
@end lisp
@end deffn

@anchor{package-development-manifest}
@deffn {Procedure} package->development-manifest package [system] [#:target]
Return a manifest for the @dfn{development inputs} of @var{package} for
@var{system}, optionally when cross-compiling to @var{target}.
Development inputs include both explicit and implicit inputs of
@var{package}.

Like the @option{-D} option of @command{guix shell}
(@pxref{shell-development-option, @command{guix shell -D}}), the
resulting manifest describes the environment in which one can develop
@var{package}.  For example, suppose you're willing to set up a
development environment for Inkscape, with the addition of Git for
version control; you can describe that ``bill of materials'' with the
following manifest:

@lisp
(use-modules (gnu packages inkscape)          ;for 'inkscape'
             (gnu packages version-control))  ;for 'git'

(concatenate-manifests
 (list (package->development-manifest inkscape)
       (packages->manifest (list git))))
@end lisp

In this example, the development manifest that
@code{package->development-manifest} returns includes the compiler
(GCC), the many supporting libraries (Boost, GLib, GTK, etc.), and a
couple of additional development tools---these are the dependencies
@command{guix show inkscape} lists.
@end deffn

@c TODO: Move (gnu packages) interface to a section of its own.

Last, the @code{(gnu packages)} module provides higher-level facilities
to build manifests.  In particular, it lets you look up packages by
name---see below.

@deffn {Procedure} specifications->manifest specs
Given @var{specs}, a list of specifications such as @code{"emacs@@25.2"}
or @code{"guile:debug"}, return a manifest.  Specs have the format that
command-line tools such as @command{guix install} and @command{guix
package} understand (@pxref{Invoking guix package}).

As an example, it lets you rewrite the Git manifest that we saw earlier
like this:

@lisp
(specifications->manifest '("git" "git:send-email"))
@end lisp

Notice that we do not need to worry about @code{use-modules}, importing
the right set of modules, and referring to the right variables.
Instead, we directly refer to packages in the same way as on the command
line, which can often be more convenient.
@end deffn

@c TODO: specifications->package, etc.


@node Build Systems
@section Build Systems

@cindex build system
Each package definition specifies a @dfn{build system} and arguments for
that build system (@pxref{Defining Packages}).  This @code{build-system}
field represents the build procedure of the package, as well as implicit
dependencies of that build procedure.

Build systems are @code{<build-system>} objects.  The interface to
create and manipulate them is provided by the @code{(guix build-system)}
module, and actual build systems are exported by specific modules.

@cindex bag (low-level package representation)
Under the hood, build systems first compile package objects to
@dfn{bags}.  A @dfn{bag} is like a package, but with less
ornamentation---in other words, a bag is a lower-level representation of
a package, which includes all the inputs of that package, including some
that were implicitly added by the build system.  This intermediate
representation is then compiled to a derivation (@pxref{Derivations}).
The @code{package-with-c-toolchain} is an example of a way to change the
implicit inputs that a package's build system pulls in (@pxref{package
Reference, @code{package-with-c-toolchain}}).

Build systems accept an optional list of @dfn{arguments}.  In package
definitions, these are passed @i{via} the @code{arguments} field
(@pxref{Defining Packages}).  They are typically keyword arguments
(@pxref{Optional Arguments, keyword arguments in Guile,, guile, GNU
Guile Reference Manual}).  The value of these arguments is usually
evaluated in the @dfn{build stratum}---i.e., by a Guile process launched
by the daemon (@pxref{Derivations}).

The main build system is @code{gnu-build-system}, which implements the
standard build procedure for GNU and many other packages.  It
is provided by the @code{(guix build-system gnu)} module.

@defvar gnu-build-system
@code{gnu-build-system} represents the GNU Build System, and variants
thereof (@pxref{Configuration, configuration and makefile conventions,,
standards, GNU Coding Standards}).

@cindex build phases
In a nutshell, packages using it are configured, built, and installed with
the usual @code{./configure && make && make check && make install}
command sequence.  In practice, a few additional steps are often needed.
All these steps are split up in separate @dfn{phases}.
@xref{Build Phases}, for more info on build phases and ways to customize
them.

In addition, this build system ensures that the ``standard'' environment
for GNU packages is available.  This includes tools such as GCC, libc,
Coreutils, Bash, Make, Diffutils, grep, and sed (see the @code{(guix
build-system gnu)} module for a complete list).  We call these the
@dfn{implicit inputs} of a package, because package definitions do not
have to mention them.

This build system supports a number of keyword arguments, which can be
passed @i{via} the @code{arguments} field of a package.  Here are some
of the main parameters:

@table @code
@item #:phases
This argument specifies build-side code that evaluates to an alist of
build phases.  @xref{Build Phases}, for more information.

@item #:configure-flags
This is a list of flags (strings) passed to the @command{configure}
script.  @xref{Defining Packages}, for an example.

@item #:make-flags
This list of strings contains flags passed as arguments to
@command{make} invocations in the @code{build}, @code{check}, and
@code{install} phases.

@item #:out-of-source?
This Boolean, @code{#f} by default, indicates whether to run builds in a
build directory separate from the source tree.

When it is true, the @code{configure} phase creates a separate build
directory, changes to that directory, and runs the @code{configure}
script from there.  This is useful for packages that require it, such as
@code{glibc}.

@item #:tests?
This Boolean, @code{#t} by default, indicates whether the @code{check}
phase should run the package's test suite.

@item #:test-target
This string, @code{"check"} by default, gives the name of the makefile
target used by the @code{check} phase.

@item #:parallel-build?
@itemx #:parallel-tests?
These Boolean values specify whether to build, respectively run the test
suite, in parallel, with the @code{-j} flag of @command{make}.  When
they are true, @code{make} is passed @code{-j@var{n}}, where @var{n} is
the number specified as the @option{--cores} option of
@command{guix-daemon} or that of the @command{guix} client command
(@pxref{Common Build Options, @option{--cores}}).

@cindex RUNPATH, validation
@item #:validate-runpath?
This Boolean, @code{#t} by default, determines whether to ``validate''
the @code{RUNPATH} of ELF binaries (@code{.so} shared libraries as well
as executables) previously installed by the @code{install} phase.
@xref{phase-validate-runpath, the @code{validate-runpath} phase}, for
details.

@item #:substitutable?
This Boolean, @code{#t} by default, tells whether the package outputs
should be substitutable---i.e., whether users should be able to obtain
substitutes for them instead of building locally (@pxref{Substitutes}).

@item #:allowed-references
@itemx #:disallowed-references
When true, these arguments must be a list of dependencies that must not
appear among the references of the build results.  If, upon build
completion, some of these references are retained, the build process
fails.

This is useful to ensure that a package does not erroneously keep a
reference to some of it build-time inputs, in cases where doing so
would, for example, unnecessarily increase its size (@pxref{Invoking
guix size}).
@end table

Most other build systems support these keyword arguments.
@end defvar

Other @code{<build-system>} objects are defined to support other
conventions and tools used by free software packages.  They inherit most
of @code{gnu-build-system}, and differ mainly in the set of inputs
implicitly added to the build process, and in the list of phases
executed.  Some of these build systems are listed below.

@defvar agda-build-system
This variable is exported by @code{(guix build-system agda)}.  It
implements a build procedure for Agda libraries.

It adds @code{agda} to the set of inputs.  A different Agda can be
specified with the @code{#:agda} key.

The @code{#:plan} key is a list of cons cells @code{(@var{regexp}
. @var{parameters})}, where @var{regexp} is a regexp that should match
the @code{.agda} files to build, and @var{parameters} is an optional
list of parameters that will be passed to @code{agda} when type-checking
it.

When the library uses Haskell to generate a file containing all imports,
the convenience @code{#:gnu-and-haskell?} can be set to @code{#t} to add
@code{ghc} and the standard inputs of @code{gnu-build-system} to the
input list.  You will still need to manually add a phase or tweak the
@code{'build} phase, as in the definition of @code{agda-stdlib}.

@end defvar

@defvar ant-build-system
This variable is exported by @code{(guix build-system ant)}.  It
implements the build procedure for Java packages that can be built with
@url{https://ant.apache.org/, Ant build tool}.

It adds both @code{ant} and the @dfn{Java Development Kit} (JDK) as
provided by the @code{icedtea} package to the set of inputs.  Different
packages can be specified with the @code{#:ant} and @code{#:jdk}
parameters, respectively.

When the original package does not provide a suitable Ant build file,
the parameter @code{#:jar-name} can be used to generate a minimal Ant
build file @file{build.xml} with tasks to build the specified jar
archive.  In this case the parameter @code{#:source-dir} can be used to
specify the source sub-directory, defaulting to ``src''.

The @code{#:main-class} parameter can be used with the minimal ant
buildfile to specify the main class of the resulting jar.  This makes the
jar file executable.  The @code{#:test-include} parameter can be used to
specify the list of junit tests to run.  It defaults to
@code{(list "**/*Test.java")}.  The @code{#:test-exclude} can be used to
disable some tests.  It defaults to @code{(list "**/Abstract*.java")},
because abstract classes cannot be run as tests.

The parameter @code{#:build-target} can be used to specify the Ant task
that should be run during the @code{build} phase.  By default the
``jar'' task will be run.

@end defvar

@defvar android-ndk-build-system
@cindex Android distribution
@cindex Android NDK build system
This variable is exported by @code{(guix build-system android-ndk)}.  It
implements a build procedure for Android NDK (native development kit)
packages using a Guix-specific build process.

The build system assumes that packages install their public interface
(header) files to the subdirectory @file{include} of the @code{out} output and
their libraries to the subdirectory @file{lib} the @code{out} output.

It's also assumed that the union of all the dependencies of a package
has no conflicting files.

For the time being, cross-compilation is not supported - so right now
the libraries and header files are assumed to be host tools.

@end defvar

@defvar asdf-build-system/source
@defvarx asdf-build-system/sbcl
@defvarx asdf-build-system/ecl

These variables, exported by @code{(guix build-system asdf)}, implement
build procedures for Common Lisp packages using
@url{https://common-lisp.net/project/asdf/, ``ASDF''}.  ASDF is a system
definition facility for Common Lisp programs and libraries.

The @code{asdf-build-system/source} system installs the packages in
source form, and can be loaded using any common lisp implementation, via
ASDF@.  The others, such as @code{asdf-build-system/sbcl}, install binary
systems in the format which a particular implementation understands.
These build systems can also be used to produce executable programs, or
lisp images which contain a set of packages pre-loaded.

The build system uses naming conventions.  For binary packages, the
package name should be prefixed with the lisp implementation, such as
@code{sbcl-} for @code{asdf-build-system/sbcl}.

Additionally, the corresponding source package should be labeled using
the same convention as Python packages (@pxref{Python Modules}), using
the @code{cl-} prefix.

In order to create executable programs and images, the build-side
procedures @code{build-program} and @code{build-image} can be used.
They should be called in a build phase after the
@code{create-asdf-configuration} phase, so that the system which was
just built can be used within the resulting image.  @code{build-program}
requires a list of Common Lisp expressions to be passed as the
@code{#:entry-program} argument.

By default, all the @file{.asd} files present in the sources are read to
find system definitions.  The @code{#:asd-files} parameter can be used
to specify the list of @file{.asd} files to read.  Furthermore, if the
package defines a system for its tests in a separate file, it will be
loaded before the tests are run if it is specified by the
@code{#:test-asd-file} parameter.  If it is not set, the files
@code{<system>-tests.asd}, @code{<system>-test.asd}, @code{tests.asd},
and @code{test.asd} will be tried if they exist.

If for some reason the package must be named in a different way than the
naming conventions suggest, or if several systems must be compiled, the
@code{#:asd-systems} parameter can be used to specify the list of system
names.

@end defvar

@defvar cargo-build-system
@cindex Rust programming language
@cindex Cargo (Rust build system)
This variable is exported by @code{(guix build-system cargo)}.  It
supports builds of packages using Cargo, the build tool of the
@uref{https://www.rust-lang.org, Rust programming language}.

It adds @code{rustc} and @code{cargo} to the set of inputs.
A different Rust package can be specified with the @code{#:rust} parameter.

Regular cargo dependencies should be added to the package definition similarly
to other packages; those needed only at build time to native-inputs, others to
inputs.  If you need to add source-only crates then you should add them to via
the @code{#:cargo-inputs} parameter as a list of name and spec pairs, where the
spec can be a package or a source definition.  Note that the spec must
evaluate to a path to a gzipped tarball which includes a @code{Cargo.toml}
file at its root, or it will be ignored.  Similarly, cargo dev-dependencies
should be added to the package definition via the
@code{#:cargo-development-inputs} parameter.

In its @code{configure} phase, this build system will make any source inputs
specified in the @code{#:cargo-inputs} and @code{#:cargo-development-inputs}
parameters available to cargo.  It will also remove an included
@code{Cargo.lock} file to be recreated by @code{cargo} during the
@code{build} phase.  The @code{package} phase will run @code{cargo package}
to create a source crate for future use.  The @code{install} phase installs
the binaries defined by the crate.  Unless @code{install-source? #f} is
defined it will also install a source crate repository of itself and unpacked
sources, to ease in future hacking on rust packages.
@end defvar

@defvar chicken-build-system
This variable is exported by @code{(guix build-system chicken)}.  It
builds @uref{https://call-cc.org/, CHICKEN Scheme} modules, also called
``eggs'' or ``extensions''.  CHICKEN generates C source code, which then
gets compiled by a C compiler, in this case GCC.

This build system adds @code{chicken} to the package inputs, as well as
the packages of @code{gnu-build-system}.

The build system can't (yet) deduce the egg's name automatically, so just like
with @code{go-build-system} and its @code{#:import-path}, you should define
@code{#:egg-name} in the package's @code{arguments} field.

For example, if you are packaging the @code{srfi-1} egg:

@lisp
(arguments '(#:egg-name "srfi-1"))
@end lisp

Egg dependencies must be defined in @code{propagated-inputs}, not @code{inputs}
because CHICKEN doesn't embed absolute references in compiled eggs.
Test dependencies should go to @code{native-inputs}, as usual.
@end defvar

@defvar copy-build-system
This variable is exported by @code{(guix build-system copy)}.  It
supports builds of simple packages that don't require much compiling,
mostly just moving files around.

It adds much of the @code{gnu-build-system} packages to the set of
inputs.  Because of this, the @code{copy-build-system} does not require
all the boilerplate code often needed for the
@code{trivial-build-system}.

To further simplify the file installation process, an
@code{#:install-plan} argument is exposed to let the packager specify
which files go where.  The install plan is a list of @code{(@var{source}
@var{target} [@var{filters}])}.  @var{filters} are optional.

@itemize
@item When @var{source} matches a file or directory without trailing slash, install it to @var{target}.
@itemize
@item If @var{target} has a trailing slash, install @var{source} basename beneath @var{target}.
@item Otherwise install @var{source} as @var{target}.
@end itemize

@item When @var{source} is a directory with a trailing slash, or when @var{filters} are used,
the trailing slash of @var{target} is implied with the same meaning
as above.
@itemize
@item Without @var{filters}, install the full @var{source} @emph{content} to @var{target}.
@item With @var{filters} among @code{#:include}, @code{#:include-regexp}, @code{#:exclude},
@code{#:exclude-regexp}, only select files are installed depending on
the filters.  Each filters is specified by a list of strings.
@itemize
@item With @code{#:include}, install all the files which the path suffix matches
at least one of the elements in the given list.
@item With @code{#:include-regexp}, install all the files which the
subpaths match at least one of the regular expressions in the given
list.
@item The @code{#:exclude} and @code{#:exclude-regexp} filters
are the complement of their inclusion counterpart.  Without @code{#:include} flags,
install all files but those matching the exclusion filters.
If both inclusions and exclusions are specified, the exclusions are done
on top of the inclusions.
@end itemize
@end itemize
In all cases, the paths relative to @var{source} are preserved within
@var{target}.
@end itemize

Examples:

@itemize
@item @code{("foo/bar" "share/my-app/")}: Install @file{bar} to @file{share/my-app/bar}.
@item @code{("foo/bar" "share/my-app/baz")}: Install @file{bar} to @file{share/my-app/baz}.
@item @code{("foo/" "share/my-app")}: Install the content of @file{foo} inside @file{share/my-app},
e.g., install @file{foo/sub/file} to @file{share/my-app/sub/file}.
@item @code{("foo/" "share/my-app" #:include ("sub/file"))}: Install only @file{foo/sub/file} to
@file{share/my-app/sub/file}.
@item @code{("foo/sub" "share/my-app" #:include ("file"))}: Install @file{foo/sub/file} to
@file{share/my-app/file}.
@end itemize
@end defvar

@defvar vim-build-system
This variable is exported by @code{(guix build-system vim)}.  It is an
extension of the @code{copy-build-system}, installing Vim and Neovim plugins
into locations where these two text editors know to find their plugins, using
their packpaths.

Packages which are prefixed with @code{vim-} will be installed in Vim's
packpath, while those prefixed with @code{neovim-} will be installed in
Neovim's packpath.  If there is a @code{doc} directory with the plugin then
helptags will be generated automatically.

There are a couple of keywords added with the @code{vim-build-system}:
@itemize
@item With @code{plugin-name} it is possible to set the name of the plugin.
While by default this is set to the name and version of the package, it is
often more helpful to set this to name which the upstream author calls their
plugin.  This is the name used for @command{:packadd} from inside Vim.
@item With @code{install-plan} it is possible to augment the built-in
install-plan of the @code{vim-build-system}.  This is particularly helpful if
you have files which should be installed in other locations.  For more
information about using the @code{install-plan}, see the
@code{copy-build-system} (@pxref{Build Systems, @code{copy-build-system}}).
@item With @code{#:vim} it is possible to add this package to Vim's packpath,
in addition to if it is added automatically because of the @code{vim-} prefix
in the package's name.
@item With @code{#:neovim} it is possible to add this package to Neovim's
packpath, in addition to if it is added automatically because of the
@code{neovim-} prefix in the package's name.
@item With @code{#:mode} it is possible to adjust the path which the plugin is
installed into.  By default the plugin is installed into @code{start} and other
options are available, including @code{opt}.  Adding a plugin into @code{opt}
will mean you will need to run, for example, @command{:packadd foo} to load the
@code{foo} plugin from inside of Vim.
@end itemize
@end defvar

@cindex Clojure (programming language)
@cindex simple Clojure build system
@defvar clojure-build-system
This variable is exported by @code{(guix build-system clojure)}.  It implements
a simple build procedure for @uref{https://clojure.org/, Clojure} packages
using plain old @code{compile} in Clojure.  Cross-compilation is not supported
yet.

It adds @code{clojure}, @code{icedtea} and @code{zip} to the set of inputs.
Different packages can be specified with the @code{#:clojure}, @code{#:jdk} and
@code{#:zip} parameters, respectively.

A list of source directories, test directories and jar names can be specified
with the @code{#:source-dirs}, @code{#:test-dirs} and @code{#:jar-names}
parameters, respectively.  Compile directory and main class can be specified
with the @code{#:compile-dir} and @code{#:main-class} parameters, respectively.
Other parameters are documented below.

This build system is an extension of @code{ant-build-system}, but with the
following phases changed:

@table @code

@item build
This phase calls @code{compile} in Clojure to compile source files and runs
@command{jar} to create jars from both source files and compiled files
according to the include list and exclude list specified in
@code{#:aot-include} and @code{#:aot-exclude}, respectively.  The exclude list
has priority over the include list.  These lists consist of symbols
representing Clojure libraries or the special keyword @code{#:all} representing
all Clojure libraries found under the source directories.  The parameter
@code{#:omit-source?} decides if source should be included into the jars.

@item check
This phase runs tests according to the include list and exclude list specified
in @code{#:test-include} and @code{#:test-exclude}, respectively.  Their
meanings are analogous to that of @code{#:aot-include} and
@code{#:aot-exclude}, except that the special keyword @code{#:all} now
stands for all Clojure libraries found under the test directories.  The
parameter @code{#:tests?} decides if tests should be run.

@item install
This phase installs all jars built previously.
@end table

Apart from the above, this build system also contains an additional phase:

@table @code

@item install-doc
This phase installs all top-level files with base name matching
@code{%doc-regex}.  A different regex can be specified with the
@code{#:doc-regex} parameter.  All files (recursively) inside the documentation
directories specified in @code{#:doc-dirs} are installed as well.
@end table
@end defvar

@defvar cmake-build-system
This variable is exported by @code{(guix build-system cmake)}.  It
implements the build procedure for packages using the
@url{https://www.cmake.org, CMake build tool}.

It automatically adds the @code{cmake} package to the set of inputs.
Which package is used can be specified with the @code{#:cmake}
parameter.

The @code{#:configure-flags} parameter is taken as a list of flags
passed to the @command{cmake} command.  The @code{#:build-type}
parameter specifies in abstract terms the flags passed to the compiler;
it defaults to @code{"RelWithDebInfo"} (short for ``release mode with
debugging information''), which roughly means that code is compiled with
@code{-O2 -g}, as is the case for Autoconf-based packages by default.
@end defvar

@defvar composer-build-system
This variable is exported by @code{(guix build-system composer)}.  It
implements the build procedure for packages using
@url{https://getcomposer.org/, Composer}, the PHP package manager.

It automatically adds the @code{php} package to the set of inputs.  Which
package is used can be specified with the @code{#:php} parameter.

The @code{#:test-target} parameter is used to control which script is run
for the tests.  By default, the @code{test} script is run if it exists.  If
the script does not exist, the build system will run @code{phpunit} from the
source directory, assuming there is a @file{phpunit.xml} file.
@end defvar

@defvar dune-build-system
This variable is exported by @code{(guix build-system dune)}.  It
supports builds of packages using @uref{https://dune.build/, Dune}, a build
tool for the OCaml programming language.  It is implemented as an extension
of the @code{ocaml-build-system} which is described below.  As such, the
@code{#:ocaml} and @code{#:findlib} parameters can be passed to this build
system.

It automatically adds the @code{dune} package to the set of inputs.
Which package is used can be specified with the @code{#:dune}
parameter.

There is no @code{configure} phase because dune packages typically don't
need to be configured.  The @code{#:build-flags} parameter is taken as a
list of flags passed to the @code{dune} command during the build.

The @code{#:jbuild?} parameter can be passed to use the @code{jbuild}
command instead of the more recent @code{dune} command while building
a package.  Its default value is @code{#f}.

The @code{#:package} parameter can be passed to specify a package name, which
is useful when a package contains multiple packages and you want to build
only one of them.  This is equivalent to passing the @code{-p} argument to
@code{dune}.

@end defvar

@defvar elm-build-system
This variable is exported by @code{(guix build-system elm)}.  It implements a
build procedure for @url{https://elm-lang.org, Elm} packages similar to
@samp{elm install}.

The build system adds an Elm compiler package to the set of inputs.  The
default compiler package (currently @code{elm-sans-reactor}) can be overridden
using the @code{#:elm} argument.  Additionally, Elm packages needed by the
build system itself are added as implicit inputs if they are not already
present: to suppress this behavior, use the
@code{#:implicit-elm-package-inputs?} argument, which is primarily useful for
bootstrapping.

The @code{"dependencies"} and @code{"test-dependencies"} in an Elm package's
@file{elm.json} file correspond to @code{propagated-inputs} and @code{inputs},
respectively.

Elm requires a particular structure for package names: @pxref{Elm Packages}
for more details, including utilities provided by @code{(guix build-system
elm)}.

There are currently a few noteworthy limitations to @code{elm-build-system}:

@itemize
@item
The build system is focused on @dfn{packages} in the Elm sense of the word:
Elm @dfn{projects} which declare @code{@{ "type": "package" @}} in their
@file{elm.json} files.  Using @code{elm-build-system} to build Elm
@dfn{applications} (which declare @code{@{ "type": "application" @}}) is
possible, but requires ad-hoc modifications to the build phases.  For
examples, see the definitions of the @code{elm-todomvc} example application and
the @code{elm} package itself (because the front-end for the
@samp{elm reactor} command is an Elm application).

@item
Elm supports multiple versions of a package coexisting simultaneously under
@env{ELM_HOME}, but this does not yet work well with @code{elm-build-system}.
This limitation primarily affects Elm applications, because they specify
exact versions for their dependencies, whereas Elm packages specify supported
version ranges.  As a workaround, the example applications mentioned above use
the @code{patch-application-dependencies} procedure provided by
@code{(guix build elm-build-system)} to rewrite their @file{elm.json} files to
refer to the package versions actually present in the build environment.
Alternatively, Guix package transformations (@pxref{Defining Package
Variants}) could be used to rewrite an application's entire dependency graph.

@item
We are not yet able to run tests for Elm projects because neither
@url{https://github.com/mpizenberg/elm-test-rs, @command{elm-test-rs}} nor the
Node.js-based @url{https://github.com/rtfeldman/node-test-runner,
@command{elm-test}} runner has been packaged for Guix yet.
@end itemize
@end defvar

@defvar go-build-system
This variable is exported by @code{(guix build-system go)}.  It
implements a build procedure for Go packages using the standard
@url{https://golang.org/cmd/go/#hdr-Compile_packages_and_dependencies,
Go build mechanisms}.

The user is expected to provide a value for the key @code{#:import-path}
and, in some cases, @code{#:unpack-path}.  The
@url{https://golang.org/doc/code.html#ImportPaths, import path}
corresponds to the file system path expected by the package's build
scripts and any referring packages, and provides a unique way to
refer to a Go package.  It is typically based on a combination of the
package source code's remote URI and file system hierarchy structure.  In
some cases, you will need to unpack the package's source code to a
different directory structure than the one indicated by the import path,
and @code{#:unpack-path} should be used in such cases.

Packages that provide Go libraries should install their source code into
the built output.  The key @code{#:install-source?}, which defaults to
@code{#t}, controls whether or not the source code is installed.  It can
be set to @code{#f} for packages that only provide executable files.

Packages can be cross-built, and if a specific architecture or operating
system is desired then the keywords @code{#:goarch} and @code{#:goos}
can be used to force the package to be built for that architecture and
operating system.  The combinations known to Go can be found
@url{https://golang.org/doc/install/source#environment,
in their documentation}.

The key @code{#:go} can be used to specify the Go compiler package with
which to build the package.

@end defvar

@defvar glib-or-gtk-build-system
This variable is exported by @code{(guix build-system glib-or-gtk)}.  It
is intended for use with packages making use of GLib or GTK+.

This build system adds the following two phases to the ones defined by
@code{gnu-build-system}:

@table @code
@item glib-or-gtk-wrap
The phase @code{glib-or-gtk-wrap} ensures that programs in
@file{bin/} are able to find GLib ``schemas'' and
@uref{https://developer.gnome.org/gtk3/stable/gtk-running.html, GTK+
modules}.  This is achieved by wrapping the programs in launch scripts
that appropriately set the @env{XDG_DATA_DIRS} and @env{GTK_PATH}
environment variables.

It is possible to exclude specific package outputs from that wrapping
process by listing their names in the
@code{#:glib-or-gtk-wrap-excluded-outputs} parameter.  This is useful
when an output is known not to contain any GLib or GTK+ binaries, and
where wrapping would gratuitously add a dependency of that output on
GLib and GTK+.

@item glib-or-gtk-compile-schemas
The phase @code{glib-or-gtk-compile-schemas} makes sure that all
@uref{https://developer.gnome.org/gio/stable/glib-compile-schemas.html,
GSettings schemas} of GLib are compiled.  Compilation is performed by the
@command{glib-compile-schemas} program.  It is provided by the package
@code{glib:bin} which is automatically imported by the build system.
The @code{glib} package providing @command{glib-compile-schemas} can be
specified with the @code{#:glib} parameter.
@end table

Both phases are executed after the @code{install} phase.
@end defvar

@defvar guile-build-system
This build system is for Guile packages that consist exclusively of Scheme
code and that are so lean that they don't even have a makefile, let alone a
@file{configure} script.  It compiles Scheme code using @command{guild
compile} (@pxref{Compilation,,, guile, GNU Guile Reference Manual}) and
installs the @file{.scm} and @file{.go} files in the right place.  It also
installs documentation.

This build system supports cross-compilation by using the
@option{--target} option of @samp{guild compile}.

Packages built with @code{guile-build-system} must provide a Guile package in
their @code{native-inputs} field.
@end defvar

@defvar julia-build-system
This variable is exported by @code{(guix build-system julia)}.  It
implements the build procedure used by @uref{https://julialang.org/,
julia} packages, which essentially is similar to running @samp{julia -e
'using Pkg; Pkg.add(package)'} in an environment where
@env{JULIA_LOAD_PATH} contains the paths to all Julia package inputs.
Tests are run by calling @code{/test/runtests.jl}.

The Julia package name and uuid is read from the file
@file{Project.toml}.  These values can be overridden by passing the
argument @code{#:julia-package-name} (which must be correctly
capitalized) or @code{#:julia-package-uuid}.

Julia packages usually manage their binary dependencies via
@code{JLLWrappers.jl}, a Julia package that creates a module (named
after the wrapped library followed by @code{_jll.jl}.

To add the binary path @code{_jll.jl} packages, you need to patch the
files under @file{src/wrappers/}, replacing the call to the macro
@code{JLLWrappers.@@generate_wrapper_header}, adding as a second
argument containing the store path the binary.

As an example, in the MbedTLS Julia package, we add a build phase
(@pxref{Build Phases}) to insert the absolute file name of the wrapped
MbedTLS package:

@lisp
(add-after 'unpack 'override-binary-path
  (lambda* (#:key inputs #:allow-other-keys)
    (for-each (lambda (wrapper)
                (substitute* wrapper
                  (("generate_wrapper_header.*")
                   (string-append
                    "generate_wrapper_header(\"MbedTLS\", \""
                    (assoc-ref inputs "mbedtls") "\")\n"))))
              ;; There's a Julia file for each platform, override them all.
              (find-files "src/wrappers/" "\\.jl$"))))
@end lisp

Some older packages that aren't using @file{Project.toml} yet, will
require this file to be created, too.  It is internally done if the
arguments @code{#:julia-package-name} and @code{#:julia-package-uuid}
are provided.
@end defvar

@defvar maven-build-system
This variable is exported by @code{(guix build-system maven)}.  It implements
a build procedure for @uref{https://maven.apache.org, Maven} packages.  Maven
is a dependency and lifecycle management tool for Java.  A user of Maven
specifies dependencies and plugins in a @file{pom.xml} file that Maven reads.
When Maven does not have one of the dependencies or plugins in its repository,
it will download them and use them to build the package.

The maven build system ensures that maven will not try to download any
dependency by running in offline mode.  Maven will fail if a dependency is
missing.  Before running Maven, the @file{pom.xml} (and subprojects) are
modified to specify the version of dependencies and plugins that match the
versions available in the guix build environment.  Dependencies and plugins
must be installed in the fake maven repository at @file{lib/m2}, and are
symlinked into a proper repository before maven is run.  Maven is instructed
to use that repository for the build and installs built artifacts there.
Changed files are copied to the @file{lib/m2} directory of the package output.

You can specify a @file{pom.xml} file with the @code{#:pom-file} argument,
or let the build system use the default @file{pom.xml} file in the sources.

In case you need to specify a dependency's version manually, you can use the
@code{#:local-packages} argument.  It takes an association list where the key
is the groupId of the package and its value is an association list where the
key is the artifactId of the package and its value is the version you want to
override in the @file{pom.xml}.

Some packages use dependencies or plugins that are not useful at runtime nor
at build time in Guix.  You can alter the @file{pom.xml} file to remove them
using the @code{#:exclude} argument.  Its value is an association list where
the key is the groupId of the plugin or dependency you want to remove, and
the value is a list of artifactId you want to remove.

You can override the default @code{jdk} and @code{maven} packages with the
corresponding argument, @code{#:jdk} and @code{#:maven}.

The @code{#:maven-plugins} argument is a list of maven plugins used during
the build, with the same format as the @code{inputs} fields of the package
declaration.  Its default value is @code{(default-maven-plugins)} which is
also exported.
@end defvar

@defvar minetest-mod-build-system
This variable is exported by @code{(guix build-system minetest)}.  It
implements a build procedure for @uref{https://www.minetest.net, Minetest}
mods, which consists of copying Lua code, images and other resources to
the location Minetest searches for mods.  The build system also minimises
PNG images and verifies that Minetest can load the mod without errors.
@end defvar

@defvar minify-build-system
This variable is exported by @code{(guix build-system minify)}.  It
implements a minification procedure for simple JavaScript packages.

It adds @code{uglify-js} to the set of inputs and uses it to compress
all JavaScript files in the @file{src} directory.  A different minifier
package can be specified with the @code{#:uglify-js} parameter, but it
is expected that the package writes the minified code to the standard
output.

When the input JavaScript files are not all located in the @file{src}
directory, the parameter @code{#:javascript-files} can be used to
specify a list of file names to feed to the minifier.
@end defvar

@defvar mozilla-build-system
This variable is exported by @code{(guix build-system mozilla)}.  It
sets the @code{--target} and @code{--host} configuration flags to what
software developed by Mozilla expects -- due to historical reasons,
Mozilla software expects @code{--host} to be the system that is
cross-compiled from and @code{--target} to be the system that is
cross-compiled to, contrary to the standard Autotools conventions.
@end defvar

@defvar ocaml-build-system
This variable is exported by @code{(guix build-system ocaml)}.  It implements
a build procedure for @uref{https://ocaml.org, OCaml} packages, which consists
of choosing the correct set of commands to run for each package.  OCaml
packages can expect many different commands to be run.  This build system will
try some of them.

When the package has a @file{setup.ml} file present at the top-level, it will
run @code{ocaml setup.ml -configure}, @code{ocaml setup.ml -build} and
@code{ocaml setup.ml -install}.  The build system will assume that this file
was generated by @uref{http://oasis.forge.ocamlcore.org/, OASIS} and will take
care of setting the prefix and enabling tests if they are not disabled.  You
can pass configure and build flags with the @code{#:configure-flags} and
@code{#:build-flags}.  The @code{#:test-flags} key can be passed to change the
set of flags used to enable tests.  The @code{#:use-make?} key can be used to
bypass this system in the build and install phases.

When the package has a @file{configure} file, it is assumed that it is a
hand-made configure script that requires a different argument format than
in the @code{gnu-build-system}.  You can add more flags with the
@code{#:configure-flags} key.

When the package has a @file{Makefile} file (or @code{#:use-make?} is
@code{#t}), it will be used and more flags can be passed to the build and
install phases with the @code{#:make-flags} key.

Finally, some packages do not have these files and use a somewhat standard
location for its build system.  In that case, the build system will run
@code{ocaml pkg/pkg.ml} or @code{ocaml pkg/build.ml} and take care of
providing the path to the required findlib module.  Additional flags can
be passed via the @code{#:build-flags} key.  Install is taken care of by
@command{opam-installer}.  In this case, the @code{opam} package must
be added to the @code{native-inputs} field of the package definition.

Note that most OCaml packages assume they will be installed in the same
directory as OCaml, which is not what we want in guix.  In particular, they
will install @file{.so} files in their module's directory, which is usually
fine because it is in the OCaml compiler directory.  In guix though, these
libraries cannot be found and we use @env{CAML_LD_LIBRARY_PATH}.  This
variable points to @file{lib/ocaml/site-lib/stubslibs} and this is where
@file{.so} libraries should be installed.
@end defvar

@defvar python-build-system
This variable is exported by @code{(guix build-system python)}.  It
implements the more or less standard build procedure used by Python
packages, which consists in running @code{python setup.py build} and
then @code{python setup.py install --prefix=/gnu/store/@dots{}}.

For packages that install stand-alone Python programs under @code{bin/},
it takes care of wrapping these programs so that their
@env{GUIX_PYTHONPATH} environment variable points to all the Python
libraries they depend on.

Which Python package is used to perform the build can be specified with
the @code{#:python} parameter.  This is a useful way to force a package
to be built for a specific version of the Python interpreter, which
might be necessary if the package is only compatible with a single
interpreter version.

By default guix calls @code{setup.py} under control of
@code{setuptools}, much like @command{pip} does.  Some packages are not
compatible with setuptools (and pip), thus you can disable this by
setting the @code{#:use-setuptools?} parameter to @code{#f}.

If a @code{"python"} output is available, the package is installed into it
instead of the default @code{"out"} output. This is useful for packages that
include a Python package as only a part of the software, and thus want to
combine the phases of @code{python-build-system} with another build system.
Python bindings are a common usecase.
@end defvar

@defvar pyproject-build-system
This is a variable exported by @code{guix build-system pyproject}.  It
is based on @var{python-build-system}, and adds support for
@file{pyproject.toml} and @url{https://peps.python.org/pep-0517/, PEP 517}.
It also supports a variety of build backends and test frameworks.

The API is slightly different from @var{python-build-system}:
@itemize
@item
@code{#:use-setuptools?} and @code{#:test-target} is removed.
@item
@code{#:build-backend} is added.  It defaults to @code{#false} and will try
to guess the appropriate backend based on @file{pyproject.toml}.
@item
@code{#:test-backend} is added.  It defaults to @code{#false} and will guess
an appropriate test backend based on what is available in package inputs.
@item
@code{#:test-flags} is added.  The default is @code{'()}.  These flags are
passed as arguments to the test command.  Note that flags for verbose output
is always enabled on supported backends.
@end itemize

It is considered ``experimental'' in that the implementation details are
not set in stone yet, however users are encouraged to try it for new
Python projects (even those using @file{setup.py}).  The API is subject to
change, but any breaking changes in the Guix channel will be dealt with.

Eventually this build system will be deprecated and merged back into
@var{python-build-system}, probably some time in 2024.
@end defvar

@defvar perl-build-system
This variable is exported by @code{(guix build-system perl)}.  It
implements the standard build procedure for Perl packages, which either
consists in running @code{perl Build.PL --prefix=/gnu/store/@dots{}},
followed by @code{Build} and @code{Build install}; or in running
@code{perl Makefile.PL PREFIX=/gnu/store/@dots{}}, followed by
@code{make} and @code{make install}, depending on which of
@code{Build.PL} or @code{Makefile.PL} is present in the package
distribution.  Preference is given to the former if both @code{Build.PL}
and @code{Makefile.PL} exist in the package distribution.  This
preference can be reversed by specifying @code{#t} for the
@code{#:make-maker?} parameter.

The initial @code{perl Makefile.PL} or @code{perl Build.PL} invocation
passes flags specified by the @code{#:make-maker-flags} or
@code{#:module-build-flags} parameter, respectively.

Which Perl package is used can be specified with @code{#:perl}.
@end defvar

@defvar renpy-build-system
This variable is exported by @code{(guix build-system renpy)}.  It implements
the more or less standard build procedure used by Ren'py games, which consists
of loading @code{#:game} once, thereby creating bytecode for it.

It further creates a wrapper script in @code{bin/} and a desktop entry in
@code{share/applications}, both of which can be used to launch the game.

Which Ren'py package is used can be specified with @code{#:renpy}.
Games can also be installed in outputs other than ``out'' by using
@code{#:output}.
@end defvar

@defvar qt-build-system
This variable is exported by @code{(guix build-system qt)}.  It
is intended for use with applications using Qt or KDE.

This build system adds the following two phases to the ones defined by
@code{cmake-build-system}:

@table @code
@item check-setup
The phase @code{check-setup} prepares the environment for running
the checks as commonly used by Qt test programs.
For now this only sets some environment variables:
@code{QT_QPA_PLATFORM=offscreen},
@code{DBUS_FATAL_WARNINGS=0} and
@code{CTEST_OUTPUT_ON_FAILURE=1}.

This phase is added before the @code{check} phase.
It's a separate phase to ease adjusting if necessary.

@item qt-wrap
The phase @code{qt-wrap}
searches for Qt5 plugin paths, QML paths and some XDG in the inputs
and output.  In case some path is found, all programs in the output's
@file{bin/}, @file{sbin/}, @file{libexec/} and @file{lib/libexec/} directories
are wrapped in scripts defining the necessary environment variables.

It is possible to exclude specific package outputs from that wrapping process
by listing their names in the @code{#:qt-wrap-excluded-outputs} parameter.
This is useful when an output is known not to contain any Qt binaries, and
where wrapping would gratuitously add a dependency of that output on Qt, KDE,
or such.

This phase is added after the @code{install} phase.
@end table
@end defvar

@defvar r-build-system
This variable is exported by @code{(guix build-system r)}.  It
implements the build procedure used by @uref{https://r-project.org, R}
packages, which essentially is little more than running @samp{R CMD
INSTALL --library=/gnu/store/@dots{}} in an environment where
@env{R_LIBS_SITE} contains the paths to all R package inputs.  Tests are
run after installation using the R function
@code{tools::testInstalledPackage}.
@end defvar

@defvar rakudo-build-system
This variable is exported by @code{(guix build-system rakudo)}.  It
implements the build procedure used by @uref{https://rakudo.org/,
Rakudo} for @uref{https://perl6.org/, Perl6} packages.  It installs the
package to @code{/gnu/store/@dots{}/NAME-VERSION/share/perl6} and
installs the binaries, library files and the resources, as well as wrap
the files under the @code{bin/} directory.  Tests can be skipped by
passing @code{#f} to the @code{tests?} parameter.

Which rakudo package is used can be specified with @code{rakudo}.
Which perl6-tap-harness package used for the tests can be specified with
@code{#:prove6} or removed by passing @code{#f} to the
@code{with-prove6?} parameter.
Which perl6-zef package used for tests and installing can be specified
with @code{#:zef} or removed by passing @code{#f} to the
@code{with-zef?} parameter.
@end defvar

@defvar rebar-build-system
This variable is exported by @code{(guix build-system rebar)}.  It
implements a build procedure around @uref{https://rebar3.org,rebar3},
a build system for programs written in the Erlang language.

It adds both @code{rebar3} and the @code{erlang} to the set of inputs.
Different packages can be specified with the @code{#:rebar} and
@code{#:erlang} parameters, respectively.

This build system is based on @code{gnu-build-system}, but with the
following phases changed:

@table @code

@item unpack
This phase, after unpacking the source like the @code{gnu-build-system}
does, checks for a file @code{contents.tar.gz} at the top-level of the
source.  If this file exists, it will be unpacked, too.  This eases
handling of package hosted at @uref{https://hex.pm/},
the Erlang and Elixir package repository.

@item bootstrap
@item configure
There are no @code{bootstrap} and @code{configure} phase because erlang
packages typically don’t need to be configured.

@item build
This phase runs @code{rebar3 compile}
with the flags listed in @code{#:rebar-flags}.

@item check
Unless @code{#:tests? #f} is passed,
this phase runs @code{rebar3 eunit},
or some other target specified with @code{#:test-target},
with the flags listed in @code{#:rebar-flags},

@item install
This installs the files created in the @i{default} profile, or some
other profile specified with @code{#:install-profile}.

@end table
@end defvar

@defvar texlive-build-system
This variable is exported by @code{(guix build-system texlive)}.  It is
used to build TeX packages in batch mode with a specified engine.  The
build system sets the @env{TEXINPUTS} variable to find all TeX source
files in the inputs.

By default it tries to run @code{luatex} on all @file{.ins} files, and
if it fails to find any, on all @file{.dtx} files.  A different engine
and format can be specified with, respectively, the @code{#:tex-engine}
and @code{#:tex-format} arguments.  Different build targets can be
specified with the @code{#:build-targets} argument, which expects a list
of file names.

It also generates font metrics (i.e., @file{.tfm} files) out of Metafont
files whenever possible.  Likewise, it can also create TeX formats
(i.e., @file{.fmt} files) listed in the @code{#:create-formats}
argument, and generate a symbolic link from @file{bin/} directory to any
script located in @file{texmf-dist/scripts/}, provided its file name is
listed in @code{#:link-scripts} argument.

The build system adds @code{texlive-bin} from @code{(gnu packages tex)}
to the native inputs.  It can be overridden with the
@code{#:texlive-bin} argument.

The package @code{texlive-latex-bin}, from the same module, contains
most of the tools for building TeX Live packages; for convenience, it is
also added by default to the native inputs.  However, this can be
troublesome when building a dependency of @code{texlive-latex-bin}
itself.  In this particular situation, the @code{#:texlive-latex-bin?}
argument should be set to @code{#f}.
@end defvar

@defvar ruby-build-system
This variable is exported by @code{(guix build-system ruby)}.  It
implements the RubyGems build procedure used by Ruby packages, which
involves running @code{gem build} followed by @code{gem install}.

The @code{source} field of a package that uses this build system
typically references a gem archive, since this is the format that Ruby
developers use when releasing their software.  The build system unpacks
the gem archive, potentially patches the source, runs the test suite,
repackages the gem, and installs it.  Additionally, directories and
tarballs may be referenced to allow building unreleased gems from Git or
a traditional source release tarball.

Which Ruby package is used can be specified with the @code{#:ruby}
parameter.  A list of additional flags to be passed to the @command{gem}
command can be specified with the @code{#:gem-flags} parameter.
@end defvar

@defvar waf-build-system
This variable is exported by @code{(guix build-system waf)}.  It
implements a build procedure around the @code{waf} script.  The common
phases---@code{configure}, @code{build}, and @code{install}---are
implemented by passing their names as arguments to the @code{waf}
script.

The @code{waf} script is executed by the Python interpreter.  Which
Python package is used to run the script can be specified with the
@code{#:python} parameter.
@end defvar

@defvar zig-build-system
This variable is exported by @code{(guix build-system zig)}.  It implements
the build procedures for the @uref{https://ziglang.org/, Zig}
build system (@command{zig build} command).

Selecting this build system adds @code{zig} to the package inputs, in
addition to the packages of @code{gnu-build-system}.

There is no @code{configure} phase because Zig packages typically do not
need to be configured.  The @code{#:zig-build-flags} parameter is a list of
flags that are passed to the @code{zig} command during the build.  The
@code{#:zig-test-flags} parameter is a list of flags that are passed to the
@code{zig test} command during the @code{check} phase.  The default compiler
package can be overridden with the @code{#:zig} argument.

The optional @code{zig-release-type} parameter declares the type of release.
Possible values are: @code{safe}, @code{fast}, or @code{small}. The default
value is @code{#f}, which causes the release flag to be omitted from the
@code{zig} command.  That results in a @code{debug} build.
@end defvar

@defvar scons-build-system
This variable is exported by @code{(guix build-system scons)}.  It
implements the build procedure used by the SCons software construction
tool.  This build system runs @code{scons} to build the package,
@code{scons test} to run tests, and then @code{scons install} to install
the package.

Additional flags to be passed to @code{scons} can be specified with the
@code{#:scons-flags} parameter.  The default build and install targets
can be overridden with @code{#:build-targets} and
@code{#:install-targets} respectively.  The version of Python used to
run SCons can be specified by selecting the appropriate SCons package
with the @code{#:scons} parameter.
@end defvar

@defvar haskell-build-system
This variable is exported by @code{(guix build-system haskell)}.  It
implements the Cabal build procedure used by Haskell packages, which
involves running @code{runhaskell Setup.hs configure
--prefix=/gnu/store/@dots{}} and @code{runhaskell Setup.hs build}.
Instead of installing the package by running @code{runhaskell Setup.hs
install}, to avoid trying to register libraries in the read-only
compiler store directory, the build system uses @code{runhaskell
Setup.hs copy}, followed by @code{runhaskell Setup.hs register}.  In
addition, the build system generates the package documentation by
running @code{runhaskell Setup.hs haddock}, unless @code{#:haddock? #f}
is passed.  Optional Haddock parameters can be passed with the help of
the @code{#:haddock-flags} parameter.  If the file @code{Setup.hs} is
not found, the build system looks for @code{Setup.lhs} instead.

Which Haskell compiler is used can be specified with the @code{#:haskell}
parameter which defaults to @code{ghc}.
@end defvar

@defvar dub-build-system
This variable is exported by @code{(guix build-system dub)}.  It
implements the Dub build procedure used by D packages, which
involves running @code{dub build} and @code{dub run}.
Installation is done by copying the files manually.

Which D compiler is used can be specified with the @code{#:ldc}
parameter which defaults to @code{ldc}.
@end defvar

@anchor{emacs-build-system}
@defvar emacs-build-system
This variable is exported by @code{(guix build-system emacs)}.  It
implements an installation procedure similar to the packaging system
of Emacs itself (@pxref{Packages,,, emacs, The GNU Emacs Manual}).

It first creates the @code{@code{package}-autoloads.el} file, then it
byte compiles all Emacs Lisp files.  Differently from the Emacs
packaging system, the Info documentation files are moved to the standard
documentation directory and the @file{dir} file is deleted.  The Elisp
package files are installed directly under @file{share/emacs/site-lisp}.
@end defvar

@defvar font-build-system
This variable is exported by @code{(guix build-system font)}.  It
implements an installation procedure for font packages where upstream
provides pre-compiled TrueType, OpenType, etc.@: font files that merely
need to be copied into place.  It copies font files to standard
locations in the output directory.
@end defvar

@defvar meson-build-system
This variable is exported by @code{(guix build-system meson)}.  It
implements the build procedure for packages that use
@url{https://mesonbuild.com, Meson} as their build system.

It adds both Meson and @uref{https://ninja-build.org/, Ninja} to the set
of inputs, and they can be changed with the parameters @code{#:meson}
and @code{#:ninja} if needed.

This build system is an extension of @code{gnu-build-system}, but with the
following phases changed to some specific for Meson:

@table @code

@item configure
The phase runs @code{meson} with the flags specified in
@code{#:configure-flags}.  The flag @option{--buildtype} is always set to
@code{debugoptimized} unless something else is specified in
@code{#:build-type}.

@item build
The phase runs @code{ninja} to build the package in parallel by default, but
this can be changed with @code{#:parallel-build?}.

@item check
The phase runs @samp{meson test} with a base set of options that cannot
be overridden.  This base set of options can be extended via the
@code{#:test-options} argument, for example to select or skip a specific
test suite.

@item install
The phase runs @code{ninja install} and can not be changed.
@end table

Apart from that, the build system also adds the following phases:

@table @code

@item fix-runpath
This phase ensures that all binaries can find the libraries they need.
It searches for required libraries in subdirectories of the package
being built, and adds those to @code{RUNPATH} where needed.  It also
removes references to libraries left over from the build phase by
@code{meson}, such as test dependencies, that aren't actually required
for the program to run.

@item glib-or-gtk-wrap
This phase is the phase provided by @code{glib-or-gtk-build-system}, and it
is not enabled by default.  It can be enabled with @code{#:glib-or-gtk?}.

@item glib-or-gtk-compile-schemas
This phase is the phase provided by @code{glib-or-gtk-build-system}, and it
is not enabled by default.  It can be enabled with @code{#:glib-or-gtk?}.
@end table
@end defvar

@defvar linux-module-build-system
@code{linux-module-build-system} allows building Linux kernel modules.

@cindex build phases
This build system is an extension of @code{gnu-build-system}, but with the
following phases changed:

@table @code

@item configure
This phase configures the environment so that the Linux kernel's Makefile
can be used to build the external kernel module.

@item build
This phase uses the Linux kernel's Makefile in order to build the external
kernel module.

@item install
This phase uses the Linux kernel's Makefile in order to install the external
kernel module.
@end table

It is possible and useful to specify the Linux kernel to use for building
the module (in the @code{arguments} form of a package using the
@code{linux-module-build-system}, use the key @code{#:linux} to specify it).
@end defvar

@defvar node-build-system
This variable is exported by @code{(guix build-system node)}.  It
implements the build procedure used by @uref{https://nodejs.org,
Node.js}, which implements an approximation of the @code{npm install}
command, followed by an @code{npm test} command.

Which Node.js package is used to interpret the @code{npm} commands can
be specified with the @code{#:node} parameter which defaults to
@code{node}.
@end defvar

@defvar tree-sitter-build-system

This variable is exported by @code{(guix build-system tree-sitter)}.  It
implements procedures to compile grammars for the
@url{https://tree-sitter.github.io/tree-sitter/, Tree-sitter} parsing
library.  It essentially runs @code{tree-sitter generate} to translate
@code{grammar.js} grammars to JSON and then to C.  Which it then
compiles to native code.

Tree-sitter packages may support multiple grammars, so this build system
supports a @code{#:grammar-directories} keyword to specify a list of
locations where a @code{grammar.js} file may be found.

Grammars sometimes depend on each other, such as C++ depending on C and
TypeScript depending on JavaScript.  You may use inputs to declare such
dependencies.

@end defvar

Lastly, for packages that do not need anything as sophisticated, a
``trivial'' build system is provided.  It is trivial in the sense that
it provides basically no support: it does not pull any implicit inputs,
and does not have a notion of build phases.

@defvar trivial-build-system
This variable is exported by @code{(guix build-system trivial)}.

This build system requires a @code{#:builder} argument.  This argument
must be a Scheme expression that builds the package output(s)---as
with @code{build-expression->derivation} (@pxref{Derivations,
@code{build-expression->derivation}}).
@end defvar

@defvar channel-build-system
This variable is exported by @code{(guix build-system channel)}.

This build system is meant primarily for internal use.  A package using
this build system must have a channel specification as its @code{source}
field (@pxref{Channels}); alternatively, its source can be a directory
name, in which case an additional @code{#:commit} argument must be
supplied to specify the commit being built (a hexadecimal string).

Optionally, a @code{#:channels} argument specifying additional channels
can be provided.

The resulting package is a Guix instance of the given channel(s), similar
to how @command{guix time-machine} would build it.
@end defvar

@node Build Phases
@section Build Phases

@cindex build phases, for packages
Almost all package build systems implement a notion @dfn{build phases}:
a sequence of actions that the build system executes, when you build the
package, leading to the installed byproducts in the store.  A notable
exception is the ``bare-bones'' @code{trivial-build-system}
(@pxref{Build Systems}).

As discussed in the previous section, those build systems provide a
standard list of phases.  For @code{gnu-build-system}, the main build
phases are the following:

@table @code
@item set-paths
Define search path environment variables for all the input packages,
including @env{PATH} (@pxref{Search Paths}).

@item unpack
Unpack the source tarball, and change the current directory to the
extracted source tree.  If the source is actually a directory, copy it
to the build tree, and enter that directory.

@item patch-source-shebangs
Patch shebangs encountered in source files so they refer to the right
store file names.  For instance, this changes @code{#!/bin/sh} to
@code{#!/gnu/store/@dots{}-bash-4.3/bin/sh}.

@item configure
Run the @file{configure} script with a number of default options, such
as @option{--prefix=/gnu/store/@dots{}}, as well as the options specified
by the @code{#:configure-flags} argument.

@item build
Run @code{make} with the list of flags specified with
@code{#:make-flags}.  If the @code{#:parallel-build?} argument is true
(the default), build with @code{make -j}.

@item check
Run @code{make check}, or some other target specified with
@code{#:test-target}, unless @code{#:tests? #f} is passed.  If the
@code{#:parallel-tests?} argument is true (the default), run @code{make
check -j}.

@item install
Run @code{make install} with the flags listed in @code{#:make-flags}.

@item patch-shebangs
Patch shebangs on the installed executable files.

@item strip
Strip debugging symbols from ELF files (unless @code{#:strip-binaries?}
is false), copying them to the @code{debug} output when available
(@pxref{Installing Debugging Files}).

@cindex RUNPATH, validation
@anchor{phase-validate-runpath}
@item validate-runpath
Validate the @code{RUNPATH} of ELF binaries, unless
@code{#:validate-runpath?} is false (@pxref{Build Systems}).

This validation step consists in making sure that all the shared
libraries needed by an ELF binary, which are listed as @code{DT_NEEDED}
entries in its @code{PT_DYNAMIC} segment, appear in the
@code{DT_RUNPATH} entry of that binary.  In other words, it ensures that
running or using those binaries will not result in a ``file not found''
error at run time.  @xref{Options, @option{-rpath},, ld, The GNU
Linker}, for more information on @code{RUNPATH}.

@end table

Other build systems have similar phases, with some variations.  For
example, @code{cmake-build-system} has same-named phases but its
@code{configure} phases runs @code{cmake} instead of @code{./configure}.
Others, such as @code{python-build-system}, have a wholly different list
of standard phases.  All this code runs on the @dfn{build side}: it is
evaluated when you actually build the package, in a dedicated build
process spawned by the build daemon (@pxref{Invoking guix-daemon}).

Build phases are represented as association lists or ``alists''
(@pxref{Association Lists,,, guile, GNU Guile Reference Manual}) where
each key is a symbol for the name of the phase and the associated value
is a procedure that accepts an arbitrary number of arguments.  By
convention, those procedures receive information about the build in the
form of @dfn{keyword parameters}, which they can use or ignore.

@vindex %standard-phases
For example, here is how @code{(guix build gnu-build-system)} defines
@code{%standard-phases}, the variable holding its alist of build
phases@footnote{We present a simplified view of those build phases, but
do take a look at @code{(guix build gnu-build-system)} to see all the
details!}:

@lisp
;; The build phases of 'gnu-build-system'.

(define* (unpack #:key source #:allow-other-keys)
  ;; Extract the source tarball.
  (invoke "tar" "xvf" source))

(define* (configure #:key outputs #:allow-other-keys)
  ;; Run the 'configure' script.  Install to output "out".
  (let ((out (assoc-ref outputs "out")))
    (invoke "./configure"
            (string-append "--prefix=" out))))

(define* (build #:allow-other-keys)
  ;; Compile.
  (invoke "make"))

(define* (check #:key (test-target "check") (tests? #true)
                #:allow-other-keys)
  ;; Run the test suite.
  (if tests?
      (invoke "make" test-target)
      (display "test suite not run\n")))

(define* (install #:allow-other-keys)
  ;; Install files to the prefix 'configure' specified.
  (invoke "make" "install"))

(define %standard-phases
  ;; The list of standard phases (quite a few are omitted
  ;; for brevity).  Each element is a symbol/procedure pair.
  (list (cons 'unpack unpack)
        (cons 'configure configure)
        (cons 'build build)
        (cons 'check check)
        (cons 'install install)))
@end lisp

This shows how @code{%standard-phases} is defined as a list of
symbol/procedure pairs (@pxref{Pairs,,, guile, GNU Guile Reference
Manual}).  The first pair associates the @code{unpack} procedure with
the @code{unpack} symbol---a name; the second pair defines the
@code{configure} phase similarly, and so on.  When building a package
that uses @code{gnu-build-system} with its default list of phases, those
phases are executed sequentially.  You can see the name of each phase
started and completed in the build log of packages that you build.

Let's now look at the procedures themselves.  Each one is defined with
@code{define*}: @code{#:key} lists keyword parameters the procedure
accepts, possibly with a default value, and @code{#:allow-other-keys}
specifies that other keyword parameters are ignored (@pxref{Optional
Arguments,,, guile, GNU Guile Reference Manual}).

The @code{unpack} procedure honors the @code{source} parameter, which
the build system uses to pass the file name of the source tarball (or
version control checkout), and it ignores other parameters.  The
@code{configure} phase only cares about the @code{outputs} parameter, an
alist mapping package output names to their store file name
(@pxref{Packages with Multiple Outputs}).  It extracts the file name of
for @code{out}, the default output, and passes it to
@command{./configure} as the installation prefix, meaning that
@command{make install} will eventually copy all the files in that
directory (@pxref{Configuration, configuration and makefile
conventions,, standards, GNU Coding Standards}).  @code{build} and
@code{install} ignore all their arguments.  @code{check} honors the
@code{test-target} argument, which specifies the name of the Makefile
target to run tests; it prints a message and skips tests when
@code{tests?} is false.

@cindex build phases, customizing
The list of phases used for a particular package can be changed with the
@code{#:phases} parameter of the build system.  Changing the set of
build phases boils down to building a new alist of phases based on the
@code{%standard-phases} alist described above.  This can be done with
standard alist procedures such as @code{alist-delete} (@pxref{SRFI-1
Association Lists,,, guile, GNU Guile Reference Manual}); however, it is
more convenient to do so with @code{modify-phases} (@pxref{Build
Utilities, @code{modify-phases}}).

Here is an example of a package definition that removes the
@code{configure} phase of @code{%standard-phases} and inserts a new
phase before the @code{build} phase, called
@code{set-prefix-in-makefile}:

@lisp
(define-public example
  (package
    (name "example")
    ;; other fields omitted
    (build-system gnu-build-system)
    (arguments
     (list
      #:phases
      #~(modify-phases %standard-phases
          (delete 'configure)
          (add-before 'build 'set-prefix-in-makefile
            (lambda* (#:key inputs #:allow-other-keys)
              ;; Modify the makefile so that its
              ;; 'PREFIX' variable points to #$output and
              ;; 'XMLLINT' points to the correct path.
              (substitute* "Makefile"
                (("PREFIX =.*")
                 (string-append "PREFIX = " #$output "\n"))
                (("XMLLINT =.*")
                 (string-append "XMLLINT = "
                                (search-input-file inputs "/bin/xmllint")
                                "\n"))))))))))
@end lisp

The new phase that is inserted is written as an anonymous procedure,
introduced with @code{lambda*}; it looks for the @file{xmllint}
executable under a @file{/bin} directory among the package's inputs
(@pxref{package Reference}).  It also honors the @code{outputs} parameter
we have seen before.  @xref{Build Utilities}, for more about
the helpers used by this phase, and for more examples of
@code{modify-phases}.

@quotation Tip
You can inspect the code associated with a package's @code{#:phases}
argument interactively, at the REPL (@pxref{Using Guix Interactively}).
@end quotation

@cindex code staging
@cindex staging, of code
Keep in mind that build phases are code evaluated at the time the
package is actually built.  This explains why the whole
@code{modify-phases} expression above is quoted (it comes after the
@code{'} or apostrophe): it is @dfn{staged} for later execution.
@xref{G-Expressions}, for an explanation of code staging and the
@dfn{code strata} involved.

@node Build Utilities
@section Build Utilities

As soon as you start writing non-trivial package definitions
(@pxref{Defining Packages}) or other build actions
(@pxref{G-Expressions}), you will likely start looking for helpers for
``shell-like'' actions---creating directories, copying and deleting
files recursively, manipulating build phases, and so on.  The
@code{(guix build utils)} module provides such utility procedures.

Most build systems load @code{(guix build utils)} (@pxref{Build
Systems}).  Thus, when writing custom build phases for your package
definitions, you can usually assume those procedures are in scope.

When writing G-expressions, you can import @code{(guix build utils)} on
the ``build side'' using @code{with-imported-modules} and then put it in
scope with the @code{use-modules} form (@pxref{Using Guile Modules,,,
guile, GNU Guile Reference Manual}):

@lisp
(with-imported-modules '((guix build utils))  ;import it
  (computed-file "empty-tree"
                 #~(begin
                     ;; Put it in scope.
                     (use-modules (guix build utils))

                     ;; Happily use its 'mkdir-p' procedure.
                     (mkdir-p (string-append #$output "/a/b/c")))))
@end lisp

The remainder of this section is the reference for most of the utility
procedures provided by @code{(guix build utils)}.

@c TODO Document what's missing.

@subsection Dealing with Store File Names

This section documents procedures that deal with store file names.

@deffn {Procedure} %store-directory
Return the directory name of the store.
@end deffn

@deffn {Procedure} store-file-name? file
Return true if @var{file} is in the store.
@end deffn

@deffn {Procedure} strip-store-file-name file
Strip the @file{/gnu/store} and hash from @var{file}, a store file name.
The result is typically a @code{"@var{package}-@var{version}"} string.
@end deffn

@deffn {Procedure} package-name->name+version name
Given @var{name}, a package name like @code{"foo-0.9.1b"}, return two
values: @code{"foo"} and @code{"0.9.1b"}.  When the version part is
unavailable, @var{name} and @code{#f} are returned.  The first hyphen
followed by a digit is considered to introduce the version part.
@end deffn

@subsection File Types

The procedures below deal with files and file types.

@deffn {Procedure} directory-exists? dir
Return @code{#t} if @var{dir} exists and is a directory.
@end deffn

@deffn {Procedure} executable-file? file
Return @code{#t} if @var{file} exists and is executable.
@end deffn

@deffn {Procedure} symbolic-link? file
Return @code{#t} if @var{file} is a symbolic link (aka. a ``symlink'').
@end deffn

@deffn {Procedure} elf-file? file
@deffnx {Procedure} ar-file? file
@deffnx {Procedure} gzip-file? file
Return @code{#t} if @var{file} is, respectively, an ELF file, an
@code{ar} archive (such as a @file{.a} static library), or a gzip file.
@end deffn

@deffn {Procedure} reset-gzip-timestamp file [#:keep-mtime? #t]
If @var{file} is a gzip file, reset its embedded timestamp (as with
@command{gzip --no-name}) and return true.  Otherwise return @code{#f}.
When @var{keep-mtime?} is true, preserve @var{file}'s modification time.
@end deffn

@subsection File Manipulation

The following procedures and macros help create, modify, and delete
files.  They provide functionality comparable to common shell utilities
such as @command{mkdir -p}, @command{cp -r}, @command{rm -r}, and
@command{sed}.  They complement Guile's extensive, but low-level, file
system interface (@pxref{POSIX,,, guile, GNU Guile Reference Manual}).

@defmac with-directory-excursion directory body @dots{}
Run @var{body} with @var{directory} as the process's current directory.

Essentially, this macro changes the current directory to @var{directory}
before evaluating @var{body}, using @code{chdir} (@pxref{Processes,,,
guile, GNU Guile Reference Manual}).  It changes back to the initial
directory when the dynamic extent of @var{body} is left, be it @i{via}
normal procedure return or @i{via} a non-local exit such as an
exception.
@end defmac

@deffn {Procedure} mkdir-p dir
Create directory @var{dir} and all its ancestors.
@end deffn

@deffn {Procedure} install-file file directory
Create @var{directory} if it does not exist and copy @var{file} in there
under the same name.
@end deffn

@deffn {Procedure} make-file-writable file
Make @var{file} writable for its owner.
@end deffn

@deffn {Procedure} copy-recursively source destination @
  [#:log (current-output-port)] [#:follow-symlinks? #f] @
  [#:copy-file copy-file] [#:keep-mtime? #f] [#:keep-permissions? #t]
Copy @var{source} directory to @var{destination}.  Follow symlinks if
@var{follow-symlinks?}  is true; otherwise, just preserve them.  Call
@var{copy-file} to copy regular files.  When @var{keep-mtime?} is true,
keep the modification time of the files in @var{source} on those of
@var{destination}.  When @var{keep-permissions?} is true, preserve file
permissions.  Write verbose output to the @var{log} port.
@end deffn

@deffn {Procedure} delete-file-recursively dir [#:follow-mounts? #f]
Delete @var{dir} recursively, like @command{rm -rf}, without following
symlinks.  Don't follow mount points either, unless @var{follow-mounts?}
is true.  Report but ignore errors.
@end deffn

@defmac substitute* file @
  ((regexp match-var@dots{}) body@dots{}) @dots{}
Substitute @var{regexp} in @var{file} by the string returned by
@var{body}.  @var{body} is evaluated with each @var{match-var} bound to
the corresponding positional regexp sub-expression.  For example:

@lisp
(substitute* file
  (("hello")
   "good morning\n")
  (("foo([a-z]+)bar(.*)$" all letters end)
   (string-append "baz" letters end)))
@end lisp

Here, anytime a line of @var{file} contains @code{hello}, it is replaced
by @code{good morning}.  Anytime a line of @var{file} matches the second
regexp, @code{all} is bound to the complete match, @code{letters} is bound
to the first sub-expression, and @code{end} is bound to the last one.

When one of the @var{match-var} is @code{_}, no variable is bound to the
corresponding match substring.

Alternatively, @var{file} may be a list of file names, in which case
they are all subject to the substitutions.

Be careful about using @code{$} to match the end of a line; by itself it
won't match the terminating newline of a line.  For example, to match a
whole line ending with a backslash, one needs a regex like
@code{"(.*)\\\\\n$"}.
@end defmac

@subsection File Search

@cindex file, searching
This section documents procedures to search and filter files.

@deffn {Procedure} file-name-predicate regexp
Return a predicate that returns true when passed a file name whose base
name matches @var{regexp}.
@end deffn

@deffn {Procedure} find-files dir [pred] @
  [#:stat lstat] [#:directories? #f] [#:fail-on-error? #f]
Return the lexicographically sorted list of files under @var{dir} for
which @var{pred} returns true.  @var{pred} is passed two arguments: the
absolute file name, and its stat buffer; the default predicate always
returns true.  @var{pred} can also be a regular expression, in which
case it is equivalent to @code{(file-name-predicate @var{pred})}.
@var{stat} is used to obtain file information; using @code{lstat} means
that symlinks are not followed.  If @var{directories?} is true, then
directories will also be included.  If @var{fail-on-error?} is true,
raise an exception upon error.
@end deffn

Here are a few examples where we assume that the current directory is
the root of the Guix source tree:

@lisp
;; List all the regular files in the current directory.
(find-files ".")
@result{} ("./.dir-locals.el" "./.gitignore" @dots{})

;; List all the .scm files under gnu/services.
(find-files "gnu/services" "\\.scm$")
@result{} ("gnu/services/admin.scm" "gnu/services/audio.scm" @dots{})

;; List ar files in the current directory.
(find-files "." (lambda (file stat) (ar-file? file)))
@result{} ("./libformat.a" "./libstore.a" @dots{})
@end lisp

@deffn {Procedure} which program
Return the complete file name for @var{program} as found in
@code{$PATH}, or @code{#f} if @var{program} could not be found.
@end deffn

@deffn {Procedure} search-input-file inputs name
@deffnx {Procedure} search-input-directory inputs name
Return the complete file name for @var{name} as found in @var{inputs};
@code{search-input-file} searches for a regular file and
@code{search-input-directory} searches for a directory.  If @var{name}
could not be found, an exception is raised.

Here, @var{inputs} must be an association list like @code{inputs} and
@code{native-inputs} as available to build phases (@pxref{Build
Phases}).
@end deffn

Here is a (simplified) example of how @code{search-input-file} is used
in a build phase of the @code{wireguard-tools} package:

@lisp
(add-after 'install 'wrap-wg-quick
  (lambda* (#:key inputs outputs #:allow-other-keys)
    (let ((coreutils (string-append (assoc-ref inputs "coreutils")
                                    "/bin")))
      (wrap-program (search-input-file outputs "bin/wg-quick")
        #:sh (search-input-file inputs "bin/bash")
        `("PATH" ":" prefix ,(list coreutils))))))
@end lisp

@subsection Program Invocation

@cindex program invocation, from Scheme
@cindex invoking programs, from Scheme
You'll find handy procedures to spawn processes in this module,
essentially convenient wrappers around Guile's @code{system*}
(@pxref{Processes, @code{system*},, guile, GNU Guile Reference Manual}).

@deffn {Procedure} invoke program args@dots{}
Invoke @var{program} with the given @var{args}.  Raise an
@code{&invoke-error} exception if the exit code is non-zero; otherwise
return @code{#t}.

The advantage compared to @code{system*} is that you do not need to
check the return value.  This reduces boilerplate in shell-script-like
snippets for instance in package build phases.
@end deffn

@deffn {Procedure} invoke-error? c
Return true if @var{c} is an @code{&invoke-error} condition.
@end deffn

@deffn {Procedure} invoke-error-program c
@deffnx {Procedure} invoke-error-arguments c
@deffnx {Procedure} invoke-error-exit-status c
@deffnx {Procedure} invoke-error-term-signal c
@deffnx {Procedure} invoke-error-stop-signal c
Access specific fields of @var{c}, an @code{&invoke-error} condition.
@end deffn

@deffn {Procedure} report-invoke-error c [port]
Report to @var{port} (by default the current error port) about @var{c},
an @code{&invoke-error} condition, in a human-friendly way.

Typical usage would look like this:

@lisp
(use-modules (srfi srfi-34) ;for 'guard'
             (guix build utils))

(guard (c ((invoke-error? c)
           (report-invoke-error c)))
  (invoke "date" "--imaginary-option"))

@print{} command "date" "--imaginary-option" failed with status 1
@end lisp
@end deffn

@deffn {Procedure} invoke/quiet program args@dots{}
Invoke @var{program} with @var{args} and capture @var{program}'s
standard output and standard error.  If @var{program} succeeds, print
nothing and return the unspecified value; otherwise, raise a
@code{&message} error condition that includes the status code and the
output of @var{program}.

Here's an example:

@lisp
(use-modules (srfi srfi-34) ;for 'guard'
             (srfi srfi-35) ;for 'message-condition?'
             (guix build utils))

(guard (c ((message-condition? c)
           (display (condition-message c))))
  (invoke/quiet "date")  ;all is fine
  (invoke/quiet "date" "--imaginary-option"))

@print{} 'date --imaginary-option' exited with status 1; output follows:

    date: unrecognized option '--imaginary-option'
    Try 'date --help' for more information.
@end lisp
@end deffn

@subsection Build Phases

@cindex build phases
The @code{(guix build utils)} also contains tools to manipulate build
phases as used by build systems (@pxref{Build Systems}).  Build phases
are represented as association lists or ``alists'' (@pxref{Association
Lists,,, guile, GNU Guile Reference Manual}) where each key is a symbol
naming the phase and the associated value is a procedure (@pxref{Build
Phases}).

Guile core and the @code{(srfi srfi-1)} module both provide tools to
manipulate alists.  The @code{(guix build utils)} module complements
those with tools written with build phases in mind.

@cindex build phases, modifying
@defmac modify-phases phases clause@dots{}
Modify @var{phases} sequentially as per each @var{clause}, which may
have one of the following forms:

@lisp
(delete @var{old-phase-name})
(replace @var{old-phase-name} @var{new-phase})
(add-before @var{old-phase-name} @var{new-phase-name} @var{new-phase})
(add-after @var{old-phase-name} @var{new-phase-name} @var{new-phase})
@end lisp

Where every @var{phase-name} above is an expression evaluating to a
symbol, and @var{new-phase} an expression evaluating to a procedure.
@end defmac

The example below is taken from the definition of the @code{grep}
package.  It adds a phase to run after the @code{install} phase, called
@code{fix-egrep-and-fgrep}.  That phase is a procedure (@code{lambda*}
is for anonymous procedures) that takes a @code{#:outputs} keyword
argument and ignores extra keyword arguments (@pxref{Optional
Arguments,,, guile, GNU Guile Reference Manual}, for more on
@code{lambda*} and optional and keyword arguments.)  The phase uses
@code{substitute*} to modify the installed @file{egrep} and @file{fgrep}
scripts so that they refer to @code{grep} by its absolute file name:

@lisp
(modify-phases %standard-phases
  (add-after 'install 'fix-egrep-and-fgrep
    ;; Patch 'egrep' and 'fgrep' to execute 'grep' via its
    ;; absolute file name instead of searching for it in $PATH.
    (lambda* (#:key outputs #:allow-other-keys)
      (let* ((out (assoc-ref outputs "out"))
             (bin (string-append out "/bin")))
        (substitute* (list (string-append bin "/egrep")
                           (string-append bin "/fgrep"))
          (("^exec grep")
           (string-append "exec " bin "/grep")))))))
@end lisp

In the example below, phases are modified in two ways: the standard
@code{configure} phase is deleted, presumably because the package does
not have a @file{configure} script or anything similar, and the default
@code{install} phase is replaced by one that manually copies the
executable files to be installed:

@lisp
(modify-phases %standard-phases
  (delete 'configure)      ;no 'configure' script
  (replace 'install
    (lambda* (#:key outputs #:allow-other-keys)
      ;; The package's Makefile doesn't provide an "install"
      ;; rule so do it by ourselves.
      (let ((bin (string-append (assoc-ref outputs "out")
                                "/bin")))
        (install-file "footswitch" bin)
        (install-file "scythe" bin)))))
@end lisp

@c TODO: Add more examples.

@subsection Wrappers

@cindex program wrappers
@cindex wrapping programs
It is not unusual for a command to require certain environment variables
to be set for proper functioning, typically search paths (@pxref{Search
Paths}).  Failing to do that, the command might fail to find files or
other commands it relies on, or it might pick the ``wrong''
ones---depending on the environment in which it runs.  Examples include:

@itemize
@item
a shell script that assumes all the commands it uses are in @env{PATH};

@item
a Guile program that assumes all its modules are in @env{GUILE_LOAD_PATH}
and @env{GUILE_LOAD_COMPILED_PATH};

@item
a Qt application that expects to find certain plugins in
@env{QT_PLUGIN_PATH}.
@end itemize

For a package writer, the goal is to make sure commands always work the
same rather than depend on some external settings.  One way to achieve
that is to @dfn{wrap} commands in a thin script that sets those
environment variables, thereby ensuring that those run-time dependencies
are always found.  The wrapper would be used to set @env{PATH},
@env{GUILE_LOAD_PATH}, or @env{QT_PLUGIN_PATH} in the examples above.

To ease that task, the @code{(guix build utils)} module provides a
couple of helpers to wrap commands.

@deffn {Procedure} wrap-program program [#:sh sh] [#:rest variables]
Make a wrapper for @var{program}.  @var{variables} should look like this:

@lisp
'(@var{variable} @var{delimiter} @var{position} @var{list-of-directories})
@end lisp

where @var{delimiter} is optional.  @code{:} will be used if
@var{delimiter} is not given.

For example, this call:

@lisp
(wrap-program "foo"
              '("PATH" ":" = ("/gnu/.../bar/bin"))
              '("CERT_PATH" suffix ("/gnu/.../baz/certs"
                                    "/qux/certs")))
@end lisp

will copy @file{foo} to @file{.foo-real} and create the file @file{foo}
with the following contents:

@example
#!location/of/bin/bash
export PATH="/gnu/.../bar/bin"
export CERT_PATH="$CERT_PATH$@{CERT_PATH:+:@}/gnu/.../baz/certs:/qux/certs"
exec -a $0 location/of/.foo-real "$@@"
@end example

If @var{program} has previously been wrapped by @code{wrap-program}, the
wrapper is extended with definitions for @var{variables}.  If it is not,
@var{sh} will be used as the interpreter.
@end deffn

@deffn {Procedure} wrap-script program [#:guile guile] [#:rest variables]
Wrap the script @var{program} such that @var{variables} are set first.
The format of @var{variables} is the same as in the @code{wrap-program}
procedure.  This procedure differs from @code{wrap-program} in that it
does not create a separate shell script.  Instead, @var{program} is
modified directly by prepending a Guile script, which is interpreted as
a comment in the script's language.

Special encoding comments as supported by Python are recreated on the
second line.

Note that this procedure can only be used once per file as Guile scripts are
not supported.
@end deffn

@node Search Paths
@section Search Paths

@cindex search path
Many programs and libraries look for input data in a @dfn{search path},
a list of directories: shells like Bash look for executables in the
command search path, a C compiler looks for @file{.h} files in its
header search path, the Python interpreter looks for @file{.py}
files in its search path, the spell checker has a search path for
dictionaries, and so on.

Search paths can usually be defined or overridden @i{via} environment
variables (@pxref{Environment Variables,,, libc, The GNU C Library
Reference Manual}).  For example, the search paths mentioned above can
be changed by defining the @env{PATH}, @env{C_INCLUDE_PATH},
@env{PYTHONPATH} (or @env{GUIX_PYTHONPATH}), and @env{DICPATH}
environment variables---you know, all these something-PATH variables
that you need to get right or things ``won't be found''.

You may have noticed from the command line that Guix ``knows'' which
search path environment variables should be defined, and how.  When you
install packages in your default profile, the file
@file{~/.guix-profile/etc/profile} is created, which you can ``source''
from the shell to set those variables.  Likewise, if you ask
@command{guix shell} to create an environment containing Python and
NumPy, a Python library, and if you pass it the @option{--search-paths}
option, it will tell you about @env{PATH} and @env{GUIX_PYTHONPATH}
(@pxref{Invoking guix shell}):

@example
$ guix shell python python-numpy --pure --search-paths
export PATH="/gnu/store/@dots{}-profile/bin"
export GUIX_PYTHONPATH="/gnu/store/@dots{}-profile/lib/python3.9/site-packages"
@end example

When you omit @option{--search-paths}, it defines these environment
variables right away, such that Python can readily find NumPy:

@example
$ guix shell python python-numpy -- python3
Python 3.9.6 (default, Jan  1 1970, 00:00:01)
[GCC 10.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import numpy
>>> numpy.version.version
'1.20.3'
@end example

For this to work, the definition of the @code{python} package
@emph{declares} the search path it cares about and its associated
environment variable, @env{GUIX_PYTHONPATH}.  It looks like this:

@lisp
(package
  (name "python")
  (version "3.9.9")
  ;; some fields omitted...
  (native-search-paths
   (list (search-path-specification
          (variable "GUIX_PYTHONPATH")
          (files (list "lib/python/3.9/site-packages"))))))
@end lisp

What this @code{native-search-paths} field says is that, when the
@code{python} package is used, the @env{GUIX_PYTHONPATH} environment
variable must be defined to include all the
@file{lib/python/3.9/site-packages} sub-directories encountered in its
environment.  (The @code{native-} bit means that, if we are in a
cross-compilation environment, only native inputs may be added to the
search path; @pxref{package Reference, @code{search-paths}}.)
In the NumPy example above, the profile where
@code{python} appears contains exactly one such sub-directory, and
@env{GUIX_PYTHONPATH} is set to that.  When there are several
@file{lib/python/3.9/site-packages}---this is the case in package build
environments---they are all added to @env{GUIX_PYTHONPATH}, separated by
colons (@code{:}).

@quotation Note
Notice that @env{GUIX_PYTHONPATH} is specified as part of the definition
of the @code{python} package, and @emph{not} as part of that of
@code{python-numpy}.  This is because this environment variable
``belongs'' to Python, not NumPy: Python actually reads the value of
that variable and honors it.

Corollary: if you create a profile that does not contain @code{python},
@code{GUIX_PYTHONPATH} will @emph{not} be defined, even if it contains
packages that provide @file{.py} files:

@example
$ guix shell python-numpy --search-paths --pure
export PATH="/gnu/store/@dots{}-profile/bin"
@end example

This makes a lot of sense if we look at this profile in isolation: no
software in this profile would read @env{GUIX_PYTHONPATH}.
@end quotation

Of course, there are many variations on that theme: some packages honor
more than one search path, some use separators other than colon, some
accumulate several directories in their search path, and so on.  A more
complex example is the search path of libxml2: the value of the
@env{XML_CATALOG_FILES} environment variable is space-separated, it must
contain a list of @file{catalog.xml} files (not directories), which are
to be found in @file{xml} sub-directories---nothing less.  The search
path specification looks like this:

@lisp
(package
  (name "libxml2")
  ;; some fields omitted
  (native-search-paths
   (list (search-path-specification
          (variable "XML_CATALOG_FILES")
          (separator " ")
          (files '("xml"))
          (file-pattern "^catalog\\.xml$")
          (file-type 'regular)))))
@end lisp

Worry not, search path specifications are usually not this tricky.

The @code{(guix search-paths)} module defines the data type of search
path specifications and a number of helper procedures.  Below is the
reference of search path specifications.

@deftp {Data Type} search-path-specification
The data type for search path specifications.

@table @asis
@item @code{variable}
The name of the environment variable for this search path (a string).

@item @code{files}
The list of sub-directories (strings) that should be added to the search
path.

@item @code{separator} (default: @code{":"})
The string used to separate search path components.

As a special case, a @code{separator} value of @code{#f} specifies a
``single-component search path''---in other words, a search path that
cannot contain more than one element.  This is useful in some cases,
such as the @code{SSL_CERT_DIR} variable (honored by OpenSSL, cURL, and
a few other packages) or the @code{ASPELL_DICT_DIR} variable (honored by
the GNU Aspell spell checker), both of which must point to a single
directory.

@item @code{file-type} (default: @code{'directory})
The type of file being matched---@code{'directory} or @code{'regular},
though it can be any symbol returned by @code{stat:type} (@pxref{File
System, @code{stat},, guile, GNU Guile Reference Manual}).

In the libxml2 example above, we would match regular files; in the
Python example, we would match directories.

@item @code{file-pattern} (default: @code{#f})
This must be either @code{#f} or a regular expression specifying
files to be matched @emph{within} the sub-directories specified by the
@code{files} field.

Again, the libxml2 example shows a situation where this is needed.
@end table
@end deftp

Some search paths are not tied by a single package but to many packages.
To reduce duplications, some of them are pre-defined in @code{(guix
search-paths)}.

@defvar $SSL_CERT_DIR
@defvarx $SSL_CERT_FILE
These two search paths indicate where X.509 certificates can be found
(@pxref{X.509 Certificates}).
@end defvar

These pre-defined search paths can be used as in the following example:

@lisp
(package
  (name "curl")
  ;; some fields omitted ...
  (native-search-paths (list $SSL_CERT_DIR $SSL_CERT_FILE)))
@end lisp

How do you turn search path specifications on one hand and a bunch of
directories on the other hand in a set of environment variable
definitions?  That's the job of @code{evaluate-search-paths}.

@deffn {Procedure} evaluate-search-paths search-paths directories [getenv]
Evaluate @var{search-paths}, a list of search-path specifications, for
@var{directories}, a list of directory names, and return a list of
specification/value pairs.  Use @var{getenv} to determine the current
settings and report only settings not already effective.
@end deffn

The @code{(guix profiles)} provides a higher-level helper procedure,
@code{load-profile}, that sets the environment variables of a profile.

@node The Store
@section The Store

@cindex store
@cindex store items
@cindex store paths

Conceptually, the @dfn{store} is the place where derivations that have
been built successfully are stored---by default, @file{/gnu/store}.
Sub-directories in the store are referred to as @dfn{store items} or
sometimes @dfn{store paths}.  The store has an associated database that
contains information such as the store paths referred to by each store
path, and the list of @emph{valid} store items---results of successful
builds.  This database resides in @file{@var{localstatedir}/guix/db},
where @var{localstatedir} is the state directory specified @i{via}
@option{--localstatedir} at configure time, usually @file{/var}.

The store is @emph{always} accessed by the daemon on behalf of its clients
(@pxref{Invoking guix-daemon}).  To manipulate the store, clients
connect to the daemon over a Unix-domain socket, send requests to it,
and read the result---these are remote procedure calls, or RPCs.

@quotation Note
Users must @emph{never} modify files under @file{/gnu/store} directly.
This would lead to inconsistencies and break the immutability
assumptions of Guix's functional model (@pxref{Introduction}).

@xref{Invoking guix gc, @command{guix gc --verify}}, for information on
how to check the integrity of the store and attempt recovery from
accidental modifications.
@end quotation

The @code{(guix store)} module provides procedures to connect to the
daemon, and to perform RPCs.  These are described below.  By default,
@code{open-connection}, and thus all the @command{guix} commands,
connect to the local daemon or to the URI specified by the
@env{GUIX_DAEMON_SOCKET} environment variable.

@defvr {Environment Variable} GUIX_DAEMON_SOCKET
When set, the value of this variable should be a file name or a URI
designating the daemon endpoint.  When it is a file name, it denotes a
Unix-domain socket to connect to.  In addition to file names, the
supported URI schemes are:

@table @code
@item file
@itemx unix
These are for Unix-domain sockets.
@code{file:///var/guix/daemon-socket/socket} is equivalent to
@file{/var/guix/daemon-socket/socket}.

@item guix
@cindex daemon, remote access
@cindex remote access to the daemon
@cindex daemon, cluster setup
@cindex clusters, daemon setup
These URIs denote connections over TCP/IP, without encryption nor
authentication of the remote host.  The URI must specify the host name
and optionally a port number (by default port 44146 is used):

@example
guix://master.guix.example.org:1234
@end example

This setup is suitable on local networks, such as clusters, where only
trusted nodes may connect to the build daemon at
@code{master.guix.example.org}.

The @option{--listen} option of @command{guix-daemon} can be used to
instruct it to listen for TCP connections (@pxref{Invoking guix-daemon,
@option{--listen}}).

@item ssh
@cindex SSH access to build daemons
These URIs allow you to connect to a remote daemon over SSH@.  This
feature requires Guile-SSH (@pxref{Requirements}) and a working
@command{guile} binary in @env{PATH} on the destination machine.  It
supports public key and GSSAPI authentication.  A typical URL might look
like this:

@example
ssh://charlie@@guix.example.org:22
@end example

As for @command{guix copy}, the usual OpenSSH client configuration files
are honored (@pxref{Invoking guix copy}).
@end table

Additional URI schemes may be supported in the future.

@c XXX: Remove this note when the protocol incurs fewer round trips
@c and when (guix derivations) no longer relies on file system access.
@quotation Note
The ability to connect to remote build daemons is considered
experimental as of @value{VERSION}.  Please get in touch with us to
share any problems or suggestions you may have (@pxref{Contributing}).
@end quotation
@end defvr

@deffn {Procedure} open-connection [uri] [#:reserve-space? #t]
Connect to the daemon over the Unix-domain socket at @var{uri} (a string).  When
@var{reserve-space?} is true, instruct it to reserve a little bit of
extra space on the file system so that the garbage collector can still
operate should the disk become full.  Return a server object.

@var{file} defaults to @code{%default-socket-path}, which is the normal
location given the options that were passed to @command{configure}.
@end deffn

@deffn {Procedure} close-connection server
Close the connection to @var{server}.
@end deffn

@defvar current-build-output-port
This variable is bound to a SRFI-39 parameter, which refers to the port
where build and error logs sent by the daemon should be written.
@end defvar

Procedures that make RPCs all take a server object as their first
argument.

@cindex invalid store items
@deffn {Procedure} valid-path? server path
Return @code{#t} when @var{path} designates a valid store item and
@code{#f} otherwise (an invalid item may exist on disk but still be
invalid, for instance because it is the result of an aborted or failed
build).

A @code{&store-protocol-error} condition is raised if @var{path} is not
prefixed by the store directory (@file{/gnu/store}).
@end deffn

@deffn {Procedure} add-text-to-store server name text [references]
Add @var{text} under file @var{name} in the store, and return its store
path.  @var{references} is the list of store paths referred to by the
resulting store path.
@end deffn

@deffn {Procedure} build-derivations store derivations [mode]
Build @var{derivations}, a list of @code{<derivation>} objects, @file{.drv}
file names, or derivation/output pairs, using the specified
@var{mode}---@code{(build-mode normal)} by default.
@end deffn

Note that the @code{(guix monads)} module provides a monad as well as
monadic versions of the above procedures, with the goal of making it
more convenient to work with code that accesses the store (@pxref{The
Store Monad}).

@c FIXME
@i{This section is currently incomplete.}

@node Derivations
@section Derivations

@cindex derivations
Low-level build actions and the environment in which they are performed
are represented by @dfn{derivations}.  A derivation contains the
following pieces of information:

@itemize
@item
The outputs of the derivation---derivations produce at least one file or
directory in the store, but may produce more.

@item
@cindex build-time dependencies
@cindex dependencies, build-time
The inputs of the derivation---i.e., its build-time dependencies---which may
be other derivations or plain files in the store (patches, build scripts,
etc.).

@item
The system type targeted by the derivation---e.g., @code{x86_64-linux}.

@item
The file name of a build script in the store, along with the arguments
to be passed.

@item
A list of environment variables to be defined.

@end itemize

@cindex derivation path
Derivations allow clients of the daemon to communicate build actions to
the store.  They exist in two forms: as an in-memory representation,
both on the client- and daemon-side, and as files in the store whose
name end in @file{.drv}---these files are referred to as @dfn{derivation
paths}.  Derivations paths can be passed to the @code{build-derivations}
procedure to perform the build actions they prescribe (@pxref{The
Store}).

@cindex fixed-output derivations
Operations such as file downloads and version-control checkouts for
which the expected content hash is known in advance are modeled as
@dfn{fixed-output derivations}.  Unlike regular derivations, the outputs
of a fixed-output derivation are independent of its inputs---e.g., a
source code download produces the same result regardless of the download
method and tools being used.

@cindex references
@cindex run-time dependencies
@cindex dependencies, run-time
The outputs of derivations---i.e., the build results---have a set of
@dfn{references}, as reported by the @code{references} RPC or the
@command{guix gc --references} command (@pxref{Invoking guix gc}).  References
are the set of run-time dependencies of the build results.  References are a
subset of the inputs of the derivation; this subset is automatically computed
by the build daemon by scanning all the files in the outputs.

The @code{(guix derivations)} module provides a representation of
derivations as Scheme objects, along with procedures to create and
otherwise manipulate derivations.  The lowest-level primitive to create
a derivation is the @code{derivation} procedure:

@deffn {Procedure} derivation store name builder args @
  [#:outputs '("out")] [#:hash #f] [#:hash-algo #f] @
  [#:recursive? #f] [#:inputs '()] [#:env-vars '()] @
  [#:system (%current-system)] [#:references-graphs #f] @
  [#:allowed-references #f] [#:disallowed-references #f] @
  [#:leaked-env-vars #f] [#:local-build? #f] @
  [#:substitutable? #t] [#:properties '()]
Build a derivation with the given arguments, and return the resulting
@code{<derivation>} object.

When @var{hash} and @var{hash-algo} are given, a
@dfn{fixed-output derivation} is created---i.e., one whose result is
known in advance, such as a file download.  If, in addition,
@var{recursive?} is true, then that fixed output may be an executable
file or a directory and @var{hash} must be the hash of an archive
containing this output.

When @var{references-graphs} is true, it must be a list of file
name/store path pairs.  In that case, the reference graph of each store
path is exported in the build environment in the corresponding file, in
a simple text format.

When @var{allowed-references} is true, it must be a list of store items
or outputs that the derivation's output may refer to.  Likewise,
@var{disallowed-references}, if true, must be a list of things the
outputs may @emph{not} refer to.

When @var{leaked-env-vars} is true, it must be a list of strings
denoting environment variables that are allowed to ``leak'' from the
daemon's environment to the build environment.  This is only applicable
to fixed-output derivations---i.e., when @var{hash} is true.  The main
use is to allow variables such as @code{http_proxy} to be passed to
derivations that download files.

When @var{local-build?} is true, declare that the derivation is not a
good candidate for offloading and should rather be built locally
(@pxref{Daemon Offload Setup}).  This is the case for small derivations
where the costs of data transfers would outweigh the benefits.

When @var{substitutable?} is false, declare that substitutes of the
derivation's output should not be used (@pxref{Substitutes}).  This is
useful, for instance, when building packages that capture details of the
host CPU instruction set.

@var{properties} must be an association list describing ``properties'' of the
derivation.  It is kept as-is, uninterpreted, in the derivation.
@end deffn

@noindent
Here's an example with a shell script as its builder, assuming
@var{store} is an open connection to the daemon, and @var{bash} points
to a Bash executable in the store:

@lisp
(use-modules (guix utils)
             (guix store)
             (guix derivations))

(let ((builder   ; add the Bash script to the store
        (add-text-to-store store "my-builder.sh"
                           "echo hello world > $out\n" '())))
  (derivation store "foo"
              bash `("-e" ,builder)
              #:inputs `((,bash) (,builder))
              #:env-vars '(("HOME" . "/homeless"))))
@result{} #<derivation /gnu/store/@dots{}-foo.drv => /gnu/store/@dots{}-foo>
@end lisp

As can be guessed, this primitive is cumbersome to use directly.  A
better approach is to write build scripts in Scheme, of course!  The
best course of action for that is to write the build code as a
``G-expression'', and to pass it to @code{gexp->derivation}.  For more
information, @pxref{G-Expressions}.

Once upon a time, @code{gexp->derivation} did not exist and constructing
derivations with build code written in Scheme was achieved with
@code{build-expression->derivation}, documented below.  This procedure
is now deprecated in favor of the much nicer @code{gexp->derivation}.

@deffn {Procedure} build-expression->derivation store name exp @
       [#:system (%current-system)] [#:inputs '()] @
       [#:outputs '("out")] [#:hash #f] [#:hash-algo #f] @
       [#:recursive? #f] [#:env-vars '()] [#:modules '()] @
       [#:references-graphs #f] [#:allowed-references #f] @
       [#:disallowed-references #f] @
       [#:local-build? #f] [#:substitutable? #t] [#:guile-for-build #f]
Return a derivation that executes Scheme expression @var{exp} as a
builder for derivation @var{name}.  @var{inputs} must be a list of
@code{(name drv-path sub-drv)} tuples; when @var{sub-drv} is omitted,
@code{"out"} is assumed.  @var{modules} is a list of names of Guile
modules from the current search path to be copied in the store,
compiled, and made available in the load path during the execution of
@var{exp}---e.g., @code{((guix build utils) (guix build
gnu-build-system))}.

@var{exp} is evaluated in an environment where @code{%outputs} is bound
to a list of output/path pairs, and where @code{%build-inputs} is bound
to a list of string/output-path pairs made from @var{inputs}.
Optionally, @var{env-vars} is a list of string pairs specifying the name
and value of environment variables visible to the builder.  The builder
terminates by passing the result of @var{exp} to @code{exit}; thus, when
@var{exp} returns @code{#f}, the build is considered to have failed.

@var{exp} is built using @var{guile-for-build} (a derivation).  When
@var{guile-for-build} is omitted or is @code{#f}, the value of the
@code{%guile-for-build} fluid is used instead.

See the @code{derivation} procedure for the meaning of
@var{references-graphs}, @var{allowed-references},
@var{disallowed-references}, @var{local-build?}, and
@var{substitutable?}.
@end deffn

@noindent
Here's an example of a single-output derivation that creates a directory
containing one file:

@lisp
(let ((builder '(let ((out (assoc-ref %outputs "out")))
                  (mkdir out)    ; create /gnu/store/@dots{}-goo
                  (call-with-output-file (string-append out "/test")
                    (lambda (p)
                      (display '(hello guix) p))))))
  (build-expression->derivation store "goo" builder))

@result{} #<derivation /gnu/store/@dots{}-goo.drv => @dots{}>
@end lisp


@node The Store Monad
@section The Store Monad

@cindex monad

The procedures that operate on the store described in the previous
sections all take an open connection to the build daemon as their first
argument.  Although the underlying model is functional, they either have
side effects or depend on the current state of the store.

The former is inconvenient: the connection to the build daemon has to be
carried around in all those functions, making it impossible to compose
functions that do not take that parameter with functions that do.  The
latter can be problematic: since store operations have side effects
and/or depend on external state, they have to be properly sequenced.

@cindex monadic values
@cindex monadic functions
This is where the @code{(guix monads)} module comes in.  This module
provides a framework for working with @dfn{monads}, and a particularly
useful monad for our uses, the @dfn{store monad}.  Monads are a
construct that allows two things: associating ``context'' with values
(in our case, the context is the store), and building sequences of
computations (here computations include accesses to the store).  Values
in a monad---values that carry this additional context---are called
@dfn{monadic values}; procedures that return such values are called
@dfn{monadic procedures}.

Consider this ``normal'' procedure:

@lisp
(define (sh-symlink store)
  ;; Return a derivation that symlinks the 'bash' executable.
  (let* ((drv (package-derivation store bash))
         (out (derivation->output-path drv))
         (sh  (string-append out "/bin/bash")))
    (build-expression->derivation store "sh"
                                  `(symlink ,sh %output))))
@end lisp

Using @code{(guix monads)} and @code{(guix gexp)}, it may be rewritten
as a monadic function:

@lisp
(define (sh-symlink)
  ;; Same, but return a monadic value.
  (mlet %store-monad ((drv (package->derivation bash)))
    (gexp->derivation "sh"
                      #~(symlink (string-append #$drv "/bin/bash")
                                 #$output))))
@end lisp

There are several things to note in the second version: the @code{store}
parameter is now implicit and is ``threaded'' in the calls to the
@code{package->derivation} and @code{gexp->derivation} monadic
procedures, and the monadic value returned by @code{package->derivation}
is @dfn{bound} using @code{mlet} instead of plain @code{let}.

As it turns out, the call to @code{package->derivation} can even be
omitted since it will take place implicitly, as we will see later
(@pxref{G-Expressions}):

@lisp
(define (sh-symlink)
  (gexp->derivation "sh"
                    #~(symlink (string-append #$bash "/bin/bash")
                               #$output)))
@end lisp

@c See
@c <https://syntaxexclamation.wordpress.com/2014/06/26/escaping-continuations/>
@c for the funny quote.
Calling the monadic @code{sh-symlink} has no effect.  As someone once
said, ``you exit a monad like you exit a building on fire: by running''.
So, to exit the monad and get the desired effect, one must use
@code{run-with-store}:

@lisp
(run-with-store (open-connection) (sh-symlink))
@result{} /gnu/store/...-sh-symlink
@end lisp

Note that the @code{(guix monad-repl)} module extends the Guile REPL with
new ``commands'' to make it easier to deal with monadic procedures:
@code{run-in-store}, and @code{enter-store-monad} (@pxref{Using Guix
Interactively}).  The former is used
to ``run'' a single monadic value through the store:

@example
scheme@@(guile-user)> ,run-in-store (package->derivation hello)
$1 = #<derivation /gnu/store/@dots{}-hello-2.9.drv => @dots{}>
@end example

The latter enters a recursive REPL, where all the return values are
automatically run through the store:

@example
scheme@@(guile-user)> ,enter-store-monad
store-monad@@(guile-user) [1]> (package->derivation hello)
$2 = #<derivation /gnu/store/@dots{}-hello-2.9.drv => @dots{}>
store-monad@@(guile-user) [1]> (text-file "foo" "Hello!")
$3 = "/gnu/store/@dots{}-foo"
store-monad@@(guile-user) [1]> ,q
scheme@@(guile-user)>
@end example

@noindent
Note that non-monadic values cannot be returned in the
@code{store-monad} REPL.

Other meta-commands are available at the REPL, such as @code{,build} to
build a file-like object (@pxref{Using Guix Interactively}).

The main syntactic forms to deal with monads in general are provided by
the @code{(guix monads)} module and are described below.

@defmac with-monad monad body @dots{}
Evaluate any @code{>>=} or @code{return} forms in @var{body} as being
in @var{monad}.
@end defmac

@defmac return val
Return a monadic value that encapsulates @var{val}.
@end defmac

@defmac >>= mval mproc @dots{}
@dfn{Bind} monadic value @var{mval}, passing its ``contents'' to monadic
procedures @var{mproc}@dots{}@footnote{This operation is commonly
referred to as ``bind'', but that name denotes an unrelated procedure in
Guile.  Thus we use this somewhat cryptic symbol inherited from the
Haskell language.}.  There can be one @var{mproc} or several of them, as
in this example:

@lisp
(run-with-state
    (with-monad %state-monad
      (>>= (return 1)
           (lambda (x) (return (+ 1 x)))
           (lambda (x) (return (* 2 x)))))
  'some-state)

@result{} 4
@result{} some-state
@end lisp
@end defmac

@defmac mlet monad ((var mval) @dots{}) body @dots{}
@defmacx mlet* monad ((var mval) @dots{}) body @dots{}
Bind the variables @var{var} to the monadic values @var{mval} in
@var{body}, which is a sequence of expressions.  As with the bind
operator, this can be thought of as ``unpacking'' the raw, non-monadic
value ``contained'' in @var{mval} and making @var{var} refer to that
raw, non-monadic value within the scope of the @var{body}.  The form
(@var{var} -> @var{val}) binds @var{var} to the ``normal'' value
@var{val}, as per @code{let}.  The binding operations occur in sequence
from left to right.  The last expression of @var{body} must be a monadic
expression, and its result will become the result of the @code{mlet} or
@code{mlet*} when run in the @var{monad}.

@code{mlet*} is to @code{mlet} what @code{let*} is to @code{let}
(@pxref{Local Bindings,,, guile, GNU Guile Reference Manual}).
@end defmac

@defmac mbegin monad mexp @dots{}
Bind @var{mexp} and the following monadic expressions in sequence,
returning the result of the last expression.  Every expression in the
sequence must be a monadic expression.

This is akin to @code{mlet}, except that the return values of the
monadic expressions are ignored.  In that sense, it is analogous to
@code{begin}, but applied to monadic expressions.
@end defmac

@defmac mwhen condition mexp0 mexp* @dots{}
When @var{condition} is true, evaluate the sequence of monadic
expressions @var{mexp0}..@var{mexp*} as in an @code{mbegin}.  When
@var{condition} is false, return @code{*unspecified*} in the current
monad.  Every expression in the sequence must be a monadic expression.
@end defmac

@defmac munless condition mexp0 mexp* @dots{}
When @var{condition} is false, evaluate the sequence of monadic
expressions @var{mexp0}..@var{mexp*} as in an @code{mbegin}.  When
@var{condition} is true, return @code{*unspecified*} in the current
monad.  Every expression in the sequence must be a monadic expression.
@end defmac

@cindex state monad
The @code{(guix monads)} module provides the @dfn{state monad}, which
allows an additional value---the state---to be @emph{threaded} through
monadic procedure calls.

@defvar %state-monad
The state monad.  Procedures in the state monad can access and change
the state that is threaded.

Consider the example below.  The @code{square} procedure returns a value
in the state monad.  It returns the square of its argument, but also
increments the current state value:

@lisp
(define (square x)
  (mlet %state-monad ((count (current-state)))
    (mbegin %state-monad
      (set-current-state (+ 1 count))
      (return (* x x)))))

(run-with-state (sequence %state-monad (map square (iota 3))) 0)
@result{} (0 1 4)
@result{} 3
@end lisp

When ``run'' through @code{%state-monad}, we obtain that additional state
value, which is the number of @code{square} calls.
@end defvar

@deffn {Monadic Procedure} current-state
Return the current state as a monadic value.
@end deffn

@deffn {Monadic Procedure} set-current-state @var{value}
Set the current state to @var{value} and return the previous state as a
monadic value.
@end deffn

@deffn {Monadic Procedure} state-push @var{value}
Push @var{value} to the current state, which is assumed to be a list,
and return the previous state as a monadic value.
@end deffn

@deffn {Monadic Procedure} state-pop
Pop a value from the current state and return it as a monadic value.
The state is assumed to be a list.
@end deffn

@deffn {Procedure} run-with-state mval [state]
Run monadic value @var{mval} starting with @var{state} as the initial
state.  Return two values: the resulting value, and the resulting state.
@end deffn

The main interface to the store monad, provided by the @code{(guix
store)} module, is as follows.

@defvar %store-monad
The store monad---an alias for @code{%state-monad}.

Values in the store monad encapsulate accesses to the store.  When its
effect is needed, a value of the store monad must be ``evaluated'' by
passing it to the @code{run-with-store} procedure (see below).
@end defvar

@deffn {Procedure} run-with-store store mval @
  [#:guile-for-build] [#:system (%current-system)]
Run @var{mval}, a monadic value in the store monad, in @var{store}, an
open store connection.
@end deffn

@deffn {Monadic Procedure} text-file @var{name} @var{text} [@var{references}]
Return as a monadic value the absolute file name in the store of the file
containing @var{text}, a string.  @var{references} is a list of store items that the
resulting text file refers to; it defaults to the empty list.
@end deffn

@deffn {Monadic Procedure} binary-file @var{name} @var{data} [@var{references}]
Return as a monadic value the absolute file name in the store of the file
containing @var{data}, a bytevector.  @var{references} is a list of store
items that the resulting binary file refers to; it defaults to the empty list.
@end deffn

@deffn {Monadic Procedure} interned-file @var{file} [@var{name}] @
         [#:recursive? #t] [#:select? (const #t)]
Return the name of @var{file} once interned in the store.  Use
@var{name} as its store name, or the basename of @var{file} if
@var{name} is omitted.

When @var{recursive?} is true, the contents of @var{file} are added
recursively; if @var{file} designates a flat file and @var{recursive?}
is true, its contents are added, and its permission bits are kept.

When @var{recursive?} is true, call @code{(@var{select?} @var{file}
@var{stat})} for each directory entry, where @var{file} is the entry's
absolute file name and @var{stat} is the result of @code{lstat}; exclude
entries for which @var{select?} does not return true.

The example below adds a file to the store, under two different names:

@lisp
(run-with-store (open-connection)
  (mlet %store-monad ((a (interned-file "README"))
                      (b (interned-file "README" "LEGU-MIN")))
    (return (list a b))))

@result{} ("/gnu/store/rwm@dots{}-README" "/gnu/store/44i@dots{}-LEGU-MIN")
@end lisp

@end deffn

The @code{(guix packages)} module exports the following package-related
monadic procedures:

@deffn {Monadic Procedure} package-file @var{package} [@var{file}] @
       [#:system (%current-system)] [#:target #f] @
       [#:output "out"]
Return as a monadic
value in the absolute file name of @var{file} within the @var{output}
directory of @var{package}.  When @var{file} is omitted, return the name
of the @var{output} directory of @var{package}.  When @var{target} is
true, use it as a cross-compilation target triplet.

Note that this procedure does @emph{not} build @var{package}.  Thus, the
result might or might not designate an existing file.  We recommend not
using this procedure unless you know what you are doing.
@end deffn

@deffn {Monadic Procedure} package->derivation @var{package} [@var{system}]
@deffnx {Monadic Procedure} package->cross-derivation @var{package} @
          @var{target} [@var{system}]
Monadic version of @code{package-derivation} and
@code{package-cross-derivation} (@pxref{Defining Packages}).
@end deffn


@node G-Expressions
@section G-Expressions

@cindex G-expression
@cindex build code quoting
So we have ``derivations'', which represent a sequence of build actions
to be performed to produce an item in the store (@pxref{Derivations}).
These build actions are performed when asking the daemon to actually
build the derivations; they are run by the daemon in a container
(@pxref{Invoking guix-daemon}).

@cindex code staging
@cindex staging, of code
@cindex strata of code
It should come as no surprise that we like to write these build actions
in Scheme.  When we do that, we end up with two @dfn{strata} of Scheme
code@footnote{The term @dfn{stratum} in this context was coined by
Manuel Serrano et al.@: in the context of their work on Hop.  Oleg
Kiselyov, who has written insightful
@url{http://okmij.org/ftp/meta-programming/#meta-scheme, essays and code
on this topic}, refers to this kind of code generation as
@dfn{staging}.}: the ``host code''---code that defines packages, talks
to the daemon, etc.---and the ``build code''---code that actually
performs build actions, such as making directories, invoking
@command{make}, and so on (@pxref{Build Phases}).

To describe a derivation and its build actions, one typically needs to
embed build code inside host code.  It boils down to manipulating build
code as data, and the homoiconicity of Scheme---code has a direct
representation as data---comes in handy for that.  But we need more than
the normal @code{quasiquote} mechanism in Scheme to construct build
expressions.

The @code{(guix gexp)} module implements @dfn{G-expressions}, a form of
S-expressions adapted to build expressions.  G-expressions, or
@dfn{gexps}, consist essentially of three syntactic forms: @code{gexp},
@code{ungexp}, and @code{ungexp-splicing} (or simply: @code{#~},
@code{#$}, and @code{#$@@}), which are comparable to
@code{quasiquote}, @code{unquote}, and @code{unquote-splicing},
respectively (@pxref{Expression Syntax, @code{quasiquote},, guile,
GNU Guile Reference Manual}).  However, there are major differences:

@itemize
@item
Gexps are meant to be written to a file and run or manipulated by other
processes.

@item
When a high-level object such as a package or derivation is unquoted
inside a gexp, the result is as if its output file name had been
introduced.

@item
Gexps carry information about the packages or derivations they refer to,
and these dependencies are automatically added as inputs to the build
processes that use them.
@end itemize

@cindex lowering, of high-level objects in gexps
This mechanism is not limited to package and derivation
objects: @dfn{compilers} able to ``lower'' other high-level objects to
derivations or files in the store can be defined,
such that these objects can also be inserted
into gexps.  For example, a useful type of high-level objects that can be
inserted in a gexp is ``file-like objects'', which make it easy to
add files to the store and to refer to them in
derivations and such (see @code{local-file} and @code{plain-file}
below).

To illustrate the idea, here is an example of a gexp:

@lisp
(define build-exp
  #~(begin
      (mkdir #$output)
      (chdir #$output)
      (symlink (string-append #$coreutils "/bin/ls")
               "list-files")))
@end lisp

This gexp can be passed to @code{gexp->derivation}; we obtain a
derivation that builds a directory containing exactly one symlink to
@file{/gnu/store/@dots{}-coreutils-8.22/bin/ls}:

@lisp
(gexp->derivation "the-thing" build-exp)
@end lisp

As one would expect, the @code{"/gnu/store/@dots{}-coreutils-8.22"} string is
substituted to the reference to the @var{coreutils} package in the
actual build code, and @var{coreutils} is automatically made an input to
the derivation.  Likewise, @code{#$output} (equivalent to @code{(ungexp
output)}) is replaced by a string containing the directory name of the
output of the derivation.

@cindex cross compilation
In a cross-compilation context, it is useful to distinguish between
references to the @emph{native} build of a package---that can run on the
host---versus references to cross builds of a package.  To that end, the
@code{#+} plays the same role as @code{#$}, but is a reference to a
native package build:

@lisp
(gexp->derivation "vi"
   #~(begin
       (mkdir #$output)
       (mkdir (string-append #$output "/bin"))
       (system* (string-append #+coreutils "/bin/ln")
                "-s"
                (string-append #$emacs "/bin/emacs")
                (string-append #$output "/bin/vi")))
   #:target "aarch64-linux-gnu")
@end lisp

@noindent
In the example above, the native build of @var{coreutils} is used, so
that @command{ln} can actually run on the host; but then the
cross-compiled build of @var{emacs} is referenced.

@cindex imported modules, for gexps
@findex with-imported-modules
Another gexp feature is @dfn{imported modules}: sometimes you want to be
able to use certain Guile modules from the ``host environment'' in the
gexp, so those modules should be imported in the ``build environment''.
The @code{with-imported-modules} form allows you to express that:

@lisp
(let ((build (with-imported-modules '((guix build utils))
               #~(begin
                   (use-modules (guix build utils))
                   (mkdir-p (string-append #$output "/bin"))))))
  (gexp->derivation "empty-dir"
                    #~(begin
                        #$build
                        (display "success!\n")
                        #t)))
@end lisp

@noindent
In this example, the @code{(guix build utils)} module is automatically
pulled into the isolated build environment of our gexp, such that
@code{(use-modules (guix build utils))} works as expected.

@cindex module closure
@findex source-module-closure
Usually you want the @emph{closure} of the module to be imported---i.e.,
the module itself and all the modules it depends on---rather than just
the module; failing to do that, attempts to use the module will fail
because of missing dependent modules.  The @code{source-module-closure}
procedure computes the closure of a module by looking at its source file
headers, which comes in handy in this case:

@lisp
(use-modules (guix modules))   ;for 'source-module-closure'

(with-imported-modules (source-module-closure
                         '((guix build utils)
                           (gnu build image)))
  (gexp->derivation "something-with-vms"
                    #~(begin
                        (use-modules (guix build utils)
                                     (gnu build image))
                        @dots{})))
@end lisp

@cindex extensions, for gexps
@findex with-extensions
In the same vein, sometimes you want to import not just pure-Scheme
modules, but also ``extensions'' such as Guile bindings to C libraries
or other ``full-blown'' packages.  Say you need the @code{guile-json}
package available on the build side, here's how you would do it:

@lisp
(use-modules (gnu packages guile))  ;for 'guile-json'

(with-extensions (list guile-json)
  (gexp->derivation "something-with-json"
                    #~(begin
                        (use-modules (json))
                        @dots{})))
@end lisp

The syntactic form to construct gexps is summarized below.

@defmac #~@var{exp}
@defmacx (gexp @var{exp})
Return a G-expression containing @var{exp}.  @var{exp} may contain one
or more of the following forms:

@table @code
@item #$@var{obj}
@itemx (ungexp @var{obj})
Introduce a reference to @var{obj}.  @var{obj} may have one of the
supported types, for example a package or a
derivation, in which case the @code{ungexp} form is replaced by its
output file name---e.g., @code{"/gnu/store/@dots{}-coreutils-8.22}.

If @var{obj} is a list, it is traversed and references to supported
objects are substituted similarly.

If @var{obj} is another gexp, its contents are inserted and its
dependencies are added to those of the containing gexp.

If @var{obj} is another kind of object, it is inserted as is.

@item #$@var{obj}:@var{output}
@itemx (ungexp @var{obj} @var{output})
This is like the form above, but referring explicitly to the
@var{output} of @var{obj}---this is useful when @var{obj} produces
multiple outputs (@pxref{Packages with Multiple Outputs}).

Sometimes a gexp unconditionally refers to the @code{"out"} output, but
the user of that gexp would still like to insert a reference to another
output.  The @code{gexp-input} procedure aims to address that.
@xref{gexp-input}.

@item #+@var{obj}
@itemx #+@var{obj}:output
@itemx (ungexp-native @var{obj})
@itemx (ungexp-native @var{obj} @var{output})
Same as @code{ungexp}, but produces a reference to the @emph{native}
build of @var{obj} when used in a cross compilation context.

@item #$output[:@var{output}]
@itemx (ungexp output [@var{output}])
Insert a reference to derivation output @var{output}, or to the main
output when @var{output} is omitted.

This only makes sense for gexps passed to @code{gexp->derivation}.

@item #$@@@var{lst}
@itemx (ungexp-splicing @var{lst})
Like the above, but splices the contents of @var{lst} inside the
containing list.

@item #+@@@var{lst}
@itemx (ungexp-native-splicing @var{lst})
Like the above, but refers to native builds of the objects listed in
@var{lst}.

@end table

G-expressions created by @code{gexp} or @code{#~} are run-time objects
of the @code{gexp?} type (see below).
@end defmac

@defmac with-imported-modules modules body@dots{}
Mark the gexps defined in @var{body}@dots{} as requiring @var{modules}
in their execution environment.

Each item in @var{modules} can be the name of a module, such as
@code{(guix build utils)}, or it can be a module name, followed by an
arrow, followed by a file-like object:

@lisp
`((guix build utils)
  (guix gcrypt)
  ((guix config) => ,(scheme-file "config.scm"
                                  #~(define-module @dots{}))))
@end lisp

@noindent
In the example above, the first two modules are taken from the search
path, and the last one is created from the given file-like object.

This form has @emph{lexical} scope: it has an effect on the gexps
directly defined in @var{body}@dots{}, but not on those defined, say, in
procedures called from @var{body}@dots{}.
@end defmac

@defmac with-extensions extensions body@dots{}
Mark the gexps defined in @var{body}@dots{} as requiring
@var{extensions} in their build and execution environment.
@var{extensions} is typically a list of package objects such as those
defined in the @code{(gnu packages guile)} module.

Concretely, the packages listed in @var{extensions} are added to the
load path while compiling imported modules in @var{body}@dots{}; they
are also added to the load path of the gexp returned by
@var{body}@dots{}.
@end defmac

@deffn {Procedure} gexp? obj
Return @code{#t} if @var{obj} is a G-expression.
@end deffn

G-expressions are meant to be written to disk, either as code building
some derivation, or as plain files in the store.  The monadic procedures
below allow you to do that (@pxref{The Store Monad}, for more
information about monads).

@deffn {Monadic Procedure} gexp->derivation @var{name} @var{exp} @
       [#:system (%current-system)] [#:target #f] [#:graft? #t] @
       [#:hash #f] [#:hash-algo #f] @
       [#:recursive? #f] [#:env-vars '()] [#:modules '()] @
       [#:module-path @code{%load-path}] @
       [#:effective-version "2.2"] @
       [#:references-graphs #f] [#:allowed-references #f] @
       [#:disallowed-references #f] @
       [#:leaked-env-vars #f] @
       [#:script-name (string-append @var{name} "-builder")] @
       [#:deprecation-warnings #f] @
       [#:local-build? #f] [#:substitutable? #t] @
       [#:properties '()] [#:guile-for-build #f]
Return a derivation @var{name} that runs @var{exp} (a gexp) with
@var{guile-for-build} (a derivation) on @var{system}; @var{exp} is
stored in a file called @var{script-name}.  When @var{target} is true,
it is used as the cross-compilation target triplet for packages referred
to by @var{exp}.

@var{modules} is deprecated in favor of @code{with-imported-modules}.
Its meaning is to
make @var{modules} available in the evaluation context of @var{exp};
@var{modules} is a list of names of Guile modules searched in
@var{module-path} to be copied in the store, compiled, and made available in
the load path during the execution of @var{exp}---e.g., @code{((guix
build utils) (guix build gnu-build-system))}.

@var{effective-version} determines the string to use when adding extensions of
@var{exp} (see @code{with-extensions}) to the search path---e.g., @code{"2.2"}.

@var{graft?} determines whether packages referred to by @var{exp} should be grafted when
applicable.

When @var{references-graphs} is true, it must be a list of tuples of one of the
following forms:

@example
(@var{file-name} @var{obj})
(@var{file-name} @var{obj} @var{output})
(@var{file-name} @var{gexp-input})
(@var{file-name} @var{store-item})
@end example

The right-hand-side of each element of @var{references-graphs} is automatically made
an input of the build process of @var{exp}.  In the build environment, each
@var{file-name} contains the reference graph of the corresponding item, in a simple
text format.

@var{allowed-references} must be either @code{#f} or a list of output names and packages.
In the latter case, the list denotes store items that the result is allowed to
refer to.  Any reference to another store item will lead to a build error.
Similarly for @var{disallowed-references}, which can list items that must not be
referenced by the outputs.

@var{deprecation-warnings} determines whether to show deprecation warnings while
compiling modules.  It can be @code{#f}, @code{#t}, or @code{'detailed}.

The other arguments are as for @code{derivation} (@pxref{Derivations}).
@end deffn

@cindex file-like objects
The @code{local-file}, @code{plain-file}, @code{computed-file},
@code{program-file}, and @code{scheme-file} procedures below return
@dfn{file-like objects}.  That is, when unquoted in a G-expression,
these objects lead to a file in the store.  Consider this G-expression:

@lisp
#~(system* #$(file-append glibc "/sbin/nscd") "-f"
           #$(local-file "/tmp/my-nscd.conf"))
@end lisp

The effect here is to ``intern'' @file{/tmp/my-nscd.conf} by copying it
to the store.  Once expanded, for instance @i{via}
@code{gexp->derivation}, the G-expression refers to that copy under
@file{/gnu/store}; thus, modifying or removing the file in @file{/tmp}
does not have any effect on what the G-expression does.
@code{plain-file} can be used similarly; it differs in that the file
content is directly passed as a string.

@deffn {Procedure} local-file file [name] [#:recursive? #f] [#:select? (const #t)]
Return an object representing local file @var{file} to add to the store;
this object can be used in a gexp.  If @var{file} is a literal string
denoting a relative file name, it is looked up relative to the source
file where it appears; if @var{file} is not a literal string, it is
looked up relative to the current working directory at run time.
@var{file} will be added to the store under @var{name}--by default the
base name of @var{file}.

When @var{recursive?} is true, the contents of @var{file} are added recursively; if @var{file}
designates a flat file and @var{recursive?} is true, its contents are added, and its
permission bits are kept.

When @var{recursive?} is true, call @code{(@var{select?} @var{file}
@var{stat})} for each directory entry, where @var{file} is the entry's
absolute file name and @var{stat} is the result of @code{lstat}; exclude
entries for which @var{select?} does not return true.

@var{file} can be wrapped in the @code{assume-valid-file-name} syntactic
keyword. When this is done, there will not be a warning when
@code{local-file} is used with a non-literal path.  The path is still
looked up relative to the current working directory at run time.
Wrapping is done like this:

@lisp
(define alice-key-file-path "alice.pub")
;; ...
(local-file (assume-valid-file-name alice-key-file-path))
@end lisp

This is the declarative counterpart of the @code{interned-file} monadic
procedure (@pxref{The Store Monad, @code{interned-file}}).
@end deffn

@deffn {Procedure} plain-file name content
Return an object representing a text file called @var{name} with the given
@var{content} (a string or a bytevector) to be added to the store.

This is the declarative counterpart of @code{text-file}.
@end deffn

@deffn {Procedure} computed-file name gexp [#:local-build? #t] [#:options '()]
Return an object representing the store item @var{name}, a file or
directory computed by @var{gexp}.  When @var{local-build?} is true (the
default), the derivation is built locally.  @var{options} is a list of
additional arguments to pass to @code{gexp->derivation}.

This is the declarative counterpart of @code{gexp->derivation}.
@end deffn

@deffn {Monadic Procedure} gexp->script @var{name} @var{exp} @
  [#:guile (default-guile)] [#:module-path %load-path] @
  [#:system (%current-system)] [#:target #f]
Return an executable script @var{name} that runs @var{exp} using
@var{guile}, with @var{exp}'s imported modules in its search path.
Look up @var{exp}'s modules in @var{module-path}.

The example below builds a script that simply invokes the @command{ls}
command:

@lisp
(use-modules (guix gexp) (gnu packages base))

(gexp->script "list-files"
              #~(execl #$(file-append coreutils "/bin/ls")
                       "ls"))
@end lisp

When ``running'' it through the store (@pxref{The Store Monad,
@code{run-with-store}}), we obtain a derivation that produces an
executable file @file{/gnu/store/@dots{}-list-files} along these lines:

@example
#!/gnu/store/@dots{}-guile-2.0.11/bin/guile -ds
!#
(execl "/gnu/store/@dots{}-coreutils-8.22"/bin/ls" "ls")
@end example
@end deffn

@deffn {Procedure} program-file name exp [#:guile #f] [#:module-path %load-path]
Return an object representing the executable store item @var{name} that
runs @var{gexp}.  @var{guile} is the Guile package used to execute that
script.  Imported modules of @var{gexp} are looked up in @var{module-path}.

This is the declarative counterpart of @code{gexp->script}.
@end deffn

@deffn {Monadic Procedure} gexp->file @var{name} @var{exp} @
            [#:set-load-path? #t] [#:module-path %load-path] @
            [#:splice? #f] @
            [#:guile (default-guile)]
Return a derivation that builds a file @var{name} containing @var{exp}.
When @var{splice?}  is true, @var{exp} is considered to be a list of
expressions that will be spliced in the resulting file.

When @var{set-load-path?} is true, emit code in the resulting file to
set @code{%load-path} and @code{%load-compiled-path} to honor
@var{exp}'s imported modules.  Look up @var{exp}'s modules in
@var{module-path}.

The resulting file holds references to all the dependencies of @var{exp}
or a subset thereof.
@end deffn

@deffn {Procedure} scheme-file name exp [#:splice? #f] @
           [#:guile #f] [#:set-load-path? #t]
Return an object representing the Scheme file @var{name} that contains
@var{exp}.  @var{guile} is the Guile package used to produce that file.

This is the declarative counterpart of @code{gexp->file}.
@end deffn

@deffn {Monadic Procedure} text-file* @var{name} @var{text} @dots{}
Return as a monadic value a derivation that builds a text file
containing all of @var{text}.  @var{text} may list, in addition to
strings, objects of any type that can be used in a gexp: packages,
derivations, local file objects, etc.  The resulting store file holds
references to all these.

This variant should be preferred over @code{text-file} anytime the file
to create will reference items from the store.  This is typically the
case when building a configuration file that embeds store file names,
like this:

@lisp
(define (profile.sh)
  ;; Return the name of a shell script in the store that
  ;; initializes the 'PATH' environment variable.
  (text-file* "profile.sh"
              "export PATH=" coreutils "/bin:"
              grep "/bin:" sed "/bin\n"))
@end lisp

In this example, the resulting @file{/gnu/store/@dots{}-profile.sh} file
will reference @var{coreutils}, @var{grep}, and @var{sed}, thereby
preventing them from being garbage-collected during its lifetime.
@end deffn

@deffn {Procedure} mixed-text-file name text @dots{}
Return an object representing store file @var{name} containing
@var{text}.  @var{text} is a sequence of strings and file-like objects,
as in:

@lisp
(mixed-text-file "profile"
                 "export PATH=" coreutils "/bin:" grep "/bin")
@end lisp

This is the declarative counterpart of @code{text-file*}.
@end deffn

@deffn {Procedure} file-union name files
Return a @code{<computed-file>} that builds a directory containing all of @var{files}.
Each item in @var{files} must be a two-element list where the first element is the
file name to use in the new directory, and the second element is a gexp
denoting the target file.  Here's an example:

@lisp
(file-union "etc"
            `(("hosts" ,(plain-file "hosts"
                                    "127.0.0.1 localhost"))
              ("bashrc" ,(plain-file "bashrc"
                                     "alias ls='ls --color=auto'"))))
@end lisp

This yields an @code{etc} directory containing these two files.
@end deffn

@deffn {Procedure} directory-union name things
Return a directory that is the union of @var{things}, where @var{things} is a list of
file-like objects denoting directories.  For example:

@lisp
(directory-union "guile+emacs" (list guile emacs))
@end lisp

yields a directory that is the union of the @code{guile} and @code{emacs} packages.
@end deffn

@deffn {Procedure} file-append obj suffix @dots{}
Return a file-like object that expands to the concatenation of @var{obj}
and @var{suffix}, where @var{obj} is a lowerable object and each
@var{suffix} is a string.

As an example, consider this gexp:

@lisp
(gexp->script "run-uname"
              #~(system* #$(file-append coreutils
                                        "/bin/uname")))
@end lisp

The same effect could be achieved with:

@lisp
(gexp->script "run-uname"
              #~(system* (string-append #$coreutils
                                        "/bin/uname")))
@end lisp

There is one difference though: in the @code{file-append} case, the
resulting script contains the absolute file name as a string, whereas in
the second case, the resulting script contains a @code{(string-append
@dots{})} expression to construct the file name @emph{at run time}.
@end deffn

@defmac let-system system body@dots{}
@defmacx let-system (system target) body@dots{}
Bind @var{system} to the currently targeted system---e.g.,
@code{"x86_64-linux"}---within @var{body}.

In the second case, additionally bind @var{target} to the current
cross-compilation target---a GNU triplet such as
@code{"arm-linux-gnueabihf"}---or @code{#f} if we are not
cross-compiling.

@code{let-system} is useful in the occasional case where the object
spliced into the gexp depends on the target system, as in this example:

@lisp
#~(system*
   #+(let-system system
       (cond ((string-prefix? "armhf-" system)
              (file-append qemu "/bin/qemu-system-arm"))
             ((string-prefix? "x86_64-" system)
              (file-append qemu "/bin/qemu-system-x86_64"))
             (else
              (error "dunno!"))))
   "-net" "user" #$image)
@end lisp
@end defmac

@defmac with-parameters ((parameter value) @dots{}) exp
This macro is similar to the @code{parameterize} form for
dynamically-bound @dfn{parameters} (@pxref{Parameters,,, guile, GNU
Guile Reference Manual}).  The key difference is that it takes effect
when the file-like object returned by @var{exp} is lowered to a
derivation or store item.

A typical use of @code{with-parameters} is to force the system in effect
for a given object:

@lisp
(with-parameters ((%current-system "i686-linux"))
  coreutils)
@end lisp

The example above returns an object that corresponds to the i686 build
of Coreutils, regardless of the current value of @code{%current-system}.
@end defmac

@anchor{gexp-input}
@deffn {Procedure} gexp-input @var{obj} [@var{output}] [#:native? #f]
Return a @dfn{gexp input} record for the given @var{output} of file-like
object @var{obj}, with @code{#:native?} determining whether this is a
native reference (as with @code{ungexp-native}) or not.

This procedure is helpful when you want to pass a reference to a
specific output of an object to some procedure that may not know about
that output.  For example, assume you have this procedure, which takes
one file-like object:

@lisp
(define (make-symlink target)
  (computed-file "the-symlink"
                 #~(symlink #$target #$output)))
@end lisp

Here @code{make-symlink} can only ever refer to the default output of
@var{target}---the @code{"out"} output (@pxref{Packages with Multiple
Outputs}).  To have it refer to, say, the @code{"lib"} output of the
@code{hwloc} package, you can call it like so:

@lisp
(make-symlink (gexp-input hwloc "lib"))
@end lisp

You can also compose it like any other file-like object:

@lisp
(make-symlink
  (file-append (gexp-input hwloc "lib") "/lib/libhwloc.so"))
@end lisp
@end deffn

Of course, in addition to gexps embedded in ``host'' code, there are
also modules containing build tools.  To make it clear that they are
meant to be used in the build stratum, these modules are kept in the
@code{(guix build @dots{})} name space.

@cindex lowering, of high-level objects in gexps
Internally, high-level objects are @dfn{lowered}, using their compiler,
to either derivations or store items.  For instance, lowering a package
yields a derivation, and lowering a @code{plain-file} yields a store
item.  This is achieved using the @code{lower-object} monadic procedure.

@deffn {Monadic Procedure} lower-object @var{obj} [@var{system}] @
           [#:target #f]
Return as a value in @code{%store-monad} the derivation or store item
corresponding to @var{obj} for @var{system}, cross-compiling for
@var{target} if @var{target} is true.  @var{obj} must be an object that
has an associated gexp compiler, such as a @code{<package>}.
@end deffn

@deffn {Procedure} gexp->approximate-sexp gexp
Sometimes, it may be useful to convert a G-exp into a S-exp.  For
example, some linters (@pxref{Invoking guix lint}) peek into the build
phases of a package to detect potential problems.  This conversion can
be achieved with this procedure.  However, some information can be lost
in the process.  More specifically, lowerable objects will be silently
replaced with some arbitrary object -- currently the list
@code{(*approximate*)}, but this may change.
@end deffn

@node Invoking guix repl
@section Invoking @command{guix repl}

@cindex @command{guix repl}
@cindex REPL, read-eval-print loop, script
The @command{guix repl} command makes it easier to program Guix in Guile
by launching a Guile @dfn{read-eval-print loop} (REPL) for interactive
programming (@pxref{Using Guile Interactively,,, guile,
GNU Guile Reference Manual}), or by running Guile scripts
(@pxref{Running Guile Scripts,,, guile,
GNU Guile Reference Manual}).
Compared to just launching the @command{guile}
command, @command{guix repl} guarantees that all the Guix modules and all its
dependencies are available in the search path.

The general syntax is:

@example
guix repl @var{options} [@var{file} @var{args}]
@end example

When a @var{file} argument is provided, @var{file} is
executed as a Guile scripts:

@example
guix repl my-script.scm
@end example

To pass arguments to the script, use @code{--} to prevent them from
being interpreted as arguments to @command{guix repl} itself:

@example
guix repl -- my-script.scm --input=foo.txt
@end example

To make a script executable directly from the shell, using the guix
executable that is on the user's search path, add the following two
lines at the top of the script:

@example
@code{#!/usr/bin/env -S guix repl --}
@code{!#}
@end example

To make a script that launches an interactive REPL directly from the
shell, use the @code{--interactive} flag:

@example
@code{#!/usr/bin/env -S guix repl --interactive}
@code{!#}
@end example

Without a file name argument, a Guile REPL is started, allowing for
interactive use (@pxref{Using Guix Interactively}):

@example
$ guix repl
scheme@@(guile-user)> ,use (gnu packages base)
scheme@@(guile-user)> coreutils
$1 = #<package coreutils@@8.29 gnu/packages/base.scm:327 3e28300>
@end example

@cindex inferiors
In addition, @command{guix repl} implements a simple machine-readable REPL
protocol for use by @code{(guix inferior)}, a facility to interact with
@dfn{inferiors}, separate processes running a potentially different revision
of Guix.

The available options are as follows:

@table @code
@item --list-types
Display the @var{TYPE} options for @command{guix repl --type=TYPE} and
exit.

@item --type=@var{type}
@itemx -t @var{type}
Start a REPL of the given @var{TYPE}, which can be one of the following:

@table @code
@item guile
This is default, and it spawns a standard full-featured Guile REPL.
@item machine
Spawn a REPL that uses the machine-readable protocol.  This is the protocol
that the @code{(guix inferior)} module speaks.
@end table

@item --listen=@var{endpoint}
By default, @command{guix repl} reads from standard input and writes to
standard output.  When this option is passed, it will instead listen for
connections on @var{endpoint}.  Here are examples of valid options:

@table @code
@item --listen=tcp:37146
Accept connections on localhost on port 37146.

@item --listen=unix:/tmp/socket
Accept connections on the Unix-domain socket @file{/tmp/socket}.
@end table

@item --interactive
@itemx -i
Launch the interactive REPL after @var{file} is executed.

@item --load-path=@var{directory}
@itemx -L @var{directory}
Add @var{directory} to the front of the package module search path
(@pxref{Package Modules}).

This allows users to define their own packages and make them visible to
the script or REPL.

@item -q
Inhibit loading of the @file{~/.guile} file.  By default, that
configuration file is loaded when spawning a @code{guile} REPL.
@end table

@node Using Guix Interactively
@section Using Guix Interactively

@cindex interactive use
@cindex REPL, read-eval-print loop
The @command{guix repl} command gives you access to a warm and friendly
@dfn{read-eval-print loop} (REPL) (@pxref{Invoking guix repl}).  If
you're getting into Guix programming---defining your own packages,
writing manifests, defining services for Guix System or Guix Home,
etc.---you will surely find it convenient to toy with ideas at the REPL.

If you use Emacs, the most convenient way to do that is with Geiser
(@pxref{The Perfect Setup}), but you do not have to use Emacs to enjoy
the REPL@.  When using @command{guix repl} or @command{guile} in the
terminal, we recommend using Readline for completion and Colorized to
get colorful output.  To do that, you can run:

@example
guix install guile guile-readline guile-colorized
@end example

@noindent
... and then create a @file{.guile} file in your home directory containing
this:

@lisp
(use-modules (ice-9 readline) (ice-9 colorized))

(activate-readline)
(activate-colorized)
@end lisp

The REPL lets you evaluate Scheme code; you type a Scheme expression at
the prompt, and the REPL prints what it evaluates to:

@example
$ guix repl
scheme@@(guix-user)> (+ 2 3)
$1 = 5
scheme@@(guix-user)> (string-append "a" "b")
$2 = "ab"
@end example

It becomes interesting when you start fiddling with Guix at the REPL.
The first thing you'll want to do is to ``import'' the @code{(guix)}
module, which gives access to the main part of the programming
interface, and perhaps a bunch of useful Guix modules.  You could type
@code{(use-modules (guix))}, which is valid Scheme code to import a
module (@pxref{Using Guile Modules,,, guile, GNU Guile Reference
Manual}), but the REPL provides the @code{use} @dfn{command} as a
shorthand notation (@pxref{REPL Commands,,, guile, GNU Guile Reference
Manual}):

@example
scheme@@(guix-user)> ,use (guix)
scheme@@(guix-user)> ,use (gnu packages base)
@end example

Notice that REPL commands are introduced by a leading comma.  A REPL
command like @code{use} is not valid Scheme code; it's interpreted
specially by the REPL.

Guix extends the Guile REPL with additional commands for convenience.
Among those, the @code{build} command comes in handy: it ensures that
the given file-like object is built, building it if needed, and returns
its output file name(s).  In the example below, we build the
@code{coreutils} and @code{grep} packages, as well as a ``computed
file'' (@pxref{G-Expressions, @code{computed-file}}), and we use the
@code{scandir} procedure to list the files in Grep's @code{/bin}
directory:

@example
scheme@@(guix-user)> ,build coreutils
$1 = "/gnu/store/@dots{}-coreutils-8.32-debug"
$2 = "/gnu/store/@dots{}-coreutils-8.32"
scheme@@(guix-user)> ,build grep
$3 = "/gnu/store/@dots{}-grep-3.6"
scheme@@(guix-user)> ,build (computed-file "x" #~(mkdir #$output))
building /gnu/store/@dots{}-x.drv...
$4 = "/gnu/store/@dots{}-x"
scheme@@(guix-user)> ,use(ice-9 ftw)
scheme@@(guix-user)> (scandir (string-append $3 "/bin"))
$5 = ("." ".." "egrep" "fgrep" "grep")
@end example

As a packager, you may be willing to inspect the build phases or flags
of a given package; this is particularly useful when relying a lot on
inheritance to define package variants (@pxref{Defining Package
Variants}) or when package arguments are a result of some computation,
both of which can make it harder to foresee what ends up in the package
arguments.  Additional commands let you inspect those package arguments:

@example
scheme@@(guix-user)> ,phases grep
$1 = (modify-phases %standard-phases
       (add-after 'install 'fix-egrep-and-fgrep
         (lambda* (#:key outputs #:allow-other-keys)
           (let* ((out (assoc-ref outputs "out"))
                  (bin (string-append out "/bin")))
             (substitute* (list (string-append bin "/egrep")
                                (string-append bin "/fgrep"))
               (("^exec grep")
                (string-append "exec " bin "/grep")))))))
scheme@@(guix-user)> ,configure-flags findutils
$2 = (list "--localstatedir=/var")
scheme@@(guix-user)> ,make-flags binutils
$3 = '("MAKEINFO=true")
@end example

At a lower-level, a useful command is @code{lower}: it takes a file-like
object and ``lowers'' it into a derivation (@pxref{Derivations}) or a
store file:

@example
scheme@@(guix-user)> ,lower grep
$6 = #<derivation /gnu/store/@dots{}-grep-3.6.drv => /gnu/store/@dots{}-grep-3.6 7f0e639115f0>
scheme@@(guix-user)> ,lower (plain-file "x" "Hello!")
$7 = "/gnu/store/@dots{}-x"
@end example

The full list of REPL commands can be seen by typing @code{,help guix}
and is given below for reference.

@deffn {REPL command} build @var{object}
Lower @var{object} and build it if it's not already built, returning its
output file name(s).
@end deffn

@deffn {REPL command} lower @var{object}
Lower @var{object} into a derivation or store file name and return it.
@end deffn

@deffn {REPL command} verbosity @var{level}
Change build verbosity to @var{level}.

This is similar to the @option{--verbosity} command-line option
(@pxref{Common Build Options}): level 0 means total silence, level 1
shows build events only, and higher levels print build logs.
@end deffn

@deffn {REPL command} phases @var{package}
@deffnx {REPL command} configure-flags @var{package}
@deffnx {REPL command} make-flags @var{package}
These REPL commands return the value of one element of the
@code{arguments} field of @var{package} (@pxref{package Reference}): the
first one show the staged code associated with @code{#:phases}
(@pxref{Build Phases}), the second shows the code for
@code{#:configure-flags}, and @code{,make-flags} returns the code for
@code{#:make-flags}.
@end deffn

@deffn {REPL command} run-in-store @var{exp}
Run @var{exp}, a monadic expression, through the store monad.
@xref{The Store Monad}, for more information.
@end deffn

@deffn {REPL command} enter-store-monad
Enter a new REPL to evaluate monadic expressions (@pxref{The Store
Monad}).  You can quit this ``inner'' REPL by typing @code{,q}.
@end deffn

@c *********************************************************************
@node Utilities
@chapter Utilities

This section describes Guix command-line utilities.  Some of them are
primarily targeted at developers and users who write new package
definitions, while others are more generally useful.  They complement
the Scheme programming interface of Guix in a convenient way.

@menu
* Invoking guix build::         Building packages from the command line.
* Invoking guix edit::          Editing package definitions.
* Invoking guix download::      Downloading a file and printing its hash.
* Invoking guix hash::          Computing the cryptographic hash of a file.
* Invoking guix import::        Importing package definitions.
* Invoking guix refresh::       Updating package definitions.
* Invoking guix style::         Styling package definitions.
* Invoking guix lint::          Finding errors in package definitions.
* Invoking guix size::          Profiling disk usage.
* Invoking guix graph::         Visualizing the graph of packages.
* Invoking guix publish::       Sharing substitutes.
* Invoking guix challenge::     Challenging substitute servers.
* Invoking guix copy::          Copying to and from a remote store.
* Invoking guix container::     Process isolation.
* Invoking guix weather::       Assessing substitute availability.
* Invoking guix processes::     Listing client processes.
@end menu

@node Invoking guix build
@section Invoking @command{guix build}

@cindex package building
@cindex @command{guix build}
The @command{guix build} command builds packages or derivations and
their dependencies, and prints the resulting store paths.  Note that it
does not modify the user's profile---this is the job of the
@command{guix package} command (@pxref{Invoking guix package}).  Thus,
it is mainly useful for distribution developers.

The general syntax is:

@example
guix build @var{options} @var{package-or-derivation}@dots{}
@end example

As an example, the following command builds the latest versions of Emacs
and of Guile, displays their build logs, and finally displays the
resulting directories:

@example
guix build emacs guile
@end example

Similarly, the following command builds all the available packages:

@example
guix build --quiet --keep-going \
  $(guix package -A | awk '@{ print $1 "@@" $2 @}')
@end example

@var{package-or-derivation} may be either the name of a package found in
the software distribution such as @code{coreutils} or
@code{coreutils@@8.20}, or a derivation such as
@file{/gnu/store/@dots{}-coreutils-8.19.drv}.  In the former case, a
package with the corresponding name (and optionally version) is searched
for among the GNU distribution modules (@pxref{Package Modules}).

Alternatively, the @option{--expression} option may be used to specify a
Scheme expression that evaluates to a package; this is useful when
disambiguating among several same-named packages or package variants is
needed.

There may be zero or more @var{options}.  The available options are
described in the subsections below.

@menu
* Common Build Options::        Build options for most commands.
* Package Transformation Options::  Creating variants of packages.
* Additional Build Options::    Options specific to 'guix build'.
* Debugging Build Failures::    Real life packaging experience.
@end menu

@node Common Build Options
@subsection Common Build Options

A number of options that control the build process are common to
@command{guix build} and other commands that can spawn builds, such as
@command{guix package} or @command{guix archive}.  These are the
following:

@table @code

@item --load-path=@var{directory}
@itemx -L @var{directory}
Add @var{directory} to the front of the package module search path
(@pxref{Package Modules}).

This allows users to define their own packages and make them visible to
the command-line tools.

@item --keep-failed
@itemx -K
Keep the build tree of failed builds.  Thus, if a build fails, its build
tree is kept under @file{/tmp}, in a directory whose name is shown at
the end of the build log.  This is useful when debugging build issues.
@xref{Debugging Build Failures}, for tips and tricks on how to debug
build issues.

This option implies @option{--no-offload}, and it has no effect when
connecting to a remote daemon with a @code{guix://} URI (@pxref{The
Store, the @env{GUIX_DAEMON_SOCKET} variable}).

@item --keep-going
@itemx -k
Keep going when some of the derivations fail to build; return only once
all the builds have either completed or failed.

The default behavior is to stop as soon as one of the specified
derivations has failed.

@item --dry-run
@itemx -n
Do not build the derivations.

@anchor{fallback-option}
@item --fallback
When substituting a pre-built binary fails, fall back to building
packages locally (@pxref{Substitution Failure}).

@item --substitute-urls=@var{urls}
@anchor{client-substitute-urls}
Consider @var{urls} the whitespace-separated list of substitute source
URLs, overriding the default list of URLs of @command{guix-daemon}
(@pxref{daemon-substitute-urls,, @command{guix-daemon} URLs}).

This means that substitutes may be downloaded from @var{urls}, provided
they are signed by a key authorized by the system administrator
(@pxref{Substitutes}).

When @var{urls} is the empty string, substitutes are effectively
disabled.

@item --no-substitutes
Do not use substitutes for build products.  That is, always build things
locally instead of allowing downloads of pre-built binaries
(@pxref{Substitutes}).

@item --no-grafts
Do not ``graft'' packages.  In practice, this means that package updates
available as grafts are not applied.  @xref{Security Updates}, for more
information on grafts.

@item --rounds=@var{n}
Build each derivation @var{n} times in a row, and raise an error if
consecutive build results are not bit-for-bit identical.

This is a useful way to detect non-deterministic builds processes.
Non-deterministic build processes are a problem because they make it
practically impossible for users to @emph{verify} whether third-party
binaries are genuine.  @xref{Invoking guix challenge}, for more.

When used in conjunction with @option{--keep-failed}, the differing
output is kept in the store, under @file{/gnu/store/@dots{}-check}.
This makes it easy to look for differences between the two results.

@item --no-offload
Do not use offload builds to other machines (@pxref{Daemon Offload
Setup}).  That is, always build things locally instead of offloading
builds to remote machines.

@item --max-silent-time=@var{seconds}
When the build or substitution process remains silent for more than
@var{seconds}, terminate it and report a build failure.

By default, the daemon's setting is honored (@pxref{Invoking
guix-daemon, @option{--max-silent-time}}).

@item --timeout=@var{seconds}
Likewise, when the build or substitution process lasts for more than
@var{seconds}, terminate it and report a build failure.

By default, the daemon's setting is honored (@pxref{Invoking
guix-daemon, @option{--timeout}}).

@c Note: This option is actually not part of %standard-build-options but
@c most programs honor it.
@cindex verbosity, of the command-line tools
@cindex build logs, verbosity
@item -v @var{level}
@itemx --verbosity=@var{level}
Use the given verbosity @var{level}, an integer.  Choosing 0 means that
no output is produced, 1 is for quiet output; 2 is similar to 1 but it
additionally displays download URLs; 3 shows all the build log output on
standard error.

@item --cores=@var{n}
@itemx -c @var{n}
Allow the use of up to @var{n} CPU cores for the build.  The special
value @code{0} means to use as many CPU cores as available.

@item --max-jobs=@var{n}
@itemx -M @var{n}
Allow at most @var{n} build jobs in parallel.  @xref{Invoking
guix-daemon, @option{--max-jobs}}, for details about this option and the
equivalent @command{guix-daemon} option.

@item --debug=@var{level}
Produce debugging output coming from the build daemon.  @var{level} must be an
integer between 0 and 5; higher means more verbose output.  Setting a level of
4 or more may be helpful when debugging setup issues with the build daemon.

@end table

Behind the scenes, @command{guix build} is essentially an interface to
the @code{package-derivation} procedure of the @code{(guix packages)}
module, and to the @code{build-derivations} procedure of the @code{(guix
derivations)} module.

In addition to options explicitly passed on the command line,
@command{guix build} and other @command{guix} commands that support
building honor the @env{GUIX_BUILD_OPTIONS} environment variable.

@defvr {Environment Variable} GUIX_BUILD_OPTIONS
Users can define this variable to a list of command line options that
will automatically be used by @command{guix build} and other
@command{guix} commands that can perform builds, as in the example
below:

@example
$ export GUIX_BUILD_OPTIONS="--no-substitutes -c 2 -L /foo/bar"
@end example

These options are parsed independently, and the result is appended to
the parsed command-line options.
@end defvr


@node Package Transformation Options
@subsection Package Transformation Options

@cindex package variants
Another set of command-line options supported by @command{guix build}
and also @command{guix package} are @dfn{package transformation
options}.  These are options that make it possible to define @dfn{package
variants}---for instance, packages built from different source code.
This is a convenient way to create customized packages on the fly
without having to type in the definitions of package variants
(@pxref{Defining Packages}).

Package transformation options are preserved across upgrades:
@command{guix upgrade} attempts to apply transformation options
initially used when creating the profile to the upgraded packages.

The available options are listed below.  Most commands support them and
also support a @option{--help-transform} option that lists all the
available options and a synopsis (these options are not shown in the
@option{--help} output for brevity).

@table @code

@cindex performance, tuning code
@cindex optimization, of package code
@cindex tuning, of package code
@cindex SIMD support
@cindex tunable packages
@cindex package multi-versioning
@item --tune[=@var{cpu}]
Use versions of the packages marked as ``tunable'' optimized for
@var{cpu}.  When @var{cpu} is @code{native}, or when it is omitted, tune
for the CPU on which the @command{guix} command is running.

Valid @var{cpu} names are those recognized by the underlying compiler,
by default the GNU Compiler Collection.  On x86_64 processors, this
includes CPU names such as @code{nehalem}, @code{haswell}, and
@code{skylake} (@pxref{x86 Options, @code{-march},, gcc, Using the GNU
Compiler Collection (GCC)}).

As new generations of CPUs come out, they augment the standard
instruction set architecture (ISA) with additional instructions, in
particular instructions for single-instruction/multiple-data (SIMD)
parallel processing.  For example, while Core2 and Skylake CPUs both
implement the x86_64 ISA, only the latter supports AVX2 SIMD
instructions.

The primary gain one can expect from @option{--tune} is for programs
that can make use of those SIMD capabilities @emph{and} that do not
already have a mechanism to select the right optimized code at run time.
Packages that have the @code{tunable?} property set are considered
@dfn{tunable packages} by the @option{--tune} option; a package
definition with the property set looks like this:

@lisp
(package
  (name "hello-simd")
  ;; ...

  ;; This package may benefit from SIMD extensions so
  ;; mark it as "tunable".
  (properties '((tunable? . #t))))
@end lisp

Other packages are not considered tunable.  This allows Guix to use
generic binaries in the cases where tuning for a specific CPU is
unlikely to provide any gain.

Tuned packages are built with @code{-march=@var{CPU}}; under the hood,
the @option{-march} option is passed to the actual wrapper by a compiler
wrapper.  Since the build machine may not be able to run code for the
target CPU micro-architecture, the test suite is not run when building a
tuned package.

To reduce rebuilds to the minimum, tuned packages are @emph{grafted}
onto packages that depend on them (@pxref{Security Updates, grafts}).
Thus, using @option{--no-grafts} cancels the effect of @option{--tune}.

We call this technique @dfn{package multi-versioning}: several variants
of tunable packages may be built, one for each CPU variant.  It is the
coarse-grain counterpart of @dfn{function multi-versioning} as
implemented by the GNU tool chain (@pxref{Function Multiversioning,,,
gcc, Using the GNU Compiler Collection (GCC)}).

@item --with-source=@var{source}
@itemx --with-source=@var{package}=@var{source}
@itemx --with-source=@var{package}@@@var{version}=@var{source}
Use @var{source} as the source of @var{package}, and @var{version} as
its version number.
@var{source} must be a file name or a URL, as for @command{guix
download} (@pxref{Invoking guix download}).

When @var{package} is omitted,
it is taken to be the package name specified on the
command line that matches the base of @var{source}---e.g.,
if @var{source} is @code{/src/guile-2.0.10.tar.gz}, the corresponding
package is @code{guile}.

Likewise, when @var{version} is omitted, the version string is inferred from
@var{source}; in the previous example, it is @code{2.0.10}.

This option allows users to try out versions of packages other than the
one provided by the distribution.  The example below downloads
@file{ed-1.7.tar.gz} from a GNU mirror and uses that as the source for
the @code{ed} package:

@example
guix build ed --with-source=mirror://gnu/ed/ed-1.4.tar.gz
@end example

As a developer, @option{--with-source} makes it easy to test release
candidates, and even to test their impact on packages that depend on
them:

@example
guix build elogind --with-source=@dots{}/shepherd-0.9.0rc1.tar.gz
@end example

@dots{} or to build from a checkout in a pristine environment:

@example
$ git clone git://git.sv.gnu.org/guix.git
$ guix build guix --with-source=guix@@1.0=./guix
@end example

@item --with-input=@var{package}=@var{replacement}
Replace dependency on @var{package} by a dependency on
@var{replacement}.  @var{package} must be a package name, and
@var{replacement} must be a package specification such as @code{guile}
or @code{guile@@1.8}.

For instance, the following command builds Guix, but replaces its
dependency on the current stable version of Guile with a dependency on
the legacy version of Guile, @code{guile@@2.2}:

@example
guix build --with-input=guile=guile@@2.2 guix
@end example

This is a recursive, deep replacement.  So in this example, both
@code{guix} and its dependency @code{guile-json} (which also depends on
@code{guile}) get rebuilt against @code{guile@@2.2}.

This is implemented using the @code{package-input-rewriting/spec} Scheme
procedure (@pxref{Defining Packages, @code{package-input-rewriting/spec}}).

@item --with-graft=@var{package}=@var{replacement}
This is similar to @option{--with-input} but with an important difference:
instead of rebuilding the whole dependency chain, @var{replacement} is
built and then @dfn{grafted} onto the binaries that were initially
referring to @var{package}.  @xref{Security Updates}, for more
information on grafts.

For example, the command below grafts version 3.5.4 of GnuTLS onto Wget
and all its dependencies, replacing references to the version of GnuTLS
they currently refer to:

@example
guix build --with-graft=gnutls=gnutls@@3.5.4 wget
@end example

This has the advantage of being much faster than rebuilding everything.
But there is a caveat: it works if and only if @var{package} and
@var{replacement} are strictly compatible---for example, if they provide
a library, the application binary interface (ABI) of those libraries
must be compatible.  If @var{replacement} is somehow incompatible with
@var{package}, then the resulting package may be unusable.  Use with
care!

@cindex debugging info, rebuilding
@item --with-debug-info=@var{package}
Build @var{package} in a way that preserves its debugging info and graft
it onto packages that depend on it.  This is useful if @var{package}
does not already provide debugging info as a @code{debug} output
(@pxref{Installing Debugging Files}).

For example, suppose you're experiencing a crash in Inkscape and would
like to see what's up in GLib, a library deep down in Inkscape's
dependency graph.  GLib lacks a @code{debug} output, so debugging is
tough.  Fortunately, you rebuild GLib with debugging info and tack it on
Inkscape:

@example
guix install inkscape --with-debug-info=glib
@end example

Only GLib needs to be recompiled so this takes a reasonable amount of
time.  @xref{Installing Debugging Files}, for more info.

@quotation Note
Under the hood, this option works by passing the @samp{#:strip-binaries?
#f} to the build system of the package of interest (@pxref{Build
Systems}).  Most build systems support that option but some do not.  In
that case, an error is raised.

Likewise, if a C/C++ package is built without @code{-g} (which is rarely
the case), debugging info will remain unavailable even when
@code{#:strip-binaries?} is false.
@end quotation

@cindex tool chain, changing the build tool chain of a package
@item --with-c-toolchain=@var{package}=@var{toolchain}
This option changes the compilation of @var{package} and everything that
depends on it so that they get built with @var{toolchain} instead of the
default GNU tool chain for C/C++.

Consider this example:

@example
guix build octave-cli \
  --with-c-toolchain=fftw=gcc-toolchain@@10 \
  --with-c-toolchain=fftwf=gcc-toolchain@@10
@end example

The command above builds a variant of the @code{fftw} and @code{fftwf}
packages using version 10 of @code{gcc-toolchain} instead of the default
tool chain, and then builds a variant of the GNU@tie{}Octave
command-line interface using them.  GNU@tie{}Octave itself is also built
with @code{gcc-toolchain@@10}.

This other example builds the Hardware Locality (@code{hwloc}) library
and its dependents up to @code{intel-mpi-benchmarks} with the Clang C
compiler:

@example
guix build --with-c-toolchain=hwloc=clang-toolchain \
           intel-mpi-benchmarks
@end example

@quotation Note
There can be application binary interface (ABI) incompatibilities among
tool chains.  This is particularly true of the C++ standard library and
run-time support libraries such as that of OpenMP@.  By rebuilding all
dependents with the same tool chain, @option{--with-c-toolchain} minimizes
the risks of incompatibility but cannot entirely eliminate them.  Choose
@var{package} wisely.
@end quotation

@item --with-git-url=@var{package}=@var{url}
@cindex Git, using the latest commit
@cindex latest commit, building
Build @var{package} from the latest commit of the @code{master} branch of the
Git repository at @var{url}.  Git sub-modules of the repository are fetched,
recursively.

For example, the following command builds the NumPy Python library against the
latest commit of the master branch of Python itself:

@example
guix build python-numpy \
  --with-git-url=python=https://github.com/python/cpython
@end example

This option can also be combined with @option{--with-branch} or
@option{--with-commit} (see below).

@cindex continuous integration
Obviously, since it uses the latest commit of the given branch, the result of
such a command varies over time.  Nevertheless it is a convenient way to
rebuild entire software stacks against the latest commit of one or more
packages.  This is particularly useful in the context of continuous
integration (CI).

Checkouts are kept in a cache under @file{~/.cache/guix/checkouts} to speed up
consecutive accesses to the same repository.  You may want to clean it up once
in a while to save disk space.

@item --with-branch=@var{package}=@var{branch}
Build @var{package} from the latest commit of @var{branch}.  If the
@code{source} field of @var{package} is an origin with the @code{git-fetch}
method (@pxref{origin Reference}) or a @code{git-checkout} object, the
repository URL is taken from that @code{source}.  Otherwise you have to use
@option{--with-git-url} to specify the URL of the Git repository.

For instance, the following command builds @code{guile-sqlite3} from the
latest commit of its @code{master} branch, and then builds @code{guix} (which
depends on it) and @code{cuirass} (which depends on @code{guix}) against this
specific @code{guile-sqlite3} build:

@example
guix build --with-branch=guile-sqlite3=master cuirass
@end example

@item --with-commit=@var{package}=@var{commit}
This is similar to @option{--with-branch}, except that it builds from
@var{commit} rather than the tip of a branch.  @var{commit} must be a valid
Git commit SHA1 identifier, a tag, or a @command{git describe} style
identifier such as @code{1.0-3-gabc123}.

@item --with-patch=@var{package}=@var{file}
Add @var{file} to the list of patches applied to @var{package}, where
@var{package} is a spec such as @code{python@@3.8} or @code{glibc}.
@var{file} must contain a patch; it is applied with the flags specified
in the @code{origin} of @var{package} (@pxref{origin Reference}), which
by default includes @code{-p1} (@pxref{patch Directories,,, diffutils,
Comparing and Merging Files}).

As an example, the command below rebuilds Coreutils with the GNU C
Library (glibc) patched with the given patch:

@example
guix build coreutils --with-patch=glibc=./glibc-frob.patch
@end example

In this example, glibc itself as well as everything that leads to
Coreutils in the dependency graph is rebuilt.

@cindex configure flags, changing them
@item --with-configure-flag=@var{package}=@var{flag}
Append @var{flag} to the configure flags of @var{package}, where
@var{package} is a spec such as @code{guile@@3.0} or @code{glibc}.  The
build system of @var{package} must support the @code{#:configure-flags}
argument.

For example, the command below builds GNU@tie{}Hello with the
configure flag @code{--disable-nls}:

@example
guix build hello --with-configure-flag=hello=--disable-nls
@end example

The following command passes an extra flag to @command{cmake} as it
builds @code{lapack}:

@example
guix build lapack \
  --with-configure-flag=lapack=-DBUILD_SHARED_LIBS=OFF
@end example

@quotation Note
Under the hood, this option works by passing the
@samp{#:configure-flags} argument to the build system of the package of
interest (@pxref{Build Systems}).  Most build systems support that
option but some do not.  In that case, an error is raised.
@end quotation

@cindex upstream, latest version
@item --with-latest=@var{package}
@itemx --with-version=@var{package}=@var{version}
So you like living on the bleeding edge?  The @option{--with-latest}
option is for you!  It
replaces occurrences of @var{package} in the dependency graph with its
latest upstream version, as reported by @command{guix refresh}
(@pxref{Invoking guix refresh}).

It does so by determining the latest upstream release of @var{package}
(if possible), downloading it, and authenticating it @emph{if} it comes
with an OpenPGP signature.

As an example, the command below builds Guix against the latest version
of Guile-JSON:

@example
guix build guix --with-latest=guile-json
@end example

The @option{--with-version} works similarly except that it lets you
specify that you want precisely @var{version}, assuming that version
exists upstream.  For example, to spawn a development environment with
SciPy built against version 1.22.4 of NumPy (skipping its test suite
because hey, we're not gonna wait this long), you would run:

@example
guix shell python python-scipy --with-version=python-numpy=1.22.4
@end example

@quotation Warning
Because they depend on source code published at a given point in time on
upstream servers, deployments made with @option{--with-latest} and
@option{--with-version} may be non-reproducible: source might disappear
or be modified in place on the servers.

To deploy old software versions without compromising on reproducibility,
@pxref{Invoking guix time-machine, @command{guix time-machine}}.
@end quotation

There are limitations.  First, in cases where the tool cannot or does
not know how to authenticate source code, you are at risk of running
malicious code; a warning is emitted in this case.  Second, this option
simply changes the source used in the existing package definitions,
which is not always sufficient: there might be additional dependencies
that need to be added, patches to apply, and more generally the quality
assurance work that Guix developers normally do will be missing.

You've been warned!  When those limitations are acceptable, it's a
snappy way to stay on top.  We encourage you to submit patches updating
the actual package definitions once you have successfully tested an
upgrade with @option{--with-latest} (@pxref{Contributing}).

@cindex test suite, skipping
@item --without-tests=@var{package}
Build @var{package} without running its tests.  This can be useful in
situations where you want to skip the lengthy test suite of a
intermediate package, or if a package's test suite fails in a
non-deterministic fashion.  It should be used with care because running
the test suite is a good way to ensure a package is working as intended.

Turning off tests leads to a different store item.  Consequently, when
using this option, anything that depends on @var{package} must be
rebuilt, as in this example:

@example
guix install --without-tests=python python-notebook
@end example

The command above installs @code{python-notebook} on top of
@code{python} built without running its test suite.  To do so, it also
rebuilds everything that depends on @code{python}, including
@code{python-notebook} itself.

Internally, @option{--without-tests} relies on changing the
@code{#:tests?} option of a package's @code{check} phase (@pxref{Build
Systems}).  Note that some packages use a customized @code{check} phase
that does not respect a @code{#:tests? #f} setting.  Therefore,
@option{--without-tests} has no effect on these packages.

@end table

Wondering how to achieve the same effect using Scheme code, for example
in your manifest, or how to write your own package transformation?
@xref{Defining Package Variants}, for an overview of the programming
interfaces available.

@node Additional Build Options
@subsection Additional Build Options

The command-line options presented below are specific to @command{guix
build}.

@table @code

@item --quiet
@itemx -q
Build quietly, without displaying the build log; this is equivalent to
@option{--verbosity=0}.  Upon completion, the build log is kept in @file{/var}
(or similar) and can always be retrieved using the @option{--log-file} option.

@item --file=@var{file}
@itemx -f @var{file}
Build the package, derivation, or other file-like object that the code within
@var{file} evaluates to (@pxref{G-Expressions, file-like objects}).

As an example, @var{file} might contain a package definition like this
(@pxref{Defining Packages}):

@lisp
@include package-hello.scm
@end lisp

The @var{file} may also contain a JSON representation of one or more
package definitions.  Running @code{guix build -f} on @file{hello.json}
with the following contents would result in building the packages
@code{myhello} and @code{greeter}:

@example
@verbatiminclude package-hello.json
@end example

@item --manifest=@var{manifest}
@itemx -m @var{manifest}
Build all packages listed in the given @var{manifest}
(@pxref{profile-manifest, @option{--manifest}}).

@item --expression=@var{expr}
@itemx -e @var{expr}
Build the package or derivation @var{expr} evaluates to.

For example, @var{expr} may be @code{(@@ (gnu packages guile)
guile-1.8)}, which unambiguously designates this specific variant of
version 1.8 of Guile.

Alternatively, @var{expr} may be a G-expression, in which case it is used
as a build program passed to @code{gexp->derivation}
(@pxref{G-Expressions}).

Lastly, @var{expr} may refer to a zero-argument monadic procedure
(@pxref{The Store Monad}).  The procedure must return a derivation as a
monadic value, which is then passed through @code{run-with-store}.

@item --source
@itemx -S
Build the source derivations of the packages, rather than the packages
themselves.

For instance, @code{guix build -S gcc} returns something like
@file{/gnu/store/@dots{}-gcc-4.7.2.tar.bz2}, which is the GCC
source tarball.

The returned source tarball is the result of applying any patches and
code snippets specified in the package @code{origin} (@pxref{Defining
Packages}).

@cindex source, verification
As with other derivations, the result of building a source derivation
can be verified using the @option{--check} option (@pxref{build-check}).
This is useful to validate that a (potentially already built or
substituted, thus cached) package source matches against its declared
hash.

Note that @command{guix build -S} compiles the sources only of the
specified packages.  They do not include the sources of statically
linked dependencies and by themselves are insufficient for reproducing
the packages.

@item --sources
Fetch and return the source of @var{package-or-derivation} and all their
dependencies, recursively.  This is a handy way to obtain a local copy
of all the source code needed to build @var{packages}, allowing you to
eventually build them even without network access.  It is an extension
of the @option{--source} option and can accept one of the following
optional argument values:

@table @code
@item package
This value causes the @option{--sources} option to behave in the same way
as the @option{--source} option.

@item all
Build the source derivations of all packages, including any source that
might be listed as @code{inputs}.  This is the default value.

@example
$ guix build --sources tzdata
The following derivations will be built:
   /gnu/store/@dots{}-tzdata2015b.tar.gz.drv
   /gnu/store/@dots{}-tzcode2015b.tar.gz.drv
@end example

@item transitive
Build the source derivations of all packages, as well of all transitive
inputs to the packages.  This can be used e.g.@: to
prefetch package source for later offline building.

@example
$ guix build --sources=transitive tzdata
The following derivations will be built:
   /gnu/store/@dots{}-tzcode2015b.tar.gz.drv
   /gnu/store/@dots{}-findutils-4.4.2.tar.xz.drv
   /gnu/store/@dots{}-grep-2.21.tar.xz.drv
   /gnu/store/@dots{}-coreutils-8.23.tar.xz.drv
   /gnu/store/@dots{}-make-4.1.tar.xz.drv
   /gnu/store/@dots{}-bash-4.3.tar.xz.drv
@dots{}
@end example

@end table

@item --system=@var{system}
@itemx -s @var{system}
Attempt to build for @var{system}---e.g., @code{i686-linux}---instead of
the system type of the build host.  The @command{guix build} command allows
you to repeat this option several times, in which case it builds for all the
specified systems; other commands ignore extraneous @option{-s} options.

@quotation Note
The @option{--system} flag is for @emph{native} compilation and must not
be confused with cross-compilation.  See @option{--target} below for
information on cross-compilation.
@end quotation

An example use of this is on Linux-based systems, which can emulate
different personalities.  For instance, passing
@option{--system=i686-linux} on an @code{x86_64-linux} system or
@option{--system=armhf-linux} on an @code{aarch64-linux} system allows
you to build packages in a complete 32-bit environment.

@quotation Note
Building for an @code{armhf-linux} system is unconditionally enabled on
@code{aarch64-linux} machines, although certain aarch64 chipsets do not
allow for this functionality, notably the ThunderX.
@end quotation

Similarly, when transparent emulation with QEMU and @code{binfmt_misc}
is enabled (@pxref{Virtualization Services,
@code{qemu-binfmt-service-type}}), you can build for any system for
which a QEMU @code{binfmt_misc} handler is installed.

Builds for a system other than that of the machine you are using can
also be offloaded to a remote machine of the right architecture.
@xref{Daemon Offload Setup}, for more information on offloading.

@item --target=@var{triplet}
@cindex cross-compilation
Cross-build for @var{triplet}, which must be a valid GNU triplet, such
as @code{"aarch64-linux-gnu"} (@pxref{Specifying Target Triplets, GNU
configuration triplets,, autoconf, Autoconf}).

@item --list-systems
List all the supported systems, that can be passed as an argument to
@option{--system}.

@item --list-targets
List all the supported targets, that can be passed as an argument to
@option{--target}.

@anchor{build-check}
@item --check
@cindex determinism, checking
@cindex reproducibility, checking
Rebuild @var{package-or-derivation}, which are already available in the
store, and raise an error if the build results are not bit-for-bit
identical.

This mechanism allows you to check whether previously installed
substitutes are genuine (@pxref{Substitutes}), or whether the build result
of a package is deterministic.  @xref{Invoking guix challenge}, for more
background information and tools.

When used in conjunction with @option{--keep-failed}, the differing
output is kept in the store, under @file{/gnu/store/@dots{}-check}.
This makes it easy to look for differences between the two results.

@item --repair
@cindex repairing store items
@cindex corruption, recovering from
Attempt to repair the specified store items, if they are corrupt, by
re-downloading or rebuilding them.

This operation is not atomic and thus restricted to @code{root}.

@item --derivations
@itemx -d
Return the derivation paths, not the output paths, of the given
packages.

@item --root=@var{file}
@itemx -r @var{file}
@cindex GC roots, adding
@cindex garbage collector roots, adding
Make @var{file} a symlink to the result, and register it as a garbage
collector root.

Consequently, the results of this @command{guix build} invocation are
protected from garbage collection until @var{file} is removed.  When
that option is omitted, build results are eligible for garbage
collection as soon as the build completes.  @xref{Invoking guix gc}, for
more on GC roots.

@item --log-file
@cindex build logs, access
Return the build log file names or URLs for the given
@var{package-or-derivation}, or raise an error if build logs are
missing.

This works regardless of how packages or derivations are specified.  For
instance, the following invocations are equivalent:

@example
guix build --log-file $(guix build -d guile)
guix build --log-file $(guix build guile)
guix build --log-file guile
guix build --log-file -e '(@@ (gnu packages guile) guile-2.0)'
@end example

If a log is unavailable locally, and unless @option{--no-substitutes} is
passed, the command looks for a corresponding log on one of the
substitute servers (as specified with @option{--substitute-urls}).

So for instance, imagine you want to see the build log of GDB on
@code{aarch64}, but you are actually on an @code{x86_64} machine:

@example
$ guix build --log-file gdb -s aarch64-linux
https://@value{SUBSTITUTE-SERVER-1}/log/@dots{}-gdb-7.10
@end example

You can freely access a huge library of build logs!
@end table

@node Debugging Build Failures
@subsection Debugging Build Failures

@cindex build failures, debugging
When defining a new package (@pxref{Defining Packages}), you will
probably find yourself spending some time debugging and tweaking the
build until it succeeds.  To do that, you need to operate the build
commands yourself in an environment as close as possible to the one the
build daemon uses.

To that end, the first thing to do is to use the @option{--keep-failed}
or @option{-K} option of @command{guix build}, which will keep the
failed build tree in @file{/tmp} or whatever directory you specified as
@env{TMPDIR} (@pxref{Common Build Options, @option{--keep-failed}}).

From there on, you can @command{cd} to the failed build tree and source
the @file{environment-variables} file, which contains all the
environment variable definitions that were in place when the build
failed.  So let's say you're debugging a build failure in package
@code{foo}; a typical session would look like this:

@example
$ guix build foo -K
@dots{} @i{build fails}
$ cd /tmp/guix-build-foo.drv-0
$ source ./environment-variables
$ cd foo-1.2
@end example

Now, you can invoke commands as if you were the daemon (almost) and
troubleshoot your build process.

Sometimes it happens that, for example, a package's tests pass when you
run them manually but they fail when the daemon runs them.  This can
happen because the daemon runs builds in containers where, unlike in our
environment above, network access is missing, @file{/bin/sh} does not
exist, etc. (@pxref{Build Environment Setup}).

In such cases, you may need to inspect the build process from within a
container similar to the one the build daemon creates:

@example
$ guix build -K foo
@dots{}
$ cd /tmp/guix-build-foo.drv-0
$ guix shell --no-grafts -C -D foo strace gdb
[env]# source ./environment-variables
[env]# cd foo-1.2
@end example

Here, @command{guix shell -C} creates a container and spawns a new
shell in it (@pxref{Invoking guix shell}).  The @command{strace gdb}
part adds the @command{strace} and @command{gdb} commands to
the container, which you may find handy while debugging.  The
@option{--no-grafts} option makes sure we get the exact same
environment, with ungrafted packages (@pxref{Security Updates}, for more
info on grafts).

To get closer to a container like that used by the build daemon, we can
remove @file{/bin/sh}:

@example
[env]# rm /bin/sh
@end example

(Don't worry, this is harmless: this is all happening in the throw-away
container created by @command{guix shell}.)

The @command{strace} command is probably not in the search path, but we
can run:

@example
[env]# $GUIX_ENVIRONMENT/bin/strace -f -o log make check
@end example

In this way, not only you will have reproduced the environment variables
the daemon uses, you will also be running the build process in a container
similar to the one the daemon uses.


@node Invoking guix edit
@section Invoking @command{guix edit}

@cindex @command{guix edit}
@cindex package definition, editing
So many packages, so many source files!  The @command{guix edit} command
facilitates the life of users and packagers by pointing their editor at
the source file containing the definition of the specified packages.
For instance:

@example
guix edit gcc@@4.9 vim
@end example

@noindent
launches the program specified in the @env{VISUAL} or in the
@env{EDITOR} environment variable to view the recipe of GCC@tie{}4.9.3
and that of Vim.

If you are using a Guix Git checkout (@pxref{Building from Git}), or
have created your own packages on @env{GUIX_PACKAGE_PATH}
(@pxref{Package Modules}), you will be able to edit the package
recipes.  In other cases, you will be able to examine the read-only recipes
for packages currently in the store.

Instead of @env{GUIX_PACKAGE_PATH}, the command-line option
@option{--load-path=@var{directory}} (or in short @option{-L
@var{directory}}) allows you to add @var{directory} to the front of the
package module search path and so make your own packages visible.

@node Invoking guix download
@section Invoking @command{guix download}

@cindex @command{guix download}
@cindex downloading package sources
When writing a package definition, developers typically need to download
a source tarball, compute its SHA256 hash, and write that
hash in the package definition (@pxref{Defining Packages}).  The
@command{guix download} tool helps with this task: it downloads a file
from the given URI, adds it to the store, and prints both its file name
in the store and its SHA256 hash.

The fact that the downloaded file is added to the store saves bandwidth:
when the developer eventually tries to build the newly defined package
with @command{guix build}, the source tarball will not have to be
downloaded again because it is already in the store.  It is also a
convenient way to temporarily stash files, which may be deleted
eventually (@pxref{Invoking guix gc}).

The @command{guix download} command supports the same URIs as used in
package definitions.  In particular, it supports @code{mirror://} URIs.
@code{https} URIs (HTTP over TLS) are supported @emph{provided} the
Guile bindings for GnuTLS are available in the user's environment; when
they are not available, an error is raised.  @xref{Guile Preparations,
how to install the GnuTLS bindings for Guile,, gnutls-guile,
GnuTLS-Guile}, for more information.

@command{guix download} verifies HTTPS server certificates by loading
the certificates of X.509 authorities from the directory pointed to by
the @env{SSL_CERT_DIR} environment variable (@pxref{X.509
Certificates}), unless @option{--no-check-certificate} is used.

Alternatively, @command{guix download} can also retrieve a Git
repository, possibly a specific commit, tag, or branch.

The following options are available:

@table @code
@item --hash=@var{algorithm}
@itemx -H @var{algorithm}
Compute a hash using the specified @var{algorithm}.  @xref{Invoking guix
hash}, for more information.

@item --format=@var{fmt}
@itemx -f @var{fmt}
Write the hash in the format specified by @var{fmt}.  For more
information on the valid values for @var{fmt}, @pxref{Invoking guix hash}.

@item --no-check-certificate
Do not validate the X.509 certificates of HTTPS servers.

When using this option, you have @emph{absolutely no guarantee} that you
are communicating with the authentic server responsible for the given
URL, which makes you vulnerable to ``man-in-the-middle'' attacks.

@item --output=@var{file}
@itemx -o @var{file}
Save the downloaded file to @var{file} instead of adding it to the
store.

@item --git
@itemx -g
Checkout the Git repository at the latest commit on the default branch.

@item --commit=@var{commit-or-tag}
Checkout the Git repository at @var{commit-or-tag}.

@var{commit-or-tag} can be either a tag or a commit defined in the Git
repository.

@item --branch=@var{branch}
Checkout the Git repository at @var{branch}.

The repository will be checked out at the latest commit of @var{branch},
which must be a valid branch of the Git repository.

@item --recursive
@itemx -r
Recursively clone the Git repository.
@end table

@node Invoking guix hash
@section Invoking @command{guix hash}

@cindex @command{guix hash}
The @command{guix hash} command computes the hash of a file.
It is primarily a convenience tool for anyone contributing to the
distribution: it computes the cryptographic hash of one or more files, which can be
used in the definition of a package (@pxref{Defining Packages}).

The general syntax is:

@example
guix hash @var{option} @var{file} ...
@end example

When @var{file} is @code{-} (a hyphen), @command{guix hash} computes the
hash of data read from standard input.  @command{guix hash} has the
following options:

@table @code

@item --hash=@var{algorithm}
@itemx -H @var{algorithm}
Compute a hash using the specified @var{algorithm}, @code{sha256} by
default.

@var{algorithm} must be the name of a cryptographic hash algorithm
supported by Libgcrypt @i{via} Guile-Gcrypt---e.g., @code{sha512} or
@code{sha3-256} (@pxref{Hash Functions,,, guile-gcrypt, Guile-Gcrypt
Reference Manual}).

@item --format=@var{fmt}
@itemx -f @var{fmt}
Write the hash in the format specified by @var{fmt}.

Supported formats: @code{base64}, @code{nix-base32}, @code{base32}, @code{base16}
(@code{hex} and @code{hexadecimal} can be used as well).

If the @option{--format} option is not specified, @command{guix hash}
will output the hash in @code{nix-base32}.  This representation is used
in the definitions of packages.

@item --recursive
@itemx -r
The @option{--recursive} option is deprecated in favor of
@option{--serializer=nar} (see below); @option{-r} remains accepted as a
convenient shorthand.

@item --serializer=@var{type}
@itemx -S @var{type}
Compute the hash on @var{file} using @var{type} serialization.

@var{type} may be one of the following:

@table @code
@item none
This is the default: it computes the hash of a file's contents.

@item nar
Compute the hash of a ``normalized archive'' (or ``nar'') containing
@var{file}, including its children if it is a directory.  Some of the
metadata of @var{file} is part of the archive; for instance, when
@var{file} is a regular file, the hash is different depending on whether
@var{file} is executable or not.  Metadata such as time stamps have no
impact on the hash (@pxref{Invoking guix archive}, for more info on the
nar format).
@c FIXME: Replace xref above with xref to an ``Archive'' section when
@c it exists.

@item git
Compute the hash of the file or directory as a Git ``tree'', following
the same method as the Git version control system.
@end table

@item --exclude-vcs
@itemx -x
When combined with @option{--recursive}, exclude version control system
directories (@file{.bzr}, @file{.git}, @file{.hg}, etc.).

@vindex git-fetch
As an example, here is how you would compute the hash of a Git checkout,
which is useful when using the @code{git-fetch} method (@pxref{origin
Reference}):

@example
$ git clone http://example.org/foo.git
$ cd foo
$ guix hash -x --serializer=nar .
@end example
@end table

@node Invoking guix import
@section Invoking @command{guix import}

@cindex importing packages
@cindex package import
@cindex package conversion
@cindex Invoking @command{guix import}
The @command{guix import} command is useful for people who would like to
add a package to the distribution with as little work as
possible---a legitimate demand.  The command knows of a few
repositories from which it can ``import'' package metadata.  The result
is a package definition, or a template thereof, in the format we know
(@pxref{Defining Packages}).

The general syntax is:

@example
guix import [@var{global-options}@dots{}] @var{importer} @var{package} [@var{options}@dots{}]
@end example

@var{importer} specifies the source from which to import package
metadata, and @var{options} specifies a package identifier and other
options specific to @var{importer}. @command{guix import} itself has the
following @var{global-options}:

@table @code
@item --insert=@var{file}
@itemx -i @var{file}
Insert the package definition(s) that the @var{importer} generated into the
specified @var{file}, either in alphabetical order among existing package
definitions, or at the end of the file otherwise.
@end table

Some of the importers rely on the ability to run the @command{gpgv} command.
For these, GnuPG must be installed and in @code{$PATH}; run @code{guix install
gnupg} if needed.

Currently, the available ``importers'' are:

@table @code
@item gnu
Import metadata for the given GNU package.  This provides a template
for the latest version of that GNU package, including the hash of its
source tarball, and its canonical synopsis and description.

Additional information such as the package dependencies and its
license needs to be figured out manually.

For example, the following command returns a package definition for
GNU@tie{}Hello:

@example
guix import gnu hello
@end example

Specific command-line options are:

@table @code
@item --key-download=@var{policy}
As for @command{guix refresh}, specify the policy to handle missing
OpenPGP keys when verifying the package signature.  @xref{Invoking guix
refresh, @option{--key-download}}.
@end table

@item pypi
@cindex pypi
Import metadata from the @uref{https://pypi.python.org/, Python Package
Index}.  Information is taken from the JSON-formatted description
available at @code{pypi.python.org} and usually includes all the relevant
information, including package dependencies.  For maximum efficiency, it
is recommended to install the @command{unzip} utility, so that the
importer can unzip Python wheels and gather data from them.

The command below imports metadata for the latest version of the
@code{itsdangerous} Python package:

@example
guix import pypi itsdangerous
@end example

You can also ask for a specific version:

@example
guix import pypi itsdangerous@@1.1.0
@end example

@table @code
@item --recursive
@itemx -r
Traverse the dependency graph of the given upstream package recursively
and generate package expressions for all those packages that are not yet
in Guix.
@end table

@item gem
@cindex gem
Import metadata from @uref{https://rubygems.org/, RubyGems}.  Information
is taken from the JSON-formatted description available at
@code{rubygems.org} and includes most relevant information, including
runtime dependencies.  There are some caveats, however.  The metadata
doesn't distinguish between synopses and descriptions, so the same string
is used for both fields.  Additionally, the details of non-Ruby
dependencies required to build native extensions is unavailable and left
as an exercise to the packager.

The command below imports metadata for the @code{rails} Ruby package:

@example
guix import gem rails
@end example

You can also ask for a specific version:

@example
guix import gem rails@@7.0.4
@end example

@table @code
@item --recursive
@itemx -r
Traverse the dependency graph of the given upstream package recursively
and generate package expressions for all those packages that are not yet
in Guix.
@end table

@item minetest
@cindex minetest
@cindex ContentDB
Import metadata from @uref{https://content.minetest.net, ContentDB}.
Information is taken from the JSON-formatted metadata provided through
@uref{https://content.minetest.net/help/api/, ContentDB's API} and
includes most relevant information, including dependencies.  There are
some caveats, however.  The license information is often incomplete.
The commit hash is sometimes missing.  The descriptions are in the
Markdown format, but Guix uses Texinfo instead.  Texture packs and
subgames are unsupported.

The command below imports metadata for the Mesecons mod by Jeija:

@example
guix import minetest Jeija/mesecons
@end example

The author name can also be left out:

@example
guix import minetest mesecons
@end example

@table @code
@item --recursive
@itemx -r
Traverse the dependency graph of the given upstream package recursively
and generate package expressions for all those packages that are not yet
in Guix.
@end table

@item cpan
@cindex CPAN
Import metadata from @uref{https://www.metacpan.org/, MetaCPAN}.
Information is taken from the JSON-formatted metadata provided through
@uref{https://fastapi.metacpan.org/, MetaCPAN's API} and includes most
relevant information, such as module dependencies.  License information
should be checked closely.  If Perl is available in the store, then the
@code{corelist} utility will be used to filter core modules out of the
list of dependencies.

The command below imports metadata for the Acme::Boolean Perl module:

@example
guix import cpan Acme::Boolean
@end example

@item cran
@cindex CRAN
@cindex Bioconductor
Import metadata from @uref{https://cran.r-project.org/, CRAN}, the
central repository for the @uref{https://r-project.org, GNU@tie{}R
statistical and graphical environment}.

Information is extracted from the @file{DESCRIPTION} file of the package.

The command below imports metadata for the Cairo R package:

@example
guix import cran Cairo
@end example

You can also ask for a specific version:

@example
guix import cran rasterVis@@0.50.3
@end example

When @option{--recursive} is added, the importer will traverse the
dependency graph of the given upstream package recursively and generate
package expressions for all those packages that are not yet in Guix.

When @option{--style=specification} is added, the importer will generate
package definitions whose inputs are package specifications instead of
references to package variables.  This is useful when generated package
definitions are to be appended to existing user modules, as the list of
used package modules need not be changed.  The default is
@option{--style=variable}.

When @option{--prefix=license:} is added, the importer will prefix
license atoms with @code{license:}, allowing a prefixed import of
@code{(guix licenses)}.

When @option{--archive=bioconductor} is added, metadata is imported from
@uref{https://www.bioconductor.org/, Bioconductor}, a repository of R
packages for the analysis and comprehension of high-throughput
genomic data in bioinformatics.

Information is extracted from the @file{DESCRIPTION} file contained in the
package archive.

The command below imports metadata for the GenomicRanges R package:

@example
guix import cran --archive=bioconductor GenomicRanges
@end example

Finally, you can also import R packages that have not yet been published on
CRAN or Bioconductor as long as they are in a git repository.  Use
@option{--archive=git} followed by the URL of the git repository:

@example
guix import cran --archive=git https://github.com/immunogenomics/harmony
@end example

@item texlive
@cindex TeX Live
@cindex CTAN
Import TeX package information from the TeX Live package database for
TeX packages that are part of the @uref{https://www.tug.org/texlive/,
TeX Live distribution}.

Information about the package is obtained from the TeX Live package
database, a plain text file that is included in the
@code{texlive-scripts} package.  The source code is downloaded from
possibly multiple locations in the SVN repository of the Tex Live
project.  Note that therefore SVN must be installed and in @code{$PATH};
run @code{guix install subversion} if needed.

The command below imports metadata for the @code{fontspec} TeX package:

@example
guix import texlive fontspec
@end example

Additional options include:

@table @code
@item --recursive
@itemx -r
Traverse the dependency graph of the given upstream package recursively
and generate package expressions for all those packages that are not yet
in Guix.
@end table

@item json
@cindex JSON, import
Import package metadata from a local JSON file.  Consider the following
example package definition in JSON format:

@example
@{
  "name": "hello",
  "version": "2.10",
  "source": "mirror://gnu/hello/hello-2.10.tar.gz",
  "build-system": "gnu",
  "home-page": "https://www.gnu.org/software/hello/",
  "synopsis": "Hello, GNU world: An example GNU package",
  "description": "GNU Hello prints a greeting.",
  "license": "GPL-3.0+",
  "native-inputs": ["gettext"]
@}
@end example

The field names are the same as for the @code{<package>} record
(@xref{Defining Packages}).  References to other packages are provided
as JSON lists of quoted package specification strings such as
@code{guile} or @code{guile@@2.0}.

The importer also supports a more explicit source definition using the
common fields for @code{<origin>} records:

@example
@{
  @dots{}
  "source": @{
    "method": "url-fetch",
    "uri": "mirror://gnu/hello/hello-2.10.tar.gz",
    "sha256": @{
      "base32": "0ssi1wpaf7plaswqqjwigppsg5fyh99vdlb9kzl7c9lng89ndq1i"
    @}
  @}
  @dots{}
@}
@end example

The command below reads metadata from the JSON file @code{hello.json}
and outputs a package expression:

@example
guix import json hello.json
@end example

@item hackage
@cindex hackage
Import metadata from the Haskell community's central package archive
@uref{https://hackage.haskell.org/, Hackage}.  Information is taken from
Cabal files and includes all the relevant information, including package
dependencies.

Specific command-line options are:

@table @code
@item --stdin
@itemx -s
Read a Cabal file from standard input.
@item --no-test-dependencies
@itemx -t
Do not include dependencies required only by the test suites.
@item --cabal-environment=@var{alist}
@itemx -e @var{alist}
@var{alist} is a Scheme alist defining the environment in which the
Cabal conditionals are evaluated.  The accepted keys are: @code{os},
@code{arch}, @code{impl} and a string representing the name of a flag.
The value associated with a flag has to be either the symbol
@code{true} or @code{false}.  The value associated with other keys
has to conform to the Cabal file format definition.  The default value
associated with the keys @code{os}, @code{arch} and @code{impl} is
@samp{linux}, @samp{x86_64} and @samp{ghc}, respectively.
@item --recursive
@itemx -r
Traverse the dependency graph of the given upstream package recursively
and generate package expressions for all those packages that are not yet
in Guix.
@end table

The command below imports metadata for the latest version of the
HTTP Haskell package without including test dependencies and
specifying the value of the flag @samp{network-uri} as @code{false}:

@example
guix import hackage -t -e "'((\"network-uri\" . false))" HTTP
@end example

A specific package version may optionally be specified by following the
package name by an at-sign and a version number as in the following example:

@example
guix import hackage mtl@@2.1.3.1
@end example

@item stackage
@cindex stackage
The @code{stackage} importer is a wrapper around the @code{hackage} one.
It takes a package name, looks up the package version included in a
long-term support (LTS) @uref{https://www.stackage.org, Stackage}
release and uses the @code{hackage} importer to retrieve its metadata.
Note that it is up to you to select an LTS release compatible with the
GHC compiler used by Guix.

Specific command-line options are:

@table @code
@item --no-test-dependencies
@itemx -t
Do not include dependencies required only by the test suites.
@item --lts-version=@var{version}
@itemx -l @var{version}
@var{version} is the desired LTS release version.  If omitted the latest
release is used.
@item --recursive
@itemx -r
Traverse the dependency graph of the given upstream package recursively
and generate package expressions for all those packages that are not yet
in Guix.
@end table

The command below imports metadata for the HTTP Haskell package
included in the LTS Stackage release version 7.18:

@example
guix import stackage --lts-version=7.18 HTTP
@end example

@item elpa
@cindex elpa
Import metadata from an Emacs Lisp Package Archive (ELPA) package
repository (@pxref{Packages,,, emacs, The GNU Emacs Manual}).

Specific command-line options are:

@table @code
@item --archive=@var{repo}
@itemx -a @var{repo}
@var{repo} identifies the archive repository from which to retrieve the
information.  Currently the supported repositories and their identifiers
are:
@itemize -
@item
@uref{https://elpa.gnu.org/packages, GNU}, selected by the @code{gnu}
identifier.  This is the default.

Packages from @code{elpa.gnu.org} are signed with one of the keys
contained in the GnuPG keyring at
@file{share/emacs/25.1/etc/package-keyring.gpg} (or similar) in the
@code{emacs} package (@pxref{Package Installation, ELPA package
signatures,, emacs, The GNU Emacs Manual}).

@item
@uref{https://elpa.nongnu.org/nongnu/, NonGNU}, selected by the
@code{nongnu} identifier.

@item
@uref{https://stable.melpa.org/packages, MELPA-Stable}, selected by the
@code{melpa-stable} identifier.

@item
@uref{https://melpa.org/packages, MELPA}, selected by the @code{melpa}
identifier.
@end itemize

@item --recursive
@itemx -r
Traverse the dependency graph of the given upstream package recursively
and generate package expressions for all those packages that are not yet
in Guix.
@end table

@item crate
@cindex crate
Import metadata from the crates.io Rust package repository
@uref{https://crates.io, crates.io}, as in this example:

@example
guix import crate blake2-rfc
@end example

The crate importer also allows you to specify a version string:

@example
guix import crate constant-time-eq@@0.1.0
@end example

Additional options include:

@table @code
@item --recursive
@itemx -r
Traverse the dependency graph of the given upstream package recursively
and generate package expressions for all those packages that are not yet
in Guix.
@item --recursive-dev-dependencies
If @option{--recursive-dev-dependencies} is specified, also the recursively
imported packages contain their development dependencies, which are recursively
imported as well.
@item --allow-yanked
If no non-yanked version of a crate is available, use the latest yanked
version instead instead of aborting.
@end table

@item elm
@cindex elm
Import metadata from the Elm package repository
@uref{https://package.elm-lang.org, package.elm-lang.org}, as in this example:

@example
guix import elm elm-explorations/webgl
@end example

The Elm importer also allows you to specify a version string:

@example
guix import elm elm-explorations/webgl@@1.1.3
@end example

Additional options include:

@table @code
@item --recursive
@itemx -r
Traverse the dependency graph of the given upstream package recursively
and generate package expressions for all those packages that are not yet
in Guix.
@end table

@item npm-binary
@cindex npm
@cindex Node.js
Import metadata from the @uref{https://registry.npmjs.org, npm
Registry}, as in this example:

@example
guix import npm-binary buffer-crc32
@end example

The npm-binary importer also allows you to specify a version string:

@example
guix import npm-binary buffer-crc32@@1.0.0
@end example

@quotation Note
Generated package expressions skip the build step of the
@code{node-build-system}. As such, generated package expressions often
refer to transpiled or generated files, instead of being built from
source.
@end quotation

Additional options include:

@table @code
@item --recursive
@itemx -r
Traverse the dependency graph of the given upstream package recursively
and generate package expressions for all those packages that are not yet
in Guix.
@end table

@item opam
@cindex OPAM
@cindex OCaml
Import metadata from the @uref{https://opam.ocaml.org/, OPAM} package
repository used by the OCaml community.

Additional options include:

@table @code
@item --recursive
@itemx -r
Traverse the dependency graph of the given upstream package recursively
and generate package expressions for all those packages that are not yet
in Guix.
@end table

@item composer
@cindex Composer
@cindex PHP
Import metadata from the @uref{https://getcomposer.org/, Composer} package
archive used by the PHP community, as in this example:

@example
guix import composer phpunit/phpunit
@end example

Additional options include:

@table @code
@item --recursive
@itemx -r
Traverse the dependency graph of the given upstream package recursively
and generate package expressions for all those packages that are not yet
in Guix.
@item --repo
By default, packages are searched in the official OPAM repository.  This
option, which can be used more than once, lets you add other repositories
which will be searched for packages.  It accepts as valid arguments:

@itemize
@item the name of a known repository - can be one of @code{opam},
      @code{coq} (equivalent to @code{coq-released}),
	  @code{coq-core-dev}, @code{coq-extra-dev} or @code{grew}.
@item the URL of a repository as expected by the
      @code{opam repository add} command (for instance, the URL equivalent
	  of the above @code{opam} name would be
	  @uref{https://opam.ocaml.org}).
@item the path to a local copy of a repository (a directory containing a
      @file{packages/} sub-directory).
@end itemize

Repositories are assumed to be passed to this option by order of
preference.  The additional repositories will not replace the default
@code{opam} repository, which is always kept as a fallback.

Also, please note that versions are not compared across repositories.
The first repository (from left to right) that has at least one version
of a given package will prevail over any others, and the version
imported will be the latest one found @emph{in this repository only}.

@end table

@item go
@cindex go
Import metadata for a Go module using
@uref{https://proxy.golang.org, proxy.golang.org}.

@example
guix import go gopkg.in/yaml.v2
@end example

It is possible to use a package specification with a @code{@@VERSION}
suffix to import a specific version.

Additional options include:

@table @code
@item --recursive
@itemx -r
Traverse the dependency graph of the given upstream package recursively
and generate package expressions for all those packages that are not yet
in Guix.
@item --pin-versions
When using this option, the importer preserves the exact versions of the
Go modules dependencies instead of using their latest available
versions.  This can be useful when attempting to import packages that
recursively depend on former versions of themselves to build.  When
using this mode, the symbol of the package is made by appending the
version to its name, so that multiple versions of the same package can
coexist.
@end table

@item egg
@cindex egg
Import metadata for @uref{https://wiki.call-cc.org/eggs, CHICKEN eggs}.
The information is taken from @file{PACKAGE.egg} files found in the
@uref{git://code.call-cc.org/eggs-5-all, eggs-5-all} Git
repository.  However, it does not provide all the information that we
need, there is no ``description'' field, and the licenses used are not
always precise (BSD is often used instead of BSD-N).

@example
guix import egg sourcehut
@end example

You can also ask for a specific version:

@example
guix import egg arrays@@1.0
@end example

Additional options include:
@table @code
@item --recursive
@itemx -r
Traverse the dependency graph of the given upstream package recursively
and generate package expressions for all those packages that are not yet
in Guix.
@end table

@item hexpm
@cindex hexpm
Import metadata from the hex.pm Erlang and Elixir package repository
@uref{https://hex.pm, hex.pm}, as in this example:

@example
guix import hexpm stun
@end example

The importer tries to determine the build system used by the package.

The hexpm importer also allows you to specify a version string:

@example
guix import hexpm cf@@0.3.0
@end example

Additional options include:

@table @code
@item --recursive
@itemx -r
Traverse the dependency graph of the given upstream package recursively
and generate package expressions for all those packages that are not yet
in Guix.
@end table
@end table

The structure of the @command{guix import} code is modular.  It would be
useful to have more importers for other package formats, and your help
is welcome here (@pxref{Contributing}).

@node Invoking guix refresh
@section Invoking @command{guix refresh}

@cindex @command {guix refresh}
The primary audience of the @command{guix refresh} command is packagers.
As a user, you may be interested in the @option{--with-latest} option,
which can bring you package update superpowers built upon @command{guix
refresh} (@pxref{Package Transformation Options,
@option{--with-latest}}).  By default, @command{guix refresh} reports
any packages provided by the distribution that are outdated compared to
the latest upstream version, like this:

@example
$ guix refresh
gnu/packages/gettext.scm:29:13: gettext would be upgraded from 0.18.1.1 to 0.18.2.1
gnu/packages/glib.scm:77:12: glib would be upgraded from 2.34.3 to 2.37.0
@end example

Alternatively, one can specify packages to consider, in which case a
warning is emitted for packages that lack an updater:

@example
$ guix refresh coreutils guile guile-ssh
gnu/packages/ssh.scm:205:2: warning: no updater for guile-ssh
gnu/packages/guile.scm:136:12: guile would be upgraded from 2.0.12 to 2.0.13
@end example

@command{guix refresh} browses the upstream repository of each package and determines
the highest version number of the releases therein.  The command
knows how to update specific types of packages: GNU packages, ELPA
packages, etc.---see the documentation for @option{--type} below.  There
are many packages, though, for which it lacks a method to determine
whether a new upstream release is available.  However, the mechanism is
extensible, so feel free to get in touch with us to add a new method!

@table @code

@item --recursive
Consider the packages specified, and all the packages upon which they depend.

@example
$ guix refresh --recursive coreutils
gnu/packages/acl.scm:40:13: acl would be upgraded from 2.2.53 to 2.3.1
gnu/packages/m4.scm:30:12: 1.4.18 is already the latest version of m4
gnu/packages/xml.scm:68:2: warning: no updater for expat
gnu/packages/multiprecision.scm:40:12: 6.1.2 is already the latest version of gmp
@dots{}
@end example

@end table

If for some reason you don't want to update to the latest version, you
can update to a specific version by appending an equal sign and the
desired version number to the package specification.  Note that not all
updaters support this; an error is reported when an updater cannot
refresh to the specified version.

@example
$ guix refresh trytond-party
gnu/packages/guile.scm:392:2: guile would be upgraded from 3.0.3 to 3.0.5
$ guix refresh -u guile=3.0.4
@dots{}
gnu/packages/guile.scm:392:2: guile: updating from version 3.0.3 to version 3.0.4...
@dots{}
$ guix refresh -u guile@@2.0=2.0.12
@dots{}
gnu/packages/guile.scm:147:2: guile: updating from version 2.0.10 to version 2.0.12...
@dots{}
@end example

In some specific cases, you may have many packages specified via a
manifest or a module selection which should all be updated together; for
these cases, the @option{--target-version} option can be provided to have
them all refreshed to the same version, as shown in the examples below:

@example
$ guix refresh qtbase qtdeclarative --target-version=6.5.2
gnu/packages/qt.scm:1248:13: qtdeclarative would be upgraded from 6.3.2 to 6.5.2
gnu/packages/qt.scm:584:2: qtbase would be upgraded from 6.3.2 to 6.5.2
@end example

@example
$ guix refresh --manifest=qt5-manifest.scm --target-version=5.15.10
gnu/packages/qt.scm:1173:13: qtxmlpatterns would be upgraded from 5.15.8 to 5.15.10
gnu/packages/qt.scm:1202:13: qtdeclarative would be upgraded from 5.15.8 to 5.15.10
gnu/packages/qt.scm:1762:13: qtserialbus would be upgraded from 5.15.8 to 5.15.10
gnu/packages/qt.scm:2070:13: qtquickcontrols2 would be upgraded from 5.15.8 to 5.15.10
@dots{}
@end example

Sometimes the upstream name differs from the package name used in Guix,
and @command{guix refresh} needs a little help.  Most updaters honor the
@code{upstream-name} property in package definitions, which can be used
to that effect:

@lisp
(define-public network-manager
  (package
    (name "network-manager")
    ;; @dots{}
    (properties '((upstream-name . "NetworkManager")))))
@end lisp

When passed @option{--update}, it modifies distribution source files to
update the version numbers and source code hashes of those package
definitions, as well as possibly their inputs (@pxref{Defining Packages}).
This is achieved by downloading
each package's latest source tarball and its associated OpenPGP
signature, authenticating the downloaded tarball against its signature
using @command{gpgv}, and finally computing its hash---note that GnuPG must be
installed and in @code{$PATH}; run @code{guix install gnupg} if needed.

When the public
key used to sign the tarball is missing from the user's keyring, an
attempt is made to automatically retrieve it from a public key server;
when this is successful, the key is added to the user's keyring; otherwise,
@command{guix refresh} reports an error.

The following options are supported:

@table @code

@item --expression=@var{expr}
@itemx -e @var{expr}
Consider the package @var{expr} evaluates to.

This is useful to precisely refer to a package, as in this example:

@example
guix refresh -l -e '(@@@@ (gnu packages commencement) glibc-final)'
@end example

This command lists the dependents of the ``final'' libc (essentially all
the packages).

@item --update
@itemx -u
Update distribution source files (package definitions) in place.  This is
usually run from a checkout of the Guix source tree (@pxref{Running
Guix Before It Is Installed}):

@example
./pre-inst-env guix refresh -s non-core -u
@end example

@xref{Defining Packages}, for more information on package definitions.
You can also run it on packages from a third-party channel:

@example
guix refresh -L /path/to/channel -u @var{package}
@end example

@xref{Creating a Channel}, on how to create a channel.

This command updates the version and source code hash of the package.
Depending on the updater being used, it can also update the various
@samp{inputs} fields of the package.  In some cases, the updater might
get inputs wrong---it might not know about an extra input that's
necessary, or it might add an input that should be avoided.

@cindex @code{updater-extra-inputs}, package property
@cindex @code{updater-ignored-inputs}, package property
To address that, packagers can add properties stating inputs that should
be added to those found by the updater or inputs that should be ignored:
the @code{updater-extra-inputs} and @code{updater-ignored-inputs}
properties pertain to ``regular'' inputs, and there are equivalent
properties for @samp{native} and @samp{propagated} inputs.  In the
example below, we tell the updater that we need @samp{openmpi} as an
additional input:

@lisp
(define-public python-mpi4py
  (package
    (name "python-mpi4py")
    ;; @dots{}
    (inputs (list openmpi))
    (properties
     '((updater-extra-inputs . ("openmpi"))))))
@end lisp

That way, @command{guix refresh -u python-mpi4py} will leave the
@samp{openmpi} input, even if it is not among the inputs it would
normally add.

@item --select=[@var{subset}]
@itemx -s @var{subset}
Select all the packages in @var{subset}, one of @code{core}, @code{non-core}
or @code{module:@var{name}}.

The @code{core} subset refers to all the packages at the core of the
distribution---i.e., packages that are used to build ``everything
else''.  This includes GCC, libc, Binutils, Bash, etc.  Usually,
changing one of these packages in the distribution entails a rebuild of
all the others.  Thus, such updates are an inconvenience to users in
terms of build time or bandwidth used to achieve the upgrade.

The @code{non-core} subset refers to the remaining packages.  It is
typically useful in cases where an update of the core packages would be
inconvenient.

The @code{module:@var{name}} subset refers to all the packages in a
specified guile module.  The module can be specified as
@code{module:guile} or @code{module:(gnu packages guile)}, the former is
a shorthand for the later.

@item --manifest=@var{file}
@itemx -m @var{file}
Select all the packages from the manifest in @var{file}.  This is useful to
check if any packages of the user manifest can be updated.

@item --type=@var{updater}
@itemx -t @var{updater}
Select only packages handled by @var{updater} (may be a comma-separated
list of updaters).  Currently, @var{updater} may be one of:

@table @code
@item gnu
the updater for GNU packages;
@item savannah
the updater for packages hosted at @uref{https://savannah.gnu.org, Savannah};
@item sourceforge
the updater for packages hosted at @uref{https://sourceforge.net, SourceForge};
@item gnome
the updater for GNOME packages;
@item kde
the updater for KDE packages;
@item xorg
the updater for X.org packages;
@item kernel.org
the updater for packages hosted on kernel.org;
@item egg
the updater for @uref{https://wiki.call-cc.org/eggs/, Egg} packages;
@item elpa
the updater for @uref{https://elpa.gnu.org/, ELPA} packages;
@item cran
the updater for @uref{https://cran.r-project.org/, CRAN} packages;
@item bioconductor
the updater for @uref{https://www.bioconductor.org/, Bioconductor} R packages;
@item cpan
the updater for @uref{https://www.cpan.org/, CPAN} packages;
@item pypi
the updater for @uref{https://pypi.python.org, PyPI} packages.
@item gem
the updater for @uref{https://rubygems.org, RubyGems} packages.
@item github
the updater for @uref{https://github.com, GitHub} packages.
@item hackage
the updater for @uref{https://hackage.haskell.org, Hackage} packages.
@item stackage
the updater for @uref{https://www.stackage.org, Stackage} packages.
@item crate
the updater for @uref{https://crates.io, Crates} packages.
@item launchpad
the updater for @uref{https://launchpad.net, Launchpad} packages.
@item generic-html
a generic updater that crawls the HTML page where the source tarball of
the package is hosted, when applicable, or the HTML page specified by
the @code{release-monitoring-url} property of the package.

@item generic-git
a generic updater for packages hosted on Git repositories.  It tries to
be smart about parsing Git tag names, but if it is not able to parse the
tag name and compare tags correctly, users can define the following
properties for a package.

@itemize
@item @code{release-tag-prefix}: a regular expression for matching a prefix of
the tag name.

@item @code{release-tag-suffix}: a regular expression for matching a suffix of
the tag name.

@item @code{release-tag-version-delimiter}: a string used as the delimiter in
the tag name for separating the numbers of the version.

@item @code{accept-pre-releases}: by default, the updater will ignore
pre-releases; to make it also look for pre-releases, set the this
property to @code{#t}.

@end itemize

@lisp
(package
  (name "foo")
  ;; ...
  (properties
    '((release-tag-prefix . "^release0-")
      (release-tag-suffix . "[a-z]?$")
      (release-tag-version-delimiter . ":"))))
@end lisp


@end table

For instance, the following command only checks for updates of Emacs
packages hosted at @code{elpa.gnu.org} and for updates of CRAN packages:

@example
$ guix refresh --type=elpa,cran
gnu/packages/statistics.scm:819:13: r-testthat would be upgraded from 0.10.0 to 0.11.0
gnu/packages/emacs.scm:856:13: emacs-auctex would be upgraded from 11.88.6 to 11.88.9
@end example

@item --list-updaters
List available updaters and exit (see @option{--type} above).

For each updater, display the fraction of packages it covers; at the
end, display the fraction of packages covered by all these updaters.
@end table

In addition, @command{guix refresh} can be passed one or more package
names, as in this example:

@example
$ ./pre-inst-env guix refresh -u emacs idutils gcc@@4.8
@end example

@noindent
The command above specifically updates the @code{emacs} and
@code{idutils} packages.  The @option{--select} option would have no
effect in this case.  You might also want to update definitions that
correspond to the packages installed in your profile:

@example
$ ./pre-inst-env guix refresh -u \
       $(guix package --list-installed | cut -f1)
@end example

When considering whether to upgrade a package, it is sometimes
convenient to know which packages would be affected by the upgrade and
should be checked for compatibility.  For this the following option may
be used when passing @command{guix refresh} one or more package names:

@table @code

@item --list-dependent
@itemx -l
List top-level dependent packages that would need to be rebuilt as a
result of upgrading one or more packages.

@xref{Invoking guix graph, the @code{reverse-package} type of
@command{guix graph}}, for information on how to visualize the list of
dependents of a package.

@end table

Be aware that the @option{--list-dependent} option only
@emph{approximates} the rebuilds that would be required as a result of
an upgrade.  More rebuilds might be required under some circumstances.

@example
$ guix refresh --list-dependent flex
Building the following 120 packages would ensure 213 dependent packages are rebuilt:
hop@@2.4.0 emacs-geiser@@0.13 notmuch@@0.18 mu@@0.9.9.5 cflow@@1.4 idutils@@4.6 @dots{}
@end example

The command above lists a set of packages that could be built to check
for compatibility with an upgraded @code{flex} package.

@table @code

@item --list-transitive
@itemx -T
List all the packages which one or more packages depend upon.

@example
$ guix refresh --list-transitive flex
flex@@2.6.4 depends on the following 25 packages: perl@@5.28.0 help2man@@1.47.6
bison@@3.0.5 indent@@2.2.10 tar@@1.30 gzip@@1.9 bzip2@@1.0.6 xz@@5.2.4 file@@5.33 @dots{}
@end example

@end table

The command above lists a set of packages which, when changed, would cause
@code{flex} to be rebuilt.

The following options can be used to customize GnuPG operation:

@table @code

@item --gpg=@var{command}
Use @var{command} as the GnuPG 2.x command.  @var{command} is searched
for in @code{$PATH}.

@item --keyring=@var{file}
Use @var{file} as the keyring for upstream keys.  @var{file} must be in the
@dfn{keybox format}.  Keybox files usually have a name ending in @file{.kbx}
and the GNU@tie{}Privacy Guard (GPG) can manipulate these files
(@pxref{kbxutil, @command{kbxutil},, gnupg, Using the GNU Privacy Guard}, for
information on a tool to manipulate keybox files).

When this option is omitted, @command{guix refresh} uses
@file{~/.config/guix/upstream/trustedkeys.kbx} as the keyring for upstream
signing keys.  OpenPGP signatures are checked against keys from this keyring;
missing keys are downloaded to this keyring as well (see
@option{--key-download} below).

You can export keys from your default GPG keyring into a keybox file using
commands like this one:

@example
gpg --export rms@@gnu.org | kbxutil --import-openpgp >> mykeyring.kbx
@end example

Likewise, you can fetch keys to a specific keybox file like this:

@example
gpg --no-default-keyring --keyring mykeyring.kbx \
  --recv-keys @value{OPENPGP-SIGNING-KEY-ID}
@end example

@xref{GPG Configuration Options, @option{--keyring},, gnupg, Using the GNU
Privacy Guard}, for more information on GPG's @option{--keyring} option.

@item --key-download=@var{policy}
Handle missing OpenPGP keys according to @var{policy}, which may be one
of:

@table @code
@item always
Always download missing OpenPGP keys from the key server, and add them
to the user's GnuPG keyring.

@item never
Never try to download missing OpenPGP keys.  Instead just bail out.

@item interactive
When a package signed with an unknown OpenPGP key is encountered, ask
the user whether to download it or not.  This is the default behavior.
@end table

@item --key-server=@var{host}
Use @var{host} as the OpenPGP key server when importing a public key.

@item --load-path=@var{directory}
@itemx -L @var{directory}
Add @var{directory} to the front of the package module search path
(@pxref{Package Modules}).

This allows users to define their own packages and make them visible to
the command-line tools.

@end table

The @code{github} updater uses the
@uref{https://developer.github.com/v3/, GitHub API} to query for new
releases.  When used repeatedly e.g.@: when refreshing all packages,
GitHub will eventually refuse to answer any further API requests.  By
default 60 API requests per hour are allowed, and a full refresh on all
GitHub packages in Guix requires more than this.  Authentication with
GitHub through the use of an API token alleviates these limits.  To use
an API token, set the environment variable @env{GUIX_GITHUB_TOKEN} to a
token procured from @uref{https://github.com/settings/tokens} or
otherwise.


@node Invoking guix style
@section Invoking @command{guix style}

@cindex @command{guix style}
@cindex styling rules
@cindex lint, code style
@cindex format, code style
@cindex format conventions
The @command{guix style} command helps users and packagers alike style
their package definitions and configuration files according to the
latest fashionable trends.  It can either reformat whole files, with the
@option{--whole-file} option, or apply specific @dfn{styling rules} to
individual package definitions.  The command currently provides the
following styling rules:

@itemize
@item
formatting package definitions according to the project's conventions
(@pxref{Formatting Code});

@item
rewriting package inputs to the ``new style'', as explained below.
@end itemize

The way package inputs are written is going through a transition
(@pxref{package Reference}, for more on package inputs).  Until version
1.3.0, package inputs were written using the ``old style'', where each
input was given an explicit label, most of the time the package name:

@lisp
(package
  ;; @dots{}
  ;; The "old style" (deprecated).
  (inputs `(("libunistring" ,libunistring)
            ("libffi" ,libffi))))
@end lisp

Today, the old style is deprecated and the preferred style looks like
this:

@lisp
(package
  ;; @dots{}
  ;; The "new style".
  (inputs (list libunistring libffi)))
@end lisp

Likewise, uses of @code{alist-delete} and friends to manipulate inputs
is now deprecated in favor of @code{modify-inputs} (@pxref{Defining
Package Variants}, for more info on @code{modify-inputs}).

In the vast majority of cases, this is a purely mechanical change on the
surface syntax that does not even incur a package rebuild.  Running
@command{guix style -S inputs} can do that for you, whether you're working on
packages in Guix proper or in an external channel.

The general syntax is:

@example
guix style [@var{options}] @var{package}@dots{}
@end example

This causes @command{guix style} to analyze and rewrite the definition
of @var{package}@dots{} or, when @var{package} is omitted, of @emph{all}
the packages.  The @option{--styling} or @option{-S} option allows you
to select the style rule, the default rule being @code{format}---see
below.

To reformat entire source files, the syntax is:

@example
guix style --whole-file @var{file}@dots{}
@end example

The available options are listed below.

@table @code
@item --dry-run
@itemx -n
Show source file locations that would be edited but do not modify them.

@item --whole-file
@itemx -f
Reformat the given files in their entirety.  In that case, subsequent
arguments are interpreted as file names (rather than package names), and
the @option{--styling} option has no effect.

As an example, here is how you might reformat your operating system
configuration (you need write permissions for the file):

@example
guix style -f /etc/config.scm
@end example

@item --styling=@var{rule}
@itemx -S @var{rule}
Apply @var{rule}, one of the following styling rules:

@table @code
@item format
Format the given package definition(s)---this is the default styling
rule.  For example, a packager running Guix on a checkout
(@pxref{Running Guix Before It Is Installed}) might want to reformat the
definition of the Coreutils package like so:

@example
./pre-inst-env guix style coreutils
@end example

@item inputs
Rewrite package inputs to the ``new style'', as described above.  This
is how you would rewrite inputs of package @code{whatnot} in your own
channel:

@example
guix style -L ~/my/channel -S inputs whatnot
@end example

Rewriting is done in a conservative way: preserving comments and bailing
out if it cannot make sense of the code that appears in an inputs field.
The @option{--input-simplification} option described below provides
fine-grain control over when inputs should be simplified.

@item arguments
Rewrite package arguments to use G-expressions (@pxref{G-Expressions}).
For example, consider this package definition:

@lisp
(define-public my-package
  (package
    ;; @dots{}
    (arguments      ;old-style quoted arguments
     '(#:make-flags '("V=1")
       #:phases (modify-phases %standard-phases
                  (delete 'build))))))
@end lisp

@noindent
Running @command{guix style -S arguments} on this package would rewrite
its @code{arguments} field like to:

@lisp
(define-public my-package
  (package
    ;; @dots{}
    (arguments
      (list #:make-flags #~'("V=1")
            #:phases #~(modify-phases %standard-phases
                         (delete 'build))))))
@end lisp

Note that changes made by the @code{arguments} rule do not entail a
rebuild of the affected packages.  Furthermore, if a package definition
happens to be using G-expressions already, @command{guix style} leaves
it unchanged.
@end table

@item --list-stylings
@itemx -l
List and describe the available styling rules and exit.

@item --load-path=@var{directory}
@itemx -L @var{directory}
Add @var{directory} to the front of the package module search path
(@pxref{Package Modules}).

@item --expression=@var{expr}
@itemx -e @var{expr}
Style the package @var{expr} evaluates to.

For example, running:

@example
guix style -e '(@@ (gnu packages gcc) gcc-5)'
@end example

styles the @code{gcc-5} package definition.

@item --input-simplification=@var{policy}
When using the @code{inputs} styling rule, with @samp{-S inputs}, this
option specifies the package input simplification policy for cases where
an input label does not match the corresponding package name.
@var{policy} may be one of the following:

@table @code
@item silent
Simplify inputs only when the change is ``silent'', meaning that the
package does not need to be rebuilt (its derivation is unchanged).

@item safe
Simplify inputs only when that is ``safe'' to do: the package might need
to be rebuilt, but the change is known to have no observable effect.

@item always
Simplify inputs even when input labels do not match package names, and
even if that might have an observable effect.
@end table

The default is @code{silent}, meaning that input simplifications do not
trigger any package rebuild.
@end table

@node Invoking guix lint
@section Invoking @command{guix lint}

@cindex @command{guix lint}
@cindex package, checking for errors
The @command{guix lint} command is meant to help package developers avoid
common errors and use a consistent style.  It runs a number of checks on
a given set of packages in order to find common mistakes in their
definitions.  Available @dfn{checkers} include (see
@option{--list-checkers} for a complete list):

@table @code
@item synopsis
@itemx description
Validate certain typographical and stylistic rules about package
descriptions and synopses.

@item inputs-should-be-native
Identify inputs that should most likely be native inputs.

@item source
@itemx home-page
@itemx mirror-url
@itemx github-url
@itemx source-file-name
Probe @code{home-page} and @code{source} URLs and report those that are
invalid.  Suggest a @code{mirror://} URL when applicable.  If the
@code{source} URL redirects to a GitHub URL, recommend usage of the GitHub
URL@.  Check that the source file name is meaningful, e.g.@: is not just a
version number or ``git-checkout'', without a declared @code{file-name}
(@pxref{origin Reference}).

@item source-unstable-tarball
Parse the @code{source} URL to determine if a tarball from GitHub is
autogenerated or if it is a release tarball.  Unfortunately GitHub's
autogenerated tarballs are sometimes regenerated.

@item derivation
Check that the derivation of the given packages can be successfully
computed for all the supported systems (@pxref{Derivations}).

@item profile-collisions
Check whether installing the given packages in a profile would lead to
collisions.  Collisions occur when several packages with the same name
but a different version or a different store file name are propagated.
@xref{package Reference, @code{propagated-inputs}}, for more information
on propagated inputs.

@item archival
@cindex Software Heritage, source code archive
@cindex archival of source code, Software Heritage
Checks whether the package's source code is archived at
@uref{https://www.softwareheritage.org, Software Heritage}.

When the source code that is not archived comes from a version-control system
(VCS)---e.g., it's obtained with @code{git-fetch}, send Software Heritage a
``save'' request so that it eventually archives it.  This ensures that the
source will remain available in the long term, and that Guix can fall back to
Software Heritage should the source code disappear from its original host.
The status of recent ``save'' requests can be
@uref{https://archive.softwareheritage.org/save/#requests, viewed on-line}.

When source code is a tarball obtained with @code{url-fetch}, simply print a
message when it is not archived.  As of this writing, Software Heritage does
not allow requests to save arbitrary tarballs; we are working on ways to
ensure that non-VCS source code is also archived.

Software Heritage
@uref{https://archive.softwareheritage.org/api/#rate-limiting, limits the
request rate per IP address}.  When the limit is reached, @command{guix lint}
prints a message and the @code{archival} checker stops doing anything until
that limit has been reset.

@item cve
@cindex security vulnerabilities
@cindex CVE, Common Vulnerabilities and Exposures
Report known vulnerabilities found in the Common Vulnerabilities and
Exposures (CVE) databases of the current and past year
@uref{https://nvd.nist.gov/vuln/data-feeds, published by the US
NIST}.

To view information about a particular vulnerability, visit pages such as:

@itemize
@item
@indicateurl{https://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-YYYY-ABCD}
@item
@indicateurl{https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-YYYY-ABCD}
@end itemize

@noindent
where @code{CVE-YYYY-ABCD} is the CVE identifier---e.g.,
@code{CVE-2015-7554}.

Package developers can specify in package recipes the
@uref{https://nvd.nist.gov/products/cpe,Common Platform Enumeration (CPE)}
name and version of the package when they differ from the name or version
that Guix uses, as in this example:

@lisp
(package
  (name "grub")
  ;; @dots{}
  ;; CPE calls this package "grub2".
  (properties '((cpe-name . "grub2")
                (cpe-version . "2.3"))))
@end lisp

@c See <https://www.openwall.com/lists/oss-security/2017/03/15/3>.
Some entries in the CVE database do not specify which version of a
package they apply to, and would thus ``stick around'' forever.  Package
developers who found CVE alerts and verified they can be ignored can
declare them as in this example:

@lisp
(package
  (name "t1lib")
  ;; @dots{}
  ;; These CVEs no longer apply and can be safely ignored.
  (properties `((lint-hidden-cve . ("CVE-2011-0433"
                                    "CVE-2011-1553"
                                    "CVE-2011-1554"
                                    "CVE-2011-5244")))))
@end lisp

@item formatting
Warn about obvious source code formatting issues: trailing white space,
use of tabulations, etc.

@item input-labels
Report old-style input labels that do not match the name of the
corresponding package.  This aims to help migrate from the ``old input
style''.  @xref{package Reference}, for more information on package
inputs and input styles.  @xref{Invoking guix style}, on how to migrate
to the new style.
@end table

The general syntax is:

@example
guix lint @var{options} @var{package}@dots{}
@end example

If no package is given on the command line, then all packages are checked.
The @var{options} may be zero or more of the following:

@table @code
@item --list-checkers
@itemx -l
List and describe all the available checkers that will be run on packages
and exit.

@item --checkers
@itemx -c
Only enable the checkers specified in a comma-separated list using the
names returned by @option{--list-checkers}.

@item --exclude
@itemx -x
Only disable the checkers specified in a comma-separated list using the
names returned by @option{--list-checkers}.

@item --expression=@var{expr}
@itemx -e @var{expr}
Consider the package @var{expr} evaluates to.

This is useful to unambiguously designate packages, as in this example:

@example
guix lint -c archival -e '(@@ (gnu packages guile) guile-3.0)'
@end example

@item --no-network
@itemx -n
Only enable the checkers that do not depend on Internet access.

@item --load-path=@var{directory}
@itemx -L @var{directory}
Add @var{directory} to the front of the package module search path
(@pxref{Package Modules}).

This allows users to define their own packages and make them visible to
the command-line tools.

@end table

@node Invoking guix size
@section Invoking @command{guix size}

@cindex size
@cindex package size
@cindex closure
@cindex @command{guix size}
The @command{guix size} command helps package developers profile the
disk usage of packages.  It is easy to overlook the impact of an
additional dependency added to a package, or the impact of using a
single output for a package that could easily be split (@pxref{Packages
with Multiple Outputs}).  Such are the typical issues that
@command{guix size} can highlight.

The command can be passed one or more package specifications
such as @code{gcc@@4.8}
or @code{guile:debug}, or a file name in the store.  Consider this
example:

@example
$ guix size coreutils
store item                               total    self
/gnu/store/@dots{}-gcc-5.5.0-lib           60.4    30.1  38.1%
/gnu/store/@dots{}-glibc-2.27              30.3    28.8  36.6%
/gnu/store/@dots{}-coreutils-8.28          78.9    15.0  19.0%
/gnu/store/@dots{}-gmp-6.1.2               63.1     2.7   3.4%
/gnu/store/@dots{}-bash-static-4.4.12       1.5     1.5   1.9%
/gnu/store/@dots{}-acl-2.2.52              61.1     0.4   0.5%
/gnu/store/@dots{}-attr-2.4.47             60.6     0.2   0.3%
/gnu/store/@dots{}-libcap-2.25             60.5     0.2   0.2%
total: 78.9 MiB
@end example

@cindex closure
The store items listed here constitute the @dfn{transitive closure} of
Coreutils---i.e., Coreutils and all its dependencies, recursively---as
would be returned by:

@example
$ guix gc -R /gnu/store/@dots{}-coreutils-8.23
@end example

Here the output shows three columns next to store items.  The first column,
labeled ``total'', shows the size in mebibytes (MiB) of the closure of
the store item---that is, its own size plus the size of all its
dependencies.  The next column, labeled ``self'', shows the size of the
item itself.  The last column shows the ratio of the size of the item
itself to the space occupied by all the items listed here.

In this example, we see that the closure of Coreutils weighs in at
79@tie{}MiB, most of which is taken by libc and GCC's run-time support
libraries.  (That libc and GCC's libraries represent a large fraction of
the closure is not a problem @i{per se} because they are always available
on the system anyway.)

Since the command also accepts store file names, assessing the size of
a build result is straightforward:

@example
guix size $(guix system build config.scm)
@end example

When the package(s) passed to @command{guix size} are available in the
store@footnote{More precisely, @command{guix size} looks for the
@emph{ungrafted} variant of the given package(s), as returned by
@code{guix build @var{package} --no-grafts}.  @xref{Security Updates},
for information on grafts.}, @command{guix size} queries the daemon to determine its
dependencies, and measures its size in the store, similar to @command{du
-ms --apparent-size} (@pxref{du invocation,,, coreutils, GNU
Coreutils}).

When the given packages are @emph{not} in the store, @command{guix size}
reports information based on the available substitutes
(@pxref{Substitutes}).  This makes it possible to profile the disk usage of
store items that are not even on disk, only available remotely.

You can also specify several package names:

@example
$ guix size coreutils grep sed bash
store item                               total    self
/gnu/store/@dots{}-coreutils-8.24          77.8    13.8  13.4%
/gnu/store/@dots{}-grep-2.22               73.1     0.8   0.8%
/gnu/store/@dots{}-bash-4.3.42             72.3     4.7   4.6%
/gnu/store/@dots{}-readline-6.3            67.6     1.2   1.2%
@dots{}
total: 102.3 MiB
@end example

@noindent
In this example we see that the combination of the four packages takes
102.3@tie{}MiB in total, which is much less than the sum of each closure
since they have a lot of dependencies in common.

When looking at the profile returned by @command{guix size}, you may
find yourself wondering why a given package shows up in the profile at
all.  To understand it, you can use @command{guix graph --path -t
references} to display the shortest path between the two packages
(@pxref{Invoking guix graph}).

The available options are:

@table @option

@item --substitute-urls=@var{urls}
Use substitute information from @var{urls}.
@xref{client-substitute-urls, the same option for @code{guix build}}.

@item --sort=@var{key}
Sort lines according to @var{key}, one of the following options:

@table @code
@item self
the size of each item (the default);
@item closure
the total size of the item's closure.
@end table

@item --map-file=@var{file}
Write a graphical map of disk usage in PNG format to @var{file}.

For the example above, the map looks like this:

@image{images/coreutils-size-map,5in,, map of Coreutils disk usage
produced by @command{guix size}}

This option requires that
@uref{https://wingolog.org/software/guile-charting/, Guile-Charting} be
installed and visible in Guile's module search path.  When that is not
the case, @command{guix size} fails as it tries to load it.

@item --system=@var{system}
@itemx -s @var{system}
Consider packages for @var{system}---e.g., @code{x86_64-linux}.

@item --load-path=@var{directory}
@itemx -L @var{directory}
Add @var{directory} to the front of the package module search path
(@pxref{Package Modules}).

This allows users to define their own packages and make them visible to
the command-line tools.
@end table

@node Invoking guix graph
@section Invoking @command{guix graph}

@cindex DAG
@cindex @command{guix graph}
@cindex package dependencies
Packages and their dependencies form a @dfn{graph}, specifically a
directed acyclic graph (DAG).  It can quickly become difficult to have a
mental model of the package DAG, so the @command{guix graph} command
provides a visual representation of the DAG@.  By default,
@command{guix graph} emits a DAG representation in the input format of
@uref{https://www.graphviz.org/, Graphviz}, so its output can be passed
directly to the @command{dot} command of Graphviz.  It can also emit an
HTML page with embedded JavaScript code to display a ``chord diagram''
in a Web browser, using the @uref{https://d3js.org/, d3.js} library, or
emit Cypher queries to construct a graph in a graph database supporting
the @uref{https://www.opencypher.org/, openCypher} query language.  With
@option{--path}, it simply displays the shortest path between two
packages.  The general syntax is:

@example
guix graph @var{options} @var{package}@dots{}
@end example

For example, the following command generates a PDF file representing the
package DAG for the GNU@tie{}Core Utilities, showing its build-time
dependencies:

@example
guix graph coreutils | dot -Tpdf > dag.pdf
@end example

The output looks like this:

@image{images/coreutils-graph,2in,,Dependency graph of the GNU Coreutils}

Nice little graph, no?

You may find it more pleasant to navigate the graph interactively with
@command{xdot} (from the @code{xdot} package):

@example
guix graph coreutils | xdot -
@end example

But there is more than one graph!  The one above is concise: it is the
graph of package objects, omitting implicit inputs such as GCC, libc,
grep, etc.  It is often useful to have such a concise graph, but
sometimes one may want to see more details.  @command{guix graph} supports
several types of graphs, allowing you to choose the level of detail:

@table @code
@item package
This is the default type used in the example above.  It shows the DAG of
package objects, excluding implicit dependencies.  It is concise, but
filters out many details.

@item reverse-package
This shows the @emph{reverse} DAG of packages.  For example:

@example
guix graph --type=reverse-package ocaml
@end example

...@: yields the graph of packages that @emph{explicitly} depend on OCaml (if
you are also interested in cases where OCaml is an implicit dependency, see
@code{reverse-bag} below).

Note that for core packages this can yield huge graphs.  If all you want
is to know the number of packages that depend on a given package, use
@command{guix refresh --list-dependent} (@pxref{Invoking guix refresh,
@option{--list-dependent}}).

@item bag-emerged
This is the package DAG, @emph{including} implicit inputs.

For instance, the following command:

@example
guix graph --type=bag-emerged coreutils
@end example

...@: yields this bigger graph:

@image{images/coreutils-bag-graph,,5in,Detailed dependency graph of the GNU Coreutils}

At the bottom of the graph, we see all the implicit inputs of
@var{gnu-build-system} (@pxref{Build Systems, @code{gnu-build-system}}).

Now, note that the dependencies of these implicit inputs---that is, the
@dfn{bootstrap dependencies} (@pxref{Bootstrapping})---are not shown
here, for conciseness.

@item bag
Similar to @code{bag-emerged}, but this time including all the bootstrap
dependencies.

@item bag-with-origins
Similar to @code{bag}, but also showing origins and their dependencies.

@item reverse-bag
This shows the @emph{reverse} DAG of packages.  Unlike @code{reverse-package},
it also takes implicit dependencies into account.  For example:

@example
guix graph -t reverse-bag dune
@end example

@noindent
...@: yields the graph of all packages that depend on Dune, directly or
indirectly.  Since Dune is an @emph{implicit} dependency of many packages
@i{via} @code{dune-build-system}, this shows a large number of packages,
whereas @code{reverse-package} would show very few if any.

@item derivation
This is the most detailed representation: It shows the DAG of
derivations (@pxref{Derivations}) and plain store items.  Compared to
the above representation, many additional nodes are visible, including
build scripts, patches, Guile modules, etc.

For this type of graph, it is also possible to pass a @file{.drv} file
name instead of a package name, as in:

@example
guix graph -t derivation $(guix system build -d my-config.scm)
@end example

@item module
This is the graph of @dfn{package modules} (@pxref{Package Modules}).
For example, the following command shows the graph for the package
module that defines the @code{guile} package:

@example
guix graph -t module guile | xdot -
@end example
@end table

All the types above correspond to @emph{build-time dependencies}.  The
following graph type represents the @emph{run-time dependencies}:

@table @code
@item references
This is the graph of @dfn{references} of a package output, as returned
by @command{guix gc --references} (@pxref{Invoking guix gc}).

If the given package output is not available in the store, @command{guix
graph} attempts to obtain dependency information from substitutes.

Here you can also pass a store file name instead of a package name.  For
example, the command below produces the reference graph of your profile
(which can be big!):

@example
guix graph -t references $(readlink -f ~/.guix-profile)
@end example

@item referrers
This is the graph of the @dfn{referrers} of a store item, as returned by
@command{guix gc --referrers} (@pxref{Invoking guix gc}).

This relies exclusively on local information from your store.  For
instance, let us suppose that the current Inkscape is available in 10
profiles on your machine; @command{guix graph -t referrers inkscape}
will show a graph rooted at Inkscape and with those 10 profiles linked
to it.

It can help determine what is preventing a store item from being garbage
collected.

@end table

@cindex shortest path, between packages
Often, the graph of the package you are interested in does not fit on
your screen, and anyway all you want to know is @emph{why} that package
actually depends on some seemingly unrelated package.  The
@option{--path} option instructs @command{guix graph} to display the
shortest path between two packages (or derivations, or store items,
etc.):

@example
$ guix graph --path emacs libunistring
emacs@@26.3
mailutils@@3.9
libunistring@@0.9.10
$ guix graph --path -t derivation emacs libunistring
/gnu/store/@dots{}-emacs-26.3.drv
/gnu/store/@dots{}-mailutils-3.9.drv
/gnu/store/@dots{}-libunistring-0.9.10.drv
$ guix graph --path -t references emacs libunistring
/gnu/store/@dots{}-emacs-26.3
/gnu/store/@dots{}-libidn2-2.2.0
/gnu/store/@dots{}-libunistring-0.9.10
@end example

Sometimes you still want to visualize the graph but would like to trim
it so it can actually be displayed.  One way to do it is via the
@option{--max-depth} (or @option{-M}) option, which lets you specify the
maximum depth of the graph.  In the example below, we visualize only
@code{libreoffice} and the nodes whose distance to @code{libreoffice} is
at most 2:

@example
guix graph -M 2 libreoffice | xdot -f fdp -
@end example

Mind you, that's still a big ball of spaghetti, but at least
@command{dot} can render it quickly and it can be browsed somewhat.

The available options are the following:

@table @option
@item --type=@var{type}
@itemx -t @var{type}
Produce a graph output of @var{type}, where @var{type} must be one of
the values listed above.

@item --list-types
List the supported graph types.

@item --backend=@var{backend}
@itemx -b @var{backend}
Produce a graph using the selected @var{backend}.

@item --list-backends
List the supported graph backends.

Currently, the available backends are Graphviz and d3.js.

@item --path
Display the shortest path between two nodes of the type specified by
@option{--type}.  The example below shows the shortest path between
@code{libreoffice} and @code{llvm} according to the references of
@code{libreoffice}:

@example
$ guix graph --path -t references libreoffice llvm
/gnu/store/@dots{}-libreoffice-6.4.2.2
/gnu/store/@dots{}-libepoxy-1.5.4
/gnu/store/@dots{}-mesa-19.3.4
/gnu/store/@dots{}-llvm-9.0.1
@end example

@item --expression=@var{expr}
@itemx -e @var{expr}
Consider the package @var{expr} evaluates to.

This is useful to precisely refer to a package, as in this example:

@example
guix graph -e '(@@@@ (gnu packages commencement) gnu-make-final)'
@end example

@item --system=@var{system}
@itemx -s @var{system}
Display the graph for @var{system}---e.g., @code{i686-linux}.

The package dependency graph is largely architecture-independent, but there
are some architecture-dependent bits that this option allows you to visualize.

@item --load-path=@var{directory}
@itemx -L @var{directory}
Add @var{directory} to the front of the package module search path
(@pxref{Package Modules}).

This allows users to define their own packages and make them visible to
the command-line tools.
@end table

On top of that, @command{guix graph} supports all the usual package
transformation options (@pxref{Package Transformation Options}).  This
makes it easy to view the effect of a graph-rewriting transformation
such as @option{--with-input}.  For example, the command below outputs
the graph of @code{git} once @code{openssl} has been replaced by
@code{libressl} everywhere in the graph:

@example
guix graph git --with-input=openssl=libressl
@end example

So many possibilities, so much fun!

@node Invoking guix publish
@section Invoking @command{guix publish}

@cindex @command{guix publish}
The purpose of @command{guix publish} is to enable users to easily share
their store with others, who can then use it as a substitute server
(@pxref{Substitutes}).

When @command{guix publish} runs, it spawns an HTTP server which allows
anyone with network access to obtain substitutes from it.  This means
that any machine running Guix can also act as if it were a build farm,
since the HTTP interface is compatible with Cuirass, the software behind
the @code{@value{SUBSTITUTE-SERVER-1}} build farm.

For security, each substitute is signed, allowing recipients to check
their authenticity and integrity (@pxref{Substitutes}).  Because
@command{guix publish} uses the signing key of the system, which is only
readable by the system administrator, it must be started as root; the
@option{--user} option makes it drop root privileges early on.

The signing key pair must be generated before @command{guix publish} is
launched, using @command{guix archive --generate-key} (@pxref{Invoking
guix archive}).

When the @option{--advertise} option is passed, the server advertises
its availability on the local network using multicast DNS (mDNS) and DNS
service discovery (DNS-SD), currently @i{via} Guile-Avahi (@pxref{Top,,,
guile-avahi, Using Avahi in Guile Scheme Programs}).

The general syntax is:

@example
guix publish @var{options}@dots{}
@end example

Running @command{guix publish} without any additional arguments will
spawn an HTTP server on port 8080:

@example
guix publish
@end example

@cindex socket activation, for @command{guix publish}
@command{guix publish} can also be started following the systemd
``socket activation'' protocol (@pxref{Service De- and Constructors,
@code{make-systemd-constructor},, shepherd, The GNU Shepherd Manual}).

Once a publishing server has been authorized, the daemon may download
substitutes from it.  @xref{Getting Substitutes from Other Servers}.

By default, @command{guix publish} compresses archives on the fly as it
serves them.  This ``on-the-fly'' mode is convenient in that it requires
no setup and is immediately available.  However, when serving lots of
clients, we recommend using the @option{--cache} option, which enables
caching of the archives before they are sent to clients---see below for
details.  The @command{guix weather} command provides a handy way to
check what a server provides (@pxref{Invoking guix weather}).

As a bonus, @command{guix publish} also serves as a content-addressed
mirror for source files referenced in @code{origin} records
(@pxref{origin Reference}).  For instance, assuming @command{guix
publish} is running on @code{example.org}, the following URL returns the
raw @file{hello-2.10.tar.gz} file with the given SHA256 hash
(represented in @code{nix-base32} format, @pxref{Invoking guix hash}):

@example
http://example.org/file/hello-2.10.tar.gz/sha256/0ssi1@dots{}ndq1i
@end example

Obviously, these URLs only work for files that are in the store; in
other cases, they return 404 (``Not Found'').

@cindex build logs, publication
Build logs are available from @code{/log} URLs like:

@example
http://example.org/log/gwspk@dots{}-guile-2.2.3
@end example

@noindent
When @command{guix-daemon} is configured to save compressed build logs,
as is the case by default (@pxref{Invoking guix-daemon}), @code{/log}
URLs return the compressed log as-is, with an appropriate
@code{Content-Type} and/or @code{Content-Encoding} header.  We recommend
running @command{guix-daemon} with @option{--log-compression=gzip} since
Web browsers can automatically decompress it, which is not the case with
Bzip2 compression.

The following options are available:

@table @code
@item --port=@var{port}
@itemx -p @var{port}
Listen for HTTP requests on @var{port}.

@item --listen=@var{host}
Listen on the network interface for @var{host}.  The default is to
accept connections from any interface.

@item --user=@var{user}
@itemx -u @var{user}
Change privileges to @var{user} as soon as possible---i.e., once the
server socket is open and the signing key has been read.

@item --compression[=@var{method}[:@var{level}]]
@itemx -C [@var{method}[:@var{level}]]
Compress data using the given @var{method} and @var{level}.  @var{method} is
one of @code{lzip}, @code{zstd}, and @code{gzip}; when @var{method} is
omitted, @code{gzip} is used.

When @var{level} is zero, disable compression.  The range 1 to 9 corresponds
to different compression levels: 1 is the fastest, and 9 is the best
(CPU-intensive).  The default is 3.

Usually, @code{lzip} compresses noticeably better than @code{gzip} for a
small increase in CPU usage; see
@uref{https://nongnu.org/lzip/lzip_benchmark.html,benchmarks on the lzip
Web page}.  However, @code{lzip} achieves low decompression throughput
(on the order of 50@tie{}MiB/s on modern hardware), which can be a
bottleneck for someone who downloads over a fast network connection.

The compression ratio of @code{zstd} is between that of @code{lzip} and
that of @code{gzip}; its main advantage is a
@uref{https://facebook.github.io/zstd/,high decompression speed}.

Unless @option{--cache} is used, compression occurs on the fly and
the compressed streams are not
cached.  Thus, to reduce load on the machine that runs @command{guix
publish}, it may be a good idea to choose a low compression level, to
run @command{guix publish} behind a caching proxy, or to use
@option{--cache}.  Using @option{--cache} has the advantage that it
allows @command{guix publish} to add @code{Content-Length} HTTP header
to its responses.

This option can be repeated, in which case every substitute gets compressed
using all the selected methods, and all of them are advertised.  This is
useful when users may not support all the compression methods: they can select
the one they support.

@item --cache=@var{directory}
@itemx -c @var{directory}
Cache archives and meta-data (@code{.narinfo} URLs) to @var{directory}
and only serve archives that are in cache.

When this option is omitted, archives and meta-data are created
on-the-fly.  This can reduce the available bandwidth, especially when
compression is enabled, since this may become CPU-bound.  Another
drawback of the default mode is that the length of archives is not known
in advance, so @command{guix publish} does not add a
@code{Content-Length} HTTP header to its responses, which in turn
prevents clients from knowing the amount of data being downloaded.

Conversely, when @option{--cache} is used, the first request for a store
item (@i{via} a @code{.narinfo} URL) triggers a
background process to @dfn{bake} the archive---computing its
@code{.narinfo} and compressing the archive, if needed.  Once the
archive is cached in @var{directory}, subsequent requests succeed and
are served directly from the cache, which guarantees that clients get
the best possible bandwidth.

That first @code{.narinfo} request nonetheless returns 200, provided the
requested store item is ``small enough'', below the cache bypass
threshold---see @option{--cache-bypass-threshold} below.  That way,
clients do not have to wait until the archive is baked.  For larger
store items, the first @code{.narinfo} request returns 404, meaning that
clients have to wait until the archive is baked.

The ``baking'' process is performed by worker threads.  By default, one
thread per CPU core is created, but this can be customized.  See
@option{--workers} below.

When @option{--ttl} is used, cached entries are automatically deleted
when they have expired.

@item --workers=@var{N}
When @option{--cache} is used, request the allocation of @var{N} worker
threads to ``bake'' archives.

@item --ttl=@var{ttl}
Produce @code{Cache-Control} HTTP headers that advertise a time-to-live
(TTL) of @var{ttl}.  @var{ttl} must denote a duration: @code{5d} means 5
days, @code{1m} means 1 month, and so on.

This allows the user's Guix to keep substitute information in cache for
@var{ttl}.  However, note that @code{guix publish} does not itself
guarantee that the store items it provides will indeed remain available
for as long as @var{ttl}.

Additionally, when @option{--cache} is used, cached entries that have
not been accessed for @var{ttl} and that no longer have a corresponding
item in the store, may be deleted.

@item --negative-ttl=@var{ttl}
Similarly produce @code{Cache-Control} HTTP headers to advertise the
time-to-live (TTL) of @emph{negative} lookups---missing store items, for
which the HTTP 404 code is returned.  By default, no negative TTL is
advertised.

This parameter can help adjust server load and substitute latency by
instructing cooperating clients to be more or less patient when a store
item is missing.

@item --cache-bypass-threshold=@var{size}
When used in conjunction with @option{--cache}, store items smaller than
@var{size} are immediately available, even when they are not yet in
cache.  @var{size} is a size in bytes, or it can be suffixed by @code{M}
for megabytes and so on.  The default is @code{10M}.

``Cache bypass'' allows you to reduce the publication delay for clients
at the expense of possibly additional I/O and CPU use on the server
side: depending on the client access patterns, those store items can end
up being baked several times until a copy is available in cache.

Increasing the threshold may be useful for sites that have few users, or
to guarantee that users get substitutes even for store items that are
not popular.

@item --nar-path=@var{path}
Use @var{path} as the prefix for the URLs of ``nar'' files
(@pxref{Invoking guix archive, normalized archives}).

By default, nars are served at a URL such as
@code{/nar/gzip/@dots{}-coreutils-8.25}.  This option allows you to
change the @code{/nar} part to @var{path}.

@item --public-key=@var{file}
@itemx --private-key=@var{file}
Use the specific @var{file}s as the public/private key pair used to sign
the store items being published.

The files must correspond to the same key pair (the private key is used
for signing and the public key is merely advertised in the signature
metadata).  They must contain keys in the canonical s-expression format
as produced by @command{guix archive --generate-key} (@pxref{Invoking
guix archive}).  By default, @file{/etc/guix/signing-key.pub} and
@file{/etc/guix/signing-key.sec} are used.

@item --repl[=@var{port}]
@itemx -r [@var{port}]
Spawn a Guile REPL server (@pxref{REPL Servers,,, guile, GNU Guile
Reference Manual}) on @var{port} (37146 by default).  This is used
primarily for debugging a running @command{guix publish} server.
@end table

Enabling @command{guix publish} on Guix System is a one-liner: just
instantiate a @code{guix-publish-service-type} service in the @code{services} field
of the @code{operating-system} declaration (@pxref{guix-publish-service-type,
@code{guix-publish-service-type}}).

If you are instead running Guix on a ``foreign distro'', follow these
instructions:

@itemize
@item
If your host distro uses the systemd init system:

@example
# ln -s ~root/.guix-profile/lib/systemd/system/guix-publish.service \
        /etc/systemd/system/
# systemctl start guix-publish && systemctl enable guix-publish
@end example

@item
If your host distro uses the Upstart init system:

@example
# ln -s ~root/.guix-profile/lib/upstart/system/guix-publish.conf /etc/init/
# start guix-publish
@end example

@item
Otherwise, proceed similarly with your distro's init system.
@end itemize

@node Invoking guix challenge
@section Invoking @command{guix challenge}

@cindex reproducible builds
@cindex verifiable builds
@cindex @command{guix challenge}
@cindex challenge
Do the binaries provided by this server really correspond to the source
code it claims to build?  Is a package build process deterministic?
These are the questions the @command{guix challenge} command attempts to
answer.

The former is obviously an important question: Before using a substitute
server (@pxref{Substitutes}), one had better @emph{verify} that it
provides the right binaries, and thus @emph{challenge} it.  The latter
is what enables the former: If package builds are deterministic, then
independent builds of the package should yield the exact same result,
bit for bit; if a server provides a binary different from the one
obtained locally, it may be either corrupt or malicious.

We know that the hash that shows up in @file{/gnu/store} file names is
the hash of all the inputs of the process that built the file or
directory---compilers, libraries, build scripts,
etc. (@pxref{Introduction}).  Assuming deterministic build processes,
one store file name should map to exactly one build output.
@command{guix challenge} checks whether there is, indeed, a single
mapping by comparing the build outputs of several independent builds of
any given store item.

The command output looks like this:

@smallexample
$ guix challenge \
  --substitute-urls="https://@value{SUBSTITUTE-SERVER-1} https://guix.example.org" \
  openssl git pius coreutils grep
updating substitutes from 'https://@value{SUBSTITUTE-SERVER-1}'... 100.0%
updating substitutes from 'https://guix.example.org'... 100.0%
/gnu/store/@dots{}-openssl-1.0.2d contents differ:
  local hash: 0725l22r5jnzazaacncwsvp9kgf42266ayyp814v7djxs7nk963q
  https://@value{SUBSTITUTE-SERVER-1}/nar/@dots{}-openssl-1.0.2d: 0725l22r5jnzazaacncwsvp9kgf42266ayyp814v7djxs7nk963q
  https://guix.example.org/nar/@dots{}-openssl-1.0.2d: 1zy4fmaaqcnjrzzajkdn3f5gmjk754b43qkq47llbyak9z0qjyim
  differing files:
    /lib/libcrypto.so.1.1
    /lib/libssl.so.1.1

/gnu/store/@dots{}-git-2.5.0 contents differ:
  local hash: 00p3bmryhjxrhpn2gxs2fy0a15lnip05l97205pgbk5ra395hyha
  https://@value{SUBSTITUTE-SERVER-1}/nar/@dots{}-git-2.5.0: 069nb85bv4d4a6slrwjdy8v1cn4cwspm3kdbmyb81d6zckj3nq9f
  https://guix.example.org/nar/@dots{}-git-2.5.0: 0mdqa9w1p6cmli6976v4wi0sw9r4p5prkj7lzfd1877wk11c9c73
  differing file:
    /libexec/git-core/git-fsck

/gnu/store/@dots{}-pius-2.1.1 contents differ:
  local hash: 0k4v3m9z1zp8xzzizb7d8kjj72f9172xv078sq4wl73vnq9ig3ax
  https://@value{SUBSTITUTE-SERVER-1}/nar/@dots{}-pius-2.1.1: 0k4v3m9z1zp8xzzizb7d8kjj72f9172xv078sq4wl73vnq9ig3ax
  https://guix.example.org/nar/@dots{}-pius-2.1.1: 1cy25x1a4fzq5rk0pmvc8xhwyffnqz95h2bpvqsz2mpvlbccy0gs
  differing file:
    /share/man/man1/pius.1.gz

@dots{}

5 store items were analyzed:
  - 2 (40.0%) were identical
  - 3 (60.0%) differed
  - 0 (0.0%) were inconclusive
@end smallexample

@noindent
In this example, @command{guix challenge} queries all the substitute
servers for each of the fives packages specified on the command line.
It then reports those store items for which the servers obtained a
result different from the local build (if it exists) and/or different
from one another; here, the @samp{local hash} lines indicate that a
local build result was available for each of these packages and shows
its hash.

@cindex non-determinism, in package builds
As an example, @code{guix.example.org} always gets a different answer.
Conversely, @code{@value{SUBSTITUTE-SERVER-1}} agrees with local builds, except in the
case of Git.  This might indicate that the build process of Git is
non-deterministic, meaning that its output varies as a function of
various things that Guix does not fully control, in spite of building
packages in isolated environments (@pxref{Features}).  Most common
sources of non-determinism include the addition of timestamps in build
results, the inclusion of random numbers, and directory listings sorted
by inode number.  See @uref{https://reproducible-builds.org/docs/}, for
more information.

To find out what is wrong with this Git binary, the easiest approach is
to run:

@example
guix challenge git \
  --diff=diffoscope \
  --substitute-urls="https://@value{SUBSTITUTE-SERVER-1} https://guix.example.org"
@end example

This automatically invokes @command{diffoscope}, which displays detailed
information about files that differ.

Alternatively, we can do something along these lines (@pxref{Invoking guix
archive}):

@example
$ wget -q -O - https://@value{SUBSTITUTE-SERVER-1}/nar/lzip/@dots{}-git-2.5.0 \
   | lzip -d | guix archive -x /tmp/git
$ diff -ur --no-dereference /gnu/store/@dots{}-git.2.5.0 /tmp/git
@end example

This command shows the difference between the files resulting from the
local build, and the files resulting from the build on
@code{@value{SUBSTITUTE-SERVER-1}} (@pxref{Overview, Comparing and Merging Files,,
diffutils, Comparing and Merging Files}).  The @command{diff} command
works great for text files.  When binary files differ, a better option
is @uref{https://diffoscope.org/, Diffoscope}, a tool that helps
visualize differences for all kinds of files.

Once you have done that work, you can tell whether the differences are due
to a non-deterministic build process or to a malicious server.  We try
hard to remove sources of non-determinism in packages to make it easier
to verify substitutes, but of course, this is a process that
involves not just Guix, but a large part of the free software community.
In the meantime, @command{guix challenge} is one tool to help address
the problem.

If you are writing packages for Guix, you are encouraged to check
whether @code{@value{SUBSTITUTE-SERVER-1}} and other substitute servers obtain the
same build result as you did with:

@example
guix challenge @var{package}
@end example

The general syntax is:

@example
guix challenge @var{options} @var{argument}@dots{}
@end example

@noindent
where @var{argument} is a package specification such as
@code{guile@@2.0} or @code{glibc:debug} or, alternatively, a store file
name as returned, for example, by @command{guix build} or @command{guix
gc --list-live}.

When a difference is found between the hash of a locally-built item and
that of a server-provided substitute, or among substitutes provided by
different servers, the command displays it as in the example above and
its exit code is 2 (other non-zero exit codes denote other kinds of
errors).

The one option that matters is:

@table @code

@item --substitute-urls=@var{urls}
Consider @var{urls} the whitespace-separated list of substitute source
URLs to compare to.

@item --diff=@var{mode}
Upon mismatches, show differences according to @var{mode}, one of:

@table @asis
@item @code{simple} (the default)
Show the list of files that differ.

@item @code{diffoscope}
@itemx @var{command}
Invoke @uref{https://diffoscope.org/, Diffoscope}, passing it
two directories whose contents do not match.

When @var{command} is an absolute file name, run @var{command} instead
of Diffoscope.

@item @code{none}
Do not show further details about the differences.
@end table

Thus, unless @option{--diff=none} is passed, @command{guix challenge}
downloads the store items from the given substitute servers so that it
can compare them.

@item --verbose
@itemx -v
Show details about matches (identical contents) in addition to
information about mismatches.

@end table

@node Invoking guix copy
@section Invoking @command{guix copy}

@cindex @command{guix copy}
@cindex copy, of store items, over SSH
@cindex SSH, copy of store items
@cindex sharing store items across machines
@cindex transferring store items across machines
The @command{guix copy} command copies items from the store of one
machine to that of another machine over a secure shell (SSH)
connection@footnote{This command is available only when Guile-SSH was
found.  @xref{Requirements}, for details.}.  For example, the following
command copies the @code{coreutils} package, the user's profile, and all
their dependencies over to @var{host}, logged in as @var{user}:

@example
guix copy --to=@var{user}@@@var{host} \
          coreutils $(readlink -f ~/.guix-profile)
@end example

If some of the items to be copied are already present on @var{host},
they are not actually sent.

The command below retrieves @code{libreoffice} and @code{gimp} from
@var{host}, assuming they are available there:

@example
guix copy --from=@var{host} libreoffice gimp
@end example

The SSH connection is established using the Guile-SSH client, which is
compatible with OpenSSH: it honors @file{~/.ssh/known_hosts} and
@file{~/.ssh/config}, and uses the SSH agent for authentication.

The key used to sign items that are sent must be accepted by the remote
machine.  Likewise, the key used by the remote machine to sign items you
are retrieving must be in @file{/etc/guix/acl} so it is accepted by your
own daemon.  @xref{Invoking guix archive}, for more information about
store item authentication.

The general syntax is:

@example
guix copy [--to=@var{spec}|--from=@var{spec}] @var{items}@dots{}
@end example

You must always specify one of the following options:

@table @code
@item --to=@var{spec}
@itemx --from=@var{spec}
Specify the host to send to or receive from.  @var{spec} must be an SSH
spec such as @code{example.org}, @code{charlie@@example.org}, or
@code{charlie@@example.org:2222}.
@end table

The @var{items} can be either package names, such as @code{gimp}, or
store items, such as @file{/gnu/store/@dots{}-idutils-4.6}.

When specifying the name of a package to send, it is first built if
needed, unless @option{--dry-run} was specified.  Common build options
are supported (@pxref{Common Build Options}).


@node Invoking guix container
@section Invoking @command{guix container}
@cindex container
@cindex @command{guix container}
@quotation Note
As of version @value{VERSION}, this tool is experimental.  The interface
is subject to radical change in the future.
@end quotation

The purpose of @command{guix container} is to manipulate processes
running within an isolated environment, commonly known as a
``container'', typically created by the @command{guix shell}
(@pxref{Invoking guix shell}) and @command{guix system container}
(@pxref{Invoking guix system}) commands.

The general syntax is:

@example
guix container @var{action} @var{options}@dots{}
@end example

@var{action} specifies the operation to perform with a container, and
@var{options} specifies the context-specific arguments for the action.

The following actions are available:

@table @code
@item exec
Execute a command within the context of a running container.

The syntax is:

@example
guix container exec @var{pid} @var{program} @var{arguments}@dots{}
@end example

@var{pid} specifies the process ID of the running container.
@var{program} specifies an executable file name within the root file
system of the container.  @var{arguments} are the additional options that
will be passed to @var{program}.

The following command launches an interactive login shell inside a
Guix system container, started by @command{guix system container}, and whose
process ID is 9001:

@example
guix container exec 9001 /run/current-system/profile/bin/bash --login
@end example

Note that the @var{pid} cannot be the parent process of a container.  It
must be PID 1 of the container or one of its child processes.

@end table

@node Invoking guix weather
@section Invoking @command{guix weather}

@cindex @command{guix weather}
Occasionally you're grumpy because substitutes are lacking and you end
up building packages by yourself (@pxref{Substitutes}).  The
@command{guix weather} command reports on substitute availability on the
specified servers so you can have an idea of whether you'll be grumpy
today.  It can sometimes be useful info as a user, but it is primarily
useful to people running @command{guix publish} (@pxref{Invoking guix
publish}).  Sometimes substitutes @emph{are} available but they are not
authorized on your system; @command{guix weather} reports it so you can
authorize them if you want (@pxref{Getting Substitutes from Other
Servers}).

@cindex statistics, for substitutes
@cindex availability of substitutes
@cindex substitute availability
@cindex weather, substitute availability
Here's a sample run:

@example
$ guix weather --substitute-urls=https://guix.example.org
computing 5,872 package derivations for x86_64-linux...
looking for 6,128 store items on https://guix.example.org..
updating substitutes from 'https://guix.example.org'... 100.0%
https://guix.example.org
  43.4% substitutes available (2,658 out of 6,128)
  7,032.5 MiB of nars (compressed)
  19,824.2 MiB on disk (uncompressed)
  0.030 seconds per request (182.9 seconds in total)
  33.5 requests per second

  9.8% (342 out of 3,470) of the missing items are queued
  867 queued builds
      x86_64-linux: 518 (59.7%)
      i686-linux: 221 (25.5%)
      aarch64-linux: 128 (14.8%)
  build rate: 23.41 builds per hour
      x86_64-linux: 11.16 builds per hour
      i686-linux: 6.03 builds per hour
      aarch64-linux: 6.41 builds per hour
@end example

@cindex continuous integration, statistics
As you can see, it reports the fraction of all the packages for which
substitutes are available on the server---regardless of whether
substitutes are enabled, and regardless of whether this server's signing
key is authorized.  It also reports the size of the compressed archives
(``nars'') provided by the server, the size the corresponding store
items occupy in the store (assuming deduplication is turned off), and
the server's throughput.  The second part gives continuous integration
(CI) statistics, if the server supports it.  In addition, using the
@option{--coverage} option, @command{guix weather} can list ``important''
package substitutes missing on the server (see below).

To achieve that, @command{guix weather} queries over HTTP(S) meta-data
(@dfn{narinfos}) for all the relevant store items.  Like @command{guix
challenge}, it ignores signatures on those substitutes, which is
innocuous since the command only gathers statistics and cannot install
those substitutes.

The general syntax is:

@example
guix weather @var{options}@dots{} [@var{packages}@dots{}]
@end example

When @var{packages} is omitted, @command{guix weather} checks the availability
of substitutes for @emph{all} the packages, or for those specified with
@option{--manifest}; otherwise it only considers the specified packages.  It
is also possible to query specific system types with @option{--system}.
@command{guix weather} exits with a non-zero code when the fraction of
available substitutes is below 100%.

The available options are listed below.

@table @code
@item --substitute-urls=@var{urls}
@var{urls} is the space-separated list of substitute server URLs to
query.  When this option is omitted, the URLs specified with the
@option{--substitute-urls} option of @command{guix-daemon} are used or,
as a last resort, the default set of substitute URLs.

@item --system=@var{system}
@itemx -s @var{system}
Query substitutes for @var{system}---e.g., @code{aarch64-linux}.  This
option can be repeated, in which case @command{guix weather} will query
substitutes for several system types.

@item --manifest=@var{file}
Instead of querying substitutes for all the packages, only ask for those
specified in @var{file}.  @var{file} must contain a @dfn{manifest}, as
with the @code{-m} option of @command{guix package} (@pxref{Invoking
guix package}).

This option can be repeated several times, in which case the manifests
are concatenated.

@item --expression=@var{expr}
@itemx -e @var{expr}
Consider the package @var{expr} evaluates to.

A typical use case for this option is specifying a package that is
hidden and thus cannot be referred to in the usual way, as in this
example:

@example
guix weather -e '(@@@@ (gnu packages rust) rust-bootstrap)'
@end example

This option can be repeated.

@item --coverage[=@var{count}]
@itemx -c [@var{count}]
Report on substitute coverage for packages: list packages with at least
@var{count} dependents (zero by default) for which substitutes are
unavailable.  Dependent packages themselves are not listed: if @var{b} depends
on @var{a} and @var{a} has no substitutes, only @var{a} is listed, even though
@var{b} usually lacks substitutes as well.  The result looks like this:

@example
$ guix weather --substitute-urls=@value{SUBSTITUTE-URLS} -c 10
computing 8,983 package derivations for x86_64-linux...
looking for 9,343 store items on @value{SUBSTITUTE-URLS}...
updating substitutes from '@value{SUBSTITUTE-URLS}'... 100.0%
@value{SUBSTITUTE-URLS}
  64.7% substitutes available (6,047 out of 9,343)
@dots{}
2502 packages are missing from '@value{SUBSTITUTE-URLS}' for 'x86_64-linux', among which:
    58  kcoreaddons@@5.49.0      /gnu/store/@dots{}-kcoreaddons-5.49.0
    46  qgpgme@@1.11.1           /gnu/store/@dots{}-qgpgme-1.11.1
    37  perl-http-cookiejar@@0.008  /gnu/store/@dots{}-perl-http-cookiejar-0.008
    @dots{}
@end example

What this example shows is that @code{kcoreaddons} and presumably the 58
packages that depend on it have no substitutes at
@code{@value{SUBSTITUTE-SERVER-1}}; likewise for @code{qgpgme} and the 46
packages that depend on it.

If you are a Guix developer, or if you are taking care of this build farm,
you'll probably want to have a closer look at these packages: they may simply
fail to build.

@item --display-missing
Display the list of store items for which substitutes are missing.
@end table

@node Invoking guix processes
@section Invoking @command{guix processes}

@cindex @command{guix processes}
The @command{guix processes} command can be useful to developers and system
administrators, especially on multi-user machines and on build farms: it lists
the current sessions (connections to the daemon), as well as information about
the processes involved@footnote{Remote sessions, when @command{guix-daemon} is
started with @option{--listen} specifying a TCP endpoint, are @emph{not}
listed.}.  Here's an example of the information it returns:

@example
$ sudo guix processes
SessionPID: 19002
ClientPID: 19090
ClientCommand: guix shell python

SessionPID: 19402
ClientPID: 19367
ClientCommand: guix publish -u guix-publish -p 3000 -C 9 @dots{}

SessionPID: 19444
ClientPID: 19419
ClientCommand: cuirass --cache-directory /var/cache/cuirass @dots{}
LockHeld: /gnu/store/@dots{}-perl-ipc-cmd-0.96.lock
LockHeld: /gnu/store/@dots{}-python-six-bootstrap-1.11.0.lock
LockHeld: /gnu/store/@dots{}-libjpeg-turbo-2.0.0.lock
ChildPID: 20495
ChildCommand: guix offload x86_64-linux 7200 1 28800
ChildPID: 27733
ChildCommand: guix offload x86_64-linux 7200 1 28800
ChildPID: 27793
ChildCommand: guix offload x86_64-linux 7200 1 28800
@end example

In this example we see that @command{guix-daemon} has three clients:
@command{guix shell}, @command{guix publish}, and the Cuirass continuous
integration tool; their process identifier (PID) is given by the
@code{ClientPID} field.  The @code{SessionPID} field gives the PID of the
@command{guix-daemon} sub-process of this particular session.

The @code{LockHeld} fields show which store items are currently locked
by this session, which corresponds to store items being built or
substituted (the @code{LockHeld} field is not displayed when
@command{guix processes} is not running as root).  Last, by looking at
the @code{ChildPID} and @code{ChildCommand} fields, we understand that
these three builds are being offloaded (@pxref{Daemon Offload Setup}).

The output is in Recutils format so we can use the handy @command{recsel}
command to select sessions of interest (@pxref{Selection Expressions,,,
recutils, GNU recutils manual}).  As an example, the command shows the command
line and PID of the client that triggered the build of a Perl package:

@example
$ sudo guix processes | \
    recsel -p ClientPID,ClientCommand -e 'LockHeld ~ "perl"'
ClientPID: 19419
ClientCommand: cuirass --cache-directory /var/cache/cuirass @dots{}
@end example

Additional options are listed below.

@table @code
@item --format=@var{format}
@itemx -f @var{format}
Produce output in the specified @var{format}, one of:

@table @code
@item recutils
The default option.  It outputs a set of Session recutils records
that include each @code{ChildProcess} as a field.

@item normalized
Normalize the output records into record sets (@pxref{Record Sets,,,
recutils, GNU recutils manual}).  Normalizing into record sets allows
joins across record types.  The example below lists the PID of each
@code{ChildProcess} and the associated PID for @code{Session} that
spawned the @code{ChildProcess} where the @code{Session} was started
using @command{guix build}.

@example
$ guix processes --format=normalized | \
    recsel \
    -j Session \
    -t ChildProcess \
    -p Session.PID,PID \
    -e 'Session.ClientCommand ~ "guix build"'
PID: 4435
Session_PID: 4278

PID: 4554
Session_PID: 4278

PID: 4646
Session_PID: 4278
@end example
@end table
@end table

@node Foreign Architectures
@chapter Foreign Architectures

You can target computers of different CPU architectures when producing
packages (@pxref{Invoking guix package}), packs (@pxref{Invoking guix
pack}) or full systems (@pxref{Invoking guix system}).

GNU Guix supports two distinct mechanisms to target foreign
architectures:

@enumerate
@item
The traditional
@uref{https://en.wikipedia.org/wiki/Cross_compiler,cross-compilation}
mechanism.
@item
The native building mechanism which consists in building using the CPU
instruction set of the foreign system you are targeting.  It often
requires emulation, using the QEMU program for instance.
@end enumerate

@menu
* Cross-Compilation::           Cross-compiling for another architecture.
* Native Builds::               Targeting another architecture through native builds.
@end menu

@node Cross-Compilation
@section Cross-Compilation

@cindex foreign architectures
The commands supporting cross-compilation are proposing the
@option{--list-targets} and @option{--target} options.

The @option{--list-targets} option lists all the supported targets that
can be passed as an argument to @option{--target}.

@example
$ guix build --list-targets
The available targets are:

   - aarch64-linux-gnu
   - arm-linux-gnueabihf
   - avr
   - i586-pc-gnu
   - i686-linux-gnu
   - i686-w64-mingw32
   - mips64el-linux-gnu
   - or1k-elf
   - powerpc-linux-gnu
   - powerpc64le-linux-gnu
   - riscv64-linux-gnu
   - x86_64-linux-gnu
   - x86_64-linux-gnux32
   - x86_64-w64-mingw32
   - xtensa-ath9k-elf
@end example

Targets are specified as GNU triplets (@pxref{Specifying Target
Triplets, GNU configuration triplets,, autoconf, Autoconf}).

Those triplets are passed to GCC and the other underlying compilers
possibly involved when building a package, a system image or any other
GNU Guix output.

@example
$ guix build --target=aarch64-linux-gnu hello
/gnu/store/9926by9qrxa91ijkhw9ndgwp4bn24g9h-hello-2.12

$ file /gnu/store/9926by9qrxa91ijkhw9ndgwp4bn24g9h-hello-2.12/bin/hello
/gnu/store/9926by9qrxa91ijkhw9ndgwp4bn24g9h-hello-2.12/bin/hello: ELF
64-bit LSB executable, ARM aarch64 @dots{}
@end example

The major benefit of cross-compilation is that there are no performance
penalty compared to emulation using QEMU.  There are however higher
risks that some packages fail to cross-compile because fewer users are
using this mechanism extensively.

@node Native Builds
@section Native Builds

The commands that support impersonating a specific system have the
@option{--list-systems} and @option{--system} options.

The @option{--list-systems} option lists all the supported systems that
can be passed as an argument to @option{--system}.

@example
$ guix build --list-systems
The available systems are:

   - x86_64-linux [current]
   - aarch64-linux
   - armhf-linux
   - i586-gnu
   - i686-linux
   - mips64el-linux
   - powerpc-linux
   - powerpc64le-linux
   - riscv64-linux

$ guix build --system=i686-linux hello
/gnu/store/cc0km35s8x2z4pmwkrqqjx46i8b1i3gm-hello-2.12

$ file /gnu/store/cc0km35s8x2z4pmwkrqqjx46i8b1i3gm-hello-2.12/bin/hello
/gnu/store/cc0km35s8x2z4pmwkrqqjx46i8b1i3gm-hello-2.12/bin/hello: ELF
32-bit LSB executable, Intel 80386 @dots{}
@end example

In the above example, the current system is @var{x86_64-linux}.  The
@var{hello} package is however built for the @var{i686-linux} system.

This is possible because the @var{i686} CPU instruction set is a subset
of the @var{x86_64}, hence @var{i686} targeting binaries can be run on
@var{x86_64}.

Still in the context of the previous example, if picking the
@var{aarch64-linux} system and the @command{guix build
--system=aarch64-linux hello} has to build some derivations, an extra
step might be needed.

The @var{aarch64-linux} targeting binaries cannot directly be run on a
@var{x86_64-linux} system.  An emulation layer is requested.  The GNU
Guix daemon can take advantage of the Linux kernel
@uref{https://en.wikipedia.org/wiki/Binfmt_misc,binfmt_misc} mechanism
for that.  In short, the Linux kernel can defer the execution of a
binary targeting a foreign platform, here @var{aarch64-linux}, to a
userspace program, usually an emulator.

There is a service that registers QEMU as a backend for the
@code{binfmt_misc} mechanism (@pxref{Virtualization Services,
@code{qemu-binfmt-service-type}}).  On Debian based foreign
distributions, the alternative would be the @code{qemu-user-static}
package.

If the @code{binfmt_misc} mechanism is not setup correctly, the building
will fail this way:

@example
$ guix build --system=armhf-linux hello --check
@dots{}
@ unsupported-platform /gnu/store/jjn969pijv7hff62025yxpfmc8zy0aq0-hello-2.12.drv aarch64-linux
while setting up the build environment: a `aarch64-linux' is required to
build `/gnu/store/jjn969pijv7hff62025yxpfmc8zy0aq0-hello-2.12.drv', but
I am a `x86_64-linux'@dots{}
@end example

whereas, with the @code{binfmt_misc} mechanism correctly linked with
QEMU, one can expect to see:

@example
$ guix build --system=armhf-linux hello --check
/gnu/store/13xz4nghg39wpymivlwghy08yzj97hlj-hello-2.12
@end example

The main advantage of native building compared to cross-compiling, is
that more packages are likely to build correctly.  However it comes at a
price: compilation backed by QEMU is @emph{way slower} than
cross-compilation, because every instruction needs to be emulated.

The availability of substitutes for the architecture targeted by the
@code{--system} option can mitigate this problem.  An other way to work
around it is to install GNU Guix on a machine whose CPU supports
the targeted instruction set, and set it up as an offload machine
(@pxref{Daemon Offload Setup}).

@node System Configuration
@chapter System Configuration

@cindex system configuration
Guix System supports a consistent whole-system configuration
mechanism.  By that we mean that all aspects of the global system
configuration---such as the available system services, timezone and
locale settings, user accounts---are declared in a single place.  Such
a @dfn{system configuration} can be @dfn{instantiated}---i.e., effected.

One of the advantages of putting all the system configuration under the
control of Guix is that it supports transactional system upgrades, and
makes it possible to roll back to a previous system instantiation,
should something go wrong with the new one (@pxref{Features}).  Another
advantage is that it makes it easy to replicate the exact same configuration
across different machines, or at different points in time, without
having to resort to additional administration tools layered on top of
the own tools of the system.
@c Yes, we're talking of Puppet, Chef, & co. here.  ↑

This section describes this mechanism.  First we focus on the system
administrator's viewpoint---explaining how the system is configured and
instantiated.  Then we show how this mechanism can be extended, for
instance to support new system services.

@menu
* Getting Started with the System::  Your first steps.
* Using the Configuration System::  Customizing your GNU system.
* operating-system Reference::  Detail of operating-system declarations.
* File Systems::                Configuring file system mounts.
* Mapped Devices::              Block device extra processing.
* Swap Space::                  Backing RAM with disk space.
* User Accounts::               Specifying user accounts.
* Keyboard Layout::             How the system interprets key strokes.
* Locales::                     Language and cultural convention settings.
* Services::                    Specifying system services.
* Privileged Programs::         Programs running with elevated privileges.
* X.509 Certificates::          Authenticating HTTPS servers.
* Name Service Switch::         Configuring libc's name service switch.
* Initial RAM Disk::            Linux-Libre bootstrapping.
* Bootloader Configuration::    Configuring the boot loader.
* Invoking guix system::        Instantiating a system configuration.
* Invoking guix deploy::        Deploying a system configuration to a remote host.
* Running Guix in a VM::        How to run Guix System in a virtual machine.
* Defining Services::           Adding new service definitions.
@end menu

@node Getting Started with the System
@section Getting Started

@cindex system configuration file
@cindex configuration file, of the system
You're reading this section probably because you have just installed
Guix System (@pxref{System Installation}) and would like to know where
to go from here.  If you're already familiar with GNU/Linux system
administration, the way Guix System is configured is very different from
what you're used to: you won't install a system service by running
@command{guix install}, you won't configure services by modifying files
under @file{/etc}, and you won't create user accounts by invoking
@command{useradd}; instead, all these aspects are spelled out in a
@dfn{system configuration file}.

The first step with Guix System is thus to write the @dfn{system
configuration file}; luckily, system installation already generated one
for you and stored it under @file{/etc/config.scm}.

@quotation Note
You can store your system configuration file anywhere you like---it
doesn't have to be at @file{/etc/config.scm}.  It's a good idea to keep
it under version control, for instance in a
@uref{https://git-scm.com/book/en/, Git repository}.
@end quotation

The @emph{entire} configuration of the system---user accounts, system
services, timezone, locale settings---is declared in this file, which
follows this template:

@lisp
(use-modules (gnu))
(use-package-modules @dots{})
(use-service-modules @dots{})

(operating-system
  (host-name @dots{})
  (timezone @dots{})
  (locale @dots{})
  (bootloader @dots{})
  (file-systems @dots{})
  (users @dots{})
  (packages @dots{})
  (services @dots{}))
@end lisp

This configuration file is in fact a Scheme program; the first lines
pull in modules providing variables you might need in the rest of the
file---e.g., packages, services, etc.  The @code{operating-system} form
declares the system configuration as a @dfn{record} with a number of
@dfn{fields}.  @xref{Using the Configuration System}, to view complete
examples and learn what to put in there.

The second step, once you have this configuration file, is to test it.
Of course, you can skip this step if you're feeling lucky---you choose!
To do that, pass your configuration file to @command{guix system vm} (no
need to be root, you can do that as a regular user):

@example
guix system vm /etc/config.scm
@end example

@noindent
This command returns the name of a shell script that starts a virtual
machine (VM) running the system @emph{as described in the configuration
file}:

@example
/gnu/store/@dots{}-run-vm.sh
@end example

@noindent
In this VM, you can log in as @code{root} with no password.  That's a
good way to check that your configuration file is correct and that it
gives the expected result, without touching your system.  @xref{Invoking
guix system}, for more information.

@quotation Note
When using @command{guix system vm}, aspects tied to your hardware such
as file systems and mapped devices are overridden because they cannot be
meaningfully tested in the VM@.  Other aspects such as static network
configuration (@pxref{Networking Setup,
@code{static-networking-service-type}}) are @emph{not} overridden but
they may not work inside the VM@.
@end quotation

@cindex system instantiation
@cindex reconfiguring the system
The third step, once you're happy with your configuration, is to
@dfn{instantiate} it---make this configuration effective on your system.
To do that, run:

@example
sudo guix system reconfigure /etc/config.scm
@end example

@cindex upgrading system services
@cindex system services, upgrading
@noindent
This operation is @dfn{transactional}: either it succeeds and you end up
with an upgraded system, or it fails and nothing has changed.  Note that
it does @emph{not} restart system services that were already running.
Thus, to upgrade those services, you have to reboot or to explicitly
restart them; for example, to restart the secure shell (SSH) daemon, you
would run:

@example
sudo herd restart sshd
@end example

@quotation Note
System services are managed by the Shepherd (@pxref{Jump Start,,,
shepherd, The GNU Shepherd Manual}).  The @code{herd} command lets you
inspect, start, and stop services.  To view the status of services, run:

@example
sudo herd status
@end example

To view detailed information about a given service, add its name to the
command:

@example
sudo herd status sshd
@end example

@xref{Services}, for more information.
@end quotation

@cindex provenance, of the system
The system records its @dfn{provenance}---the configuration file and
channels that were used to deploy it.  You can view it like so:

@example
guix system describe
@end example

Additionally, @command{guix system reconfigure} preserves previous
system generations, which you can list:

@example
guix system list-generations
@end example

@noindent
@cindex roll back, for the system
Crucially, that means that you can always @emph{roll back} to an earlier
generation should something go wrong!  When you eventually reboot,
you'll notice a sub-menu in the bootloader that reads ``Old system
generations'': it's what allows you to boot @emph{an older generation of
your system}, should the latest generation be ``broken'' or otherwise
unsatisfying.  You can also ``permanently'' roll back, like so:

@example
sudo guix system roll-back
@end example

@noindent
Alternatively, you can use @command{guix system switch-generation} to
switch to a specific generation.

Once in a while, you'll want to delete old generations that you do not
need anymore to allow @dfn{garbage collection} to free space
(@pxref{Invoking guix gc}).  For example, to remove generations older
than 4 months, run:

@example
sudo guix system delete-generations 4m
@end example

From there on, anytime you want to change something in the system
configuration, be it adding a user account or changing parameters of a
service, you will first update your configuration file and then run
@command{guix system reconfigure} as shown above.
@cindex upgrade, of the system
Likewise, to @emph{upgrade} system software, you first fetch an
up-to-date Guix and then reconfigure your system with that new Guix:

@example
guix pull
sudo guix system reconfigure /etc/config.scm
@end example

@noindent
We recommend doing that regularly so that your system includes the
latest security updates (@pxref{Security Updates}).

@c See <https://lists.gnu.org/archive/html/guix-devel/2019-01/msg00268.html>.
@quotation Note
@cindex sudo vs. @command{guix pull}
@command{sudo guix} runs your user's @command{guix} command and
@emph{not} root's, because @command{sudo} leaves @env{PATH} unchanged.

The difference matters here, because @command{guix pull} updates
the @command{guix} command and package definitions only for the user it is run
as.  This means that if you choose to use @command{guix system reconfigure} in
root's login shell, you'll need to @command{guix pull} separately.
@end quotation

That's it!  If you're getting started with Guix entirely,
@pxref{Getting Started}.  The next sections dive in more detail into the
crux of the matter: system configuration.

@node Using the Configuration System
@section Using the Configuration System

The previous section showed the overall workflow you would follow when
administering a Guix System machine (@pxref{Getting Started with the
System}).  Let's now see in more detail what goes into the system
configuration file.

The operating system is configured by providing an
@code{operating-system} declaration in a file that can then be passed to
the @command{guix system} command (@pxref{Invoking guix system}), as
we've seen before.  A simple setup, with the default Linux-Libre kernel,
initial RAM disk, and a couple of system services added to those
provided by default looks like this:

@findex operating-system
@lisp
@include os-config-bare-bones.texi
@end lisp

The configuration is declarative.
It is code in the Scheme programming language; the whole
@code{(operating-system @dots{})} expression produces a @dfn{record}
with a number of @dfn{fields}.
Some of the fields defined
above, such as @code{host-name} and @code{bootloader}, are mandatory.
Others, such as @code{packages} and @code{services}, can be omitted, in
which case they get a default value.  @xref{operating-system Reference},
for details about all the available fields.

Below we discuss the meaning of some of the most important fields.

@quotation Troubleshooting
The configuration file is a Scheme program and you might get the syntax
or semantics wrong as you get started.  Syntactic issues such as
misplaced parentheses can often be identified by reformatting your file:

@example
guix style -f config.scm
@end example

The Cookbook has a short section to get started with the Scheme
programming language that explains the fundamentals, which you will find
helpful when hacking your configuration.  @xref{A Scheme Crash Course,,,
guix-cookbook, GNU Guix Cookbook}.
@end quotation

@unnumberedsubsec Bootloader

@cindex legacy boot, on Intel machines
@cindex BIOS boot, on Intel machines
@cindex UEFI boot
@cindex EFI boot
The @code{bootloader} field describes the method that will be used to boot
your system.  Machines based on Intel processors can boot in ``legacy'' BIOS
mode, as in the example above.  However, more recent machines rely instead on
the @dfn{Unified Extensible Firmware Interface} (UEFI) to boot.  In that case,
the @code{bootloader} field should contain something along these lines:

@lisp
(bootloader-configuration
  (bootloader grub-efi-bootloader)
  (targets '("/boot/efi")))
@end lisp

@xref{Bootloader Configuration}, for more information on the available
configuration options.

@unnumberedsubsec Globally-Visible Packages

@vindex %base-packages
The @code{packages} field lists packages that will be globally visible
on the system, for all user accounts---i.e., in every user's @env{PATH}
environment variable---in addition to the per-user profiles
(@pxref{Invoking guix package}).  The @code{%base-packages} variable
provides all the tools one would expect for basic user and administrator
tasks---including the GNU Core Utilities, the GNU Networking Utilities,
the @command{mg} lightweight text editor, @command{find}, @command{grep},
etc.  The example above adds GNU@tie{}Screen to those,
taken from the @code{(gnu packages screen)}
module (@pxref{Package Modules}).  The
@code{(list package output)} syntax can be used to add a specific output
of a package:

@lisp
(use-modules (gnu packages))
(use-modules (gnu packages dns))

(operating-system
  ;; ...
  (packages (cons (list isc-bind "utils")
                  %base-packages)))
@end lisp

@findex specification->package
Referring to packages by variable name, like @code{isc-bind} above, has
the advantage of being unambiguous; it also allows typos and such to be
diagnosed right away as ``unbound variables''.  The downside is that one
needs to know which module defines which package, and to augment the
@code{use-package-modules} line accordingly.  To avoid that, one can use
the @code{specification->package} procedure of the @code{(gnu packages)}
module, which returns the best package for a given name or name and
version:

@lisp
(use-modules (gnu packages))

(operating-system
  ;; ...
  (packages (append (map specification->package
                         '("tcpdump" "htop" "gnupg@@2.0"))
                    %base-packages)))
@end lisp

@findex specifications->packages
When a package has more than one output it can be a challenge to refer to a
specific output instead of just to the standard @code{out} output.  For these
situations one can use the @code{specifications->packages} procedure from
the @code{(gnu packages)} module.  For example:

@lisp
(use-modules (gnu packages))

(operating-system
  ;; ...
  (packages (append (specifications->packages
                      '("git" "git:send-email"))
                    %base-packages)))

@end lisp

@unnumberedsubsec System Services

@cindex services
@vindex %base-services
The @code{services} field lists @dfn{system services} to be made
available when the system starts (@pxref{Services}).
The @code{operating-system} declaration above specifies that, in
addition to the basic services, we want the OpenSSH secure shell
daemon listening on port 2222 (@pxref{Networking Services,
@code{openssh-service-type}}).  Under the hood,
@code{openssh-service-type} arranges so that @command{sshd} is started with the
right command-line options, possibly with supporting configuration files
generated as needed (@pxref{Defining Services}).

@cindex customization, of services
@findex modify-services
Occasionally, instead of using the base services as is, you will want to
customize them.  To do this, use @code{modify-services} (@pxref{Service
Reference, @code{modify-services}}) to modify the list.

@anchor{auto-login to TTY} For example, suppose you want to modify
@code{guix-daemon} and Mingetty (the console log-in) in the
@code{%base-services} list (@pxref{Base Services,
@code{%base-services}}).  To do that, you can write the following in
your operating system declaration:

@lisp
(define %my-services
  ;; My very own list of services.
  (modify-services %base-services
    (guix-service-type config =>
                       (guix-configuration
                        (inherit config)
                        ;; Fetch substitutes from example.org.
                        (substitute-urls
                          (list "https://example.org/guix"
                                "https://ci.guix.gnu.org"))))
    (mingetty-service-type config =>
                           (mingetty-configuration
                            (inherit config)
                            ;; Automatically log in as "guest".
                            (auto-login "guest")))))

(operating-system
  ;; @dots{}
  (services %my-services))
@end lisp

This changes the configuration---i.e., the service parameters---of the
@code{guix-service-type} instance, and that of all the
@code{mingetty-service-type} instances in the @code{%base-services} list
(@pxref{Auto-Login to a Specific TTY, see the cookbook for how to
auto-login one user to a specific TTY,, guix-cookbook, GNU Guix Cookbook})).
Observe how this is accomplished: first, we arrange for the original
configuration to be bound to the identifier @code{config} in the
@var{body}, and then we write the @var{body} so that it evaluates to the
desired configuration.  In particular, notice how we use @code{inherit}
to create a new configuration which has the same values as the old
configuration, but with a few modifications.

@cindex encrypted disk
The configuration for a typical ``desktop'' usage, with an encrypted
root partition, a swap file on the root partition, the X11 display
server, GNOME and Xfce (users can choose which of these desktop
environments to use at the log-in screen by pressing @kbd{F1}), network
management, power management, and more, would look like this:

@lisp
@include os-config-desktop.texi
@end lisp

A graphical system with a choice of lightweight window managers
instead of full-blown desktop environments would look like this:

@lisp
@include os-config-lightweight-desktop.texi
@end lisp

This example refers to the @file{/boot/efi} file system by its UUID,
@code{1234-ABCD}.  Replace this UUID with the right UUID on your system,
as returned by the @command{blkid} command.

@xref{Desktop Services}, for the exact list of services provided by
@code{%desktop-services}.

Again, @code{%desktop-services} is just a list of service objects.  If
you want to remove services from there, you can do so using the
procedures for list filtering (@pxref{SRFI-1 Filtering and
Partitioning,,, guile, GNU Guile Reference Manual}).  For instance, the
following expression returns a list that contains all the services in
@code{%desktop-services} minus the Avahi service:

@lisp
(remove (lambda (service)
          (eq? (service-kind service) avahi-service-type))
        %desktop-services)
@end lisp

Alternatively, the @code{modify-services} macro can be used:

@lisp
(modify-services %desktop-services
  (delete avahi-service-type))
@end lisp

@unnumberedsubsec Inspecting Services

@cindex troubleshooting, for system services
@cindex inspecting system services
@cindex system services, inspecting
As you work on your system configuration, you might wonder why some
system service doesn't show up or why the system is not as you expected.
There are several ways to inspect and troubleshoot problems.

@cindex dependency graph, of Shepherd services
First, you can inspect the dependency graph of Shepherd services like
so:

@example
guix system shepherd-graph /etc/config.scm | \
  guix shell xdot -- xdot -
@end example

This lets you visualize the Shepherd services as defined in
@file{/etc/config.scm}.  Each box is a service as would be shown by
@command{sudo herd status} on the running system, and each arrow denotes
a dependency (in the sense that if service @var{A} depends on @var{B},
then @var{B} must be started before @var{A}).

@cindex extension graph, of services
Not all ``services'' are Shepherd services though, since Guix System
uses a broader definition of the term (@pxref{Services}).  To visualize
system services and their relations at a higher level, run:

@example
guix system extension-graph /etc/config.scm | \
  guix shell xdot -- xdot -
@end example

This lets you view the @dfn{service extension graph}: how services
``extend'' each other, for instance by contributing to their
configuration.  @xref{Service Composition}, to understand the meaning of
this graph.

Last, you may also find it useful to inspect your system configuration
at the REPL (@pxref{Using Guix Interactively}).  Here is an example
session:

@example
$ guix repl
scheme@@(guix-user)> ,use (gnu)
scheme@@(guix-user)> (define os (load "config.scm"))
scheme@@(guix-user)> ,pp (map service-kind (operating-system-services os))
$1 = (#<service-type localed cabba93>
      @dots{})
@end example

@xref{Service Reference}, to learn about the Scheme interface to
manipulate and inspect services.

@unnumberedsubsec Instantiating the System

@cindex system instantiation
@cindex reconfiguring the system
Assuming the @code{operating-system} declaration
is stored in the @file{config.scm}
file, the @command{sudo guix system reconfigure config.scm} command
instantiates that configuration, and makes it the default boot
entry.  @xref{Getting Started with the System}, for an overview.

The normal way to change the system configuration is by updating this
file and re-running @command{guix system reconfigure}.  One should never
have to touch files in @file{/etc} or to run commands that modify the
system state such as @command{useradd} or @command{grub-install}.  In
fact, you must avoid that since that would not only void your warranty
but also prevent you from rolling back to previous versions of your
system, should you ever need to.

@unnumberedsubsec The Programming Interface

At the Scheme level, the bulk of an @code{operating-system} declaration
is instantiated with the following monadic procedure (@pxref{The Store
Monad}):

@deffn {Monadic Procedure} operating-system-derivation os
Return a derivation that builds @var{os}, an @code{operating-system}
object (@pxref{Derivations}).

The output of the derivation is a single directory that refers to all
the packages, configuration files, and other supporting files needed to
instantiate @var{os}.
@end deffn

This procedure is provided by the @code{(gnu system)} module.  Along
with @code{(gnu services)} (@pxref{Services}), this module contains the
guts of Guix System.  Make sure to visit it!


@node operating-system Reference
@section @code{operating-system} Reference

This section summarizes all the options available in
@code{operating-system} declarations (@pxref{Using the Configuration
System}).

@deftp {Data Type} operating-system
This is the data type representing an operating system configuration.
By that, we mean all the global system configuration, not per-user
configuration (@pxref{Using the Configuration System}).

@table @asis
@item @code{kernel} (default: @code{linux-libre})
@c footnote duplicated in @pxref{Installation}
The package object of the operating system kernel to
use@footnote{Currently only the Linux-libre kernel is fully supported.
Using GNU@tie{}mach with the GNU@tie{}Hurd is experimental and only
available when building a virtual machine disk image.}.

@cindex hurd
@item @code{hurd} (default: @code{#f})
The package object of the Hurd to be started by the kernel.  When this
field is set, produce a GNU/Hurd operating system.  In that case,
@code{kernel} must also be set to the @code{gnumach} package---the
microkernel the Hurd runs on.

@quotation Warning
This feature is experimental and only supported for disk images.
@end quotation

@item @code{kernel-loadable-modules} (default: '())
A list of objects (usually packages) to collect loadable kernel modules
from--e.g. @code{(list ddcci-driver-linux)}.

@item @code{kernel-arguments} (default: @code{%default-kernel-arguments})
List of strings or gexps representing additional arguments to pass on
the command-line of the kernel---e.g., @code{("console=ttyS0")}.

@item @code{bootloader}
The system bootloader configuration object.  @xref{Bootloader Configuration}.

@item @code{label}
This is the label (a string) as it appears in the bootloader's menu entry.
The default label includes the kernel name and version.

@item @code{keyboard-layout} (default: @code{#f})
This field specifies the keyboard layout to use in the console.  It can be
either @code{#f}, in which case the default keyboard layout is used (usually
US English), or a @code{<keyboard-layout>} record. @xref{Keyboard Layout},
for more information.

This keyboard layout is in effect as soon as the kernel has booted.  For
instance, it is the keyboard layout in effect when you type a passphrase if
your root file system is on a @code{luks-device-mapping} mapped device
(@pxref{Mapped Devices}).

@quotation Note
This does @emph{not} specify the keyboard layout used by the bootloader, nor
that used by the graphical display server.  @xref{Bootloader Configuration},
for information on how to specify the bootloader's keyboard layout.  @xref{X
Window}, for information on how to specify the keyboard layout used by the X
Window System.
@end quotation

@item @code{initrd-modules} (default: @code{%base-initrd-modules})
@cindex initrd
@cindex initial RAM disk
The list of Linux kernel modules that need to be available in the
initial RAM disk.  @xref{Initial RAM Disk}.

@item @code{initrd} (default: @code{base-initrd})
A procedure that returns an initial RAM disk for the Linux
kernel.  This field is provided to support low-level customization and
should rarely be needed for casual use.  @xref{Initial RAM Disk}.

@item @code{firmware} (default: @code{%base-firmware})
@cindex firmware
List of firmware packages loadable by the operating system kernel.

The default includes firmware needed for Atheros- and Broadcom-based
WiFi devices (Linux-libre modules @code{ath9k} and @code{b43-open},
respectively).  @xref{Hardware Considerations}, for more info on
supported hardware.

@item @code{host-name}
The host name.

@item @code{mapped-devices} (default: @code{'()})
A list of mapped devices.  @xref{Mapped Devices}.

@item @code{file-systems}
A list of file systems.  @xref{File Systems}.

@item @code{swap-devices} (default: @code{'()})
@cindex swap devices
A list of swap spaces.  @xref{Swap Space}.

@item @code{users} (default: @code{%base-user-accounts})
@itemx @code{groups} (default: @code{%base-groups})
List of user accounts and groups.  @xref{User Accounts}.

If the @code{users} list lacks a user account with UID@tie{}0, a
``root'' account with UID@tie{}0 is automatically added.

@item @code{skeletons} (default: @code{(default-skeletons)})
A list of target file name/file-like object tuples (@pxref{G-Expressions,
file-like objects}).  These are the skeleton files that will be added to
the home directory of newly-created user accounts.

For instance, a valid value may look like this:

@lisp
`((".bashrc" ,(plain-file "bashrc" "echo Hello\n"))
  (".guile" ,(plain-file "guile"
                         "(use-modules (ice-9 readline))
                          (activate-readline)")))
@end lisp

@item @code{issue} (default: @code{%default-issue})
A string denoting the contents of the @file{/etc/issue} file, which is
displayed when users log in on a text console.

@item @code{packages} (default: @code{%base-packages})
A list of packages to be installed in the global profile, which is accessible
at @file{/run/current-system/profile}.  Each element is either a package
variable or a package/output tuple.  Here's a simple example of both:

@lisp
(cons* git                     ; the default "out" output
       (list git "send-email") ; another output of git
       %base-packages)         ; the default set
@end lisp

The default set includes core utilities and it is good practice to
install non-core utilities in user profiles (@pxref{Invoking guix
package}).

@item @code{timezone} (default: @code{"Etc/UTC"})
A timezone identifying string---e.g., @code{"Europe/Paris"}.

You can run the @command{tzselect} command to find out which timezone
string corresponds to your region.  Choosing an invalid timezone name
causes @command{guix system} to fail.

@item @code{locale} (default: @code{"en_US.utf8"})
The name of the default locale (@pxref{Locale Names,,, libc, The GNU C
Library Reference Manual}).  @xref{Locales}, for more information.

@item @code{locale-definitions} (default: @code{%default-locale-definitions})
The list of locale definitions to be compiled and that may be used at
run time.  @xref{Locales}.

@item @code{locale-libcs} (default: @code{(list @var{glibc})})
The list of GNU@tie{}libc packages whose locale data and tools are used
to build the locale definitions.  @xref{Locales}, for compatibility
considerations that justify this option.

@item @code{name-service-switch} (default: @code{%default-nss})
Configuration of the libc name service switch (NSS)---a
@code{<name-service-switch>} object.  @xref{Name Service Switch}, for
details.

@item @code{services} (default: @code{%base-services})
A list of service objects denoting system services.  @xref{Services}.

@anchor{operating-system-essential-services}
@cindex essential services
@item @code{essential-services} (default: ...)
The list of ``essential services''---i.e., things like instances of
@code{system-service-type} (@pxref{Service Reference}) and
@code{host-name-service-type}, which are derived from the operating
system definition itself.  As a user you should @emph{never} need to
touch this field.

@item @code{pam-services} (default: @code{(base-pam-services)})
@cindex PAM
@cindex pluggable authentication modules
Linux @dfn{pluggable authentication module} (PAM) services.
@c FIXME: Add xref to PAM services section.

@item @code{privileged-programs} (default: @code{%default-privileged-programs})
List of @code{<privileged-program>}.  @xref{Privileged Programs}, for
more information.

@item @code{sudoers-file} (default: @code{%sudoers-specification})
@cindex sudoers file
The contents of the @file{/etc/sudoers} file as a file-like object
(@pxref{G-Expressions, @code{local-file} and @code{plain-file}}).

This file specifies which users can use the @command{sudo} command, what
they are allowed to do, and what privileges they may gain.  The default
is that only @code{root} and members of the @code{wheel} group may use
@code{sudo}.

@end table

@defmac this-operating-system
When used in the @emph{lexical scope} of an operating system field definition,
this identifier resolves to the operating system being defined.

The example below shows how to refer to the operating system being defined in
the definition of the @code{label} field:

@lisp
(use-modules (gnu) (guix))

(operating-system
  ;; ...
  (label (package-full-name
          (operating-system-kernel this-operating-system))))
@end lisp

It is an error to refer to @code{this-operating-system} outside an operating
system definition.
@end defmac

@end deftp

@node File Systems
@section File Systems

The list of file systems to be mounted is specified in the
@code{file-systems} field of the operating system declaration
(@pxref{Using the Configuration System}).  Each file system is declared
using the @code{file-system} form, like this:

@lisp
(file-system
  (mount-point "/home")
  (device "/dev/sda3")
  (type "ext4"))
@end lisp

As usual, some of the fields are mandatory---those shown in the example
above---while others can be omitted.  These are described below.

@deftp {Data Type} file-system
Objects of this type represent file systems to be mounted.  They
contain the following members:

@table @asis
@item @code{type}
This is a string specifying the type of the file system---e.g.,
@code{"ext4"}.

@item @code{mount-point}
This designates the place where the file system is to be mounted.

@item @code{device}
This names the ``source'' of the file system.  It can be one of three
things: a file system label, a file system UUID, or the name of a
@file{/dev} node.  Labels and UUIDs offer a way to refer to file
systems without having to hard-code their actual device
name@footnote{Note that, while it is tempting to use
@file{/dev/disk/by-uuid} and similar device names to achieve the same
result, this is not recommended: These special device nodes are created
by the udev daemon and may be unavailable at the time the device is
mounted.}.

@findex file-system-label
File system labels are created using the @code{file-system-label}
procedure, UUIDs are created using @code{uuid}, and @file{/dev} nodes are
plain strings.  Here's an example of a file system referred to by its
label, as shown by the @command{e2label} command:

@lisp
(file-system
  (mount-point "/home")
  (type "ext4")
  (device (file-system-label "my-home")))
@end lisp

@findex uuid
UUIDs are converted from their string representation (as shown by the
@command{tune2fs -l} command) using the @code{uuid} form@footnote{The
@code{uuid} form expects 16-byte UUIDs as defined in
@uref{https://tools.ietf.org/html/rfc4122, RFC@tie{}4122}.  This is the
form of UUID used by the ext2 family of file systems and others, but it
is different from ``UUIDs'' found in FAT file systems, for instance.},
like this:

@lisp
(file-system
  (mount-point "/home")
  (type "ext4")
  (device (uuid "4dab5feb-d176-45de-b287-9b0a6e4c01cb")))
@end lisp

When the source of a file system is a mapped device (@pxref{Mapped
Devices}), its @code{device} field @emph{must} refer to the mapped
device name---e.g., @file{"/dev/mapper/root-partition"}.
This is required so that
the system knows that mounting the file system depends on having the
corresponding device mapping established.

@item @code{flags} (default: @code{'()})
This is a list of symbols denoting mount flags.  Recognized flags
include @code{read-only}, @code{bind-mount}, @code{no-dev} (disallow
access to special files), @code{no-suid} (ignore setuid and setgid
bits), @code{no-atime} (do not update file access times),
@code{no-diratime} (likewise for directories only),
@code{strict-atime} (update file access time), @code{lazy-time} (only
update time on the in-memory version of the file inode),
@code{no-exec} (disallow program execution), and @code{shared} (make the
mount shared).
@xref{Mount-Unmount-Remount,,, libc, The GNU C Library Reference
Manual}, for more information on these flags.

@item @code{options} (default: @code{#f})
This is either @code{#f}, or a string denoting mount options passed to
the file system driver.  @xref{Mount-Unmount-Remount,,, libc, The GNU C
Library Reference Manual}, for details.

Run @command{man 8 mount} for options for various file systems, but
beware that what it lists as file-system-independent ``mount options'' are
in fact flags, and belong in the @code{flags} field described above.

The @code{file-system-options->alist} and @code{alist->file-system-options}
procedures from @code{(gnu system file-systems)} can be used to convert
file system options given as an association list to the string
representation, and vice-versa.

@item @code{mount?} (default: @code{#t})
This value indicates whether to automatically mount the file system when
the system is brought up.  When set to @code{#f}, the file system gets
an entry in @file{/etc/fstab} (read by the @command{mount} command) but
is not automatically mounted.

@item @code{needed-for-boot?} (default: @code{#f})
This Boolean value indicates whether the file system is needed when
booting.  If that is true, then the file system is mounted when the
initial RAM disk (initrd) is loaded.  This is always the case, for
instance, for the root file system.

@item @code{check?} (default: @code{#t})
This Boolean indicates whether the file system should be checked for
errors before being mounted.  How and when this happens can be further
adjusted with the following options.

@item @code{skip-check-if-clean?} (default: @code{#t})
When true, this Boolean indicates that a file system check triggered
by @code{check?} may exit early if the file system is marked as
``clean'', meaning that it was previously correctly unmounted and
should not contain errors.

Setting this to false will always force a full consistency check when
@code{check?} is true.  This may take a very long time and is not
recommended on healthy systems---in fact, it may reduce reliability!

Conversely, some primitive file systems like @code{fat} do not keep
track of clean shutdowns and will perform a full scan regardless of the
value of this option.

@item @code{repair} (default: @code{'preen})
When @code{check?} finds errors, it can (try to) repair them and
continue booting.  This option controls when and how to do so.

If false, try not to modify the file system at all.  Checking certain
file systems like @code{jfs} may still write to the device to replay
the journal.  No repairs will be attempted.

If @code{#t}, try to repair any errors found and assume ``yes'' to
all questions.  This will fix the most errors, but may be risky.

If @code{'preen}, repair only errors that are safe to fix without
human interaction.  What that means is left up to the developers of
each file system and may be equivalent to ``none'' or ``all''.

@item @code{create-mount-point?} (default: @code{#f})
When true, the mount point is created if it does not exist yet.

@item @code{mount-may-fail?} (default: @code{#f})
When true, this indicates that mounting this file system can fail but
that should not be considered an error.  This is useful in unusual
cases; an example of this is @code{efivarfs}, a file system that can
only be mounted on EFI/UEFI systems.

@item @code{dependencies} (default: @code{'()})
This is a list of @code{<file-system>} or @code{<mapped-device>} objects
representing file systems that must be mounted or mapped devices that
must be opened before (and unmounted or closed after) this one.

As an example, consider a hierarchy of mounts: @file{/sys/fs/cgroup} is
a dependency of @file{/sys/fs/cgroup/cpu} and
@file{/sys/fs/cgroup/memory}.

Another example is a file system that depends on a mapped device, for
example for an encrypted partition (@pxref{Mapped Devices}).

@item @code{shepherd-requirements} (default: @code{'()})
This is a list of symbols denoting Shepherd requirements that must be
met before mounting the file system.

As an example, an NFS file system would typically have a requirement for
@code{networking}.

Typically, file systems are mounted before most other Shepherd services
are started.  However, file systems with a non-empty
shepherd-requirements field are mounted after Shepherd services have
begun.  Any Shepherd service that depends on a file system with a
non-empty shepherd-requirements field must depend on it directly and not
on the generic symbol @code{file-systems}.
@end table
@end deftp

@deffn {Procedure} file-system-label str
This procedure returns an opaque file system label from @var{str}, a
string:

@lisp
(file-system-label "home")
@result{} #<file-system-label "home">
@end lisp

File system labels are used to refer to file systems by label rather
than by device name.  See above for examples.
@end deffn

The @code{(gnu system file-systems)} exports the following useful
variables.

@defvar %base-file-systems
These are essential file systems that are required on normal systems,
such as @code{%pseudo-terminal-file-system} and @code{%immutable-store} (see
below).  Operating system declarations should always contain at least
these.
@end defvar

@defvar %pseudo-terminal-file-system
This is the file system to be mounted as @file{/dev/pts}.  It supports
@dfn{pseudo-terminals} created @i{via} @code{openpty} and similar
functions (@pxref{Pseudo-Terminals,,, libc, The GNU C Library Reference
Manual}).  Pseudo-terminals are used by terminal emulators such as
@command{xterm}.
@end defvar

@defvar %shared-memory-file-system
This file system is mounted as @file{/dev/shm} and is used to support
memory sharing across processes (@pxref{Memory-mapped I/O,
@code{shm_open},, libc, The GNU C Library Reference Manual}).
@end defvar

@defvar %immutable-store
This file system performs a read-only ``bind mount'' of
@file{/gnu/store}, making it read-only for all the users including
@code{root}.  This prevents against accidental modification by software
running as @code{root} or by system administrators.

The daemon itself is still able to write to the store: it remounts it
read-write in its own ``name space.''
@end defvar

@defvar %binary-format-file-system
The @code{binfmt_misc} file system, which allows handling of arbitrary
executable file types to be delegated to user space.  This requires the
@code{binfmt.ko} kernel module to be loaded.
@end defvar

@defvar %fuse-control-file-system
The @code{fusectl} file system, which allows unprivileged users to mount
and unmount user-space FUSE file systems.  This requires the
@code{fuse.ko} kernel module to be loaded.
@end defvar

The @code{(gnu system uuid)} module provides tools to deal with file
system ``unique identifiers'' (UUIDs).

@deffn {Procedure} uuid str [type]
Return an opaque UUID (unique identifier) object of the given @var{type}
(a symbol) by parsing @var{str} (a string):

@lisp
(uuid "4dab5feb-d176-45de-b287-9b0a6e4c01cb")
@result{} #<<uuid> type: dce bv: @dots{}>

(uuid "1234-ABCD" 'fat)
@result{} #<<uuid> type: fat bv: @dots{}>
@end lisp

@var{type} may be one of @code{dce}, @code{iso9660}, @code{fat},
@code{ntfs}, or one of the commonly found synonyms for these.

UUIDs are another way to unambiguously refer to file systems in
operating system configuration.  See the examples above.
@end deffn


@menu
* Btrfs file system::
@end menu

@node Btrfs file system
@subsection Btrfs file system

The Btrfs has special features, such as subvolumes, that merit being
explained in more details.  The following section attempts to cover
basic as well as complex uses of a Btrfs file system with the Guix
System.

In its simplest usage, a Btrfs file system can be described, for
example, by:

@lisp
(file-system
  (mount-point "/home")
  (type "btrfs")
  (device (file-system-label "my-home")))
@end lisp

The example below is more complex, as it makes use of a Btrfs
subvolume, named @code{rootfs}.  The parent Btrfs file system is labeled
@code{my-btrfs-pool}, and is located on an encrypted device (hence the
dependency on @code{mapped-devices}):

@lisp
(file-system
  (device (file-system-label "my-btrfs-pool"))
  (mount-point "/")
  (type "btrfs")
  (options "subvol=rootfs")
  (dependencies mapped-devices))
@end lisp

Some bootloaders, for example GRUB, only mount a Btrfs partition at its
top level during the early boot, and rely on their configuration to
refer to the correct subvolume path within that top level.  The
bootloaders operating in this way typically produce their configuration
on a running system where the Btrfs partitions are already mounted and
where the subvolume information is readily available.  As an example,
@command{grub-mkconfig}, the configuration generator command shipped
with GRUB, reads @file{/proc/self/mountinfo} to determine the top-level
path of a subvolume.

The Guix System produces a bootloader configuration using the operating
system configuration as its sole input; it is therefore necessary to
extract the subvolume name on which @file{/gnu/store} lives (if any)
from that operating system configuration.  To better illustrate,
consider a subvolume named 'rootfs' which contains the root file system
data.  In such situation, the GRUB bootloader would only see the top
level of the root Btrfs partition, e.g.:

@example
/                   (top level)
├── rootfs          (subvolume directory)
    ├── gnu         (normal directory)
        ├── store   (normal directory)
[...]
@end example

Thus, the subvolume name must be prepended to the @file{/gnu/store} path
of the kernel, initrd binaries and any other files referred to in the
GRUB configuration that must be found during the early boot.

The next example shows a nested hierarchy of subvolumes and
directories:

@example
/                   (top level)
├── rootfs          (subvolume)
    ├── gnu         (normal directory)
        ├── store   (subvolume)
[...]
@end example

This scenario would work without mounting the 'store' subvolume.
Mounting 'rootfs' is sufficient, since the subvolume name matches its
intended mount point in the file system hierarchy.  Alternatively, the
'store' subvolume could be referred to by setting the @code{subvol}
option to either @code{/rootfs/gnu/store} or @code{rootfs/gnu/store}.

Finally, a more contrived example of nested subvolumes:

@example
/                           (top level)
├── root-snapshots          (subvolume)
    ├── root-current        (subvolume)
        ├── guix-store      (subvolume)
[...]
@end example

Here, the 'guix-store' subvolume doesn't match its intended mount point,
so it is necessary to mount it.  The subvolume must be fully specified,
by passing its file name to the @code{subvol} option.  To illustrate,
the 'guix-store' subvolume could be mounted on @file{/gnu/store} by using
a file system declaration such as:

@lisp
(file-system
  (device (file-system-label "btrfs-pool-1"))
  (mount-point "/gnu/store")
  (type "btrfs")
  (options "subvol=root-snapshots/root-current/guix-store,\
compress-force=zstd,space_cache=v2"))
@end lisp

@node Mapped Devices
@section Mapped Devices

@cindex device mapping
@cindex mapped devices
The Linux kernel has a notion of @dfn{device mapping}: a block device,
such as a hard disk partition, can be @dfn{mapped} into another device,
usually in @code{/dev/mapper/},
with additional processing over the data that flows through
it@footnote{Note that the GNU@tie{}Hurd makes no difference between the
concept of a ``mapped device'' and that of a file system: both boil down
to @emph{translating} input/output operations made on a file to
operations on its backing store.  Thus, the Hurd implements mapped
devices, like file systems, using the generic @dfn{translator} mechanism
(@pxref{Translators,,, hurd, The GNU Hurd Reference Manual}).}.  A
typical example is encryption device mapping: all writes to the mapped
device are encrypted, and all reads are deciphered, transparently.
Guix extends this notion by considering any device or set of devices that
are @dfn{transformed} in some way to create a new device; for instance,
RAID devices are obtained by @dfn{assembling} several other devices, such
as hard disks or partitions, into a new one that behaves as one partition.

Mapped devices are declared using the @code{mapped-device} form,
defined as follows; for examples, see below.

@deftp {Data Type} mapped-device
Objects of this type represent device mappings that will be made when
the system boots up.

@table @code
@item source
This is either a string specifying the name of the block device to be mapped,
such as @code{"/dev/sda3"}, or a list of such strings when several devices
need to be assembled for creating a new one.  In case of LVM this is a
string specifying name of the volume group to be mapped.

@item target
This string specifies the name of the resulting mapped device.  For
kernel mappers such as encrypted devices of type @code{luks-device-mapping},
specifying @code{"my-partition"} leads to the creation of
the @code{"/dev/mapper/my-partition"} device.
For RAID devices of type @code{raid-device-mapping}, the full device name
such as @code{"/dev/md0"} needs to be given.
LVM logical volumes of type @code{lvm-device-mapping} need to
be specified as @code{"VGNAME-LVNAME"}.

@item targets
This list of strings specifies names of the resulting mapped devices in case
there are several.  The format is identical to @var{target}.

@item type
This must be a @code{mapped-device-kind} object, which specifies how
@var{source} is mapped to @var{target}.
@end table
@end deftp

@defvar luks-device-mapping
This defines LUKS block device encryption using the @command{cryptsetup}
command from the package with the same name.  It relies on the
@code{dm-crypt} Linux kernel module.
@end defvar

@deffn {Procedure} luks-device-mapping-with-options [#:key-file]
Return a @code{luks-device-mapping} object, which defines LUKS block
device encryption using the @command{cryptsetup} command from the
package with the same name.  It relies on the @code{dm-crypt} Linux
kernel module.

If @code{key-file} is provided, unlocking is first attempted using that
key file.  This has an advantage of not requiring a password entry, so
it can be used (for example) to unlock RAID arrays automatically on
boot.  If key file unlock fails, password unlock is attempted as well.
Key file is not stored in the store and needs to be available at the
given location at the time of the unlock attempt.

@lisp
;; Following definition would be equivalent to running:
;;   cryptsetup open --key-file /crypto.key /dev/sdb1 data
(mapped-device
 (source "/dev/sdb1)
 (target "data)
 (type (luks-device-mapping-with-options
        #:key-file "/crypto.key")))
@end lisp
@end deffn

@defvar raid-device-mapping
This defines a RAID device, which is assembled using the @code{mdadm}
command from the package with the same name.  It requires a Linux kernel
module for the appropriate RAID level to be loaded, such as @code{raid456}
for RAID-4, RAID-5 or RAID-6, or @code{raid10} for RAID-10.
@end defvar

@cindex LVM, logical volume manager
@defvar lvm-device-mapping
This defines one or more logical volumes for the Linux
@uref{https://www.sourceware.org/lvm2/, Logical Volume Manager (LVM)}.
The volume group is activated by the @command{vgchange} command from the
@code{lvm2} package.
@end defvar

@cindex disk encryption
@cindex LUKS
The following example specifies a mapping from @file{/dev/sda3} to
@file{/dev/mapper/home} using LUKS---the
@url{https://gitlab.com/cryptsetup/cryptsetup,Linux Unified Key Setup}, a
standard mechanism for disk encryption.
The @file{/dev/mapper/home}
device can then be used as the @code{device} of a @code{file-system}
declaration (@pxref{File Systems}).

@lisp
(mapped-device
  (source "/dev/sda3")
  (target "home")
  (type luks-device-mapping))
@end lisp

Alternatively, to become independent of device numbering, one may obtain
the LUKS UUID (@dfn{unique identifier}) of the source device by a
command like:

@example
cryptsetup luksUUID /dev/sda3
@end example

and use it as follows:

@lisp
(mapped-device
  (source (uuid "cb67fc72-0d54-4c88-9d4b-b225f30b0f44"))
  (target "home")
  (type luks-device-mapping))
@end lisp

@cindex swap encryption
It is also desirable to encrypt swap space, since swap space may contain
sensitive data.  One way to accomplish that is to use a swap file in a
file system on a device mapped via LUKS encryption.  In this way, the
swap file is encrypted because the entire device is encrypted.
@xref{Swap Space}, or @xref{Preparing for Installation,,Disk
Partitioning}, for an example.

A RAID device formed of the partitions @file{/dev/sda1} and @file{/dev/sdb1}
may be declared as follows:

@lisp
(mapped-device
  (source (list "/dev/sda1" "/dev/sdb1"))
  (target "/dev/md0")
  (type raid-device-mapping))
@end lisp

The @file{/dev/md0} device can then be used as the @code{device} of a
@code{file-system} declaration (@pxref{File Systems}).
Note that the RAID level need not be given; it is chosen during the
initial creation and formatting of the RAID device and is determined
automatically later.

LVM logical volumes ``alpha'' and ``beta'' from volume group ``vg0'' can
be declared as follows:

@lisp
(mapped-device
  (source "vg0")
  (targets (list "vg0-alpha" "vg0-beta"))
  (type lvm-device-mapping))
@end lisp

Devices @file{/dev/mapper/vg0-alpha} and @file{/dev/mapper/vg0-beta} can
then be used as the @code{device} of a @code{file-system} declaration
(@pxref{File Systems}).

@node Swap Space
@section Swap Space
@cindex swap space

Swap space, as it is commonly called, is a disk area specifically
designated for paging: the process in charge of memory management
(the Linux kernel or Hurd's default pager) can decide that some memory
pages stored in RAM which belong to a running program but are unused
should be stored on disk instead.  It unloads those from the RAM,
freeing up precious fast memory, and writes them to the swap space.  If
the program tries to access that very page, the memory management
process loads it back into memory for the program to use.

A common misconception about swap is that it is only useful when small
amounts of RAM are available to the system.  However, it should be noted
that kernels often use all available RAM for disk access caching to make
I/O faster, and thus paging out unused portions of program memory will
expand the RAM available for such caching.

For a more detailed description of how memory is managed from the
viewpoint of a monolithic kernel, @pxref{Memory
Concepts,,, libc, The GNU C Library Reference Manual}.

The Linux kernel has support for swap partitions and swap files: the
former uses a whole disk partition for paging, whereas the second uses a
file on a file system for that (the file system driver needs to support
it).  On a comparable setup, both have the same performance, so one
should consider ease of use when deciding between them.  Partitions are
``simpler'' and do not need file system support, but need to be
allocated at disk formatting time (logical volumes notwithstanding),
whereas files can be allocated and deallocated at any time.

@cindex hibernation
@cindex suspend to disk
Swap space is also required to put the system into @dfn{hibernation}
(also called @dfn{suspend to disk}), whereby memory is dumped to swap
before shutdown so it can be restored when the machine is eventually
restarted.  Hibernation uses at most half the size of the RAM in the
configured swap space.  The Linux kernel needs to know about the swap
space to be used to resume from hibernation on boot (@i{via} a kernel
argument).  When using a swap file, its offset in the device holding it
also needs to be given to the kernel; that value has to be updated if
the file is initialized again as swap---e.g., because its size was
changed.

Note that swap space is not zeroed on shutdown, so sensitive data (such
as passwords) may linger on it if it was paged out.  As such, you should
consider having your swap reside on an encrypted device (@pxref{Mapped
Devices}).

@deftp {Data Type} swap-space
Objects of this type represent swap spaces.  They contain the following
members:

@table @asis
@item @code{target}
The device or file to use, either a UUID, a @code{file-system-label} or
a string, as in the definition of a @code{file-system} (@pxref{File
Systems}).

@item @code{dependencies} (default: @code{'()})
A list of @code{file-system} or @code{mapped-device} objects, upon which
the availability of the space depends.  Note that just like for
@code{file-system} objects, dependencies which are needed for boot and
mounted in early userspace are not managed by the Shepherd, and so
automatically filtered out for you.

@item @code{priority} (default: @code{#f})
Only supported by the Linux kernel.  Either @code{#f} to disable swap
priority, or an integer between 0 and 32767.  The kernel will first use
swap spaces of higher priority when paging, and use same priority spaces
on a round-robin basis.  The kernel will use swap spaces without a set
priority after prioritized spaces, and in the order that they appeared in
(not round-robin).

@item @code{discard?} (default: @code{#f})
Only supported by the Linux kernel.  When true, the kernel will notify
the disk controller of discarded pages, for example with the TRIM
operation on Solid State Drives.

@end table
@end deftp

Here are some examples:

@lisp
(swap-space (target (uuid "4dab5feb-d176-45de-b287-9b0a6e4c01cb")))
@end lisp

Use the swap partition with the given UUID@.  You can learn the UUID of a
Linux swap partition by running @command{swaplabel @var{device}}, where
@var{device} is the @file{/dev} file name of that partition.

@lisp
(swap-space
  (target (file-system-label "swap"))
  (dependencies mapped-devices))
@end lisp

Use the partition with label @code{swap}, which can be found after all
the @var{mapped-devices} mapped devices have been opened.  Again, the
@command{swaplabel} command allows you to view and change the label of a
Linux swap partition.

Here's a more involved example with the corresponding @code{file-systems} part
of an @code{operating-system} declaration.

@lisp
(file-systems
  (list (file-system
          (device (file-system-label "root"))
          (mount-point "/")
          (type "ext4"))
        (file-system
          (device (file-system-label "btrfs"))
          (mount-point "/btrfs")
          (type "btrfs"))))

(swap-devices
  (list
    (swap-space
      (target "/btrfs/swapfile")
      (dependencies (filter (file-system-mount-point-predicate "/btrfs")
                            file-systems)))))
@end lisp

Use the file @file{/btrfs/swapfile} as swap space, which depends on the
file system mounted at @file{/btrfs}.  Note how we use Guile's filter to
select the file system in an elegant fashion!

@lisp
(swap-devices
  (list
    (swap-space
      (target "/dev/mapper/my-swap")
      (dependencies mapped-devices))))

(kernel-arguments
  (cons* "resume=/dev/mapper/my-swap"
         %default-kernel-arguments))
@end lisp

The above snippet of an @code{operating-system} declaration enables
the mapped device @file{/dev/mapper/my-swap} (which may be part of an
encrypted device) as swap space, and tells the kernel to use it for
hibernation via the @code{resume} kernel argument
(@pxref{operating-system Reference}, @code{kernel-arguments}).

@lisp
(swap-devices
  (list
    (swap-space
      (target "/swapfile")
      (dependencies (filter (file-system-mount-point-predicate "/")
                            file-systems)))))

(kernel-arguments
  (cons* "resume=/dev/sda3"        ;device that holds /swapfile
         "resume_offset=92514304"  ;offset of /swapfile on device
         %default-kernel-arguments))
@end lisp

This other snippet of @code{operating-system} enables the swap file
@file{/swapfile} for hibernation by telling the kernel about the
partition containing it
(@code{resume} argument) and its offset on that partition (@code{resume_offset}
argument).  The latter value can be found in the output of the command
@command{filefrag -e} as the first number right under the
@code{physical_offset} column header (the second command extracts its
value directly):

@smallexample
$ sudo filefrag -e /swapfile
Filesystem type is: ef53
File size of /swapfile is 2463842304 (601524 blocks of 4096 bytes)
 ext:     logical_offset:        physical_offset: length:   expected: flags:
   0:        0..    2047:   92514304..  92516351:   2048:
@dots{}
$ sudo filefrag -e /swapfile | grep '^ *0:' | cut -d: -f3 | cut -d. -f1
   92514304
@end smallexample

@node User Accounts
@section User Accounts

@cindex users
@cindex accounts
@cindex user accounts
User accounts and groups are entirely managed through the
@code{operating-system} declaration.  They are specified with the
@code{user-account} and @code{user-group} forms:

@lisp
(user-account
  (name "alice")
  (group "users")
  (supplementary-groups '("wheel"   ;allow use of sudo, etc.
                          "audio"   ;sound card
                          "video"   ;video devices such as webcams
                          "cdrom")) ;the good ol' CD-ROM
  (comment "Bob's sister"))
@end lisp

Here's a user account that uses a different shell and a custom home
directory (the default would be @file{"/home/bob"}):

@lisp
(user-account
  (name "bob")
  (group "users")
  (comment "Alice's bro")
  (shell (file-append zsh "/bin/zsh"))
  (home-directory "/home/robert"))
@end lisp

When booting or upon completion of @command{guix system reconfigure},
the system ensures that only the user accounts and groups specified in
the @code{operating-system} declaration exist, and with the specified
properties.  Thus, account or group creations or modifications made by
directly invoking commands such as @command{useradd} are lost upon
reconfiguration or reboot.  This ensures that the system remains exactly
as declared.

@deftp {Data Type} user-account
Objects of this type represent user accounts.  The following members may
be specified:

@table @asis
@item @code{name}
The name of the user account.

@item @code{group}
@cindex groups
This is the name (a string) or identifier (a number) of the user group
this account belongs to.

@item @code{supplementary-groups} (default: @code{'()})
Optionally, this can be defined as a list of group names that this
account belongs to.

@item @code{uid} (default: @code{#f})
This is the user ID for this account (a number), or @code{#f}.  In the
latter case, a number is automatically chosen by the system when the
account is created.

@item @code{comment} (default: @code{""})
A comment about the account, such as the account owner's full name.

Note that, for non-system accounts, users are free to change their real
name as it appears in @file{/etc/passwd} using the @command{chfn}
command.  When they do, their choice prevails over the system
administrator's choice; reconfiguring does @emph{not} change their name.

@item @code{home-directory}
This is the name of the home directory for the account.

@item @code{create-home-directory?} (default: @code{#t})
Indicates whether the home directory of this account should be created
if it does not exist yet.

@item @code{shell} (default: Bash)
This is a G-expression denoting the file name of a program to be used as
the shell (@pxref{G-Expressions}).  For example, you would refer to the
Bash executable like this:

@lisp
(file-append bash "/bin/bash")
@end lisp

@noindent
... and to the Zsh executable like that:

@lisp
(file-append zsh "/bin/zsh")
@end lisp

@item @code{system?} (default: @code{#f})
This Boolean value indicates whether the account is a ``system''
account.  System accounts are sometimes treated specially; for instance,
graphical login managers do not list them.

@anchor{user-account-password}
@cindex password, for user accounts
@item @code{password} (default: @code{#f})
You would normally leave this field to @code{#f}, initialize user
passwords as @code{root} with the @command{passwd} command, and then let
users change it with @command{passwd}.  Passwords set with
@command{passwd} are of course preserved across reboot and
reconfiguration.

If you @emph{do} want to set an initial password for an account, then
this field must contain the encrypted password, as a string.  You can use the
@code{crypt} procedure for this purpose:

@lisp
(user-account
  (name "charlie")
  (group "users")

  ;; Specify a SHA-512-hashed initial password.
  (password (crypt "InitialPassword!" "$6$abc")))
@end lisp

@quotation Note
The hash of this initial password will be available in a file in
@file{/gnu/store}, readable by all the users, so this method must be used with
care.
@end quotation

@xref{Passphrase Storage,,, libc, The GNU C Library Reference Manual}, for
more information on password encryption, and @ref{Encryption,,, guile, GNU
Guile Reference Manual}, for information on Guile's @code{crypt} procedure.

@end table
@end deftp

@cindex groups
User group declarations are even simpler:

@lisp
(user-group (name "students"))
@end lisp

@deftp {Data Type} user-group
This type is for, well, user groups.  There are just a few fields:

@table @asis
@item @code{name}
The name of the group.

@item @code{id} (default: @code{#f})
The group identifier (a number).  If @code{#f}, a new number is
automatically allocated when the group is created.

@item @code{system?} (default: @code{#f})
This Boolean value indicates whether the group is a ``system'' group.
System groups have low numerical IDs.

@item @code{password} (default: @code{#f})
What, user groups can have a password?  Well, apparently yes.  Unless
@code{#f}, this field specifies the password of the group.

@end table
@end deftp

For convenience, a variable lists all the basic user groups one may
expect:

@defvar %base-groups
This is the list of basic user groups that users and/or packages expect
to be present on the system.  This includes groups such as ``root'',
``wheel'', and ``users'', as well as groups used to control access to
specific devices such as ``audio'', ``disk'', and ``cdrom''.
@end defvar

@defvar %base-user-accounts
This is the list of basic system accounts that programs may expect to
find on a GNU/Linux system, such as the ``nobody'' account.

Note that the ``root'' account is not included here.  It is a
special-case and is automatically added whether or not it is specified.
@end defvar

@node Keyboard Layout
@section Keyboard Layout

@cindex keyboard layout
@cindex keymap
To specify what each key of your keyboard does, you need to tell the operating
system what @dfn{keyboard layout} you want to use.  The default, when nothing
is specified, is the US English QWERTY layout for 105-key PC keyboards.
However, German speakers will usually prefer the German QWERTZ layout, French
speakers will want the AZERTY layout, and so on; hackers might prefer Dvorak
or bépo, and they might even want to further customize the effect of some of
the keys.  This section explains how to get that done.

@cindex keyboard layout, definition
There are three components that will want to know about your keyboard layout:

@itemize
@item
The @emph{bootloader} may want to know what keyboard layout you want to use
(@pxref{Bootloader Configuration, @code{keyboard-layout}}).  This is useful if
you want, for instance, to make sure that you can type the passphrase of your
encrypted root partition using the right layout.

@item
The @emph{operating system kernel}, Linux, will need that so that the console
is properly configured (@pxref{operating-system Reference,
@code{keyboard-layout}}).

@item
The @emph{graphical display server}, usually Xorg, also has its own idea of
the keyboard layout (@pxref{X Window, @code{keyboard-layout}}).
@end itemize

Guix allows you to configure all three separately but, fortunately, it allows
you to share the same keyboard layout for all three components.

@cindex XKB, keyboard layouts
Keyboard layouts are represented by records created by the
@code{keyboard-layout} procedure of @code{(gnu system keyboard)}.  Following
the X Keyboard extension (XKB), each layout has four attributes: a name (often
a language code such as ``fi'' for Finnish or ``jp'' for Japanese), an
optional variant name, an optional keyboard model name, and a possibly empty
list of additional options.  In most cases the layout name is all you care
about.

@deffn {Procedure} keyboard-layout name [variant] [#:model] [#:options '()]
Return a new keyboard layout with the given @var{name} and @var{variant}.

@var{name} must be a string such as @code{"fr"}; @var{variant} must be a
string such as @code{"bepo"} or @code{"nodeadkeys"}.  See the
@code{xkeyboard-config} package for valid options.
@end deffn

Here are a few examples:

@lisp
;; The German QWERTZ layout.  Here we assume a standard
;; "pc105" keyboard model.
(keyboard-layout "de")

;; The bépo variant of the French layout.
(keyboard-layout "fr" "bepo")

;; The Catalan layout.
(keyboard-layout "es" "cat")

;; Arabic layout with "Alt-Shift" to switch to US layout.
(keyboard-layout "ar,us" #:options '("grp:alt_shift_toggle"))

;; The Latin American Spanish layout.  In addition, the
;; "Caps Lock" key is used as an additional "Ctrl" key,
;; and the "Menu" key is used as a "Compose" key to enter
;; accented letters.
(keyboard-layout "latam"
                 #:options '("ctrl:nocaps" "compose:menu"))

;; The Russian layout for a ThinkPad keyboard.
(keyboard-layout "ru" #:model "thinkpad")

;; The "US international" layout, which is the US layout plus
;; dead keys to enter accented characters.  This is for an
;; Apple MacBook keyboard.
(keyboard-layout "us" "intl" #:model "macbook78")
@end lisp

See the @file{share/X11/xkb} directory of the @code{xkeyboard-config} package
for a complete list of supported layouts, variants, and models.

@cindex keyboard layout, configuration
Let's say you want your system to use the Turkish keyboard layout throughout
your system---bootloader, console, and Xorg.  Here's what your system
configuration would look like:

@findex set-xorg-configuration
@lisp
;; Using the Turkish layout for the bootloader, the console,
;; and for Xorg.

(operating-system
  ;; ...
  (keyboard-layout (keyboard-layout "tr"))  ;for the console
  (bootloader (bootloader-configuration
                (bootloader grub-efi-bootloader)
                (targets '("/boot/efi"))
                (keyboard-layout keyboard-layout))) ;for GRUB
  (services (cons (set-xorg-configuration
                    (xorg-configuration             ;for Xorg
                      (keyboard-layout keyboard-layout)))
                  %desktop-services)))
@end lisp

In the example above, for GRUB and for Xorg, we just refer to the
@code{keyboard-layout} field defined above, but we could just as well refer to
a different layout.  The @code{set-xorg-configuration} procedure communicates
the desired Xorg configuration to the graphical log-in manager, by default
GDM.

We've discussed how to specify the @emph{default} keyboard layout of your
system when it starts, but you can also adjust it at run time:

@itemize
@item
If you're using GNOME, its settings panel has a ``Region & Language'' entry
where you can select one or more keyboard layouts.

@item
Under Xorg, the @command{setxkbmap} command (from the same-named package)
allows you to change the current layout.  For example, this is how you would
change the layout to US Dvorak:

@example
setxkbmap us dvorak
@end example

@item
The @code{loadkeys} command changes the keyboard layout in effect in the Linux
console.  However, note that @code{loadkeys} does @emph{not} use the XKB
keyboard layout categorization described above.  The command below loads the
French bépo layout:

@example
loadkeys fr-bepo
@end example
@end itemize

@node Locales
@section Locales

@cindex locale
A @dfn{locale} defines cultural conventions for a particular language
and region of the world (@pxref{Locales,,, libc, The GNU C Library
Reference Manual}).  Each locale has a name that typically has the form
@code{@var{language}_@var{territory}.@var{codeset}}---e.g.,
@code{fr_LU.utf8} designates the locale for the French language, with
cultural conventions from Luxembourg, and using the UTF-8 encoding.

@cindex locale definition
Usually, you will want to specify the default locale for the machine
using the @code{locale} field of the @code{operating-system} declaration
(@pxref{operating-system Reference, @code{locale}}).

The selected locale is automatically added to the @dfn{locale
definitions} known to the system if needed, with its codeset inferred
from its name---e.g., @code{bo_CN.utf8} will be assumed to use the
@code{UTF-8} codeset.  Additional locale definitions can be specified in
the @code{locale-definitions} slot of @code{operating-system}---this is
useful, for instance, if the codeset could not be inferred from the
locale name.  The default set of locale definitions includes some widely
used locales, but not all the available locales, in order to save space.

For instance, to add the North Frisian locale for Germany, the value of
that field may be:

@lisp
(cons (locale-definition
        (name "fy_DE.utf8") (source "fy_DE"))
      %default-locale-definitions)
@end lisp

Likewise, to save space, one might want @code{locale-definitions} to
list only the locales that are actually used, as in:

@lisp
(list (locale-definition
        (name "ja_JP.eucjp") (source "ja_JP")
        (charset "EUC-JP")))
@end lisp

@vindex LOCPATH
The compiled locale definitions are available at
@file{/run/current-system/locale/X.Y}, where @code{X.Y} is the libc
version, which is the default location where the GNU@tie{}libc provided
by Guix looks for locale data.  This can be overridden using the
@env{LOCPATH} environment variable (@pxref{locales-and-locpath,
@env{LOCPATH} and locale packages}).

The @code{locale-definition} form is provided by the @code{(gnu system
locale)} module.  Details are given below.

@deftp {Data Type} locale-definition
This is the data type of a locale definition.

@table @asis

@item @code{name}
The name of the locale.  @xref{Locale Names,,, libc, The GNU C Library
Reference Manual}, for more information on locale names.

@item @code{source}
The name of the source for that locale.  This is typically the
@code{@var{language}_@var{territory}} part of the locale name.

@item @code{charset} (default: @code{"UTF-8"})
The ``character set'' or ``code set'' for that locale,
@uref{https://www.iana.org/assignments/character-sets, as defined by
IANA}.

@end table
@end deftp

@defvar %default-locale-definitions
A list of commonly used UTF-8 locales, used as the default
value of the @code{locale-definitions} field of @code{operating-system}
declarations.

@cindex locale name
@cindex normalized codeset in locale names
These locale definitions use the @dfn{normalized codeset} for the part
that follows the dot in the name (@pxref{Using gettextized software,
normalized codeset,, libc, The GNU C Library Reference Manual}).  So for
instance it has @code{uk_UA.utf8} but @emph{not}, say,
@code{uk_UA.UTF-8}.
@end defvar

@subsection Locale Data Compatibility Considerations

@cindex incompatibility, of locale data
@code{operating-system} declarations provide a @code{locale-libcs} field
to specify the GNU@tie{}libc packages that are used to compile locale
declarations (@pxref{operating-system Reference}).  ``Why would I
care?'', you may ask.  Well, it turns out that the binary format of
locale data is occasionally incompatible from one libc version to
another.

@c See <https://sourceware.org/ml/libc-alpha/2015-09/msg00575.html>
@c and <https://lists.gnu.org/archive/html/guix-devel/2015-08/msg00737.html>.
For instance, a program linked against libc version 2.21 is unable to
read locale data produced with libc 2.22; worse, that program
@emph{aborts} instead of simply ignoring the incompatible locale
data@footnote{Versions 2.23 and later of GNU@tie{}libc will simply skip
the incompatible locale data, which is already an improvement.}.
Similarly, a program linked against libc 2.22 can read most, but not
all, of the locale data from libc 2.21 (specifically, @env{LC_COLLATE}
data is incompatible); thus calls to @code{setlocale} may fail, but
programs will not abort.

The ``problem'' with Guix is that users have a lot of freedom: They can
choose whether and when to upgrade software in their profiles, and might
be using a libc version different from the one the system administrator
used to build the system-wide locale data.

Fortunately, unprivileged users can also install their own locale data
and define @env{GUIX_LOCPATH} accordingly (@pxref{locales-and-locpath,
@env{GUIX_LOCPATH} and locale packages}).

Still, it is best if the system-wide locale data at
@file{/run/current-system/locale} is built for all the libc versions
actually in use on the system, so that all the programs can access
it---this is especially crucial on a multi-user system.  To do that, the
administrator can specify several libc packages in the
@code{locale-libcs} field of @code{operating-system}:

@lisp
(use-package-modules base)

(operating-system
  ;; @dots{}
  (locale-libcs (list glibc-2.21 (canonical-package glibc))))
@end lisp

This example would lead to a system containing locale definitions for
both libc 2.21 and the current version of libc in
@file{/run/current-system/locale}.


@node Services
@section Services

@cindex system services
An important part of preparing an @code{operating-system} declaration is
listing @dfn{system services} and their configuration (@pxref{Using the
Configuration System}).  System services are typically daemons launched
when the system boots, or other actions needed at that time---e.g.,
configuring network access.

Guix has a broad definition of ``service'' (@pxref{Service
Composition}), but many services are managed by the GNU@tie{}Shepherd
(@pxref{Shepherd Services}).  On a running system, the @command{herd}
command allows you to list the available services, show their status,
start and stop them, or do other specific operations (@pxref{Jump
Start,,, shepherd, The GNU Shepherd Manual}).  For example:

@example
# herd status
@end example

The above command, run as @code{root}, lists the currently defined
services.  The @command{herd doc} command shows a synopsis of the given
service and its associated actions:

@example
# herd doc nscd
Run libc's name service cache daemon (nscd).

# herd doc nscd action invalidate
invalidate: Invalidate the given cache--e.g., 'hosts' for host name lookups.
@end example

The @command{start}, @command{stop}, and @command{restart} sub-commands
have the effect you would expect.  For instance, the commands below stop
the nscd service and restart the Xorg display server:

@example
# herd stop nscd
Service nscd has been stopped.
# herd restart xorg-server
Service xorg-server has been stopped.
Service xorg-server has been started.
@end example

@cindex configuration, action for shepherd services
@cindex configuration file, of a shepherd service
For some services, @command{herd configuration} returns the name of the
service's configuration file, which can be handy to inspect its
configuration:

@example
# herd configuration sshd
/gnu/store/@dots{}-sshd_config
@end example

The following sections document the available services, starting with
the core services, that may be used in an @code{operating-system}
declaration.

@menu
* Base Services::               Essential system services.
* Scheduled Job Execution::     The mcron service.
* Log Rotation::                The rottlog service.
* Networking Setup::            Setting up network interfaces.
* Networking Services::         Firewall, SSH daemon, etc.
* Unattended Upgrades::         Automated system upgrades.
* X Window::                    Graphical display.
* Printing Services::           Local and remote printer support.
* Desktop Services::            D-Bus and desktop services.
* Sound Services::              ALSA and Pulseaudio services.
* File Search Services::        Tools to search for files.
* Database Services::           SQL databases, key-value stores, etc.
* Mail Services::               IMAP, POP3, SMTP, and all that.
* Messaging Services::          Messaging services.
* Telephony Services::          Telephony services.
* File-Sharing Services::       File-sharing services.
* Monitoring Services::         Monitoring services.
* Kerberos Services::           Kerberos services.
* LDAP Services::               LDAP services.
* Web Services::                Web servers.
* Certificate Services::        TLS certificates via Let's Encrypt.
* DNS Services::                DNS daemons.
* VNC Services::                VNC daemons.
* VPN Services::                VPN daemons.
* Network File System::         NFS related services.
* Samba Services::              Samba services.
* Continuous Integration::      Cuirass and Laminar services.
* Power Management Services::   Extending battery life.
* Audio Services::              The MPD.
* Virtualization Services::     Virtualization services.
* Version Control Services::    Providing remote access to Git repositories.
* Game Services::               Game servers.
* PAM Mount Service::           Service to mount volumes when logging in.
* Guix Services::               Services relating specifically to Guix.
* Linux Services::              Services tied to the Linux kernel.
* Hurd Services::               Services specific for a Hurd System.
* Miscellaneous Services::      Other services.
@end menu

@node Base Services
@subsection Base Services

The @code{(gnu services base)} module provides definitions for the basic
services that one expects from the system.  The services exported by
this module are listed below.

@defvar %base-services
This variable contains a list of basic services (@pxref{Service Types
and Services}, for more information on service objects) one would
expect from the system: a login service (mingetty) on each tty, syslogd,
the libc name service cache daemon (nscd), the udev device manager, and
more.

This is the default value of the @code{services} field of
@code{operating-system} declarations.  Usually, when customizing a
system, you will want to append services to @code{%base-services}, like
this:

@lisp
(append (list (service avahi-service-type)
              (service openssh-service-type))
        %base-services)
@end lisp
@end defvar

@defvar special-files-service-type
This is the service that sets up ``special files'' such as
@file{/bin/sh}; an instance of it is part of @code{%base-services}.

The value associated with @code{special-files-service-type} services
must be a list of two-element lists where the first element is the ``special file''
and the second element is its target.  By default it is:

@cindex @file{/bin/sh}
@cindex @file{sh}, in @file{/bin}
@lisp
`(("/bin/sh" ,(file-append bash "/bin/sh"))
  ("/usr/bin/env" ,(file-append coreutils "/bin/env")))
@end lisp

@cindex @file{/usr/bin/env}
@cindex @file{env}, in @file{/usr/bin}
If you want to add, say, @code{/bin/bash} to your system, you can
change it to:

@lisp
`(("/bin/sh" ,(file-append bash "/bin/sh"))
  ("/usr/bin/env" ,(file-append coreutils "/bin/env"))
  ("/bin/bash" ,(file-append bash "/bin/bash")))
@end lisp

Since this is part of @code{%base-services}, you can use
@code{modify-services} to customize the set of special files
(@pxref{Service Reference, @code{modify-services}}).  But the simple way
to add a special file is @i{via} the @code{extra-special-file} procedure
(see below).
@end defvar

@deffn {Procedure} extra-special-file file target
Use @var{target} as the ``special file'' @var{file}.

For example, adding the following lines to the @code{services} field of
your operating system declaration leads to a @file{/usr/bin/env}
symlink:

@lisp
(extra-special-file "/usr/bin/env"
                    (file-append coreutils "/bin/env"))
@end lisp

This procedure is meant for @code{/bin/sh}, @code{/usr/bin/env} and
similar targets.  In particular, use for targets under @code{/etc} might
not work as expected if the target is managed by Guix in other ways.
@end deffn

@defvar host-name-service-type
Type of the service that sets the system host name, whose value
is a string. This service is included in @code{operating-system} by
default (@pxref{operating-system-essential-services,@code{essential-services}}).
@end defvar

@defvar console-font-service-type
Install the given fonts on the specified ttys (fonts are per
virtual console on the kernel Linux).  The value of this service is a list of
tty/font pairs.  The font can be the name of a font provided by the @code{kbd}
package or any valid argument to @command{setfont}, as in this example:

@lisp
`(("tty1" . "LatGrkCyr-8x16")
  ("tty2" . ,(file-append
                font-tamzen
                "/share/kbd/consolefonts/TamzenForPowerline10x20.psf"))
  ("tty3" . ,(file-append
                font-terminus
                "/share/consolefonts/ter-132n"))) ; for HDPI
@end lisp
@end defvar

@defvar hosts-service-type
Type of the service that populates the entries for (@file{/etc/hosts}).
This service type can be @emph{extended} by passing it a list of
@code{host} records.

The example below shows how to add two entries to @file{/etc/hosts}:

@c TRANSLATORS: The domain names below SHOULD NOT be translated.
@c They're domains reserved for use in documentation. (RFC6761 Section 6.5)
@c The addresses used are explained in RFC3849 and RFC5737.
@lisp
(simple-service 'add-extra-hosts
                hosts-service-type
                (list (host "192.0.2.1" "example.com"
                            '("example.net" "example.org"))
                      (host "2001:db8::1" "example.com"
                            '("example.net" "example.org"))))
@end lisp

@quotation Note
@cindex @file{/etc/hosts} default entries
By default @file{/etc/hosts} comes with the following entries:
@example
127.0.0.1 localhost @var{host-name}
::1       localhost @var{host-name}
@end example

For most setups this is what you want though if you find yourself in
the situation where you want to change the default entries, you can
do so in @code{operating-system} via @code{modify-services}
(@pxref{Service Reference,@code{modify-services}}).

The following example shows how to unset @var{host-name} from being an
alias of @code{localhost}.
@lisp
(operating-system
  ;; @dots{}

  (essential-services
   (modify-services
     (operating-system-default-essential-services this-operating-system)
     (hosts-service-type config => (list
                                     (host "127.0.0.1" "localhost")
                                     (host "::1"       "localhost"))))))
@end lisp
@end quotation
@end defvar


@deffn {Procedure} host @var{address} @var{canonical-name} [@var{aliases}]
Return a new record for the host at @var{address} with the given
@var{canonical-name} and possibly @var{aliases}.

@var{address} must be a string denoting a valid IPv4 or IPv6 address, and
@var{canonical-name} and the strings listed in @var{aliases} must be valid
host names.
@end deffn

@defvar login-service-type
Type of the service that provides a console login service, whose value
is a @code{<login-configuration>} object.
@end defvar

@deftp {Data Type} login-configuration
Data type representing the configuration of login, which specifies the
@acronym{MOTD, message of the day}, among other things.

@table @asis

@item @code{motd}
@cindex message of the day
A file-like object containing the ``message of the day''.

@item @code{allow-empty-passwords?} (default: @code{#t})
Allow empty passwords by default so that first-time users can log in when
the 'root' account has just been created.

@end table
@end deftp

@defvar mingetty-service-type
Type of the service that runs Mingetty, an implementation of the
virtual console log-in.  The value for this service is a
@code{<mingetty-configuration>} object.
@end defvar

@deftp {Data Type} mingetty-configuration
Data type representing the configuration of Mingetty, which specifies
the tty to run, among other things.

@table @asis
@item @code{tty}
The name of the console this Mingetty runs on---e.g., @code{"tty1"}.

@item @code{auto-login} (default: @code{#f})
When true, this field must be a string denoting the user name under
which the system automatically logs in.  When it is @code{#f}, a
user name and password must be entered to log in.

@item @code{login-program} (default: @code{#f})
This must be either @code{#f}, in which case the default log-in program
is used (@command{login} from the Shadow tool suite), or a gexp denoting
the name of the log-in program.

@item @code{login-pause?} (default: @code{#f})
When set to @code{#t} in conjunction with @var{auto-login}, the user
will have to press a key before the log-in shell is launched.

@item @code{clear-on-logout?} (default: @code{#t})
When set to @code{#t}, the screen will be cleared after logout.

@item @code{mingetty} (default: @var{mingetty})
The Mingetty package to use.

@end table
@end deftp

@defvar agetty-service-type
Type of the service that runs agetty, which implements virtual and
serial console log-in.  The value for this service is a
@code{<agetty-configuration>} object.
@end defvar

@deftp {Data Type} agetty-configuration
Data type representing the configuration of agetty, which specifies the
tty to run, among other things@footnote{See the @code{agetty(8)}
man page for more information.}.

@table @asis
@item @code{tty}
The name of the console this agetty runs on, as a string---e.g.,
@code{"ttyS0"}.  This argument is optional, it will default to
a reasonable default serial port used by the kernel Linux.

For this, if there is a value for an option @code{agetty.tty} in the kernel
command line, agetty will extract the device name of the serial port
from it and use that.

If not and if there is a value for an option @code{console} with a tty in
the Linux command line, agetty will extract the device name of the
serial port from it and use that.

In both cases, agetty will leave the other serial device settings
(baud rate etc.)@: alone---in the hope that Linux pinned them to the
correct values.

@item @code{baud-rate} (default: @code{#f})
A string containing a comma-separated list of one or more baud rates, in
descending order.

@item @code{term} (default: @code{#f})
A string containing the value used for the @env{TERM} environment
variable.

@item @code{eight-bits?} (default: @code{#f})
When @code{#t}, the tty is assumed to be 8-bit clean, and parity detection is
disabled.

@item @code{auto-login} (default: @code{#f})
When passed a login name, as a string, the specified user will be logged
in automatically without prompting for their login name or password.

@item @code{no-reset?} (default: @code{#f})
When @code{#t}, don't reset terminal cflags (control modes).

@item @code{host} (default: @code{#f})
This accepts a string containing the ``login_host'', which will be written
into the @file{/var/run/utmpx} file.

@item @code{remote?} (default: @code{#f})
When set to @code{#t} in conjunction with @var{host}, this will add an
@code{-r} fakehost option to the command line of the login program
specified in @var{login-program}.

@item @code{flow-control?} (default: @code{#f})
When set to @code{#t}, enable hardware (RTS/CTS) flow control.

@item @code{no-issue?} (default: @code{#f})
When set to @code{#t}, the contents of the @file{/etc/issue} file will
not be displayed before presenting the login prompt.

@item @code{init-string} (default: @code{#f})
This accepts a string that will be sent to the tty or modem before
sending anything else.  It can be used to initialize a modem.

@item @code{no-clear?} (default: @code{#f})
When set to @code{#t}, agetty will not clear the screen before showing
the login prompt.

@item @code{login-program} (default: (file-append shadow "/bin/login"))
This must be either a gexp denoting the name of a log-in program, or
unset, in which case the default value is the @command{login} from the
Shadow tool suite.

@item @code{local-line} (default: @code{#f})
Control the CLOCAL line flag.  This accepts one of three symbols as
arguments, @code{'auto}, @code{'always}, or @code{'never}.  If @code{#f},
the default value chosen by agetty is @code{'auto}.

@item @code{extract-baud?} (default: @code{#f})
When set to @code{#t}, instruct agetty to try to extract the baud rate
from the status messages produced by certain types of modems.

@item @code{skip-login?} (default: @code{#f})
When set to @code{#t}, do not prompt the user for a login name.  This
can be used with @var{login-program} field to use non-standard login
systems.

@item @code{no-newline?} (default: @code{#f})
When set to @code{#t}, do not print a newline before printing the
@file{/etc/issue} file.

@c Is this dangerous only when used with login-program, or always?
@item @code{login-options} (default: @code{#f})
This option accepts a string containing options that are passed to the
login program.  When used with the @var{login-program}, be aware that a
malicious user could try to enter a login name containing embedded
options that could be parsed by the login program.

@item @code{login-pause} (default: @code{#f})
When set to @code{#t}, wait for any key before showing the login prompt.
This can be used in conjunction with @var{auto-login} to save memory by
lazily spawning shells.

@item @code{chroot} (default: @code{#f})
Change root to the specified directory.  This option accepts a directory
path as a string.

@item @code{hangup?} (default: @code{#f})
Use the Linux system call @code{vhangup} to do a virtual hangup of the
specified terminal.

@item @code{keep-baud?} (default: @code{#f})
When set to @code{#t}, try to keep the existing baud rate.  The baud
rates from @var{baud-rate} are used when agetty receives a @key{BREAK}
character.

@item @code{timeout} (default: @code{#f})
When set to an integer value, terminate if no user name could be read
within @var{timeout} seconds.

@item @code{detect-case?} (default: @code{#f})
When set to @code{#t}, turn on support for detecting an uppercase-only
terminal.  This setting will detect a login name containing only
uppercase letters as indicating an uppercase-only terminal and turn on
some upper-to-lower case conversions.  Note that this will not support
Unicode characters.

@item @code{wait-cr?} (default: @code{#f})
When set to @code{#t}, wait for the user or modem to send a
carriage-return or linefeed character before displaying
@file{/etc/issue} or login prompt.  This is typically used with the
@var{init-string} option.

@item @code{no-hints?} (default: @code{#f})
When set to @code{#t}, do not print hints about Num, Caps, and Scroll
locks.

@item @code{no-hostname?} (default: @code{#f})
By default, the hostname is printed.  When this option is set to
@code{#t}, no hostname will be shown at all.

@item @code{long-hostname?} (default: @code{#f})
By default, the hostname is only printed until the first dot.  When this
option is set to @code{#t}, the fully qualified hostname by
@code{gethostname} or @code{getaddrinfo} is shown.

@item @code{erase-characters} (default: @code{#f})
This option accepts a string of additional characters that should be
interpreted as backspace when the user types their login name.

@item @code{kill-characters} (default: @code{#f})
This option accepts a string that should be interpreted to mean ``ignore
all previous characters'' (also called a ``kill'' character) when the user
types their login name.

@item @code{chdir} (default: @code{#f})
This option accepts, as a string, a directory path that will be changed
to before login.

@item @code{delay} (default: @code{#f})
This options accepts, as an integer, the number of seconds to sleep
before opening the tty and displaying the login prompt.

@item @code{nice} (default: @code{#f})
This option accepts, as an integer, the nice value with which to run the
@command{login} program.

@item @code{extra-options} (default: @code{'()})
This option provides an ``escape hatch'' for the user to provide arbitrary
command-line arguments to @command{agetty} as a list of strings.

@item @code{shepherd-requirement} (default: @code{'()})
The option can be used to provides extra shepherd requirements (for example
@code{'syslogd}) to the respective @code{'term-}* shepherd service.

@end table
@end deftp

@defvar kmscon-service-type
Type of the service that runs @uref{https://www.freedesktop.org/wiki/Software/kmscon,kmscon},
which implements virtual console log-in.  The value for this service is a
@code{<kmscon-configuration>} object.
@end defvar

@deftp {Data Type} kmscon-configuration
Data type representing the configuration of Kmscon, which specifies the
tty to run, among other things.

@table @asis
@item @code{virtual-terminal}
The name of the console this Kmscon runs on---e.g., @code{"tty1"}.

@item @code{login-program} (default: @code{#~(string-append #$shadow "/bin/login")})
A gexp denoting the name of the log-in program.  The default log-in program is
@command{login} from the Shadow tool suite.

@item @code{login-arguments} (default: @code{'("-p")})
A list of arguments to pass to @command{login}.

@item @code{auto-login} (default: @code{#f})
When passed a login name, as a string, the specified user will be logged
in automatically without prompting for their login name or password.

@item @code{hardware-acceleration?} (default: #f)
Whether to use hardware acceleration.

@item @code{font-engine} (default: @code{"pango"})
Font engine used in Kmscon.

@item @code{font-size} (default: @code{12})
Font size used in Kmscon.

@item @code{keyboard-layout} (default: @code{#f})
If this is @code{#f}, Kmscon uses the default keyboard layout---usually US
English (``qwerty'') for a 105-key PC keyboard.

Otherwise this must be a @code{keyboard-layout} object specifying the
keyboard layout.  @xref{Keyboard Layout}, for more information on how to
specify the keyboard layout.

@item @code{kmscon} (default: @var{kmscon})
The Kmscon package to use.

@end table
@end deftp

@cindex @abbr{nscd, name service cache daemon}
@defvar nscd-service-type
Type of the service that runs the libc @abbr{nscd, name service cache
daemon}, whose value is an @code{<nscd-configuration>} object.

For convenience, the Shepherd service for nscd provides the following actions:

@table @code
@item invalidate
@cindex nscd, cache invalidation
@cindex cache invalidation, nscd
This invalidate the given cache.  For instance, running:

@example
herd invalidate nscd hosts
@end example

@noindent
invalidates the host name lookup cache of nscd.

@item statistics
Running @command{herd statistics nscd} displays information about nscd usage
and caches.
@end table
@end defvar

@deftp {Data Type} nscd-configuration
Data type representing the @abbr{nscd, name service cache daemon}
configuration.

@table @asis

@item @code{name-services} (default: @code{'()})
List of packages denoting @dfn{name services} that must be visible to
the nscd---e.g., @code{(list @var{nss-mdns})}.

@item @code{glibc} (default: @var{glibc})
Package object denoting the GNU C Library providing the @command{nscd}
command.

@item @code{log-file} (default: @code{#f})
Name of the nscd log file.  Debugging output goes to that file when
@code{debug-level} is strictly positive, or to standard error if it is
@code{#f}.  Regular messages are written to syslog when
@code{debug-level} is zero, regardless of the value of @code{log-file}.

@item @code{debug-level} (default: @code{0})
Integer denoting the debugging levels.  Higher numbers mean that more
debugging output is logged.

@item @code{caches} (default: @code{%nscd-default-caches})
List of @code{<nscd-cache>} objects denoting things to be cached; see
below.

@end table
@end deftp

@deftp {Data Type} nscd-cache
Data type representing a cache database of nscd and its parameters.

@table @asis

@item @code{database}
This is a symbol representing the name of the database to be cached.
Valid values are @code{passwd}, @code{group}, @code{hosts}, and
@code{services}, which designate the corresponding NSS database
(@pxref{NSS Basics,,, libc, The GNU C Library Reference Manual}).

@item @code{positive-time-to-live}
@itemx @code{negative-time-to-live} (default: @code{20})
A number representing the number of seconds during which a positive or
negative lookup result remains in cache.

@item @code{check-files?} (default: @code{#t})
Whether to check for updates of the files corresponding to
@var{database}.

For instance, when @var{database} is @code{hosts}, setting this flag
instructs nscd to check for updates in @file{/etc/hosts} and to take
them into account.

@item @code{persistent?} (default: @code{#t})
Whether the cache should be stored persistently on disk.

@item @code{shared?} (default: @code{#t})
Whether the cache should be shared among users.

@item @code{max-database-size} (default: 32@tie{}MiB)
Maximum size in bytes of the database cache.

@c XXX: 'suggested-size' and 'auto-propagate?' seem to be expert
@c settings, so leave them out.

@end table
@end deftp

@defvar %nscd-default-caches
List of @code{<nscd-cache>} objects used by default by
@code{nscd-configuration} (see above).

It enables persistent and aggressive caching of service and host name
lookups.  The latter provides better host name lookup performance,
resilience in the face of unreliable name servers, and also better
privacy---often the result of host name lookups is in local cache, so
external name servers do not even need to be queried.
@end defvar

@cindex syslog
@cindex logging
@defvar syslog-service-type
Type of the service that runs the syslog daemon, whose value is a
@code{<syslog-configuration>} object.
@end defvar

To have a modified @code{syslog-configuration} come into effect after
reconfiguring your system, the @samp{reload} action should be preferred
to restarting the service, as many services such as the login manager
depend on it and would be restarted as well:

@example
# herd reload syslog
@end example

which will cause the running @command{syslogd} process to reload its
configuration.

@deftp {Data Type} syslog-configuration
Data type representing the configuration of the syslog daemon.

@table @asis
@item @code{syslogd} (default: @code{#~(string-append #$inetutils "/libexec/syslogd")})
The syslog daemon to use.

@item @code{config-file} (default: @code{%default-syslog.conf})
The syslog configuration file to use.
@xref{syslogd invocation,,, inetutils, GNU Inetutils}, for more
information on the configuration file syntax.

@end table
@end deftp

@defvar guix-service-type
This is the type of the service that runs the build daemon,
@command{guix-daemon} (@pxref{Invoking guix-daemon}).  Its value must be a
@code{guix-configuration} record as described below.
@end defvar

@anchor{guix-configuration-type}
@deftp {Data Type} guix-configuration
This data type represents the configuration of the Guix build daemon.
@xref{Invoking guix-daemon}, for more information.

@table @asis
@item @code{guix} (default: @var{guix})
The Guix package to use.  @xref{Customizing the System-Wide Guix} to
learn how to provide a package with a pre-configured set of channels.

@item @code{build-group} (default: @code{"guixbuild"})
Name of the group for build user accounts.

@item @code{build-accounts} (default: @code{10})
Number of build user accounts to create.

@item @code{authorize-key?} (default: @code{#t})
@cindex substitutes, authorization thereof
Whether to authorize the substitute keys listed in
@code{authorized-keys}---by default that of
@code{@value{SUBSTITUTE-SERVER-1}} and
@code{@value{SUBSTITUTE-SERVER-2}}
(@pxref{Substitutes}).

When @code{authorize-key?} is true, @file{/etc/guix/acl} cannot be
changed by invoking @command{guix archive --authorize}.  You must
instead adjust @code{guix-configuration} as you wish and reconfigure the
system.  This ensures that your operating system configuration file is
self-contained.

@quotation Note
When booting or reconfiguring to a system where @code{authorize-key?}
is true, the existing @file{/etc/guix/acl} file is backed up as
@file{/etc/guix/acl.bak} if it was determined to be a manually modified
file.  This is to facilitate migration from earlier versions, which
allowed for in-place modifications to @file{/etc/guix/acl}.
@end quotation

@vindex %default-authorized-guix-keys
@item @code{authorized-keys} (default: @code{%default-authorized-guix-keys})
The list of authorized key files for archive imports, as a list of
string-valued gexps (@pxref{Invoking guix archive}).  By default, it
contains that of @code{@value{SUBSTITUTE-SERVER-1}} and
@code{@value{SUBSTITUTE-SERVER-2}} (@pxref{Substitutes}).  See
@code{substitute-urls} below for an example on how to change it.

@item @code{use-substitutes?} (default: @code{#t})
Whether to use substitutes.

@item @code{substitute-urls} (default: @code{%default-substitute-urls})
The list of URLs where to look for substitutes by default.

Suppose you would like to fetch substitutes from @code{guix.example.org}
in addition to @code{@value{SUBSTITUTE-SERVER-1}}.  You will need to do
two things: (1) add @code{guix.example.org} to @code{substitute-urls},
and (2) authorize its signing key, having done appropriate checks
(@pxref{Substitute Server Authorization}).  The configuration below does
exactly that:

@lisp
(guix-configuration
  (substitute-urls
   (append (list "https://guix.example.org")
           %default-substitute-urls))
  (authorized-keys
   (append (list (local-file "./guix.example.org-key.pub"))
           %default-authorized-guix-keys)))
@end lisp

This example assumes that the file @file{./guix.example.org-key.pub}
contains the public key that @code{guix.example.org} uses to sign
substitutes.

@item @code{generate-substitute-key?} (default: @code{#t})
Whether to generate a @dfn{substitute key pair} under
@file{/etc/guix/signing-key.pub} and @file{/etc/guix/signing-key.sec} if
there is not already one.

This key pair is used when exporting store items, for instance with
@command{guix publish} (@pxref{Invoking guix publish}) or @command{guix
archive} (@pxref{Invoking guix archive}).  Generating a key pair takes a
few seconds when enough entropy is available and is only done once; you
might want to turn it off for instance in a virtual machine that does
not need it and where the extra boot time is a problem.

@anchor{guix-configuration-channels}
@item @code{channels} (default: @code{#f})
List of channels to be specified in @file{/etc/guix/channels.scm}, which
is what @command{guix pull} uses by default (@pxref{Invoking guix
pull}).

@quotation Note
When reconfiguring a system, the existing @file{/etc/guix/channels.scm}
file is backed up as @file{/etc/guix/channels.scm.bak} if it was
determined to be a manually modified file.  This is to facilitate
migration from earlier versions, which allowed for in-place
modifications to @file{/etc/guix/channels.scm}.
@end quotation

@item @code{max-silent-time} (default: @code{3600})
@itemx @code{timeout} (default: @code{(* 3600 24)})
The number of seconds of silence and the number of seconds of activity,
respectively, after which a build process times out.  A value of zero
disables the timeout.

@item @code{log-compression} (default: @code{'gzip})
The type of compression used for build logs---one of @code{gzip},
@code{bzip2}, or @code{none}.

@item @code{discover?} (default: @code{#f})
Whether to discover substitute servers on the local network using mDNS
and DNS-SD.

@anchor{guix-configuration-build-machines}
@item @code{build-machines} (default: @code{#f})
This field must be either @code{#f} or a list of gexps evaluating to a
@code{build-machine} record or to a list of @code{build-machine} records
(@pxref{Daemon Offload Setup}).

When it is @code{#f}, the @file{/etc/guix/machines.scm} file is left
untouched.  Otherwise, the list of of gexps is written to
@file{/etc/guix/machines.scm}; if a previously-existing file is found,
it is backed up as @file{/etc/guix/machines.scm.bak}.  This allows you
to declare build machines for offloading directly in the operating
system declaration, like so:

@lisp
(guix-configuration
  (build-machines
    (list #~(build-machine (name "foo.example.org") @dots{})
          #~(build-machine (name "bar.example.org") @dots{}))))
@end lisp

Additional build machines may be added @i{via} the @code{guix-extension}
mechanism (see below).

@item @code{extra-options} (default: @code{'()})
List of extra command-line options for @command{guix-daemon}.

@item @code{log-file} (default: @code{"/var/log/guix-daemon.log"})
File where @command{guix-daemon}'s standard output and standard error
are written.

@cindex HTTP proxy, for @code{guix-daemon}
@cindex proxy, for @code{guix-daemon} HTTP access
@item @code{http-proxy} (default: @code{#f})
The URL of the HTTP and HTTPS proxy used for downloading fixed-output
derivations and substitutes.

It is also possible to change the daemon's proxy at run time through the
@code{set-http-proxy} action, which restarts it:

@example
herd set-http-proxy guix-daemon http://localhost:8118
@end example

To clear the proxy settings, run:

@example
herd set-http-proxy guix-daemon
@end example

@item @code{tmpdir} (default: @code{#f})
A directory path where the @command{guix-daemon} will perform builds.

@item @code{environment} (default: @code{'()})
Environment variables to be set before starting the daemon, as a list of
@code{key=value} strings.

@end table
@end deftp

@deftp {Data Type} guix-extension
This data type represents the parameters of the Guix build daemon that
are extendable. This is the type of the object that must be used within
a guix service extension.
@xref{Service Composition}, for more information.

@table @asis
@item @code{authorized-keys} (default: @code{'()})
A list of file-like objects where each element contains a public key.

@item @code{substitute-urls} (default: @code{'()})
A list of strings where each element is a substitute URL.

@item @code{build-machines} (default: @code{'()})
A list of gexps that evaluate to @code{build-machine} records or to a list of
@code{build-machine} records.
(@pxref{Daemon Offload Setup}).

Using this field, a service may add new build machines to receive builds
offloaded by the daemon.  This is useful for a service such as
@code{hurd-vm-service-type}, which can make a GNU/Hurd virtual machine
directly usable for offloading (@pxref{hurd-vm,
@code{hurd-vm-service-type}}).

@item @code{chroot-directories} (default: @code{'()})
A list of file-like objects or strings pointing to additional directories the build daemon can use.
@end table
@end deftp

@defvar udev-service-type
Type of the service that runs udev, a service which populates the
@file{/dev} directory dynamically, whose value is a
@code{<udev-configuration>} object.

Since the file names for udev rules and hardware description files
matter, the configuration items for rules and hardware cannot simply be
plain file-like objects with the rules content, because the name would
be ignored.  Instead, they are directory file-like objects that contain
optional rules in @file{lib/udev/rules.d} and optional hardware files in
@file{lib/udev/hwdb.d}.  This way, the service can be configured with
whole packages from which to take rules and hwdb files.

The @code{udev-service-type} can be @emph{extended} with file-like
directories that respect this hierarchy.  For convenience, the
@code{udev-rule} and @code{file->udev-rule} can be used to construct
udev rules, while @code{udev-hardware} and @code{file->udev-hardware}
can be used to construct hardware description files.

In an @code{operating-system} declaration, this service type can be
@emph{extended} using procedures @code{udev-rules-service} and
@code{udev-hardware-service}.
@end defvar

@deftp {Data Type} udev-configuration
Data type representing the configuration of udev.

@table @asis
@item @code{udev} (default: @code{eudev}) (type: file-like)
Package object of the udev service.  This package is used at run-time,
when compiled for the target system.  In order to generate the
@file{hwdb.bin} hardware index, it is also used when generating the
system definition, compiled for the current system.

@item @code{rules} (default: @var{'()}) (type: list-of-file-like)
List of file-like objects denoting udev rule files under a sub-directory.

@item @code{hardware} (default: @var{'()}) (type: list-of-file-like)
List of file-like objects denoting udev hardware description files under
a sub-directory.

@end table
@end deftp

@deffn {Procedure} udev-rule @var{file-name} @var{contents}
Return a udev-rule file named @var{file-name} containing the rules
defined by the @var{contents} literal.

In the following example, a rule for a USB device is defined to be
stored in the file @file{90-usb-thing.rules}.  The rule runs a script
upon detecting a USB device with a given product identifier.

@lisp
(define %example-udev-rule
  (udev-rule
    "90-usb-thing.rules"
    (string-append "ACTION==\"add\", SUBSYSTEM==\"usb\", "
                   "ATTR@{product@}==\"Example\", "
                   "RUN+=\"/path/to/script\"")))
@end lisp
@end deffn

@deffn {Procedure} udev-hardware @var{file-name} @var{contents}
Return a udev hardware description file named @var{file-name} containing
the hardware information @var{contents}.
@end deffn

@deffn {Procedure} udev-rules-service @var{name} @var{rules} [#:groups '()]
Return a service that extends @code{udev-service-type} with @var{rules}
and @code{account-service-type} with @var{groups} as system groups.
This works by creating a singleton service type
@code{@var{name}-udev-rules}, of which the returned service is an
instance.

Here we show how it can be used to extend @code{udev-service-type}
with the previously defined rule @code{%example-udev-rule}.

@lisp
(operating-system
 ;; @dots{}
 (services
   (cons (udev-rules-service 'usb-thing %example-udev-rule)
         %desktop-services)))
@end lisp
@end deffn

@deffn {Procedure} udev-hardware-service @var{name} @var{hardware}
Return a service that extends @code{udev-service-type} with
@var{hardware}.  The service name is @code{@var{name}-udev-hardware}.
@end deffn

@deffn {Procedure} file->udev-rule @var{file-name} @var{file}
Return a udev-rule file named @var{file-name} containing the rules
defined within @var{file}, a file-like object.

The following example showcases how we can use an existing rule file.

@lisp
(use-modules (guix download)     ;for url-fetch
             (guix packages)     ;for origin
             @dots{})

(define %android-udev-rules
  (file->udev-rule
    "51-android-udev.rules"
    (let ((version "20170910"))
      (origin
       (method url-fetch)
       (uri (string-append "https://raw.githubusercontent.com/M0Rf30/"
                           "android-udev-rules/" version "/51-android.rules"))
       (sha256
        (base32 "0lmmagpyb6xsq6zcr2w1cyx9qmjqmajkvrdbhjx32gqf1d9is003"))))))
@end lisp
@end deffn

Since guix package definitions can be included in @var{rules} in order
to use all their rules under the @file{lib/udev/rules.d} sub-directory,
then in lieu of the previous @var{file->udev-rule} example, we could
have used the @var{android-udev-rules} package which exists in Guix in
the @code{(gnu packages android)} module.

@deffn {Procedure} file->udev-hardware @var{file-name} @var{file}
Return a udev hardware description file named @var{file-name} containing
the rules defined within @var{file}, a file-like object.
@end deffn

The following example shows how to use the @var{android-udev-rules}
package so that the Android tool @command{adb} can detect devices
without root privileges.  It also details how to create the
@code{adbusers} group, which is required for the proper functioning of
the rules defined within the @code{android-udev-rules} package.  To
create such a group, we must define it both as part of the
@code{supplementary-groups} of our @code{user-account} declaration, as
well as in the @var{groups} of the @code{udev-rules-service} procedure.

@lisp
(use-modules (gnu packages android)  ;for android-udev-rules
             (gnu system shadow)     ;for user-group
             @dots{})

(operating-system
  ;; @dots{}
  (users (cons (user-account
                ;; @dots{}
                (supplementary-groups
                 '("adbusers"   ;for adb
                   "wheel" "netdev" "audio" "video")))))
  ;; @dots{}
  (services
    (cons (udev-rules-service 'android android-udev-rules
                              #:groups '("adbusers"))
          %desktop-services)))
@end lisp

@defvar urandom-seed-service-type
Save some entropy in @code{%random-seed-file} to seed @file{/dev/urandom}
when rebooting.  It also tries to seed @file{/dev/urandom} from
@file{/dev/hwrng} while booting, if @file{/dev/hwrng} exists and is
readable.
@end defvar

@defvar %random-seed-file
This is the name of the file where some random bytes are saved by
@var{urandom-seed-service} to seed @file{/dev/urandom} when rebooting.
It defaults to @file{/var/lib/random-seed}.
@end defvar

@cindex mouse
@cindex gpm
@defvar gpm-service-type
This is the type of the service that runs GPM, the @dfn{general-purpose
mouse daemon}, which provides mouse support to the Linux console.  GPM
allows users to use the mouse in the console, notably to select, copy,
and paste text.

The value for services of this type must be a @code{gpm-configuration}
(see below).  This service is not part of @code{%base-services}.
@end defvar

@deftp {Data Type} gpm-configuration
Data type representing the configuration of GPM.

@table @asis
@item @code{options} (default: @code{%default-gpm-options})
Command-line options passed to @command{gpm}.  The default set of
options instruct @command{gpm} to listen to mouse events on
@file{/dev/input/mice}.  @xref{Command Line,,, gpm, gpm manual}, for
more information.

@item @code{gpm} (default: @code{gpm})
The GPM package to use.

@end table
@end deftp

@anchor{guix-publish-service-type}
@defvar guix-publish-service-type
This is the service type for @command{guix publish} (@pxref{Invoking
guix publish}).  Its value must be a @code{guix-publish-configuration}
object, as described below.

This assumes that @file{/etc/guix} already contains a signing key pair as
created by @command{guix archive --generate-key} (@pxref{Invoking guix
archive}).  If that is not the case, the service will fail to start.
@end defvar

@deftp {Data Type} guix-publish-configuration
Data type representing the configuration of the @code{guix publish}
service.

@table @asis
@item @code{guix} (default: @code{guix})
The Guix package to use.

@item @code{port} (default: @code{80})
The TCP port to listen for connections.

@item @code{host} (default: @code{"localhost"})
The host (and thus, network interface) to listen to.  Use
@code{"0.0.0.0"} to listen on all the network interfaces.

@item @code{advertise?} (default: @code{#f})
When true, advertise the service on the local network @i{via} the DNS-SD
protocol, using Avahi.

This allows neighboring Guix devices with discovery on (see
@code{guix-configuration} above) to discover this @command{guix publish}
instance and to automatically download substitutes from it.

@item @code{compression} (default: @code{'(("gzip" 3) ("zstd" 3))})
This is a list of compression method/level tuple used when compressing
substitutes.  For example, to compress all substitutes with @emph{both} lzip
at level 7 and gzip at level 9, write:

@lisp
'(("lzip" 7) ("gzip" 9))
@end lisp

Level 9 achieves the best compression ratio at the expense of increased CPU
usage, whereas level 1 achieves fast compression.  @xref{Invoking guix
publish}, for more information on the available compression methods and
the tradeoffs involved.

An empty list disables compression altogether.

@item @code{nar-path} (default: @code{"nar"})
The URL path at which ``nars'' can be fetched.  @xref{Invoking guix
publish, @option{--nar-path}}, for details.

@item @code{cache} (default: @code{#f})
When it is @code{#f}, disable caching and instead generate archives on
demand.  Otherwise, this should be the name of a directory---e.g.,
@code{"/var/cache/guix/publish"}---where @command{guix publish} caches
archives and meta-data ready to be sent.  @xref{Invoking guix publish,
@option{--cache}}, for more information on the tradeoffs involved.

@item @code{workers} (default: @code{#f})
When it is an integer, this is the number of worker threads used for
caching; when @code{#f}, the number of processors is used.
@xref{Invoking guix publish, @option{--workers}}, for more information.

@item @code{cache-bypass-threshold} (default: 10 MiB)
When @code{cache} is true, this is the maximum size in bytes of a store
item for which @command{guix publish} may bypass its cache in case of a
cache miss.  @xref{Invoking guix publish,
@option{--cache-bypass-threshold}}, for more information.

@item @code{ttl} (default: @code{#f})
When it is an integer, this denotes the @dfn{time-to-live} in seconds
of the published archives.  @xref{Invoking guix publish, @option{--ttl}},
for more information.

@item @code{negative-ttl} (default: @code{#f})
When it is an integer, this denotes the @dfn{time-to-live} in
seconds for the negative lookups.  @xref{Invoking guix publish,
@option{--negative-ttl}}, for more information.
@end table
@end deftp

@defvar rngd-service-type
Type of the service that runs rng-tools rngd, whose value is an
@code{<rngd-configuration>} object.
@end defvar

@deftp {Data Type} rngd-configuration
Data type representing the configuration of rngd.

@table @asis
@item @code{rng-tools} (default: @code{rng-tools}) (type: file-like)
Package object of the rng-tools rngd.

@item @code{device} (default: @var{"/dev/hwrng"}) (type: string)
Path of the device to add to the kernel's entropy pool.  The service
will fail if @var{device} does not exist.

@end table
@end deftp

@cindex session limits
@cindex ulimit
@cindex priority
@cindex realtime
@cindex jackd
@cindex nofile
@cindex open file descriptors
@anchor{pam-limits-service-type}
@defvar pam-limits-service-type
Type of the service that installs a configuration file for the
@uref{http://linux-pam.org/Linux-PAM-html/sag-pam_limits.html,
@code{pam_limits} module}.  The value for this service type is
a list of @code{pam-limits-entry} values, which can be used to specify
@code{ulimit} limits and @code{nice} priority limits to user sessions.
By default, the value is the empty list.

The following limits definition sets two hard and soft limits for all
login sessions of users in the @code{realtime} group:

@lisp
(service pam-limits-service-type
         (list
          (pam-limits-entry "@@realtime" 'both 'rtprio 99)
          (pam-limits-entry "@@realtime" 'both 'memlock 'unlimited)))
@end lisp

The first entry increases the maximum realtime priority for
non-privileged processes; the second entry lifts any restriction of the
maximum address space that can be locked in memory.  These settings are
commonly used for real-time audio systems.

Another useful example is raising the maximum number of open file
descriptors that can be used:

@lisp
(service pam-limits-service-type
         (list
          (pam-limits-entry "*" 'both 'nofile 100000)))
@end lisp

In the above example, the asterisk means the limit should apply to any
user.  It is important to ensure the chosen value doesn't exceed the
maximum system value visible in the @file{/proc/sys/fs/file-max} file,
else the users would be prevented from login in.  For more information
about the Pluggable Authentication Module (PAM) limits, refer to the
@samp{pam_limits} man page from the @code{linux-pam} package.
@end defvar

@defvar greetd-service-type
@uref{https://git.sr.ht/~kennylevinsen/greetd, @code{greetd}} is a minimal and
flexible login manager daemon, that makes no assumptions about what you
want to launch.

If you can run it from your shell in a TTY, greetd can start it. If it
can be taught to speak a simple JSON-based IPC protocol, then it can be
a geeter.

@code{greetd-service-type} provides necessary infrastructure for logging
in users, including:

@itemize @bullet
@item
@code{greetd} PAM service

@item
Special variation of @code{pam-mount} to mount @code{XDG_RUNTIME_DIR}
@end itemize

Here is an example of switching from @code{mingetty-service-type} to
@code{greetd-service-type}, and how different terminals could be:

@lisp
  (append
   (modify-services %base-services
     ;; greetd-service-type provides "greetd" PAM service
     (delete login-service-type)
     ;; and can be used in place of mingetty-service-type
     (delete mingetty-service-type))
   (list
    (service greetd-service-type
             (greetd-configuration
              (terminals
               (list
                ;; we can make any terminal active by default
                (greetd-terminal-configuration (terminal-vt "1") (terminal-switch #t))
                ;; we can make environment without XDG_RUNTIME_DIR set
                ;; even provide our own environment variables
                (greetd-terminal-configuration
                 (terminal-vt "2")
                 (default-session-command
                   (greetd-agreety-session
                    (extra-env '(("MY_VAR" . "1")))
                    (xdg-env? #f))))
                ;; we can use different shell instead of default bash
                (greetd-terminal-configuration
                 (terminal-vt "3")
                 (default-session-command
                   (greetd-agreety-session (command (file-append zsh "/bin/zsh")))))
                ;; we can use any other executable command as greeter
                (greetd-terminal-configuration
                 (terminal-vt "4")
                 (default-session-command (program-file "my-noop-greeter" #~(exit))))
                (greetd-terminal-configuration (terminal-vt "5"))
                (greetd-terminal-configuration (terminal-vt "6"))))))
    ;; mingetty-service-type can be used in parallel
    ;; if needed to do so, do not (delete login-service-type)
    ;; as illustrated above
    #| (service mingetty-service-type (mingetty-configuration (tty "tty8"))) |#))
@end lisp
@end defvar

@deftp {Data Type} greetd-configuration
Configuration record for the @code{greetd-service-type}.
@table @asis

@item @code{motd}
A file-like object containing the ``message of the day''.

@item @code{allow-empty-passwords?} (default: @code{#t})
Allow empty passwords by default so that first-time users can log in when
the 'root' account has just been created.

@item @code{terminals} (default: @code{'()})
List of @code{greetd-terminal-configuration} per terminal for which
@code{greetd} should be started.

@item @code{greeter-supplementary-groups} (default: @code{'()})
List of groups which should be added to @code{greeter} user. For instance:
@lisp
(greeter-supplementary-groups '("seat" "video"))
@end lisp
Note that this example will fail if @code{seat} group does not exist.
@end table
@end deftp

@deftp {Data Type} greetd-terminal-configuration
Configuration record for per terminal greetd daemon service.

@table @asis
@item @code{greetd} (default: @code{greetd})
The greetd package to use.

@item @code{config-file-name}
Configuration file name to use for greetd daemon. Generally, autogenerated
derivation based on @code{terminal-vt} value.

@item @code{log-file-name}
Log file name to use for greetd daemon. Generally, autogenerated
name based on @code{terminal-vt} value.

@item @code{terminal-vt} (default: @samp{"7"})
The VT to run on. Use of a specific VT with appropriate conflict avoidance
is recommended.

@item @code{terminal-switch} (default: @code{#f})
Make this terminal active on start of @code{greetd}.

@item @code{source-profile?} (default: @code{#t})
Whether to source @file{/etc/profile} and @file{~/.profile}, when they
exist.

@item @code{default-session-user} (default: @samp{"greeter"})
The user to use for running the greeter.

@item @code{default-session-command} (default: @code{(greetd-agreety-session)})
Can be either instance of @code{greetd-agreety-session} configuration or
@code{gexp->script} like object to use as greeter.

@end table
@end deftp

@deftp {Data Type} greetd-agreety-session
Configuration record for the agreety greetd greeter.

@table @asis
@item @code{agreety} (default: @code{greetd})
The package with @command{/bin/agreety} command.

@item @code{command} (default: @code{(file-append bash "/bin/bash")})
Command to be started by @command{/bin/agreety} on successful login.

@item @code{command-args} (default: @code{'("-l")})
Command arguments to pass to command.

@item @code{extra-env} (default: @code{'()})
Extra environment variables to set on login.

@item @code{xdg-env?} (default: @code{#t})
If true @code{XDG_RUNTIME_DIR} and @code{XDG_SESSION_TYPE} will be set
before starting command. One should note that, @code{extra-env} variables
are set right after mentioned variables, so that they can be overridden.

@end table
@end deftp

@deftp {Data Type} greetd-wlgreet-session
Generic configuration record for the wlgreet greetd greeter.

@table @asis
@item @code{wlgreet} (default: @code{wlgreet})
The package with the @command{/bin/wlgreet} command.

@item @code{command} (default: @code{(file-append sway "/bin/sway")})
Command to be started by @command{/bin/wlgreet} on successful login.

@item @code{command-args} (default: @code{'()})
Command arguments to pass to command.

@item @code{output-mode} (default: @code{"all"})
Option to use for @code{outputMode} in the TOML configuration file.

@item @code{scale} (default: @code{1})
Option to use for @code{scale} in the TOML configuration file.

@item @code{background} (default: @code{'(0 0 0 0.9)})
RGBA list to use as the background colour of the login prompt.

@item @code{headline} (default: @code{'(1 1 1 1)})
RGBA list to use as the headline colour of the UI popup.

@item @code{prompt} (default: @code{'(1 1 1 1)})
RGBA list to use as the prompt colour of the UI popup.

@item @code{prompt-error} (default: @code{'(1 1 1 1)})
RGBA list to use as the error colour of the UI popup.

@item @code{border} (default: @code{'(1 1 1 1)})
RGBA list to use as the border colour of the UI popup.

@item @code{extra-env} (default: @code{'()})
Extra environment variables to set on login.

@end table
@end deftp

@deftp {Data Type} greetd-wlgreet-sway-session
Sway-specific configuration record for the wlgreet greetd greeter.

@table @asis
@item @code{wlgreet-session} (default: @code{(greetd-wlgreet-session)})
A @code{greetd-wlgreet-session} record for generic wlgreet configuration,
on top of the Sway-specific @code{greetd-wlgreet-sway-session}.

@item @code{sway} (default: @code{sway})
The package providing the @command{/bin/sway} command.

@item @code{sway-configuration} (default: #f)
File-like object providing an additional Sway configuration file to be
prepended to the mandatory part of the configuration.

@end table

Here is an example of a greetd configuration that uses wlgreet and Sway:

@lisp
  (greetd-configuration
   ;; We need to give the greeter user these permissions, otherwise
   ;; Sway will crash on launch.
   (greeter-supplementary-groups (list "video" "input" "seat"))
   (terminals
    (list (greetd-terminal-configuration
           (terminal-vt "1")
           (terminal-switch #t)
           (default-session-command
            (greetd-wlgreet-sway-session
             (sway-configuration
              (local-file "sway-greetd.conf"))))))))
@end lisp
@end deftp

@node Scheduled Job Execution
@subsection Scheduled Job Execution

@cindex cron
@cindex mcron
@cindex scheduling jobs
The @code{(gnu services mcron)} module provides an interface to
GNU@tie{}mcron, a daemon to run jobs at scheduled times (@pxref{Top,,,
mcron, GNU@tie{}mcron}).  GNU@tie{}mcron is similar to the traditional
Unix @command{cron} daemon; the main difference is that it is
implemented in Guile Scheme, which provides a lot of flexibility when
specifying the scheduling of jobs and their actions.

The example below defines an operating system that runs the
@command{updatedb} (@pxref{Invoking updatedb,,, find, Finding Files})
and the @command{guix gc} commands (@pxref{Invoking guix gc}) daily, as
well as the @command{mkid} command on behalf of an unprivileged user
(@pxref{mkid invocation,,, idutils, ID Database Utilities}).  It uses
gexps to introduce job definitions that are passed to mcron
(@pxref{G-Expressions}).

@lisp
(use-modules (guix) (gnu) (gnu services mcron))
(use-package-modules base idutils)

(define updatedb-job
  ;; Run 'updatedb' at 3AM every day.  Here we write the
  ;; job's action as a Scheme procedure.
  #~(job '(next-hour '(3))
         (lambda ()
           (system* (string-append #$findutils "/bin/updatedb")
                    "--prunepaths=/tmp /var/tmp /gnu/store"))
         "updatedb"))

(define garbage-collector-job
  ;; Collect garbage 5 minutes after midnight every day.
  ;; The job's action is a shell command.
  #~(job "5 0 * * *"            ;Vixie cron syntax
         "guix gc -F 1G"))

(define idutils-job
  ;; Update the index database as user "charlie" at 12:15PM
  ;; and 19:15PM.  This runs from the user's home directory.
  #~(job '(next-minute-from (next-hour '(12 19)) '(15))
         (string-append #$idutils "/bin/mkid src")
         #:user "charlie"))

(operating-system
  ;; @dots{}

  ;; %BASE-SERVICES already includes an instance of
  ;; 'mcron-service-type', which we extend with additional
  ;; jobs using 'simple-service'.
  (services (cons (simple-service 'my-cron-jobs
                                   mcron-service-type
                                   (list garbage-collector-job
                                         updatedb-job
                                         idutils-job))
                  %base-services)))
@end lisp

@quotation Tip
When providing the action of a job specification as a procedure, you
should provide an explicit name for the job via the optional 3rd
argument as done in the @code{updatedb-job} example above.  Otherwise,
the job would appear as ``Lambda function'' in the output of
@command{herd schedule mcron}, which is not nearly descriptive enough!
@end quotation

@quotation Tip
Avoid calling the Guile procedures @code{execl}, @code{execle} or
@code{execlp} inside a job specification, else mcron won't be able to
output the completion status of the job.
@end quotation

For more complex jobs defined in Scheme where you need control over the top
level, for instance to introduce a @code{use-modules} form, you can move your
code to a separate program using the @code{program-file} procedure of the
@code{(guix gexp)} module (@pxref{G-Expressions}).  The example below
illustrates that.

@lisp
(define %battery-alert-job
  ;; Beep when the battery percentage falls below %MIN-LEVEL.
  #~(job
     '(next-minute (range 0 60 1))
     #$(program-file
        "battery-alert.scm"
        (with-imported-modules (source-module-closure
                                '((guix build utils)))
          #~(begin
              (use-modules (guix build utils)
                           (ice-9 popen)
                           (ice-9 regex)
                           (ice-9 textual-ports)
                           (srfi srfi-2))

              (define %min-level 20)

              (setenv "LC_ALL" "C")     ;ensure English output
              (and-let* ((input-pipe (open-pipe*
                                      OPEN_READ
                                      #$(file-append acpi "/bin/acpi")))
                         (output (get-string-all input-pipe))
                         (m (string-match "Discharging, ([0-9]+)%" output))
                         (level (string->number (match:substring m 1)))
                         ((< level %min-level)))
                (format #t "warning: Battery level is low (~a%)~%" level)
                (invoke #$(file-append beep "/bin/beep") "-r5")))))))
@end lisp

@xref{Guile Syntax, mcron job specifications,, mcron, GNU@tie{}mcron},
for more information on mcron job specifications.  Below is the
reference of the mcron service.

On a running system, you can use the @code{schedule} action of the service to
visualize the mcron jobs that will be executed next:

@example
# herd schedule mcron
@end example

@noindent
The example above lists the next five tasks that will be executed, but you can
also specify the number of tasks to display:

@example
# herd schedule mcron 10
@end example

@defvar mcron-service-type
This is the type of the @code{mcron} service, whose value is an
@code{mcron-configuration} object.

This service type can be the target of a service extension that provides
additional job specifications (@pxref{Service Composition}).  In other
words, it is possible to define services that provide additional mcron
jobs to run.
@end defvar

@c Generated via (generate-documentation) at the bottom of (gnu services
@c mcron).
@c %start of fragment
@deftp {Data Type} mcron-configuration
Available @code{mcron-configuration} fields are:

@table @asis
@item @code{mcron} (default: @code{mcron}) (type: file-like)
The mcron package to use.

@item @code{jobs} (default: @code{'()}) (type: list-of-gexps)
This is a list of gexps (@pxref{G-Expressions}), where each gexp
corresponds to an mcron job specification (@pxref{Syntax, mcron job
specifications,, mcron,GNU@tie{}mcron}).

@item @code{log?} (default: @code{#t}) (type: boolean)
Log messages to standard output.

@item @code{log-file} (default: @code{"/var/log/mcron.log"}) (type: string)
Log file location.

@item @code{log-format} (default: @code{"~1@@*~a ~a: ~a~%"}) (type: string)
@code{(ice-9 format)} format string for log messages.  The default value
produces messages like @samp{@var{pid} @var{name}: @var{message}}
(@pxref{Invoking mcron, Invoking,, mcron,GNU@tie{}mcron}).  Each message
is also prefixed by a timestamp by GNU Shepherd.

@item @code{date-format} (type: maybe-string)
@code{(srfi srfi-19)} format string for date.

@end table
@end deftp
@c %end of fragment

@node Log Rotation
@subsection Log Rotation

@cindex rottlog
@cindex log rotation
@cindex logging
Log files such as those found in @file{/var/log} tend to grow endlessly,
so it's a good idea to @dfn{rotate} them once in a while---i.e., archive
their contents in separate files, possibly compressed.  The @code{(gnu
services admin)} module provides an interface to GNU@tie{}Rot[t]log, a
log rotation tool (@pxref{Top,,, rottlog, GNU Rot[t]log Manual}).

This service is part of @code{%base-services}, and thus enabled by
default, with the default settings, for commonly encountered log files.
The example below shows how to extend it with an additional
@dfn{rotation}, should you need to do that (usually, services that
produce log files already take care of that):

@lisp
(use-modules (guix) (gnu))
(use-service-modules admin)

(define my-log-files
  ;; Log files that I want to rotate.
  '("/var/log/something.log" "/var/log/another.log"))

(operating-system
  ;; @dots{}
  (services (cons (simple-service 'rotate-my-stuff
                                  rottlog-service-type
                                  (list (log-rotation
                                         (frequency 'daily)
                                         (files my-log-files))))
                  %base-services)))
@end lisp

@defvar rottlog-service-type
This is the type of the Rottlog service, whose value is a
@code{rottlog-configuration} object.

Other services can extend this one with new @code{log-rotation} objects
(see below), thereby augmenting the set of files to be rotated.

This service type can define mcron jobs (@pxref{Scheduled Job
Execution}) to run the rottlog service.
@end defvar

@deftp {Data Type} rottlog-configuration
Data type representing the configuration of rottlog.

@table @asis
@item @code{rottlog} (default: @code{rottlog})
The Rottlog package to use.

@item @code{rc-file} (default: @code{(file-append rottlog "/etc/rc")})
The Rottlog configuration file to use (@pxref{Mandatory RC Variables,,,
rottlog, GNU Rot[t]log Manual}).

@item @code{rotations} (default: @code{%default-rotations})
A list of @code{log-rotation} objects as defined below.

@item @code{jobs}
This is a list of gexps where each gexp corresponds to an mcron job
specification (@pxref{Scheduled Job Execution}).
@end table
@end deftp

@deftp {Data Type} log-rotation
Data type representing the rotation of a group of log files.

Taking an example from the Rottlog manual (@pxref{Period Related File
Examples,,, rottlog, GNU Rot[t]log Manual}), a log rotation might be
defined like this:

@lisp
(log-rotation
  (frequency 'daily)
  (files '("/var/log/apache/*"))
  (options '("storedir apache-archives"
             "rotate 6"
             "notifempty"
             "nocompress")))
@end lisp

The list of fields is as follows:

@table @asis
@item @code{frequency} (default: @code{'weekly})
The log rotation frequency, a symbol.

@item @code{files}
The list of files or file glob patterns to rotate.

@vindex %default-log-rotation-options
@item @code{options} (default: @code{%default-log-rotation-options})
The list of rottlog options for this rotation (@pxref{Configuration
parameters,,, rottlog, GNU Rot[t]log Manual}).

@item @code{post-rotate} (default: @code{#f})
Either @code{#f} or a gexp to execute once the rotation has completed.
@end table
@end deftp

@defvar %default-rotations
Specifies weekly rotation of @code{%rotated-files} and of
@file{/var/log/guix-daemon.log}.
@end defvar

@defvar %rotated-files
The list of syslog-controlled files to be rotated.  By default it is:
@code{'("/var/log/messages" "/var/log/secure" "/var/log/debug" \
"/var/log/maillog")}.
@end defvar

Some log files just need to be deleted periodically once they are old,
without any other criterion and without any archival step.  This is the
case of build logs stored by @command{guix-daemon} under
@file{/var/log/guix/drvs} (@pxref{Invoking guix-daemon}).  The
@code{log-cleanup} service addresses this use case.  For example,
@code{%base-services} (@pxref{Base Services}) includes the following:

@lisp
;; Periodically delete old build logs.
(service log-cleanup-service-type
         (log-cleanup-configuration
          (directory "/var/log/guix/drvs")))
@end lisp

That ensures build logs do not accumulate endlessly.

@defvar log-cleanup-service-type
This is the type of the service to delete old logs.  Its value must be a
@code{log-cleanup-configuration} record as described below.
@end defvar

@deftp {Data Type} log-cleanup-configuration
Data type representing the log cleanup configuration

@table @asis
@item @code{directory}
Name of the directory containing log files.

@item @code{expiry} (default: @code{(* 6 30 24 3600)})
Age in seconds after which a file is subject to deletion (six months by
default).

@item @code{schedule} (default: @code{"30 12 01,08,15,22 * *"})
String or gexp denoting the corresponding mcron job schedule
(@pxref{Scheduled Job Execution}).
@end table
@end deftp

@cindex logging, anonymization
@subheading Anonip Service

Anonip is a privacy filter that removes IP address from web server logs.
This service creates a FIFO and filters any written lines with anonip
before writing the filtered log to a target file.

The following example sets up the FIFO
@file{/var/run/anonip/https.access.log} and writes the filtered log file
@file{/var/log/anonip/https.access.log}.

@lisp
(service anonip-service-type
         (anonip-configuration
           (input  "/var/run/anonip/https.access.log")
           (output "/var/log/anonip/https.access.log")))
@end lisp

Configure your web server to write its logs to the FIFO at
@file{/var/run/anonip/https.access.log} and collect the anonymized log
file at @file{/var/web-logs/https.access.log}.

@deftp {Data Type} anonip-configuration
This data type represents the configuration of anonip.
It has the following parameters:

@table @asis
@item @code{anonip} (default: @code{anonip})
The anonip package to use.

@item @code{input}
The file name of the input log file to process.  The service creates a
FIFO of this name.  The web server should write its logs to this FIFO.

@item @code{output}
The file name of the processed log file.
@end table

The following optional settings may be provided:

@table @asis
@item @code{skip-private?}
When @code{#true} do not mask addresses in private ranges.

@item @code{column}
A 1-based indexed column number.  Assume IP address is in the specified
column (default is 1).

@item @code{replacement}
Replacement string in case address parsing fails, e.g. @code{"0.0.0.0"}.

@item @code{ipv4mask}
Number of bits to mask in IPv4 addresses.

@item @code{ipv6mask}
Number of bits to mask in IPv6 addresses.

@item @code{increment}
Increment the IP address by the given number.  By default this is zero.

@item @code{delimiter}
Log delimiter string.

@item @code{regex}
Regular expression for detecting IP addresses.  Use this instead of @code{column}.
@end table
@end deftp


@node Networking Setup
@subsection Networking Setup

The @code{(gnu services networking)} module provides services to
configure network interfaces and set up networking on your machine.
Those services provide different ways for you to set up your machine: by
declaring a static network configuration, by running a Dynamic Host
Configuration Protocol (DHCP) client, or by running daemons such as
NetworkManager and Connman that automate the whole process,
automatically adapt to connectivity changes, and provide a high-level
user interface.

On a laptop, NetworkManager and Connman are by far the most convenient
options, which is why the default desktop services include
NetworkManager (@pxref{Desktop Services, @code{%desktop-services}}).
For a server, or for a virtual machine or a container, static network
configuration or a simple DHCP client are often more appropriate.

This section describes the various network setup services available,
starting with static network configuration.

@defvar static-networking-service-type
This is the type for statically-configured network interfaces.  Its
value must be a list of @code{static-networking} records.  Each of them
declares a set of @dfn{addresses}, @dfn{routes}, and @dfn{links}, as
shown below.

@cindex network interface controller (NIC)
@cindex NIC, networking interface controller
Here is the simplest configuration, with only one network interface
controller (NIC) and only IPv4 connectivity:

@lisp
;; Static networking for one NIC, IPv4-only.
(service static-networking-service-type
         (list (static-networking
                (addresses
                 (list (network-address
                        (device "eno1")
                        (value "10.0.2.15/24"))))
                (routes
                 (list (network-route
                        (destination "default")
                        (gateway "10.0.2.2"))))
                (name-servers '("10.0.2.3")))))
@end lisp

The snippet above can be added to the @code{services} field of your
operating system configuration (@pxref{Using the Configuration System}).
It will configure your machine to have 10.0.2.15 as its IP address, with
a 24-bit netmask for the local network---meaning that any 10.0.2.@var{x}
address is on the local area network (LAN).  Traffic to addresses
outside the local network is routed @i{via} 10.0.2.2.  Host names are
resolved by sending domain name system (DNS) queries to 10.0.2.3.
@end defvar

@deftp {Data Type} static-networking
This is the data type representing a static network configuration.

As an example, here is how you would declare the configuration of a
machine with a single network interface controller (NIC) available as
@code{eno1}, and with one IPv4 and one IPv6 address:

@lisp
;; Network configuration for one NIC, IPv4 + IPv6.
(static-networking
 (addresses (list (network-address
                   (device "eno1")
                   (value "10.0.2.15/24"))
                  (network-address
                   (device "eno1")
                   (value "2001:123:4567:101::1/64"))))
 (routes (list (network-route
                (destination "default")
                (gateway "10.0.2.2"))
               (network-route
                (destination "default")
                (gateway "2020:321:4567:42::1"))))
 (name-servers '("10.0.2.3")))
@end lisp

If you are familiar with the @command{ip} command of the
@uref{https://wiki.linuxfoundation.org/networking/iproute2,
@code{iproute2} package} found on Linux-based systems, the declaration
above is equivalent to typing:

@example
ip address add 10.0.2.15/24 dev eno1
ip address add 2001:123:4567:101::1/64 dev eno1
ip route add default via inet 10.0.2.2
ip route add default via inet6 2020:321:4567:42::1
@end example

Run @command{man 8 ip} for more info.  Venerable GNU/Linux users will
certainly know how to do it with @command{ifconfig} and @command{route},
but we'll spare you that.

The available fields of this data type are as follows:

@table @asis
@item @code{addresses}
@itemx @code{links} (default: @code{'()})
@itemx @code{routes} (default: @code{'()})
The list of @code{network-address}, @code{network-link}, and
@code{network-route} records for this network (see below).

@item @code{name-servers} (default: @code{'()})
The list of IP addresses (strings) of domain name servers.  These IP
addresses go to @file{/etc/resolv.conf}.

@item @code{provision} (default: @code{'(networking)})
If true, this should be a list of symbols for the Shepherd service
corresponding to this network configuration.

@item @code{requirement} (default @code{'()})
The list of Shepherd services depended on.
@end table
@end deftp

@deftp {Data Type} network-address
This is the data type representing the IP address of a network
interface.

@table @code
@item device
The name of the network interface for this address---e.g.,
@code{"eno1"}.

@item value
The actual IP address and network mask, in
@uref{https://en.wikipedia.org/wiki/CIDR#CIDR_notation, @acronym{CIDR,
Classless Inter-Domain Routing} notation}, as a string.

For example, @code{"10.0.2.15/24"} denotes IPv4 address 10.0.2.15 on a
24-bit sub-network---all 10.0.2.@var{x} addresses are on the same local
network.

@item ipv6?
Whether @code{value} denotes an IPv6 address.  By default this is
automatically determined.
@end table
@end deftp

@deftp {Data Type} network-route
This is the data type representing a network route.

@table @asis
@item @code{destination}
The route destination (a string), either an IP address and network mask
or @code{"default"} to denote the default route.

@item @code{source} (default: @code{#f})
The route source.

@item @code{device} (default: @code{#f})
The device used for this route---e.g., @code{"eno2"}.

@item @code{ipv6?} (default: auto)
Whether this is an IPv6 route.  By default this is automatically
determined based on @code{destination} or @code{gateway}.

@item @code{gateway} (default: @code{#f})
IP address (a string) through which traffic is routed.
@end table
@end deftp

@deftp {Data Type} network-link
Data type for a network link (@pxref{Link,,, guile-netlink,
Guile-Netlink Manual}).  During startup, network links are employed to
construct or modify existing or virtual ethernet links.  These ethernet
links can be identified by their @var{name} or @var{mac-address}.  If
there is a need to create virtual interface, @var{name} and @var{type}
fields are required.

@table @code
@item name
The name of the link---e.g., @code{"v0p0"} (default: @code{#f}).

@item type
A symbol denoting the type of the link---e.g., @code{'veth} (default: @code{#f}).

@item mac-address
The mac-address of the link---e.g., @code{"98:11:22:33:44:55"} (default: @code{#f}).

@item arguments
List of arguments for this type of link.
@end table
@end deftp

Consider a scenario where a server equipped with a network interface
which has multiple ports.  These ports are connected to a switch, which
supports @uref{https://en.wikipedia.org/wiki/Link_aggregation, link
aggregation} (also known as bonding or NIC teaming).  The switch uses
port channels to consolidate multiple physical interfaces into one
logical interface to provide higher bandwidth, load balancing, and link
redundancy.  When a port is added to a LAG (or link aggregation group),
it inherits the properties of the port-channel.  Some of these
properties are VLAN membership, trunk status, and so on.

@uref{https://en.wikipedia.org/wiki/Virtual_LAN, VLAN} (or virtual local
area network) is a logical network that is isolated from other VLANs on
the same physical network.  This can be used to segregate traffic,
improve security, and simplify network management.

With all that in mind let's configure our static network for the server.
We will bond two existing interfaces together using 802.3ad schema and on
top of it, build a VLAN interface with id 1055.  We assign a static ip
to our new VLAN interface.

@lisp
(static-networking
 (links (list (network-link
               (name "bond0")
               (type 'bond)
               (arguments '((mode . "802.3ad")
                            (miimon . 100)
                            (lacp-active . "on")
                            (lacp-rate . "fast"))))

              (network-link
               (mac-address "98:11:22:33:44:55")
               (arguments '((master . "bond0"))))

              (network-link
               (mac-address "98:11:22:33:44:56")
               (arguments '((master . "bond0"))))

              (network-link
               (name "bond0.1055")
               (type 'vlan)
               (arguments '((id . 1055)
                            (link . "bond0"))))))
 (addresses (list (network-address
                   (value "192.168.1.4/24")
                   (device "bond0.1055")))))
@end lisp

@cindex loopback device
@defvar %loopback-static-networking
This is the @code{static-networking} record representing the ``loopback
device'', @code{lo}, for IP addresses 127.0.0.1 and ::1, and providing
the @code{loopback} Shepherd service.
@end defvar

@cindex networking, with QEMU
@cindex QEMU, networking
@defvar %qemu-static-networking
This is the @code{static-networking} record representing network setup
when using QEMU's user-mode network stack on @code{eth0} (@pxref{Using
the user mode network stack,,, qemu, QEMU Documentation}).
@end defvar

@cindex DHCP, networking service
@defvar dhcp-client-service-type
This is the type of services that run @var{dhclient}, the ISC Dynamic
Host Configuration Protocol (DHCP) client.
@end defvar

@deftp {Data Type} dhcp-client-configuration
Data type representing the configuration of the ISC DHCP client service.

@table @asis
@item @code{package} (default: @code{isc-dhcp})
The ISC DHCP client package to use.

@item @code{interfaces} (default: @code{'all})
Either @code{'all} or the list of interface names that the ISC DHCP
client should listen on---e.g., @code{'("eno1")}.

When set to @code{'all}, the ISC DHCP client listens on all the
available non-loopback interfaces that can be activated.  Otherwise the
ISC DHCP client listens only on the specified interfaces.

@item @code{config-file} (default: @code{#f})
The configuration file for the ISC DHCP client.

@item @code{shepherd-requirement} (default: @code{'()})
@itemx @code{shepherd-provision} (default: @code{'(networking)})
This option can be used to provide a list of symbols naming Shepherd services
that this service will depend on, such as @code{'wpa-supplicant} or
@code{'iwd} if you require authenticated access for encrypted WiFi or Ethernet
networks.

Likewise, @code{shepherd-provision} is a list of Shepherd service names
(symbols) provided by this service.  You might want to change the
default value if you intend to run several ISC DHCP clients, only one of
which provides the @code{networking} Shepherd service.
@end table
@end deftp

@cindex NetworkManager

@defvar network-manager-service-type
This is the service type for the
@uref{https://wiki.gnome.org/Projects/NetworkManager, NetworkManager}
service. The value for this service type is a
@code{network-manager-configuration} record.

This service is part of @code{%desktop-services} (@pxref{Desktop
Services}).
@end defvar

@deftp {Data Type} network-manager-configuration
Data type representing the configuration of NetworkManager.

@table @asis
@item @code{network-manager} (default: @code{network-manager})
The NetworkManager package to use.

@item @code{shepherd-requirement} (default: @code{'(wpa-supplicant)})
This option can be used to provide a list of symbols naming Shepherd services
that this service will depend on, such as @code{'wpa-supplicant} or
@code{'iwd} if you require authenticated access for encrypted WiFi or Ethernet
networks.

@item @code{dns} (default: @code{"default"})
Processing mode for DNS, which affects how NetworkManager uses the
@code{resolv.conf} configuration file.

@table @samp
@item default
NetworkManager will update @code{resolv.conf} to reflect the nameservers
provided by currently active connections.

@item dnsmasq
NetworkManager will run @code{dnsmasq} as a local caching nameserver, using a
@dfn{conditional forwarding} configuration if you are connected to a VPN, and
then update @code{resolv.conf} to point to the local nameserver.

With this setting, you can share your network connection.  For example when
you want to share your network connection to another laptop @i{via} an
Ethernet cable, you can open @command{nm-connection-editor} and configure the
Wired connection's method for IPv4 and IPv6 to be ``Shared to other computers''
and reestablish the connection (or reboot).

You can also set up a @dfn{host-to-guest connection} to QEMU VMs
(@pxref{Installing Guix in a VM}).  With a host-to-guest connection, you can
e.g.@: access a Web server running on the VM (@pxref{Web Services}) from a Web
browser on your host system, or connect to the VM @i{via} SSH
(@pxref{Networking Services, @code{openssh-service-type}}).  To set up a
host-to-guest connection, run this command once:

@example
nmcli connection add type tun \
 connection.interface-name tap0 \
 tun.mode tap tun.owner $(id -u) \
 ipv4.method shared \
 ipv4.addresses 172.28.112.1/24
@end example

Then each time you launch your QEMU VM (@pxref{Running Guix in a VM}), pass
@option{-nic tap,ifname=tap0,script=no,downscript=no} to
@command{qemu-system-...}.

@item none
NetworkManager will not modify @code{resolv.conf}.
@end table

@item @code{vpn-plugins} (default: @code{'()})
This is the list of available plugins for virtual private networks
(VPNs).  An example of this is the @code{network-manager-openvpn}
package, which allows NetworkManager to manage VPNs @i{via} OpenVPN.

@end table
@end deftp

@cindex Connman
@defvar connman-service-type
This is the service type to run @url{https://01.org/connman,Connman},
a network connection manager.

Its value must be a @code{connman-configuration} record as in this example:

@lisp
(service connman-service-type
         (connman-configuration
           (disable-vpn? #t)))
@end lisp

See below for details about @code{connman-configuration}.
@end defvar

@deftp {Data Type} connman-configuration
Data Type representing the configuration of connman.

@table @asis
@item @code{connman} (default: @var{connman})
The connman package to use.

@item @code{shepherd-requirement} (default: @code{'()})
This option can be used to provide a list of symbols naming Shepherd services
that this service will depend on, such as @code{'wpa-supplicant} or
@code{'iwd} if you require authenticated access for encrypted WiFi or Ethernet
networks.

@item @code{disable-vpn?} (default: @code{#f})
When true, disable connman's vpn plugin.

@item @code{general-configuration} (default: @code{(connman-general-configuration)})
Configuration serialized to @file{main.conf} and passed as @option{--config}
to @command{connmand}.

@end table
@end deftp

@c %start of fragment

@deftp {Data Type} connman-general-configuration
Available @code{connman-general-configuration} fields are:

@table @asis
@item @code{input-request-timeout} (type: maybe-number)
Set input request timeout.  Default is 120 seconds.  The request for
inputs like passphrase will timeout after certain amount of time.  Use
this setting to increase the value in case of different user interface
designs.

@item @code{browser-launch-timeout} (type: maybe-number)
Set browser launch timeout.  Default is 300 seconds.  The request for
launching a browser for portal pages will timeout after certain amount
of time.  Use this setting to increase the value in case of different
user interface designs.

@item @code{background-scanning?} (type: maybe-boolean)
Enable background scanning.  Default is true.  If wifi is disconnected,
the background scanning will follow a simple back off mechanism from 3s
up to 5 minutes.  Then, it will stay in 5 minutes unless user
specifically asks for scanning through a D-Bus call.  If so, the
mechanism will start again from 3s.  This feature activates also the
background scanning while being connected, which is required for roaming
on wifi.  When @code{background-scanning?} is false, ConnMan will not
perform any scan regardless of wifi is connected or not, unless it is
requested by the user through a D-Bus call.

@item @code{use-gateways-as-timeservers?} (type: maybe-boolean)
Assume that service gateways also function as timeservers.  Default is
false.

@item @code{fallback-timeservers} (type: maybe-list)
List of Fallback timeservers.  These timeservers are used for NTP sync
when there are no timeservers set by the user or by the service, and
when @code{use-gateways-as-timeservers?} is @code{#f}.  These can
contain a mixed combination of fully qualified domain names, IPv4 and
IPv6 addresses.

@item @code{fallback-nameservers} (type: maybe-list)
List of fallback nameservers appended to the list of nameservers given
by the service.  The nameserver entries must be in numeric format, host
names are ignored.

@item @code{default-auto-connect-technologies} (type: maybe-list)
List of technologies that are marked autoconnectable by default.  The
default value for this entry when empty is @code{"ethernet"},
@code{"wifi"}, @code{"cellular"}.  Services that are automatically
connected must have been set up and saved to storage beforehand.

@item @code{default-favourite-technologies} (type: maybe-list)
List of technologies that are marked favorite by default.  The default
value for this entry when empty is @code{"ethernet"}.  Connects to
services from this technology even if not setup and saved to storage.

@item @code{always-connected-technologies} (type: maybe-list)
List of technologies which are always connected regardless of
preferred-technologies setting (@code{auto-connect?} @code{#t}).  The
default value is empty and this feature is disabled unless explicitly
enabled.

@item @code{preferred-technologies} (type: maybe-list)
List of preferred technologies from the most preferred one to the least
preferred one.  Services of the listed technology type will be tried one
by one in the order given, until one of them gets connected or they are
all tried.  A service of a preferred technology type in state 'ready'
will get the default route when compared to another preferred type
further down the list with state 'ready' or with a non-preferred type; a
service of a preferred technology type in state 'online' will get the
default route when compared to either a non-preferred type or a
preferred type further down in the list.

@item @code{network-interface-blacklist} (type: maybe-list)
List of blacklisted network interfaces.  Found interfaces will be
compared to the list and will not be handled by ConnMan, if their first
characters match any of the list entries.  Default value is
@code{"vmnet"}, @code{"vboxnet"}, @code{"virbr"}, @code{"ifb"}.

@item @code{allow-hostname-updates?} (type: maybe-boolean)
Allow ConnMan to change the system hostname.  This can happen for
example if we receive DHCP hostname option.  Default value is @code{#t}.

@item @code{allow-domainname-updates?} (type: maybe-boolean)
Allow connman to change the system domainname.  This can happen for
example if we receive DHCP domainname option.  Default value is
@code{#t}.

@item @code{single-connected-technology?} (type: maybe-boolean)
Keep only a single connected technology at any time.  When a new service
is connected by the user or a better one is found according to
preferred-technologies, the new service is kept connected and all the
other previously connected services are disconnected.  With this setting
it does not matter whether the previously connected services are in
'online' or 'ready' states, the newly connected service is the only one
that will be kept connected.  A service connected by the user will be
used until going out of network coverage.  With this setting enabled
applications will notice more network breaks than normal.  Note this
options can't be used with VPNs.  Default value is @code{#f}.

@item @code{tethering-technologies} (type: maybe-list)
List of technologies that are allowed to enable tethering.  The default
value is @code{"wifi"}, @code{"bluetooth"}, @code{"gadget"}.  Only those
technologies listed here are used for tethering.  If one wants to tether
ethernet, then add @code{"ethernet"} in the list.  Note that if ethernet
tethering is enabled, then a DHCP server is started on all ethernet
interfaces.  Tethered ethernet should never be connected to corporate or
home network as it will disrupt normal operation of these networks.  Due
to this ethernet is not tethered by default.  Do not activate ethernet
tethering unless you really know what you are doing.

@item @code{persistent-tethering-mode?} (type: maybe-boolean)
Restore earlier tethering status when returning from offline mode,
re-enabling a technology, and after restarts and reboots.  Default value
is @code{#f}.

@item @code{enable-6to4?} (type: maybe-boolean)
Automatically enable anycast 6to4 if possible.  This is not recommended,
as the use of 6to4 will generally lead to a severe degradation of
connection quality.  See RFC6343.  Default value is @code{#f} (as
recommended by RFC6343 section 4.1).

@item @code{vendor-class-id} (type: maybe-string)
Set DHCP option 60 (Vendor Class ID) to the given string.  This option
can be used by DHCP servers to identify specific clients without having
to rely on MAC address ranges, etc.

@item @code{enable-online-check?} (type: maybe-boolean)
Enable or disable use of HTTP GET as an online status check.  When a
service is in a READY state, and is selected as default, ConnMan will
issue an HTTP GET request to verify that end-to-end connectivity is
successful.  Only then the service will be transitioned to ONLINE state.
If this setting is false, the default service will remain in READY
state.  Default value is @code{#t}.

@item @code{online-check-ipv4-url} (type: maybe-string)
IPv4 URL used during the online status check.  Please refer to the
README for more detailed information.  Default value is
@uref{http://ipv4.connman.net/online/status.html}.

@item @code{online-check-ipv6-url} (type: maybe-string)
IPv6 URL used during the online status check.  Please refer to the
README for more detailed information.  Default value is
@uref{http://ipv6.connman.net/online/status.html}.

@item @code{online-check-initial-interval} (type: maybe-number)
Range of intervals between two online check requests.  Please refer to
the README for more detailed information.  Default value is @samp{1}.

@item @code{online-check-max-interval} (type: maybe-number)
Range of intervals between two online check requests.  Please refer to
the README for more detailed information.  Default value is @samp{1}.

@item @code{enable-online-to-ready-transition?} (type: maybe-boolean)
WARNING: This is an experimental feature.  In addition to
@code{enable-online-check} setting, enable or disable use of HTTP GET to
detect the loss of end-to-end connectivity.  If this setting is
@code{#f}, when the default service transitions to ONLINE state, the
HTTP GET request is no more called until next cycle, initiated by a
transition of the default service to DISCONNECT state.  If this setting
is @code{#t}, the HTTP GET request keeps being called to guarantee that
end-to-end connectivity is still successful.  If not, the default
service will transition to READY state, enabling another service to
become the default one, in replacement.  Default value is @code{#f}.

@item @code{auto-connect-roaming-services?} (type: maybe-boolean)
Automatically connect roaming services.  This is not recommended unless
you know you won't have any billing problem.  Default value is
@code{#f}.

@item @code{address-conflict-detection?} (type: maybe-boolean)
Enable or disable the implementation of IPv4 address conflict detection
according to RFC5227.  ConnMan will send probe ARP packets to see if an
IPv4 address is already in use before assigning the address to an
interface.  If an address conflict occurs for a statically configured
address, an IPv4LL address will be chosen instead (according to
RFC3927).  If an address conflict occurs for an address offered via
DHCP, ConnMan sends a DHCP DECLINE once and for the second conflict
resorts to finding an IPv4LL address.  Default value is @code{#f}.

@item @code{localtime} (type: maybe-string)
Path to localtime file.  Defaults to @file{/etc/localtime}.

@item @code{regulatory-domain-follows-timezone?} (type: maybe-boolean)
Enable regulatory domain to be changed along timezone changes.  With
this option set to true each time the timezone changes the first present
ISO3166 country code is read from
@file{/usr/share/zoneinfo/zone1970.tab} and set as regulatory domain
value.  Default value is @code{#f}.

@item @code{resolv-conf} (type: maybe-string)
Path to resolv.conf file.  If the file does not exist, but intermediate
directories exist, it will be created.  If this option is not set, it
tries to write into @file{/var/run/connman/resolv.conf} if it fails
(@file{/var/run/connman} does not exist or is not writeable).  If you do
not want to update resolv.conf, you can set @file{/dev/null}.

@end table

@end deftp

@cindex WPA Supplicant
@defvar wpa-supplicant-service-type
This is the service type to run @url{https://w1.fi/wpa_supplicant/,WPA
supplicant}, an authentication daemon required to authenticate against
encrypted WiFi or ethernet networks.
@end defvar

@deftp {Data Type} wpa-supplicant-configuration
Data type representing the configuration of WPA Supplicant.

It takes the following parameters:

@table @asis
@item @code{wpa-supplicant} (default: @code{wpa-supplicant})
The WPA Supplicant package to use.

@item @code{requirement} (default: @code{'(user-processes loopback syslogd)}
List of services that should be started before WPA Supplicant starts.

@item @code{dbus?} (default: @code{#t})
Whether to listen for requests on D-Bus.

@item @code{pid-file} (default: @code{"/var/run/wpa_supplicant.pid"})
Where to store the PID file.

@item @code{interface} (default: @code{#f})
If this is set, it must specify the name of a network interface that
WPA supplicant will control.

@item @code{config-file} (default: @code{#f})
Optional configuration file to use.

@item @code{extra-options} (default: @code{'()})
List of additional command-line arguments to pass to the daemon.
@end table
@end deftp

@cindex ModemManager
Some networking devices such as modems require special care, and this is
what the services below focus on.

@defvar modem-manager-service-type
This is the service type for the
@uref{https://wiki.gnome.org/Projects/ModemManager, ModemManager}
service.  The value for this service type is a
@code{modem-manager-configuration} record.

This service is part of @code{%desktop-services} (@pxref{Desktop
Services}).
@end defvar

@deftp {Data Type} modem-manager-configuration
Data type representing the configuration of ModemManager.

@table @asis
@item @code{modem-manager} (default: @code{modem-manager})
The ModemManager package to use.

@end table
@end deftp

@cindex USB_ModeSwitch
@cindex Modeswitching

@defvar usb-modeswitch-service-type
This is the service type for the
@uref{https://www.draisberghof.de/usb_modeswitch/, USB_ModeSwitch}
service.  The value for this service type is
a @code{usb-modeswitch-configuration} record.

When plugged in, some USB modems (and other USB devices) initially present
themselves as a read-only storage medium and not as a modem.  They need to be
@dfn{modeswitched} before they are usable.  The USB_ModeSwitch service type
installs udev rules to automatically modeswitch these devices when they are
plugged in.

This service is part of @code{%desktop-services} (@pxref{Desktop
Services}).
@end defvar

@deftp {Data Type} usb-modeswitch-configuration
Data type representing the configuration of USB_ModeSwitch.

@table @asis
@item @code{usb-modeswitch} (default: @code{usb-modeswitch})
The USB_ModeSwitch package providing the binaries for modeswitching.

@item @code{usb-modeswitch-data} (default: @code{usb-modeswitch-data})
The package providing the device data and udev rules file used by
USB_ModeSwitch.

@item @code{config-file} (default: @code{#~(string-append #$usb-modeswitch:dispatcher "/etc/usb_modeswitch.conf")})
Which config file to use for the USB_ModeSwitch dispatcher.  By default the
config file shipped with USB_ModeSwitch is used which disables logging to
@file{/var/log} among other default settings.  If set to @code{#f}, no config
file is used.

@end table
@end deftp


@node Networking Services
@subsection Networking Services

The @code{(gnu services networking)} module discussed in the previous
section provides services for more advanced setups: providing a DHCP
service for others to use, filtering packets with iptables or nftables,
running a WiFi access point with @command{hostapd}, running the
@command{inetd} ``superdaemon'', and more.  This section describes
those.

@defvar dhcpd-service-type
This type defines a service that runs a DHCP daemon.  To create a
service of this type, you must supply a @code{<dhcpd-configuration>}.
For example:

@lisp
(service dhcpd-service-type
         (dhcpd-configuration
          (config-file (local-file "my-dhcpd.conf"))
          (interfaces '("enp0s25"))))
@end lisp
@end defvar

@deftp {Data Type} dhcpd-configuration
@table @asis
@item @code{package} (default: @code{isc-dhcp})
The package that provides the DHCP daemon.  This package is expected to
provide the daemon at @file{sbin/dhcpd} relative to its output
directory.  The default package is the
@uref{https://www.isc.org/dhcp/, ISC's DHCP server}.
@item @code{config-file} (default: @code{#f})
The configuration file to use.  This is required.  It will be passed to
@code{dhcpd} via its @code{-cf} option.  This may be any ``file-like''
object (@pxref{G-Expressions, file-like objects}).  See @code{man
dhcpd.conf} for details on the configuration file syntax.
@item @code{version} (default: @code{"4"})
The DHCP version to use.  The ISC DHCP server supports the values ``4'',
``6'', and ``4o6''.  These correspond to the @code{dhcpd} program
options @code{-4}, @code{-6}, and @code{-4o6}.  See @code{man dhcpd} for
details.
@item @code{run-directory} (default: @code{"/run/dhcpd"})
The run directory to use.  At service activation time, this directory
will be created if it does not exist.
@item @code{pid-file} (default: @code{"/run/dhcpd/dhcpd.pid"})
The PID file to use.  This corresponds to the @code{-pf} option of
@code{dhcpd}.  See @code{man dhcpd} for details.
@item @code{interfaces} (default: @code{'()})
The names of the network interfaces on which dhcpd should listen for
broadcasts.  If this list is not empty, then its elements (which must be
strings) will be appended to the @code{dhcpd} invocation when starting
the daemon.  It may not be necessary to explicitly specify any
interfaces here; see @code{man dhcpd} for details.
@end table
@end deftp

@cindex hostapd service, for Wi-Fi access points
@cindex Wi-Fi access points, hostapd service
@defvar hostapd-service-type
This is the service type to run the @uref{https://w1.fi/hostapd/,
hostapd} daemon to set up WiFi (IEEE 802.11) access points and
authentication servers.  Its associated value must be a
@code{hostapd-configuration} as shown below:

@lisp
;; Use wlan1 to run the access point for "My Network".
(service hostapd-service-type
         (hostapd-configuration
          (interface "wlan1")
          (ssid "My Network")
          (channel 12)))
@end lisp
@end defvar

@deftp {Data Type} hostapd-configuration
This data type represents the configuration of the hostapd service, with
the following fields:

@table @asis
@item @code{package} (default: @code{hostapd})
The hostapd package to use.

@item @code{interface} (default: @code{"wlan0"})
The network interface to run the WiFi access point.

@item @code{ssid}
The SSID (@dfn{service set identifier}), a string that identifies this
network.

@item @code{broadcast-ssid?} (default: @code{#t})
Whether to broadcast this SSID.

@item @code{channel} (default: @code{1})
The WiFi channel to use.

@item @code{driver} (default: @code{"nl80211"})
The driver interface type.  @code{"nl80211"} is used with all Linux
mac80211 drivers.  Use @code{"none"} if building hostapd as a standalone
RADIUS server that does not control any wireless/wired driver.

@item @code{extra-settings} (default: @code{""})
Extra settings to append as-is to the hostapd configuration file.  See
@uref{https://w1.fi/cgit/hostap/plain/hostapd/hostapd.conf} for the
configuration file reference.
@end table
@end deftp

@defvar simulated-wifi-service-type
This is the type of a service to simulate WiFi networking, which can be
useful in virtual machines for testing purposes.  The service loads the
Linux kernel
@uref{https://www.kernel.org/doc/html/latest/networking/mac80211_hwsim/mac80211_hwsim.html,
@code{mac80211_hwsim} module} and starts hostapd to create a pseudo WiFi
network that can be seen on @code{wlan0}, by default.

The service's value is a @code{hostapd-configuration} record.
@end defvar


@cindex iptables
@defvar iptables-service-type
This is the service type to set up an iptables configuration.  iptables is a
packet filtering framework supported by the Linux kernel.  This service
supports configuring iptables for both IPv4 and IPv6.  A simple example
configuration rejecting all incoming connections except those to the ssh port
22 is shown below.

@lisp
(service iptables-service-type
         (iptables-configuration
          (ipv4-rules (plain-file "iptables.rules" "*filter
:INPUT ACCEPT
:FORWARD ACCEPT
:OUTPUT ACCEPT
-A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
-A INPUT -p tcp --dport 22 -j ACCEPT
-A INPUT -j REJECT --reject-with icmp-port-unreachable
COMMIT
"))
          (ipv6-rules (plain-file "ip6tables.rules" "*filter
:INPUT ACCEPT
:FORWARD ACCEPT
:OUTPUT ACCEPT
-A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT
-A INPUT -p tcp --dport 22 -j ACCEPT
-A INPUT -j REJECT --reject-with icmp6-port-unreachable
COMMIT
"))))
@end lisp
@end defvar

@deftp {Data Type} iptables-configuration
The data type representing the configuration of iptables.

@table @asis
@item @code{iptables} (default: @code{iptables})
The iptables package that provides @code{iptables-restore} and
@code{ip6tables-restore}.
@item @code{ipv4-rules} (default: @code{%iptables-accept-all-rules})
The iptables rules to use.  It will be passed to @code{iptables-restore}.
This may be any ``file-like'' object (@pxref{G-Expressions, file-like
objects}).
@item @code{ipv6-rules} (default: @code{%iptables-accept-all-rules})
The ip6tables rules to use.  It will be passed to @code{ip6tables-restore}.
This may be any ``file-like'' object (@pxref{G-Expressions, file-like
objects}).
@end table
@end deftp

@cindex nftables
@defvar nftables-service-type
This is the service type to set up a nftables configuration.  nftables is a
netfilter project that aims to replace the existing iptables, ip6tables,
arptables and ebtables framework.  It provides a new packet filtering
framework, a new user-space utility @command{nft}, and a compatibility layer
for iptables.  This service comes with a default ruleset
@code{%default-nftables-ruleset} that rejecting all incoming connections
except those to the ssh port 22.  To use it, simply write:

@lisp
(service nftables-service-type)
@end lisp
@end defvar

@deftp {Data Type} nftables-configuration
The data type representing the configuration of nftables.

@table @asis
@item @code{package} (default: @code{nftables})
The nftables package that provides @command{nft}.
@item @code{ruleset} (default: @code{%default-nftables-ruleset})
The nftables ruleset to use.  This may be any ``file-like'' object
(@pxref{G-Expressions, file-like objects}).
@end table
@end deftp

@cindex NTP (Network Time Protocol), service
@cindex ntpd, service for the Network Time Protocol daemon
@cindex real time clock
@defvar ntp-service-type
This is the type of the service running the @uref{https://www.ntp.org,
Network Time Protocol (NTP)} daemon, @command{ntpd}.  The daemon will keep the
system clock synchronized with that of the specified NTP servers.

The value of this service is an @code{ntpd-configuration} object, as described
below.
@end defvar

@deftp {Data Type} ntp-configuration
This is the data type for the NTP service configuration.

@table @asis
@item @code{servers} (default: @code{%ntp-servers})
This is the list of servers (@code{<ntp-server>} records) with which
@command{ntpd} will be synchronized.  See the @code{ntp-server} data type
definition below.

@item @code{allow-large-adjustment?} (default: @code{#t})
This determines whether @command{ntpd} is allowed to make an initial
adjustment of more than 1,000 seconds.

@item @code{ntp} (default: @code{ntp})
The NTP package to use.
@end table
@end deftp

@defvar %ntp-servers
List of host names used as the default NTP servers.  These are servers of the
@uref{https://www.ntppool.org/en/, NTP Pool Project}.
@end defvar

@deftp {Data Type} ntp-server
The data type representing the configuration of a NTP server.

@table @asis
@item @code{type} (default: @code{'server})
The type of the NTP server, given as a symbol.  One of @code{'pool},
@code{'server}, @code{'peer}, @code{'broadcast} or @code{'manycastclient}.

@item @code{address}
The address of the server, as a string.

@item @code{options}
NTPD options to use with that specific server, given as a list of option names
and/or of option names and values tuples.  The following example define a server
to use with the options @option{iburst} and @option{prefer}, as well as
@option{version} 3 and a @option{maxpoll} time of 16 seconds.

@example
(ntp-server
 (type 'server)
 (address "some.ntp.server.org")
 (options `(iburst (version 3) (maxpoll 16) prefer))))
@end example
@end table
@end deftp

@cindex OpenNTPD
@defvar openntpd-service-type
Run the @command{ntpd}, the Network Time Protocol (NTP) daemon, as implemented
by @uref{http://www.openntpd.org, OpenNTPD}.  The daemon will keep the system
clock synchronized with that of the given servers.

@lisp
(service
 openntpd-service-type
 (openntpd-configuration
  (listen-on '("127.0.0.1" "::1"))
  (sensor '("udcf0 correction 70000"))
  (constraint-from '("www.gnu.org"))
  (constraints-from '("https://www.google.com/"))))

@end lisp
@end defvar

@defvar %openntpd-servers
This variable is a list of the server addresses defined in
@code{%ntp-servers}.
@end defvar

@deftp {Data Type} openntpd-configuration
@table @asis
@item @code{openntpd} (default: @code{openntpd})
The openntpd package to use.
@item @code{listen-on} (default: @code{'("127.0.0.1" "::1")})
A list of local IP addresses or hostnames the ntpd daemon should listen on.
@item @code{query-from} (default: @code{'()})
A list of local IP address the ntpd daemon should use for outgoing queries.
@item @code{sensor} (default: @code{'()})
Specify a list of timedelta sensor devices ntpd should use.  @code{ntpd}
will listen to each sensor that actually exists and ignore non-existent ones.
See @uref{https://man.openbsd.org/ntpd.conf, upstream documentation} for more
information.
@item @code{server} (default: @code{'()})
Specify a list of IP addresses or hostnames of NTP servers to synchronize to.
@item @code{servers} (default: @code{%openntp-servers})
Specify a list of IP addresses or hostnames of NTP pools to synchronize to.
@item @code{constraint-from} (default: @code{'()})
@code{ntpd} can be configured to query the ‘Date’ from trusted HTTPS servers via TLS.
This time information is not used for precision but acts as an authenticated
constraint, thereby reducing the impact of unauthenticated NTP
man-in-the-middle attacks.
Specify a list of URLs, IP addresses or hostnames of HTTPS servers to provide
a constraint.
@item @code{constraints-from} (default: @code{'()})
As with constraint from, specify a list of URLs, IP addresses or hostnames of
HTTPS servers to provide a constraint.  Should the hostname resolve to multiple
IP addresses, @code{ntpd} will calculate a median constraint from all of them.
@end table
@end deftp

@cindex inetd
@defvar inetd-service-type
This service runs the @command{inetd} (@pxref{inetd invocation,,,
inetutils, GNU Inetutils}) daemon.  @command{inetd} listens for
connections on internet sockets, and lazily starts the specified server
program when a connection is made on one of these sockets.

The value of this service is an @code{inetd-configuration} object.  The
following example configures the @command{inetd} daemon to provide the
built-in @command{echo} service, as well as an smtp service which
forwards smtp traffic over ssh to a server @code{smtp-server} behind a
gateway @code{hostname}:

@lisp
(service
 inetd-service-type
 (inetd-configuration
  (entries (list
            (inetd-entry
             (name "echo")
             (socket-type 'stream)
             (protocol "tcp")
             (wait? #f)
             (user "root"))
            (inetd-entry
             (node "127.0.0.1")
             (name "smtp")
             (socket-type 'stream)
             (protocol "tcp")
             (wait? #f)
             (user "root")
             (program (file-append openssh "/bin/ssh"))
             (arguments
              '("ssh" "-qT" "-i" "/path/to/ssh_key"
                "-W" "smtp-server:25" "user@@hostname")))))))
@end lisp

See below for more details about @code{inetd-configuration}.
@end defvar

@deftp {Data Type} inetd-configuration
Data type representing the configuration of @command{inetd}.

@table @asis
@item @code{program} (default: @code{(file-append inetutils "/libexec/inetd")})
The @command{inetd} executable to use.

@item @code{entries} (default: @code{'()})
A list of @command{inetd} service entries.  Each entry should be created
by the @code{inetd-entry} constructor.
@end table
@end deftp

@deftp {Data Type} inetd-entry
Data type representing an entry in the @command{inetd} configuration.
Each entry corresponds to a socket where @command{inetd} will listen for
requests.

@table @asis
@item @code{node} (default: @code{#f})
Optional string, a comma-separated list of local addresses
@command{inetd} should use when listening for this service.
@xref{Configuration file,,, inetutils, GNU Inetutils} for a complete
description of all options.
@item @code{name}
A string, the name must correspond to an entry in @code{/etc/services}.
@item @code{socket-type}
One of @code{'stream}, @code{'dgram}, @code{'raw}, @code{'rdm} or
@code{'seqpacket}.
@item @code{protocol}
A string, must correspond to an entry in @code{/etc/protocols}.
@item @code{wait?} (default: @code{#t})
Whether @command{inetd} should wait for the server to exit before
listening to new service requests.
@item @code{user}
A string containing the user (and, optionally, group) name of the user
as whom the server should run.  The group name can be specified in a
suffix, separated by a colon or period, i.e.@: @code{"user"},
@code{"user:group"} or @code{"user.group"}.
@item @code{program} (default: @code{"internal"})
The server program which will serve the requests, or @code{"internal"}
if @command{inetd} should use a built-in service.
@item @code{arguments} (default: @code{'()})
A list strings or file-like objects, which are the server program's
arguments, starting with the zeroth argument, i.e.@: the name of the
program itself.  For @command{inetd}'s internal services, this entry
must be @code{'()} or @code{'("internal")}.
@end table

@xref{Configuration file,,, inetutils, GNU Inetutils} for a more
detailed discussion of each configuration field.
@end deftp

@cindex opendht, distributed hash table network service
@cindex dhtproxy, for use with jami
@defvar opendht-service-type
This is the type of the service running a @uref{https://opendht.net,
OpenDHT} node, @command{dhtnode}.  The daemon can be used to host your
own proxy service to the distributed hash table (DHT), for example to
connect to with Jami, among other applications.

@quotation Important
When using the OpenDHT proxy server, the IP addresses it ``sees'' from
the clients should be addresses reachable from other peers.  In practice
this means that a publicly reachable address is best suited for a proxy
server, outside of your private network.  For example, hosting the proxy
server on a IPv4 private local network and exposing it via port
forwarding could work for external peers, but peers local to the proxy
would have their private addresses shared with the external peers,
leading to connectivity problems.
@end quotation

The value of this service is a @code{opendht-configuration} object, as
described below.
@end defvar

@c The fields documentation has been auto-generated using the
@c configuration->documentation procedure from
@c (gnu services configuration).
@deftp {Data Type} opendht-configuration
Available @code{opendht-configuration} fields are:

@table @asis
@item @code{opendht} (default: @code{opendht}) (type: file-like)
The @code{opendht} package to use.

@item @code{peer-discovery?} (default: @code{#f}) (type: boolean)
Whether to enable the multicast local peer discovery mechanism.

@item @code{enable-logging?} (default: @code{#f}) (type: boolean)
Whether to enable logging messages to syslog.  It is disabled by default
as it is rather verbose.

@item @code{debug?} (default: @code{#f}) (type: boolean)
Whether to enable debug-level logging messages.  This has no effect if
logging is disabled.

@item @code{bootstrap-host} (default: @code{"bootstrap.jami.net:4222"}) (type: maybe-string)
The node host name that is used to make the first connection to the
network.  A specific port value can be provided by appending the
@code{:PORT} suffix.  By default, it uses the Jami bootstrap nodes, but
any host can be specified here.  It's also possible to disable
bootstrapping by explicitly setting this field to the
@code{%unset-value} value.

@item @code{port} (default: @code{4222}) (type: maybe-number)
The UDP port to bind to.  When left unspecified, an available port is
automatically selected.

@item @code{proxy-server-port} (type: maybe-number)
Spawn a proxy server listening on the specified port.

@item @code{proxy-server-port-tls} (type: maybe-number)
Spawn a proxy server listening to TLS connections on the specified port.

@end table
@end deftp

@cindex Tor
@defvar tor-service-type
Type for a service that runs the @uref{https://torproject.org, Tor}
anonymous networking daemon.  The service is configured using a
@code{<tor-configuration>} record.  By default, the Tor daemon runs as the
@code{tor} unprivileged user, which is a member of the @code{tor} group.

@cindex onion services, for Tor
Services of this type can be extended by other services to specify
@dfn{onion services} (in addition to those already specified in
@code{tor-configuration}) as in this example:

@lisp
(simple-service 'my-extra-onion-service tor-service-type
                (list (tor-onion-service-configuration
                        (name "extra-onion-service")
                        (mapping '((80 . "127.0.0.1:8080"))))))
@end lisp
@end defvar

@deftp {Data Type} tor-configuration
@table @asis
@item @code{tor} (default: @code{tor})
The package that provides the Tor daemon.  This package is expected to provide
the daemon at @file{bin/tor} relative to its output directory.  The default
package is the @uref{https://www.torproject.org, Tor Project's}
implementation.

@item @code{config-file} (default: @code{(plain-file "empty" "")})
The configuration file to use.  It will be appended to a default configuration
file, and the final configuration file will be passed to @code{tor} via its
@code{-f} option.  This may be any ``file-like'' object (@pxref{G-Expressions,
file-like objects}).  See @code{man tor} for details on the configuration file
syntax.

@item @code{hidden-services} (default: @code{'()})
The list of @code{<tor-onion-service-configuration>} records to use.
For any onion service you include in this list, appropriate
configuration to enable the onion service will be automatically added to
the default configuration file.

@item @code{socks-socket-type} (default: @code{'tcp})
The default socket type that Tor should use for its SOCKS socket.  This must
be either @code{'tcp} or @code{'unix}.  If it is @code{'tcp}, then by default
Tor will listen on TCP port 9050 on the loopback interface (i.e., localhost).
If it is @code{'unix}, then Tor will listen on the UNIX domain socket
@file{/var/run/tor/socks-sock}, which will be made writable by members of the
@code{tor} group.

If you want to customize the SOCKS socket in more detail, leave
@code{socks-socket-type} at its default value of @code{'tcp} and use
@code{config-file} to override the default by providing your own
@code{SocksPort} option.

@item @code{control-socket?} (default: @code{#f})
Whether or not to provide a ``control socket'' by which Tor can be
controlled to, for instance, dynamically instantiate tor onion services.
If @code{#t}, Tor will listen for control commands on the UNIX domain socket
@file{/var/run/tor/control-sock}, which will be made writable by members of the
@code{tor} group.

@end table
@end deftp

@cindex onion service, tor
@deftp {Data Type} tor-onion-service-configuration
Data Type representing a Tor @dfn{Onion Service} configuration.
See @url{https://community.torproject.org/onion-services/, the Tor
project's documentation} for more information.
Available @code{tor-onion-service-configuration} fields are:

@table @asis
@item @code{name} (type: string)
Name for this Onion Service.  This creates a
@file{/var/lib/tor/hidden-services/@var{name}} directory, where the
@file{hostname} file contains the @indicateurl{.onion} host name for this Onion
Service.

@item @code{mapping} (type: alist)
Association list of port to address mappings.  The following example:
@lisp
'((22 . "127.0.0.1:22")
  (80 . "127.0.0.1:8080"))
@end lisp
maps ports 22 and 80 of the Onion Service to the local ports 22 and 8080.

@end table
@end deftp

The @code{(gnu services rsync)} module provides the following services:

You might want an rsync daemon if you have files that you want available
so anyone (or just yourself) can download existing files or upload new
files.

@defvar rsync-service-type
This is the service type for the @uref{https://rsync.samba.org, rsync} daemon,
The value for this service type is a
@command{rsync-configuration} record as in this example:

@lisp
;; Export two directories over rsync.  By default rsync listens on
;; all the network interfaces.
(service rsync-service-type
         (rsync-configuration
           (modules (list (rsync-module
                            (name "music")
                            (file-name "/srv/zik")
                            (read-only? #f))
                          (rsync-module
                            (name "movies")
                            (file-name "/home/charlie/movies"))))))
@end lisp

See below for details about @code{rsync-configuration}.
@end defvar

@deftp {Data Type} rsync-configuration
Data type representing the configuration for @code{rsync-service}.

@table @asis
@item @code{package} (default: @var{rsync})
@code{rsync} package to use.

@item @code{address} (default: @code{#f})
IP address on which @command{rsync} listens for incoming connections.
If unspecified, it defaults to listening on all available addresses.

@item @code{port-number} (default: @code{873})
TCP port on which @command{rsync} listens for incoming connections.  If port
is less than @code{1024} @command{rsync} needs to be started as the
@code{root} user and group.

@item @code{pid-file} (default: @code{"/var/run/rsyncd/rsyncd.pid"})
Name of the file where @command{rsync} writes its PID.

@item @code{lock-file} (default: @code{"/var/run/rsyncd/rsyncd.lock"})
Name of the file where @command{rsync} writes its lock file.

@item @code{log-file} (default: @code{"/var/log/rsyncd.log"})
Name of the file where @command{rsync} writes its log file.

@item @code{user} (default: @code{"root"})
Owner of the @code{rsync} process.

@item @code{group} (default: @code{"root"})
Group of the @code{rsync} process.

@item @code{uid} (default: @code{"rsyncd"})
User name or user ID that file transfers to and from that module should take
place as when the daemon was run as @code{root}.

@item @code{gid} (default: @code{"rsyncd"})
Group name or group ID that will be used when accessing the module.

@item @code{modules} (default: @code{%default-modules})
List of ``modules''---i.e., directories exported over rsync.  Each
element must be a @code{rsync-module} record, as described below.
@end table
@end deftp

@deftp {Data Type} rsync-module
This is the data type for rsync ``modules''.  A module is a directory
exported over the rsync protocol.  The available fields are as follows:

@table @asis
@item @code{name}
The module name.  This is the name that shows up in URLs.  For example,
if the module is called @code{music}, the corresponding URL will be
@code{rsync://host.example.org/music}.

@item @code{file-name}
Name of the directory being exported.

@item @code{comment} (default: @code{""})
Comment associated with the module.  Client user interfaces may display
it when they obtain the list of available modules.

@item @code{read-only?} (default: @code{#t})
Whether or not client will be able to upload files.  If this is false,
the uploads will be authorized if permissions on the daemon side permit
it.

@item @code{chroot?} (default: @code{#t})
When this is true, the rsync daemon changes root to the module's
directory before starting file transfers with the client.  This improves
security, but requires rsync to run as root.

@item @code{timeout} (default: @code{300})
Idle time in seconds after which the daemon closes a connection with the
client.
@end table
@end deftp

@cindex Syncthing, file synchronization service
@cindex backup service, Syncthing
The @code{(gnu services syncthing)} module provides the following services:
@cindex syncthing

You might want a syncthing daemon if you have files between two or more
computers and want to sync them in real time, safely protected from
prying eyes.

@defvar syncthing-service-type
This is the service type for the @uref{https://syncthing.net/,
syncthing} daemon, The value for this service type is a
@command{syncthing-configuration} record as in this example:

@lisp
(service syncthing-service-type
         (syncthing-configuration (user "alice")))
@end lisp

@quotation Note
This service is also available for Guix Home, where it runs directly
with your user privileges (@pxref{Networking Home Services,
@code{home-syncthing-service-type}}).
@end quotation

See below for details about @code{syncthing-configuration}.
@end defvar

@deftp {Data Type} syncthing-configuration
Data type representing the configuration for @code{syncthing-service-type}.

@table @asis
@item @code{syncthing} (default: @var{syncthing})
@code{syncthing} package to use.

@item @code{arguments} (default: @var{'()})
List of command-line arguments passing to @code{syncthing} binary.

@item @code{logflags} (default: @var{0})
Sum of logging flags, see
@uref{https://docs.syncthing.net/users/syncthing.html#cmdoption-logflags, Syncthing documentation logflags}.

@item @code{user} (default: @var{#f})
The user as which the Syncthing service is to be run.
This assumes that the specified user exists.

@item @code{group} (default: @var{"users"})
The group as which the Syncthing service is to be run.
This assumes that the specified group exists.

@item @code{home} (default: @var{#f})
Common configuration and data directory.  The default configuration
directory is @file{$HOME} of the specified Syncthing @code{user}.

@end table
@end deftp

Furthermore, @code{(gnu services ssh)} provides the following services.
@cindex SSH
@cindex SSH server

@defvar lsh-service-type
Type of the service that runs the GNU@tie{}lsh secure shell (SSH)
daemon, @command{lshd}.  The value for this service is a
@code{<lsh-configuration>} object.
@end defvar

@deftp {Data Type} lsh-configuration
Data type representing the configuration of @command{lshd}.

@table @asis
@item @code{lsh} (default: @code{lsh}) (type: file-like)
The package object of the GNU@tie{}lsh secure shell (SSH) daemon.

@item @code{daemonic?} (default: @code{#t}) (type: boolean)
Whether to detach from the controlling terminal.

@item @code{host-key} (default: @code{"/etc/lsh/host-key"}) (type: string)
File containing the @dfn{host key}.  This file must be readable by
root only.

@item @code{interfaces} (default: @code{'()}) (type: list)
List of host names or addresses that @command{lshd} will listen on.
If empty, @command{lshd} listens for connections on all the network
interfaces.

@item @code{port-number} (default: @code{22}) (type: integer)
Port to listen on.

@item @code{allow-empty-passwords?} (default: @code{#f}) (type: boolean)
Whether to accept log-ins with empty passwords.

@item @code{root-login?} (default: @code{#f}) (type: boolean)
Whether to accept log-ins as root.

@item @code{syslog-output?} (default: @code{#t}) (type: boolean)
Whether to log @command{lshd} standard output to syslogd.
This will make the service depend on the existence of a syslogd service.

@item @code{pid-file?} (default: @code{#f}) (type: boolean)
When @code{#t}, @command{lshd} writes its PID to the file specified in
@var{pid-file}.

@item @code{pid-file} (default: @code{"/var/run/lshd.pid"}) (type: string)
File that @command{lshd} will write its PID to.

@item @code{x11-forwarding?} (default: @code{#t}) (type: boolean)
Whether to enable X11 forwarding.

@item @code{tcp/ip-forwarding?} (default: @code{#t}) (type: boolean)
Whether to enable TCP/IP forwarding.

@item @code{password-authentication?} (default: @code{#t}) (type: boolean)
Whether to accept log-ins using password authentication.

@item @code{public-key-authentication?} (default: @code{#t}) (type: boolean)
Whether to accept log-ins using public key authentication.

@item @code{initialize?} (default: @code{#t}) (type: boolean)
When @code{#f}, it is up to the user to initialize the randomness
generator (@pxref{lsh-make-seed,,, lsh, LSH Manual}), and to create
a key pair with the private key stored in file @var{host-key}
(@pxref{lshd basics,,, lsh, LSH Manual}).

@end table
@end deftp

@cindex SSH
@cindex SSH server
@defvar openssh-service-type
This is the type for the @uref{http://www.openssh.org, OpenSSH} secure
shell daemon, @command{sshd}.  Its value must be an
@code{openssh-configuration} record as in this example:

@lisp
(service openssh-service-type
         (openssh-configuration
           (x11-forwarding? #t)
           (permit-root-login 'prohibit-password)
           (authorized-keys
             `(("alice" ,(local-file "alice.pub"))
               ("bob" ,(local-file "bob.pub"))))))
@end lisp

See below for details about @code{openssh-configuration}.

This service can be extended with extra authorized keys, as in this
example:

@lisp
(service-extension openssh-service-type
                   (const `(("charlie"
                             ,(local-file "charlie.pub")))))
@end lisp
@end defvar

@deftp {Data Type} openssh-configuration
This is the configuration record for OpenSSH's @command{sshd}.

@table @asis
@item @code{openssh} (default @var{openssh})
The OpenSSH package to use.

@item @code{pid-file} (default: @code{"/var/run/sshd.pid"})
Name of the file where @command{sshd} writes its PID.

@item @code{port-number} (default: @code{22})
TCP port on which @command{sshd} listens for incoming connections.

@item @code{max-connections} (default: @code{200})
Hard limit on the maximum number of simultaneous client connections,
enforced by the inetd-style Shepherd service (@pxref{Service De- and
Constructors, @code{make-inetd-constructor},, shepherd, The GNU Shepherd
Manual}).

@item @code{permit-root-login} (default: @code{#f})
This field determines whether and when to allow logins as root.  If
@code{#f}, root logins are disallowed; if @code{#t}, they are allowed.
If it's the symbol @code{'prohibit-password}, then root logins are
permitted but not with password-based authentication.

@item @code{allow-empty-passwords?} (default: @code{#f})
When true, users with empty passwords may log in.  When false, they may
not.

@item @code{password-authentication?} (default: @code{#t})
When true, users may log in with their password.  When false, they have
other authentication methods.

@item @code{public-key-authentication?} (default: @code{#t})
When true, users may log in using public key authentication.  When
false, users have to use other authentication method.

Authorized public keys are stored in @file{~/.ssh/authorized_keys}.
This is used only by protocol version 2.

@item @code{x11-forwarding?} (default: @code{#f})
When true, forwarding of X11 graphical client connections is
enabled---in other words, @command{ssh} options @option{-X} and
@option{-Y} will work.

@item @code{allow-agent-forwarding?} (default: @code{#t})
Whether to allow agent forwarding.

@item @code{allow-tcp-forwarding?} (default: @code{#t})
Whether to allow TCP forwarding.

@item @code{gateway-ports?} (default: @code{#f})
Whether to allow gateway ports.

@item @code{challenge-response-authentication?} (default: @code{#f})
Specifies whether challenge response authentication is allowed (e.g.@: via
PAM).

@item @code{use-pam?} (default: @code{#t})
Enables the Pluggable Authentication Module interface.  If set to
@code{#t}, this will enable PAM authentication using
@code{challenge-response-authentication?} and
@code{password-authentication?}, in addition to PAM account and session
module processing for all authentication types.

Because PAM challenge response authentication usually serves an
equivalent role to password authentication, you should disable either
@code{challenge-response-authentication?} or
@code{password-authentication?}.

@item @code{print-last-log?} (default: @code{#t})
Specifies whether @command{sshd} should print the date and time of the
last user login when a user logs in interactively.

@item @code{subsystems} (default: @code{'(("sftp" "internal-sftp"))})
Configures external subsystems (e.g.@: file transfer daemon).

This is a list of two-element lists, each of which containing the
subsystem name and a command (with optional arguments) to execute upon
subsystem request.

The command @command{internal-sftp} implements an in-process SFTP
server.  Alternatively, one can specify the @command{sftp-server} command:
@lisp
(service openssh-service-type
         (openssh-configuration
          (subsystems
           `(("sftp" ,(file-append openssh "/libexec/sftp-server"))))))
@end lisp

@item @code{accepted-environment} (default: @code{'()})
List of strings describing which environment variables may be exported.

Each string gets on its own line.  See the @code{AcceptEnv} option in
@code{man sshd_config}.

This example allows ssh-clients to export the @env{COLORTERM} variable.
It is set by terminal emulators, which support colors.  You can use it in
your shell's resource file to enable colors for the prompt and commands
if this variable is set.

@lisp
(service openssh-service-type
         (openssh-configuration
           (accepted-environment '("COLORTERM"))))
@end lisp

@item @code{authorized-keys} (default: @code{'()})
@cindex authorized keys, SSH
@cindex SSH authorized keys
This is the list of authorized keys.  Each element of the list is a user
name followed by one or more file-like objects that represent SSH public
keys.  For example:

@lisp
(openssh-configuration
  (authorized-keys
    `(("rekado" ,(local-file "rekado.pub"))
      ("chris" ,(local-file "chris.pub"))
      ("root" ,(local-file "rekado.pub") ,(local-file "chris.pub")))))
@end lisp

@noindent
registers the specified public keys for user accounts @code{rekado},
@code{chris}, and @code{root}.

Additional authorized keys can be specified @i{via}
@code{service-extension}.

Note that this does @emph{not} interfere with the use of
@file{~/.ssh/authorized_keys}.

@item @code{generate-host-keys?} (default: @code{#t})
Whether to generate host key pairs with @command{ssh-keygen -A} under
@file{/etc/ssh} if there are none.

Generating key pairs takes a few seconds when enough entropy is
available and is only done once.  You might want to turn it off for
instance in a virtual machine that does not need it because host keys
are provided in some other way, and where the extra boot time is a
problem.

@item @code{log-level} (default: @code{'info})
This is a symbol specifying the logging level: @code{quiet}, @code{fatal},
@code{error}, @code{info}, @code{verbose}, @code{debug}, etc.  See the man
page for @file{sshd_config} for the full list of level names.

@item @code{extra-content} (default: @code{""})
This field can be used to append arbitrary text to the configuration file.  It
is especially useful for elaborate configurations that cannot be expressed
otherwise.  This configuration, for example, would generally disable root
logins, but permit them from one specific IP address:

@lisp
(openssh-configuration
  (extra-content "\
Match Address 192.168.0.1
  PermitRootLogin yes"))
@end lisp

@end table
@end deftp

@defvar dropbear-service-type
Type of the service that runs the
@url{https://matt.ucc.asn.au/dropbear/dropbear.html, Dropbear SSH daemon},
whose value is a @code{<dropbear-configuration>} object.

For example, to specify a Dropbear service listening on port 1234:

@lisp
(service dropbear-service-type (dropbear-configuration
                                 (port-number 1234)))
@end lisp
@end defvar

@deftp {Data Type} dropbear-configuration
This data type represents the configuration of a Dropbear SSH daemon.

@table @asis
@item @code{dropbear} (default: @var{dropbear})
The Dropbear package to use.

@item @code{port-number} (default: 22)
The TCP port where the daemon waits for incoming connections.

@item @code{syslog-output?} (default: @code{#t})
Whether to enable syslog output.

@item @code{pid-file} (default: @code{"/var/run/dropbear.pid"})
File name of the daemon's PID file.

@item @code{root-login?} (default: @code{#f})
Whether to allow @code{root} logins.

@item @code{allow-empty-passwords?} (default: @code{#f})
Whether to allow empty passwords.

@item @code{password-authentication?} (default: @code{#t})
Whether to enable password-based authentication.
@end table
@end deftp

@cindex AutoSSH
@defvar autossh-service-type
This is the type for the @uref{https://www.harding.motd.ca/autossh,
AutoSSH} program that runs a copy of @command{ssh} and monitors it,
restarting it as necessary should it die or stop passing traffic.
AutoSSH can be run manually from the command-line by passing arguments
to the binary @command{autossh} from the package @code{autossh}, but it
can also be run as a Guix service.  This latter use case is documented
here.

AutoSSH can be used to forward local traffic to a remote machine using
an SSH tunnel, and it respects the @file{~/.ssh/config} of the user it
is run as.

For example, to specify a service running autossh as the user
@code{pino} and forwarding all local connections to port @code{8081} to
@code{remote:8081} using an SSH tunnel, add this call to the operating
system's @code{services} field:

@lisp
(service autossh-service-type
         (autossh-configuration
          (user "pino")
          (ssh-options (list "-T" "-N" "-L" "8081:localhost:8081" "remote.net"))))
@end lisp
@end defvar

@deftp {Data Type} autossh-configuration
This data type represents the configuration of an AutoSSH service.

@table @asis

@item @code{user} (default @code{"autossh"})
The user as which the AutoSSH service is to be run.
This assumes that the specified user exists.

@item @code{poll} (default @code{600})
Specifies the connection poll time in seconds.

@item @code{first-poll} (default @code{#f})
Specifies how many seconds AutoSSH waits before the first connection
test.  After this first test, polling is resumed at the pace defined in
@code{poll}.  When set to @code{#f}, the first poll is not treated
specially and will also use the connection poll specified in
@code{poll}.

@item @code{gate-time} (default @code{30})
Specifies how many seconds an SSH connection must be active before it is
considered successful.

@item @code{log-level} (default @code{1})
The log level, corresponding to the levels used by syslog---so @code{0}
is the most silent while @code{7} is the chattiest.

@item @code{max-start} (default @code{#f})
The maximum number of times SSH may be (re)started before AutoSSH exits.
When set to @code{#f}, no maximum is configured and AutoSSH may restart indefinitely.

@item @code{message} (default @code{""})
The message to append to the echo message sent when testing connections.

@item @code{port} (default @code{"0"})
The ports used for monitoring the connection.  When set to @code{"0"},
monitoring is disabled.  When set to @code{"@var{n}"} where @var{n} is
a positive integer, ports @var{n} and @var{n}+1 are used for
monitoring the connection, such that port @var{n} is the base
monitoring port and @code{n+1} is the echo port.  When set to
@code{"@var{n}:@var{m}"} where @var{n} and @var{m} are positive
integers, the ports @var{n} and @var{m} are used for monitoring the
connection, such that port @var{n} is the base monitoring port and
@var{m} is the echo port.

@item @code{ssh-options} (default @code{'()})
The list of command-line arguments to pass to @command{ssh} when it is
run.  Options @option{-f} and @option{-M} are reserved for AutoSSH and
may cause undefined behaviour.

@end table
@end deftp

@cindex WebSSH
@defvar webssh-service-type
This is the type for the @uref{https://webssh.huashengdun.org/, WebSSH}
program that runs a web SSH client.  WebSSH can be run manually from the
command-line by passing arguments to the binary @command{wssh} from the
package @code{webssh}, but it can also be run as a Guix service.  This
latter use case is documented here.

For example, to specify a service running WebSSH on loopback interface
on port @code{8888} with reject policy with a list of allowed to
connection hosts, and NGINX as a reverse-proxy to this service listening
for HTTPS connection, add this call to the operating system's
@code{services} field:

@lisp
(service webssh-service-type
  (webssh-configuration (address "127.0.0.1")
                        (port 8888)
                        (policy 'reject)
                        (known-hosts '("localhost ecdsa-sha2-nistp256 AAAA…"
                                       "127.0.0.1 ecdsa-sha2-nistp256 AAAA…"))))

(service nginx-service-type
         (nginx-configuration
          (server-blocks
           (list
            (nginx-server-configuration
             (inherit %webssh-configuration-nginx)
             (server-name '("webssh.example.com"))
             (listen '("443 ssl"))
             (ssl-certificate (letsencrypt-certificate "webssh.example.com"))
             (ssl-certificate-key (letsencrypt-key "webssh.example.com"))
             (locations
              (cons (nginx-location-configuration
                     (uri "/.well-known")
                     (body '("root /var/www;")))
                    (nginx-server-configuration-locations %webssh-configuration-nginx))))))))
@end lisp
@end defvar

@deftp {Data Type} webssh-configuration
Data type representing the configuration for @code{webssh-service}.

@table @asis
@item @code{package} (default: @var{webssh})
@code{webssh} package to use.

@item @code{user-name} (default: @var{"webssh"})
User name or user ID that file transfers to and from that module should take
place.

@item @code{group-name} (default: @var{"webssh"})
Group name or group ID that will be used when accessing the module.

@item @code{address} (default: @var{#f})
IP address on which @command{webssh} listens for incoming connections.

@item @code{port} (default: @var{8888})
TCP port on which @command{webssh} listens for incoming connections.

@item @code{policy} (default: @var{#f})
Connection policy.  @var{reject} policy requires to specify @var{known-hosts}.

@item @code{known-hosts} (default: @var{'()})
List of hosts which allowed for SSH connection from @command{webssh}.

@item @code{log-file} (default: @file{"/var/log/webssh.log"})
Name of the file where @command{webssh} writes its log file.

@item @code{log-level} (default: @var{#f})
Logging level.

@end table
@end deftp

@defvar block-facebook-hosts-service-type
This service type adds a list of known Facebook hosts to the
@file{/etc/hosts} file.
(@pxref{Host Names,,, libc, The GNU C Library Reference Manual})
Each line contains an entry that maps a known server name of the Facebook
on-line service---e.g., @code{www.facebook.com}---to unroutable IPv4 and
IPv6 addresses.

This mechanism can prevent programs running locally, such as Web
browsers, from accessing Facebook.
@end defvar

The @code{(gnu services avahi)} provides the following definition.

@defvar avahi-service-type
This is the service that runs @command{avahi-daemon}, a system-wide
mDNS/DNS-SD responder that allows for service discovery and
``zero-configuration'' host name lookups (see @uref{https://avahi.org/}).
Its value must be an @code{avahi-configuration} record---see below.

This service extends the name service cache daemon (nscd) so that it can
resolve @code{.local} host names using
@uref{https://0pointer.de/lennart/projects/nss-mdns/, nss-mdns}.  @xref{Name
Service Switch}, for information on host name resolution.

Additionally, add the @var{avahi} package to the system profile so that
commands such as @command{avahi-browse} are directly usable.
@end defvar

@deftp {Data Type} avahi-configuration
Data type representation the configuration for Avahi.

@table @asis

@item @code{host-name} (default: @code{#f})
If different from @code{#f}, use that as the host name to
publish for this machine; otherwise, use the machine's actual host name.

@item @code{publish?} (default: @code{#t})
When true, allow host names and services to be published (broadcast) over the
network.

@item @code{publish-workstation?} (default: @code{#t})
When true, @command{avahi-daemon} publishes the machine's host name and IP
address via mDNS on the local network.  To view the host names published on
your local network, you can run:

@example
avahi-browse _workstation._tcp
@end example

@item @code{wide-area?} (default: @code{#f})
When true, DNS-SD over unicast DNS is enabled.

@item @code{ipv4?} (default: @code{#t})
@itemx @code{ipv6?} (default: @code{#t})
These fields determine whether to use IPv4/IPv6 sockets.

@item @code{domains-to-browse} (default: @code{'()})
This is a list of domains to browse.
@end table
@end deftp

@defvar openvswitch-service-type
This is the type of the @uref{https://www.openvswitch.org, Open vSwitch}
service, whose value should be an @code{openvswitch-configuration}
object.
@end defvar

@deftp {Data Type} openvswitch-configuration
Data type representing the configuration of Open vSwitch, a multilayer
virtual switch which is designed to enable massive network automation
through programmatic extension.

@table @asis
@item @code{package} (default: @var{openvswitch})
Package object of the Open vSwitch.

@end table
@end deftp

@defvar pagekite-service-type
This is the service type for the @uref{https://pagekite.net, PageKite} service,
a tunneling solution for making localhost servers publicly visible, even from
behind restrictive firewalls or NAT without forwarded ports.  The value for
this service type is a @code{pagekite-configuration} record.

Here's an example exposing the local HTTP and SSH daemons:

@lisp
(service pagekite-service-type
         (pagekite-configuration
           (kites '("http:@@kitename:localhost:80:@@kitesecret"
                    "raw/22:@@kitename:localhost:22:@@kitesecret"))
           (extra-file "/etc/pagekite.rc")))
@end lisp
@end defvar

@deftp {Data Type} pagekite-configuration
Data type representing the configuration of PageKite.

@table @asis
@item @code{package} (default: @var{pagekite})
Package object of PageKite.

@item @code{kitename} (default: @code{#f})
PageKite name for authenticating to the frontend server.

@item @code{kitesecret} (default: @code{#f})
Shared secret for authenticating to the frontend server.  You should probably
put this inside @code{extra-file} instead.

@item @code{frontend} (default: @code{#f})
Connect to the named PageKite frontend server instead of the
@uref{https://pagekite.net,,pagekite.net} service.

@item @code{kites} (default: @code{'("http:@@kitename:localhost:80:@@kitesecret")})
List of service kites to use.  Exposes HTTP on port 80 by default.  The format
is @code{proto:kitename:host:port:secret}.

@item @code{extra-file} (default: @code{#f})
Extra configuration file to read, which you are expected to create manually.
Use this to add additional options and manage shared secrets out-of-band.

@end table
@end deftp

@defvar yggdrasil-service-type
The service type for connecting to the @uref{https://yggdrasil-network.github.io/,
Yggdrasil network}, an early-stage implementation of a fully end-to-end
encrypted IPv6 network.

@quotation
Yggdrasil provides name-independent routing with cryptographically generated
addresses.  Static addressing means you can keep the same address as long as
you want, even if you move to a new location, or generate a new address (by
generating new keys) whenever you want.
@uref{https://yggdrasil-network.github.io/2018/07/28/addressing.html}
@end quotation

Pass it a value of @code{yggdrasil-configuration} to connect it to public
peers and/or local peers.

Here is an example using public peers and a static address.  The static
signing and encryption keys are defined in @file{/etc/yggdrasil-private.conf}
(the default value for @code{config-file}).

@lisp
;; part of the operating-system declaration
(service yggdrasil-service-type
              (yggdrasil-configuration
               (autoconf? #f) ;; use only the public peers
               (json-config
               ;; choose one from
               ;; https://github.com/yggdrasil-network/public-peers
                '((peers . #("tcp://1.2.3.4:1337"))))
               ;; /etc/yggdrasil-private.conf is the default value for config-file
               ))
@end lisp
@example
# sample content for /etc/yggdrasil-private.conf
@{
  # Your private key. DO NOT share this with anyone!
  PrivateKey: 5c750...
@}
@end example
@end defvar

@deftp {Data Type} yggdrasil-configuration
Data type representing the configuration of Yggdrasil.

@table @asis
@item @code{package} (default: @code{yggdrasil})
Package object of Yggdrasil.

@item @code{json-config} (default: @code{'()})
Contents of @file{/etc/yggdrasil.conf}.  Will be merged with
@file{/etc/yggdrasil-private.conf}.  Note that these settings are stored in
the Guix store, which is readable to all users. @strong{Do not store your
private keys in it}.  See the output of @code{yggdrasil -genconf} for a
quick overview of valid keys and their default values.

@item @code{autoconf?} (default: @code{#f})
Whether to use automatic mode.  Enabling it makes Yggdrasil use a dynamic IP
and peer with IPv6 neighbors.

@item @code{log-level} (default: @code{'info})
How much detail to include in logs.  Use @code{'debug} for more detail.

@item @code{log-to} (default: @code{'stdout})
Where to send logs.  By default, the service logs standard output to
@file{/var/log/yggdrasil.log}.  The alternative is @code{'syslog}, which
sends output to the running syslog service.

@item @code{config-file} (default: @code{"/etc/yggdrasil-private.conf"})
What HJSON file to load sensitive data from.  This is where private keys
should be stored, which are necessary to specify if you don't want a
randomized address after each restart.  Use @code{#f} to disable.  Options
defined in this file take precedence over @code{json-config}.  Use the output
of @code{yggdrasil -genconf} as a starting point.  To configure a static
address, delete everything except PrivateKey option.

@end table
@end deftp

@cindex IPFS
@defvar ipfs-service-type
The service type for connecting to the @uref{https://ipfs.io,IPFS network},
a global, versioned, peer-to-peer file system. Pass it a
@code{ipfs-configuration} to change the ports used for the gateway and API.

Here's an example configuration, using some non-standard ports:

@lisp
(service ipfs-service-type
         (ipfs-configuration
          (gateway "/ip4/127.0.0.1/tcp/8880")
          (api "/ip4/127.0.0.1/tcp/8881")))
@end lisp
@end defvar

@deftp {Data Type} ipfs-configuration
Data type representing the configuration of IPFS.

@table @asis
@item @code{package} (default: @code{go-ipfs})
Package object of IPFS.

@item @code{gateway} (default: @code{"/ip4/127.0.0.1/tcp/8082"})
Address of the gateway, in ‘multiaddress’ format.

@item @code{api} (default: @code{"/ip4/127.0.0.1/tcp/5001"})
Address of the API endpoint, in ‘multiaddress’ format.
@end table
@end deftp

@cindex keepalived
@defvar keepalived-service-type
This is the type for the @uref{https://www.keepalived.org/, Keepalived}
routing software, @command{keepalived}.  Its value must be an
@code{keepalived-configuration} record as in this example for master
machine:

@lisp
(service keepalived-service-type
         (keepalived-configuration
           (config-file (local-file "keepalived-master.conf"))))
@end lisp

where @file{keepalived-master.conf}:

@example
vrrp_instance my-group @{
  state MASTER
  interface enp9s0
  virtual_router_id 100
  priority 100
  unicast_peer @{ 10.0.0.2 @}
  virtual_ipaddress @{
    10.0.0.4/24
  @}
@}
@end example

and for backup machine:

@lisp
(service keepalived-service-type
         (keepalived-configuration
          (config-file (local-file "keepalived-backup.conf"))))
@end lisp

where @file{keepalived-backup.conf}:

@example
vrrp_instance my-group @{
  state BACKUP
  interface enp9s0
  virtual_router_id 100
  priority 99
  unicast_peer @{ 10.0.0.3 @}
  virtual_ipaddress @{
    10.0.0.4/24
  @}
@}
@end example
@end defvar

@node Unattended Upgrades
@subsection Unattended Upgrades

@cindex unattended upgrades
@cindex upgrades, unattended
Guix provides a service to perform @emph{unattended upgrades}:
periodically, the system automatically reconfigures itself from the
latest Guix.  Guix System has several properties that make unattended
upgrades safe:

@itemize
@item
upgrades are transactional (either the upgrade succeeds or it fails, but
you cannot end up with an ``in-between'' system state);
@item
the upgrade log is kept---you can view it with @command{guix system
list-generations}---and you can roll back to any previous generation,
should the upgraded system fail to behave as intended;
@item
channel code is authenticated so you know you can only run genuine code
(@pxref{Channels});
@item
@command{guix system reconfigure} prevents downgrades, which makes it
immune to @dfn{downgrade attacks}.
@end itemize

To set up unattended upgrades, add an instance of
@code{unattended-upgrade-service-type} like the one below to the list of
your operating system services:

@lisp
(service unattended-upgrade-service-type)
@end lisp

The defaults above set up weekly upgrades: every Sunday at midnight.
You do not need to provide the operating system configuration file: it
uses @file{/run/current-system/configuration.scm}, which ensures it
always uses your latest configuration---@pxref{provenance-service-type},
for more information about this file.

There are several things that can be configured, in particular the
periodicity and services (daemons) to be restarted upon completion.
When the upgrade is successful, the service takes care of deleting
system generations older that some threshold, as per @command{guix
system delete-generations}.  See the reference below for details.

To ensure that upgrades are actually happening, you can run
@command{guix system describe}.  To investigate upgrade failures, visit
the unattended upgrade log file (see below).

@defvar unattended-upgrade-service-type
This is the service type for unattended upgrades.  It sets up an mcron
job (@pxref{Scheduled Job Execution}) that runs @command{guix system
reconfigure} from the latest version of the specified channels.

Its value must be a @code{unattended-upgrade-configuration} record (see
below).
@end defvar

@deftp {Data Type} unattended-upgrade-configuration
This data type represents the configuration of the unattended upgrade
service.  The following fields are available:

@table @asis
@item @code{schedule} (default: @code{"30 01 * * 0"})
This is the schedule of upgrades, expressed as a gexp containing an
mcron job schedule (@pxref{Guile Syntax, mcron job specifications,,
mcron, GNU@tie{}mcron}).

@item @code{channels} (default: @code{#~%default-channels})
This gexp specifies the channels to use for the upgrade
(@pxref{Channels}).  By default, the tip of the official @code{guix}
channel is used.

@item @code{operating-system-file} (default: @code{"/run/current-system/configuration.scm"})
This field specifies the operating system configuration file to use.
The default is to reuse the config file of the current configuration.

There are cases, though, where referring to
@file{/run/current-system/configuration.scm} is not enough, for instance
because that file refers to extra files (SSH public keys, extra
configuration files, etc.) @i{via} @code{local-file} and similar
constructs.  For those cases, we recommend something along these lines:

@lisp
(unattended-upgrade-configuration
  (operating-system-file
    (file-append (local-file "." "config-dir" #:recursive? #t)
                 "/config.scm")))
@end lisp

The effect here is to import all of the current directory into the
store, and to refer to @file{config.scm} within that directory.
Therefore, uses of @code{local-file} within @file{config.scm} will work
as expected.  @xref{G-Expressions}, for information about
@code{local-file} and @code{file-append}.

@item @code{operating-system-expression} (default: @code{#f})
This field specifies an expression that evaluates to the operating
system to use for the upgrade.  If no value is provided the
@code{operating-system-file} field value is used.

@lisp
(unattended-upgrade-configuration
  (operating-system-expression
    #~(@@ (guix system install) installation-os)))
@end lisp

@item @code{services-to-restart} (default: @code{'(mcron)})
This field specifies the Shepherd services to restart when the upgrade
completes.

Those services are restarted right away upon completion, as with
@command{herd restart}, which ensures that the latest version is
running---remember that by default @command{guix system reconfigure}
only restarts services that are not currently running, which is
conservative: it minimizes disruption but leaves outdated services
running.

Use @command{herd status} to find out candidates for restarting.
@xref{Services}, for general information about services.  Common
services to restart would include @code{ntpd} and @code{ssh-daemon}.

By default, the @code{mcron} service is restarted.  This ensures that
the latest version of the unattended upgrade job will be used next time.

@item @code{system-expiration} (default: @code{(* 3 30 24 3600)})
This is the expiration time in seconds for system generations.  System
generations older that this amount of time are deleted with
@command{guix system delete-generations} when an upgrade completes.

@quotation Note
The unattended upgrade service does not run the garbage collector.  You
will probably want to set up your own mcron job to run @command{guix gc}
periodically.
@end quotation

@item @code{maximum-duration} (default: @code{3600})
Maximum duration in seconds for the upgrade; past that time, the upgrade
aborts.

This is primarily useful to ensure the upgrade does not end up
rebuilding or re-downloading ``the world''.

@item @code{log-file} (default: @code{"/var/log/unattended-upgrade.log"})
File where unattended upgrades are logged.
@end table
@end deftp

@node X Window
@subsection X Window

@cindex X11
@cindex X Window System
@cindex login manager
Support for the X Window graphical display system---specifically
Xorg---is provided by the @code{(gnu services xorg)} module.  Note that
there is no @code{xorg-service} procedure.  Instead, the X server is
started by the @dfn{login manager}, by default the GNOME Display Manager (GDM).

@cindex GDM
@cindex GNOME, login manager
@anchor{gdm}
GDM of course allows users to log in into window managers and desktop
environments other than GNOME; for those using GNOME, GDM is required for
features such as automatic screen locking.

@cindex window manager
To use X11, you must install at least one @dfn{window manager}---for
example the @code{windowmaker} or @code{openbox} packages---preferably
by adding it to the @code{packages} field of your operating system
definition (@pxref{operating-system Reference, system-wide packages}).

@anchor{wayland-gdm}
GDM also supports Wayland: it can itself use Wayland instead of X11 for
its user interface, and it can also start Wayland sessions.  The former is
required for the latter, to enable, set @code{wayland?} to @code{#t} in
@code{gdm-configuration}.

@defvar gdm-service-type
This is the type for the @uref{https://wiki.gnome.org/Projects/GDM/, GNOME
Desktop Manager} (GDM), a program that manages graphical display servers and
handles graphical user logins.  Its value must be a @code{gdm-configuration}
(see below).

@cindex session types
GDM looks for @dfn{session types} described by the @file{.desktop} files in
@file{/run/current-system/profile/share/xsessions} (for X11 sessions) and
@file{/run/current-system/profile/share/wayland-sessions} (for Wayland
sessions) and allows users to choose a session from the log-in screen.
Packages such as @code{gnome}, @code{xfce}, @code{i3} and @code{sway} provide
@file{.desktop} files; adding them to the system-wide set of packages
automatically makes them available at the log-in screen.

In addition, @file{~/.xsession} files are honored.  When available,
@file{~/.xsession} must be an executable that starts a window manager
and/or other X clients.
@end defvar

@deftp {Data Type} gdm-configuration
@table @asis
@item @code{auto-login?} (default: @code{#f})
@itemx @code{default-user} (default: @code{#f})
When @code{auto-login?} is false, GDM presents a log-in screen.

When @code{auto-login?} is true, GDM logs in directly as
@code{default-user}.

@item @code{auto-suspend?} (default @code{#t})
When true, GDM will automatically suspend to RAM when nobody is
physically connected.  When a machine is used via remote desktop or SSH,
this should be set to false to avoid GDM interrupting remote sessions or
rendering the machine unavailable.

@item @code{debug?} (default: @code{#f})
When true, GDM writes debug messages to its log.

@item @code{gnome-shell-assets} (default: ...)
List of GNOME Shell assets needed by GDM: icon theme, fonts, etc.

@item @code{xorg-configuration} (default: @code{(xorg-configuration)})
Configuration of the Xorg graphical server.

@item @code{x-session} (default: @code{(xinitrc)})
Script to run before starting a X session.

@item @code{xdmcp?} (default: @code{#f})
When true, enable the X Display Manager Control Protocol (XDMCP).  This
should only be enabled in trusted environments, as the protocol is not
secure.  When enabled, GDM listens for XDMCP queries on the UDP port
177.

@item @code{dbus-daemon} (default: @code{dbus-daemon-wrapper})
File name of the @code{dbus-daemon} executable.

@item @code{gdm} (default: @code{gdm})
The GDM package to use.

@item @code{wayland?} (default: @code{#f})
When true, enables Wayland in GDM, necessary to use Wayland sessions.

@item @code{wayland-session} (default: @code{gdm-wayland-session-wrapper})
The Wayland session wrapper to use, needed to setup the
environment.
@end table
@end deftp

@defvar slim-service-type
This is the type for the SLiM graphical login manager for X11.

Like GDM, SLiM looks for session types described by @file{.desktop} files and
allows users to choose a session from the log-in screen using @kbd{F1}.  It
also honors @file{~/.xsession} files.

Unlike GDM, SLiM does not spawn the user session on a different VT after
logging in, which means that you can only start one graphical session.  If you
want to be able to run multiple graphical sessions at the same time you have
to add multiple SLiM services to your system services.  The following example
shows how to replace the default GDM service with two SLiM services on tty7
and tty8.

@lisp
(use-modules (gnu services)
             (gnu services desktop)
             (gnu services xorg))

(operating-system
  ;; ...
  (services (cons* (service slim-service-type (slim-configuration
                                               (display ":0")
                                               (vt "vt7")))
                   (service slim-service-type (slim-configuration
                                               (display ":1")
                                               (vt "vt8")))
                   (modify-services %desktop-services
                     (delete gdm-service-type)))))
@end lisp

@end defvar

@deftp {Data Type} slim-configuration
Data type representing the configuration of @code{slim-service-type}.

@table @asis
@item @code{allow-empty-passwords?} (default: @code{#t})
Whether to allow logins with empty passwords.

@item @code{gnupg?} (default: @code{#f})
If enabled, @code{pam-gnupg} will attempt to automatically unlock the
user's GPG keys with the login password via @code{gpg-agent}.  The
keygrips of all keys to be unlocked should be written to
@file{~/.pam-gnupg}, and can be queried with @code{gpg -K
--with-keygrip}.  Presetting passphrases must be enabled by adding
@code{allow-preset-passphrase} in @file{~/.gnupg/gpg-agent.conf}.

@item @code{auto-login?} (default: @code{#f})
@itemx @code{default-user} (default: @code{""})
When @code{auto-login?} is false, SLiM presents a log-in screen.

When @code{auto-login?} is true, SLiM logs in directly as
@code{default-user}.

@item @code{theme} (default: @code{%default-slim-theme})
@itemx @code{theme-name} (default: @code{%default-slim-theme-name})
The graphical theme to use and its name.

@item @code{auto-login-session} (default: @code{#f})
If true, this must be the name of the executable to start as the default
session---e.g., @code{(file-append windowmaker "/bin/windowmaker")}.

If false, a session described by one of the available @file{.desktop}
files in @code{/run/current-system/profile} and @code{~/.guix-profile}
will be used.

@quotation Note
You must install at least one window manager in the system profile or in
your user profile.  Failing to do that, if @code{auto-login-session} is
false, you will be unable to log in.
@end quotation

@item @code{xorg-configuration} (default @code{(xorg-configuration)})
Configuration of the Xorg graphical server.

@item @code{display} (default @code{":0"})
The display on which to start the Xorg graphical server.

@item @code{vt} (default @code{"vt7"})
The VT on which to start the Xorg graphical server.

@item @code{xauth} (default: @code{xauth})
The XAuth package to use.

@item @code{shepherd} (default: @code{shepherd})
The Shepherd package used when invoking @command{halt} and
@command{reboot}.

@item @code{sessreg} (default: @code{sessreg})
The sessreg package used in order to register the session.

@item @code{slim} (default: @code{slim})
The SLiM package to use.
@end table
@end deftp

@defvar %default-theme
@defvarx %default-theme-name
The default SLiM theme and its name.
@end defvar


@cindex login manager
@cindex X11 login
@defvar sddm-service-type
This is the type of the service to run the
@uref{https://github.com/sddm/sddm,SDDM display manager}.  Its value
must be a @code{sddm-configuration} record (see below).

Here's an example use:

@lisp
(service sddm-service-type
         (sddm-configuration
           (auto-login-user "alice")
           (auto-login-session "xfce.desktop")))
@end lisp
@end defvar

@deftp {Data Type} sddm-configuration
This data type represents the configuration of the SDDM login manager.
The available fields are:

@table @asis
@item @code{sddm} (default: @code{sddm})
The SDDM package to use.

@quotation Note
sddm has Qt6 enabled by default. If you want to still use a Qt5 theme,
you need to set it to @code{sddm-qt5}.
@end quotation

@item @code{display-server} (default: "x11")
Select display server to use for the greeter.  Valid values are
@samp{"x11"} or @samp{"wayland"}.

@item @code{numlock} (default: "on")
Valid values are @samp{"on"}, @samp{"off"} or @samp{"none"}.

@item @code{halt-command} (default @code{#~(string-append #$shepherd "/sbin/halt")})
Command to run when halting.

@item @code{reboot-command} (default @code{#~(string-append #$shepherd "/sbin/reboot")})
Command to run when rebooting.

@item @code{theme} (default "maldives")
Theme to use.  Default themes provided by SDDM are @samp{"elarun"},
@samp{"maldives"} or @samp{"maya"}.

@item @code{themes-directory} (default "/run/current-system/profile/share/sddm/themes")
Directory to look for themes.

@item @code{faces-directory} (default "/run/current-system/profile/share/sddm/faces")
Directory to look for faces.

@item @code{default-path} (default "/run/current-system/profile/bin")
Default PATH to use.

@item @code{minimum-uid} (default: 1000)
Minimum UID displayed in SDDM and allowed for log-in.

@item @code{maximum-uid} (default: 2000)
Maximum UID to display in SDDM.

@item @code{remember-last-user?} (default #t)
Remember last user.

@item @code{remember-last-session?} (default #t)
Remember last session.

@item @code{hide-users} (default "")
Usernames to hide from SDDM greeter.

@item @code{hide-shells} (default @code{#~(string-append #$shadow "/sbin/nologin")})
Users with shells listed will be hidden from the SDDM greeter.

@item @code{session-command} (default @code{#~(string-append #$sddm "/share/sddm/scripts/wayland-session")})
Script to run before starting a wayland session.

@item @code{sessions-directory} (default "/run/current-system/profile/share/wayland-sessions")
Directory to look for desktop files starting wayland sessions.

@item @code{xorg-configuration} (default @code{(xorg-configuration)})
Configuration of the Xorg graphical server.

@item @code{xauth-path} (default @code{#~(string-append #$xauth "/bin/xauth")})
Path to xauth.

@item @code{xephyr-path} (default @code{#~(string-append #$xorg-server "/bin/Xephyr")})
Path to Xephyr.

@item @code{xdisplay-start} (default @code{#~(string-append #$sddm "/share/sddm/scripts/Xsetup")})
Script to run after starting xorg-server.

@item @code{xdisplay-stop} (default @code{#~(string-append #$sddm "/share/sddm/scripts/Xstop")})
Script to run before stopping xorg-server.

@item @code{xsession-command} (default: @code{xinitrc})
Script to run before starting a X session.

@item @code{xsessions-directory} (default: "/run/current-system/profile/share/xsessions")
Directory to look for desktop files starting X sessions.

@item @code{minimum-vt} (default: 7)
Minimum VT to use.

@item @code{auto-login-user} (default "")
User account that will be automatically logged in.
Setting this to the empty string disables auto-login.

@item @code{auto-login-session} (default "")
The @file{.desktop} file name to use as the auto-login session, or the empty string.

@item @code{relogin?} (default #f)
Relogin after logout.

@end table
@end deftp

@cindex lightdm, graphical login manager
@cindex display manager, lightdm
@anchor{lightdm}
@defvar lightdm-service-type
This is the type of the service to run the
@url{https://github.com/canonical/lightdm,LightDM display manager}.  Its
value must be a @code{lightdm-configuration} record, which is documented
below.  Among its distinguishing features are TigerVNC integration for
easily remoting your desktop as well as support for the XDMCP protocol,
which can be used by remote clients to start a session from the login
manager.

In its most basic form, it can be used simply as:

@lisp
(service lightdm-service-type)
@end lisp

A more elaborate example making use of the VNC capabilities and enabling
more features and verbose logs could look like:

@lisp
(service lightdm-service-type
         (lightdm-configuration
          (allow-empty-passwords? #t)
          (xdmcp? #t)
          (vnc-server? #t)
          (vnc-server-command
           (file-append tigervnc-server "/bin/Xvnc"
                        "  -SecurityTypes None"))
          (seats
           (list (lightdm-seat-configuration
                  (name "*")
                  (user-session "ratpoison"))))))
@end lisp
@end defvar

@c The LightDM service documentation can be auto-generated via the
@c 'generate-doc' procedure at the bottom of the (gnu services lightdm)
@c module.
@c %start of fragment
@deftp {Data Type} lightdm-configuration
Available @code{lightdm-configuration} fields are:

@table @asis
@item @code{lightdm} (default: @code{lightdm}) (type: file-like)
The lightdm package to use.

@item @code{allow-empty-passwords?} (default: @code{#f}) (type: boolean)
Whether users not having a password set can login.

@item @code{debug?} (default: @code{#f}) (type: boolean)
Enable verbose output.

@item @code{xorg-configuration} (type: xorg-configuration)
The default Xorg server configuration to use to generate the Xorg server
start script.  It can be refined per seat via the @code{xserver-command}
of the @code{<lightdm-seat-configuration>} record, if desired.

@item @code{greeters} (type: list-of-greeter-configurations)
The LightDM greeter configurations specifying the greeters to use.

@item @code{seats} (type: list-of-seat-configurations)
The seat configurations to use.  A LightDM seat is akin to a user.

@item @code{xdmcp?} (default: @code{#f}) (type: boolean)
Whether a XDMCP server should listen on port UDP 177.

@item @code{xdmcp-listen-address} (type: maybe-string)
The host or IP address the XDMCP server listens for incoming
connections.  When unspecified, listen on for any hosts/IP addresses.

@item @code{vnc-server?} (default: @code{#f}) (type: boolean)
Whether a VNC server is started.

@item @code{vnc-server-command} (type: file-like)
The Xvnc command to use for the VNC server, it's possible to provide
extra options not otherwise exposed along the command, for example to
disable security:

@lisp
(vnc-server-command (file-append tigervnc-server "/bin/Xvnc"
                                 " -SecurityTypes None" ))
@end lisp

Or to set a PasswordFile for the classic (unsecure) VncAuth
mechanism:

@lisp
(vnc-server-command (file-append tigervnc-server "/bin/Xvnc"
                                 " -PasswordFile /var/lib/lightdm/.vnc/passwd"))
@end lisp

The password file should be manually created using the
@command{vncpasswd} command.  Note that LightDM will create new sessions
for VNC users, which means they need to authenticate in the same way as
local users would.

@item @code{vnc-server-listen-address} (type: maybe-string)
The host or IP address the VNC server listens for incoming connections.
When unspecified, listen for any hosts/IP addresses.

@item @code{vnc-server-port} (default: @code{5900}) (type: number)
The TCP port the VNC server should listen to.

@item @code{extra-config} (default: @code{'()}) (type: list-of-strings)
Extra configuration values to append to the LightDM configuration file.

@end table
@end deftp


@c %end of fragment
@c %start of fragment

@deftp {Data Type} lightdm-gtk-greeter-configuration
Available @code{lightdm-gtk-greeter-configuration} fields are:

@table @asis
@item @code{lightdm-gtk-greeter} (default: @code{lightdm-gtk-greeter}) (type: file-like)
The lightdm-gtk-greeter package to use.

@item @code{assets} (default: @code{(adwaita-icon-theme gnome-themes-extra hicolor-icon-theme)}) (type: list-of-file-likes)
The list of packages complementing the greeter, such as package
providing icon themes.

@item @code{theme-name} (default: @code{"Adwaita"}) (type: string)
The name of the theme to use.

@item @code{icon-theme-name} (default: @code{"Adwaita"}) (type: string)
The name of the icon theme to use.

@item @code{cursor-theme-name} (default: @code{"Adwaita"}) (type: string)
The name of the cursor theme to use.

@item @code{cursor-theme-size} (default: @code{16}) (type: number)
The size to use for the cursor theme.

@item @code{allow-debugging?} (type: maybe-boolean)
Set to #t to enable debug log level.

@item @code{background} (type: file-like)
The background image to use.

@item @code{at-spi-enabled?} (default: @code{#f}) (type: boolean)
Enable accessibility support through the Assistive Technology Service
Provider Interface (AT-SPI).

@item @code{a11y-states} (default: @code{(contrast font keyboard reader)}) (type: list-of-a11y-states)
The accessibility features to enable, given as list of symbols.

@item @code{reader} (type: maybe-file-like)
The command to use to launch a screen reader.

@item @code{extra-config} (default: @code{'()}) (type: list-of-strings)
Extra configuration values to append to the LightDM GTK Greeter
configuration file.

@end table
@end deftp

@c %end of fragment
@c %start of fragment

@deftp {Data Type} lightdm-seat-configuration
Available @code{lightdm-seat-configuration} fields are:

@table @asis
@item @code{name} (type: seat-name)
The name of the seat.  An asterisk (*) can be used in the name to apply
the seat configuration to all the seat names it matches.

@item @code{user-session} (type: maybe-string)
The session to use by default.  The session name must be provided as a
lowercase string, such as @code{"gnome"}, @code{"ratpoison"}, etc.

@item @code{type} (default: @code{local}) (type: seat-type)
The type of the seat, either the @code{local} or @code{xremote} symbol.

@item @code{autologin-user} (type: maybe-string)
The username to automatically log in with by default.

@item @code{greeter-session} (default: @code{lightdm-gtk-greeter}) (type: greeter-session)
The greeter session to use, specified as a symbol.  Currently, only
@code{lightdm-gtk-greeter} is supported.

@item @code{xserver-command} (type: maybe-file-like)
The Xorg server command to run.

@item @code{session-wrapper} (type: file-like)
The xinitrc session wrapper to use.

@item @code{extra-config} (default: @code{'()}) (type: list-of-strings)
Extra configuration values to append to the seat configuration section.

@end table
@end deftp
@c %end of fragment


@cindex Xorg, configuration
@deftp {Data Type} xorg-configuration
This data type represents the configuration of the Xorg graphical
display server.  Note that there is no Xorg service; instead, the X
server is started by a ``display manager'' such as GDM, SDDM, LightDM or
SLiM@.  Thus, the configuration of these display managers aggregates an
@code{xorg-configuration} record.

@table @asis
@item @code{modules} (default: @code{%default-xorg-modules})
This is a list of @dfn{module packages} loaded by the Xorg
server---e.g., @code{xf86-video-vesa}, @code{xf86-input-keyboard}, and so on.

@item @code{fonts} (default: @code{%default-xorg-fonts})
This is a list of font directories to add to the server's @dfn{font path}.

@item @code{drivers} (default: @code{'()})
This must be either the empty list, in which case Xorg chooses a graphics
driver automatically, or a list of driver names that will be tried in this
order---e.g., @code{'("modesetting" "vesa")}.

@item @code{resolutions} (default: @code{'()})
When @code{resolutions} is the empty list, Xorg chooses an appropriate screen
resolution.  Otherwise, it must be a list of resolutions---e.g., @code{'((1024
768) (640 480))}.

@cindex keyboard layout, for Xorg
@cindex keymap, for Xorg
@item @code{keyboard-layout} (default: @code{#f})
If this is @code{#f}, Xorg uses the default keyboard layout---usually US
English (``qwerty'') for a 105-key PC keyboard.

Otherwise this must be a @code{keyboard-layout} object specifying the keyboard
layout in use when Xorg is running.  @xref{Keyboard Layout}, for more
information on how to specify the keyboard layout.

@item @code{extra-config} (default: @code{'()})
This is a list of strings or objects appended to the configuration file.  It
is used to pass extra text to be added verbatim to the configuration file.

@item @code{server} (default: @code{xorg-server})
This is the package providing the Xorg server.

@item @code{server-arguments} (default: @code{%default-xorg-server-arguments})
This is the list of command-line arguments to pass to the X server.  The
default is @code{-nolisten tcp}.
@end table
@end deftp

@deffn {Procedure} set-xorg-configuration config [login-manager-service-type]
Tell the log-in manager (of type @var{login-manager-service-type}) to use
@var{config}, an @code{<xorg-configuration>} record.

Since the Xorg configuration is embedded in the log-in manager's
configuration---e.g., @code{gdm-configuration}---this procedure provides a
shorthand to set the Xorg configuration.
@end deffn

@deffn {Procedure} xorg-start-command [config]
Return a @code{startx} script in which the modules, fonts, etc. specified
in @var{config}, are available.  The result should be used in place of
@code{startx}.

Usually the X server is started by a login manager.
@end deffn

@deffn {Procedure} xorg-start-command-xinit [config]
Return a @code{startx} script in which the modules, fonts,
etc. specified in @var{config} are available.  The result should be used
in place of @code{startx} and should be invoked by the user from a tty
after login.  Unlike @code{xorg-start-command}, this script calls xinit.
Therefore it works well when executed from a tty.  This script can be
set up as @code{startx} using @code{startx-command-service-type} or
@code{home-startx-command-service-type}.  If you are using a desktop
environment, you are unlikely to need this procedure.
@end deffn


@defvar screen-locker-service-type
Type for a service that adds a package for a screen locker or screen
saver to the set of privileged programs and/or add a PAM entry for it.  The
value for this service is a @code{<screen-locker-configuration>} object.

While the default behavior is to setup both a privileged program and PAM
entry, these two methods are redundant.  Screen locker programs may not
execute when PAM is configured and @code{setuid} is set on their
executable.  In this case, @code{using-setuid?} can be set to @code{#f}.

For example, to make XlockMore usable:

@lisp
(service screen-locker-service-type
         (screen-locker-configuration
           (name "xlock")
           (program (file-append xlockmore "/bin/xlock"))))
@end lisp

makes the good ol' XlockMore usable.

For example, swaylock fails to execute when compiled with PAM support
and setuid enabled.  One can thus disable setuid:

@lisp
(service screen-locker-service-type
         (screen-locker-configuration
           (name "swaylock")
           (program (file-append swaylock "/bin/swaylock"))
           (using-pam? #t)
           (using-setuid? #f)))
@end lisp

@end defvar

@deftp {Data Type} screen-locker-configuration
Available @code{screen-locker-configuration} fields are:

@table @asis
@item @code{name} (type: string)
Name of the screen locker.

@item @code{program} (type: file-like)
Path to the executable for the screen locker as a G-Expression.

@item @code{allow-empty-password?} (default: @code{#f}) (type: boolean)
Whether to allow empty passwords.

@item @code{using-pam?} (default: @code{#t}) (type: boolean)
Whether to setup PAM entry.

@item @code{using-setuid?} (default: @code{#t}) (type: boolean)
Whether to setup program as setuid binary.

@end table

@end deftp

@defvar startx-command-service-type
Add @command{startx} to the system profile putting it onto @env{PATH}.

The value for this service is a @code{<xorg-configuration>} object which
is passed to the @code{xorg-start-command-xinit} procedure producing the
@command{startx} used.  Default value is @code{(xorg-configuration)}.
@end defvar


@node Printing Services
@subsection Printing Services

@cindex printer support with CUPS
The @code{(gnu services cups)} module provides a Guix service definition
for the CUPS printing service.  To add printer support to a Guix
system, add a @code{cups-service} to the operating system definition:

@defvar cups-service-type
The service type for the CUPS print server.  Its value should be a valid
CUPS configuration (see below).  To use the default settings, simply
write:
@lisp
(service cups-service-type)
@end lisp
@end defvar

The CUPS configuration controls the basic things about your CUPS
installation: what interfaces it listens on, what to do if a print job
fails, how much logging to do, and so on.  To actually add a printer,
you have to visit the @url{http://localhost:631} URL, or use a tool such
as GNOME's printer configuration services.  By default, configuring a
CUPS service will generate a self-signed certificate if needed, for
secure connections to the print server.

Suppose you want to enable the Web interface of CUPS and also add
support for Epson printers @i{via} the @code{epson-inkjet-printer-escpr}
package and for HP printers @i{via} the @code{hplip-minimal} package.
You can do that directly, like this (you need to use the
@code{(gnu packages cups)} module):

@lisp
(service cups-service-type
         (cups-configuration
           (web-interface? #t)
           (extensions
             (list cups-filters epson-inkjet-printer-escpr hplip-minimal))))
@end lisp

@quotation Note
If you wish to use the Qt5 based GUI which comes with the hplip
package then it is suggested that you install the @code{hplip} package,
either in your OS configuration file or as your user.
@end quotation

The available configuration parameters follow.  Each parameter
definition is preceded by its type; for example, @samp{string-list foo}
indicates that the @code{foo} parameter should be specified as a list of
strings.  There is also a way to specify the configuration as a string,
if you have an old @code{cupsd.conf} file that you want to port over
from some other system; see the end for more details.

@c The following documentation was initially generated by
@c (generate-documentation) in (gnu services cups).  Manually maintained
@c documentation is better, so we shouldn't hesitate to edit below as
@c needed.  However if the change you want to make to this documentation
@c can be done in an automated way, it's probably easier to change
@c (generate-documentation) than to make it below and have to deal with
@c the churn as CUPS updates.


Available @code{cups-configuration} fields are:

@deftypevr {@code{cups-configuration} parameter} package cups
The CUPS package.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} package-list extensions (default: @code{(list brlaser cups-filters epson-inkjet-printer-escpr foomatic-filters hplip-minimal splix)})
Drivers and other extensions to the CUPS package.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} files-configuration files-configuration
Configuration of where to write logs, what directories to use for print
spools, and related privileged configuration parameters.

Available @code{files-configuration} fields are:

@deftypevr {@code{files-configuration} parameter} log-location access-log
Defines the access log filename.  Specifying a blank filename disables
access log generation.  The value @code{stderr} causes log entries to be
sent to the standard error file when the scheduler is running in the
foreground, or to the system log daemon when run in the background.  The
value @code{syslog} causes log entries to be sent to the system log
daemon.  The server name may be included in filenames using the string
@code{%s}, as in @code{/var/log/cups/%s-access_log}.

Defaults to @samp{"/var/log/cups/access_log"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} file-name cache-dir
Where CUPS should cache data.

Defaults to @samp{"/var/cache/cups"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} string config-file-perm
Specifies the permissions for all configuration files that the scheduler
writes.

Note that the permissions for the printers.conf file are currently
masked to only allow access from the scheduler user (typically root).
This is done because printer device URIs sometimes contain sensitive
authentication information that should not be generally known on the
system.  There is no way to disable this security feature.

Defaults to @samp{"0640"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} log-location error-log
Defines the error log filename.  Specifying a blank filename disables
error log generation.  The value @code{stderr} causes log entries to be
sent to the standard error file when the scheduler is running in the
foreground, or to the system log daemon when run in the background.  The
value @code{syslog} causes log entries to be sent to the system log
daemon.  The server name may be included in filenames using the string
@code{%s}, as in @code{/var/log/cups/%s-error_log}.

Defaults to @samp{"/var/log/cups/error_log"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} string fatal-errors
Specifies which errors are fatal, causing the scheduler to exit.  The
kind strings are:

@table @code
@item none
No errors are fatal.

@item all
All of the errors below are fatal.

@item browse
Browsing initialization errors are fatal, for example failed connections
to the DNS-SD daemon.

@item config
Configuration file syntax errors are fatal.

@item listen
Listen or Port errors are fatal, except for IPv6 failures on the
loopback or @code{any} addresses.

@item log
Log file creation or write errors are fatal.

@item permissions
Bad startup file permissions are fatal, for example shared TLS
certificate and key files with world-read permissions.
@end table

Defaults to @samp{"all -browse"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} boolean file-device?
Specifies whether the file pseudo-device can be used for new printer
queues.  The URI @uref{file:///dev/null} is always allowed.

Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} string group
Specifies the group name or ID that will be used when executing external
programs.

Defaults to @samp{"lp"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} string log-file-group
Specifies the group name or ID that will be used for log files.

Defaults to @samp{"lpadmin"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} string log-file-perm
Specifies the permissions for all log files that the scheduler writes.

Defaults to @samp{"0644"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} log-location page-log
Defines the page log filename.  Specifying a blank filename disables
page log generation.  The value @code{stderr} causes log entries to be
sent to the standard error file when the scheduler is running in the
foreground, or to the system log daemon when run in the background.  The
value @code{syslog} causes log entries to be sent to the system log
daemon.  The server name may be included in filenames using the string
@code{%s}, as in @code{/var/log/cups/%s-page_log}.

Defaults to @samp{"/var/log/cups/page_log"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} string remote-root
Specifies the username that is associated with unauthenticated accesses
by clients claiming to be the root user.  The default is @code{remroot}.

Defaults to @samp{"remroot"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} file-name request-root
Specifies the directory that contains print jobs and other HTTP request
data.

Defaults to @samp{"/var/spool/cups"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} sandboxing sandboxing
Specifies the level of security sandboxing that is applied to print
filters, backends, and other child processes of the scheduler; either
@code{relaxed} or @code{strict}.  This directive is currently only
used/supported on macOS.

Defaults to @samp{strict}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} file-name server-keychain
Specifies the location of TLS certificates and private keys.  CUPS will
look for public and private keys in this directory: @file{.crt} files
for PEM-encoded certificates and corresponding @file{.key} files for
PEM-encoded private keys.

Defaults to @samp{"/etc/cups/ssl"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} file-name server-root
Specifies the directory containing the server configuration files.

Defaults to @samp{"/etc/cups"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} boolean sync-on-close?
Specifies whether the scheduler calls fsync(2) after writing
configuration or state files.

Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} space-separated-string-list system-group
Specifies the group(s) to use for @code{@@SYSTEM} group authentication.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} file-name temp-dir
Specifies the directory where temporary files are stored.

Defaults to @samp{"/var/spool/cups/tmp"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} string user
Specifies the user name or ID that is used when running external
programs.

Defaults to @samp{"lp"}.
@end deftypevr

@deftypevr {@code{files-configuration} parameter} string set-env
Set the specified environment variable to be passed to child processes.

Defaults to @samp{"variable value"}.
@end deftypevr
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} access-log-level access-log-level
Specifies the logging level for the AccessLog file.  The @code{config}
level logs when printers and classes are added, deleted, or modified and
when configuration files are accessed or updated.  The @code{actions}
level logs when print jobs are submitted, held, released, modified, or
canceled, and any of the conditions for @code{config}.  The @code{all}
level logs all requests.

Defaults to @samp{actions}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} boolean auto-purge-jobs?
Specifies whether to purge job history data automatically when it is no
longer required for quotas.

Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} comma-separated-string-list browse-dns-sd-sub-types
Specifies a list of DNS-SD sub-types to advertise for each shared printer.

The default @samp{(list "_cups" "_print" "_universal")} tells clients
that CUPS sharing, IPP Everywhere, AirPrint, and Mopria are supported.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} browse-local-protocols browse-local-protocols
Specifies which protocols to use for local printer sharing.

Defaults to @samp{dnssd}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} boolean browse-web-if?
Specifies whether the CUPS web interface is advertised.

Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} boolean browsing?
Specifies whether shared printers are advertised.

Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} default-auth-type default-auth-type
Specifies the default type of authentication to use.

Defaults to @samp{Basic}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} default-encryption default-encryption
Specifies whether encryption will be used for authenticated requests.

Defaults to @samp{Required}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} string default-language
Specifies the default language to use for text and web content.

Defaults to @samp{"en"}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} string default-paper-size
Specifies the default paper size for new print queues.  @samp{"Auto"}
uses a locale-specific default, while @samp{"None"} specifies there is
no default paper size.  Specific size names are typically
@samp{"Letter"} or @samp{"A4"}.

Defaults to @samp{"Auto"}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} string default-policy
Specifies the default access policy to use.

Defaults to @samp{"default"}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} boolean default-shared?
Specifies whether local printers are shared by default.

Defaults to @samp{#t}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer dirty-clean-interval
Specifies the delay for updating of configuration and state files, in
seconds.  A value of 0 causes the update to happen as soon as possible,
typically within a few milliseconds.

Defaults to @samp{30}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} error-policy error-policy
Specifies what to do when an error occurs.  Possible values are
@code{abort-job}, which will discard the failed print job;
@code{retry-job}, which will retry the job at a later time;
@code{retry-current-job}, which retries the failed job immediately; and
@code{stop-printer}, which stops the printer.

Defaults to @samp{stop-printer}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer filter-limit
Specifies the maximum cost of filters that are run concurrently, which
can be used to minimize disk, memory, and CPU resource problems.  A
limit of 0 disables filter limiting.  An average print to a
non-PostScript printer needs a filter limit of about 200.  A PostScript
printer needs about half that (100).  Setting the limit below these
thresholds will effectively limit the scheduler to printing a single job
at any time.

Defaults to @samp{0}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer filter-nice
Specifies the scheduling priority of filters that are run to print a
job.  The nice value ranges from 0, the highest priority, to 19, the
lowest priority.

Defaults to @samp{0}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} host-name-lookups host-name-lookups
Specifies whether to do reverse lookups on connecting clients.  The
@code{double} setting causes @code{cupsd} to verify that the hostname
resolved from the address matches one of the addresses returned for that
hostname.  Double lookups also prevent clients with unregistered
addresses from connecting to your server.  Only set this option to
@code{#t} or @code{double} if absolutely required.

Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer job-kill-delay
Specifies the number of seconds to wait before killing the filters and
backend associated with a canceled or held job.

Defaults to @samp{30}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer job-retry-interval
Specifies the interval between retries of jobs in seconds.  This is
typically used for fax queues but can also be used with normal print
queues whose error policy is @code{retry-job} or
@code{retry-current-job}.

Defaults to @samp{30}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer job-retry-limit
Specifies the number of retries that are done for jobs.  This is
typically used for fax queues but can also be used with normal print
queues whose error policy is @code{retry-job} or
@code{retry-current-job}.

Defaults to @samp{5}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} boolean keep-alive?
Specifies whether to support HTTP keep-alive connections.

Defaults to @samp{#t}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer limit-request-body
Specifies the maximum size of print files, IPP requests, and HTML form
data.  A limit of 0 disables the limit check.

Defaults to @samp{0}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} multiline-string-list listen
Listens on the specified interfaces for connections.  Valid values are
of the form @var{address}:@var{port}, where @var{address} is either an
IPv6 address enclosed in brackets, an IPv4 address, or @code{*} to
indicate all addresses.  Values can also be file names of local UNIX
domain sockets.  The Listen directive is similar to the Port directive
but allows you to restrict access to specific interfaces or networks.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} location-access-control-list location-access-controls
Specifies a set of additional access controls.

Available @code{location-access-controls} fields are:

@deftypevr {@code{location-access-controls} parameter} file-name path
Specifies the URI path to which the access control applies.
@end deftypevr

@deftypevr {@code{location-access-controls} parameter} access-control-list access-controls
Access controls for all access to this path, in the same format as the
@code{access-controls} of @code{operation-access-control}.

Defaults to @samp{'()}.
@end deftypevr

@deftypevr {@code{location-access-controls} parameter} method-access-control-list method-access-controls
Access controls for method-specific access to this path.

Defaults to @samp{'()}.

Available @code{method-access-controls} fields are:

@deftypevr {@code{method-access-controls} parameter} boolean reverse?
If @code{#t}, apply access controls to all methods except the listed
methods.  Otherwise apply to only the listed methods.

Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{method-access-controls} parameter} method-list methods
Methods to which this access control applies.

Defaults to @samp{'()}.
@end deftypevr

@deftypevr {@code{method-access-controls} parameter} access-control-list access-controls
Access control directives, as a list of strings.  Each string should be
one directive, such as @samp{"Order allow,deny"}.

Defaults to @samp{'()}.
@end deftypevr
@end deftypevr
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer log-debug-history
Specifies the number of debugging messages that are retained for logging
if an error occurs in a print job.  Debug messages are logged regardless
of the LogLevel setting.

Defaults to @samp{100}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} log-level log-level
Specifies the level of logging for the ErrorLog file.  The value
@code{none} stops all logging while @code{debug2} logs everything.

Defaults to @samp{info}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} log-time-format log-time-format
Specifies the format of the date and time in the log files.  The value
@code{standard} logs whole seconds while @code{usecs} logs microseconds.

Defaults to @samp{standard}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer max-clients
Specifies the maximum number of simultaneous clients that are allowed by
the scheduler.

Defaults to @samp{100}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer max-clients-per-host
Specifies the maximum number of simultaneous clients that are allowed
from a single address.

Defaults to @samp{100}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer max-copies
Specifies the maximum number of copies that a user can print of each
job.

Defaults to @samp{9999}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer max-hold-time
Specifies the maximum time a job may remain in the @code{indefinite}
hold state before it is canceled.  A value of 0 disables cancellation of
held jobs.

Defaults to @samp{0}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer max-jobs
Specifies the maximum number of simultaneous jobs that are allowed.  Set
to 0 to allow an unlimited number of jobs.

Defaults to @samp{500}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer max-jobs-per-printer
Specifies the maximum number of simultaneous jobs that are allowed per
printer.  A value of 0 allows up to @code{max-jobs} per printer.

Defaults to @samp{0}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer max-jobs-per-user
Specifies the maximum number of simultaneous jobs that are allowed per
user.  A value of 0 allows up to @code{max-jobs} per user.

Defaults to @samp{0}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer max-job-time
Specifies the maximum time a job may take to print before it is
canceled, in seconds.  Set to 0 to disable cancellation of ``stuck'' jobs.

Defaults to @samp{10800}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer max-log-size
Specifies the maximum size of the log files before they are rotated, in
bytes.  The value 0 disables log rotation.

Defaults to @samp{1048576}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer max-subscriptions
Specifies the maximum number of simultaneous event subscriptions that are
allowed.  Set to @samp{0} to allow an unlimited number of subscriptions.

Defaults to @samp{0}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer max-subscriptions-per-job
Specifies the maximum number of simultaneous event subscriptions that are
allowed per job.  A value of @samp{0} allows up to @code{max-subscriptions}
per job.

Defaults to @samp{0}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer max-subscriptions-per-printer
Specifies the maximum number of simultaneous event subscriptions that are
allowed per printer.  A value of @samp{0} allows up to @code{max-subscriptions}
per printer.

Defaults to @samp{0}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer max-subscriptions-per-user
Specifies the maximum number of simultaneous event subscriptions that are
allowed per user.  A value of @samp{0} allows up to @code{max-subscriptions}
per user.

Defaults to @samp{0}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer multiple-operation-timeout
Specifies the maximum amount of time to allow between files in a
multiple file print job, in seconds.

Defaults to @samp{900}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} environment-variables environment-variables
Passes the specified environment variable(s) to child processes; a list
of strings.

Defaults to @samp{'()}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} policy-configuration-list policies
Specifies named access control policies.

Available @code{policy-configuration} fields are:

@deftypevr {@code{policy-configuration} parameter} string name
Name of the policy.
@end deftypevr

@deftypevr {@code{policy-configuration} parameter} string job-private-access
Specifies an access list for a job's private values.  @code{@@ACL} maps
to the printer's requesting-user-name-allowed or
requesting-user-name-denied values.  @code{@@OWNER} maps to the job's
owner.  @code{@@SYSTEM} maps to the groups listed for the
@code{system-group} field of the @code{files-configuration},
which is reified into the @code{cups-files.conf(5)} file.  Other
possible elements of the access list include specific user names, and
@code{@@@var{group}} to indicate members of a specific group.  The
access list may also be simply @code{all} or @code{default}.

Defaults to @samp{"@@OWNER @@SYSTEM"}.
@end deftypevr

@deftypevr {@code{policy-configuration} parameter} string job-private-values
Specifies the list of job values to make private, or @code{all},
@code{default}, or @code{none}.

Defaults to @samp{"job-name job-originating-host-name
job-originating-user-name phone"}.
@end deftypevr

@deftypevr {@code{policy-configuration} parameter} string subscription-private-access
Specifies an access list for a subscription's private values.
@code{@@ACL} maps to the printer's requesting-user-name-allowed or
requesting-user-name-denied values.  @code{@@OWNER} maps to the job's
owner.  @code{@@SYSTEM} maps to the groups listed for the
@code{system-group} field of the @code{files-configuration},
which is reified into the @code{cups-files.conf(5)} file.  Other
possible elements of the access list include specific user names, and
@code{@@@var{group}} to indicate members of a specific group.  The
access list may also be simply @code{all} or @code{default}.

Defaults to @samp{"@@OWNER @@SYSTEM"}.
@end deftypevr

@deftypevr {@code{policy-configuration} parameter} string subscription-private-values
Specifies the list of job values to make private, or @code{all},
@code{default}, or @code{none}.

Defaults to @samp{"notify-events notify-pull-method notify-recipient-uri
notify-subscriber-user-name notify-user-data"}.
@end deftypevr

@deftypevr {@code{policy-configuration} parameter} operation-access-control-list access-controls
Access control by IPP operation.

Defaults to @samp{'()}.
@end deftypevr
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} boolean-or-non-negative-integer preserve-job-files
Specifies whether job files (documents) are preserved after a job is
printed.  If a numeric value is specified, job files are preserved for
the indicated number of seconds after printing.  Otherwise a boolean
value applies indefinitely.

Defaults to @samp{86400}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} boolean-or-non-negative-integer preserve-job-history
Specifies whether the job history is preserved after a job is printed.
If a numeric value is specified, the job history is preserved for the
indicated number of seconds after printing.  If @code{#t}, the job
history is preserved until the MaxJobs limit is reached.

Defaults to @samp{#t}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} comma-separated-string-list-or-#f ready-paper-sizes
Specifies a list of potential paper sizes that are reported as ready,
that is: loaded.  The actual list will contain only the sizes that each
printer supports.

The default value of @code{#f} is a special case: CUPS will use
@samp{(list \"Letter\" \"Legal\" \"Tabloid\" \"4x6\" \"Env10\")}
if the default paper size is \"Letter\", and
@samp{(list \"A3\" \"A4\" \"A5\" \"A6\" \"EnvDL\")} otherwise.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer reload-timeout
Specifies the amount of time to wait for job completion before
restarting the scheduler.

Defaults to @samp{30}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} string server-admin
Specifies the email address of the server administrator.

Defaults to @samp{"root@@localhost.localdomain"}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} host-name-list-or-* server-alias
The ServerAlias directive is used for HTTP Host header validation when
clients connect to the scheduler from external interfaces.  Using the
special name @code{*} can expose your system to known browser-based DNS
rebinding attacks, even when accessing sites through a firewall.  If the
auto-discovery of alternate names does not work, we recommend listing
each alternate name with a ServerAlias directive instead of using
@code{*}.

Defaults to @samp{*}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} string server-name
Specifies the fully-qualified host name of the server.

Defaults to @samp{"localhost"}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} server-tokens server-tokens
Specifies what information is included in the Server header of HTTP
responses.  @code{None} disables the Server header.  @code{ProductOnly}
reports @code{CUPS}.  @code{Major} reports @code{CUPS 2}.  @code{Minor}
reports @code{CUPS 2.0}.  @code{Minimal} reports @code{CUPS 2.0.0}.
@code{OS} reports @code{CUPS 2.0.0 (@var{uname})} where @var{uname} is
the output of the @code{uname} command.  @code{Full} reports @code{CUPS
2.0.0 (@var{uname}) IPP/2.0}.

Defaults to @samp{Minimal}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} multiline-string-list ssl-listen
Listens on the specified interfaces for encrypted connections.  Valid
values are of the form @var{address}:@var{port}, where @var{address} is
either an IPv6 address enclosed in brackets, an IPv4 address, or
@code{*} to indicate all addresses.

Defaults to @samp{'()}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} ssl-options ssl-options
Sets encryption options.  By default, CUPS only supports encryption
using TLS v1.0 or higher using known secure cipher suites.  Security is
reduced when @code{Allow} options are used, and enhanced when @code{Deny}
options are used.  The @code{AllowRC4} option enables the 128-bit RC4 cipher
suites, which are required for some older clients.  The @code{AllowSSL3} option
enables SSL v3.0, which is required for some older clients that do not support
TLS v1.0.  The @code{DenyCBC} option disables all CBC cipher suites.  The
@code{DenyTLS1.0} option disables TLS v1.0 support - this sets the minimum
protocol version to TLS v1.1.

Defaults to @samp{'()}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} boolean strict-conformance?
Specifies whether the scheduler requires clients to strictly adhere to
the IPP specifications.

Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{cups-configuration} parameter} non-negative-integer timeout
Specifies the HTTP request timeout, in seconds.

Defaults to @samp{900}.

@end deftypevr

@deftypevr {@code{cups-configuration} parameter} boolean web-interface?
Specifies whether the web interface is enabled.

Defaults to @samp{#f}.
@end deftypevr

At this point you're probably thinking ``oh dear, Guix manual, I like
you but you can stop already with the configuration options''.  Indeed.
However, one more point: it could be that you have an existing
@code{cupsd.conf} that you want to use.  In that case, you can pass an
@code{opaque-cups-configuration} as the configuration of a
@code{cups-service-type}.

Available @code{opaque-cups-configuration} fields are:

@deftypevr {@code{opaque-cups-configuration} parameter} package cups
The CUPS package.
@end deftypevr

@deftypevr {@code{opaque-cups-configuration} parameter} string cupsd.conf
The contents of the @code{cupsd.conf}, as a string.
@end deftypevr

@deftypevr {@code{opaque-cups-configuration} parameter} string cups-files.conf
The contents of the @code{cups-files.conf} file, as a string.
@end deftypevr

For example, if your @code{cupsd.conf} and @code{cups-files.conf} are in
strings of the same name, you could instantiate a CUPS service like
this:

@lisp
(service cups-service-type
         (opaque-cups-configuration
           (cupsd.conf cupsd.conf)
           (cups-files.conf cups-files.conf)))
@end lisp


@node Desktop Services
@subsection Desktop Services

The @code{(gnu services desktop)} module provides services that are
usually useful in the context of a ``desktop'' setup---that is, on a
machine running a graphical display server, possibly with graphical user
interfaces, etc.  It also defines services that provide specific desktop
environments like GNOME, Xfce or MATE.

To simplify things, the module defines a variable containing the set of
services that users typically expect on a machine with a graphical
environment and networking:

@defvar %desktop-services
This is a list of services that builds upon @code{%base-services} and
adds or adjusts services for a typical ``desktop'' setup.

In particular, it adds a graphical login manager (@pxref{X Window,
@code{gdm-service-type}}), screen lockers, a network management tool
(@pxref{Networking Services, @code{network-manager-service-type}}) with modem
support (@pxref{Networking Services, @code{modem-manager-service-type}}),
energy and color management services, the @code{elogind} login and seat
manager, the Polkit privilege service, the GeoClue location service, the
AccountsService daemon that allows authorized users change system passwords,
a NTP client (@pxref{Networking Services}) and the Avahi daemon.
@end defvar

The @code{%desktop-services} variable can be used as the @code{services}
field of an @code{operating-system} declaration (@pxref{operating-system
Reference, @code{services}}).

Additionally, the following procedures add one (or more!) desktop
environments to a system.

@itemize
@item @code{gnome-desktop-service-type} adds GNOME,
@item @code{plasma-desktop-service-type} adds KDE Plasma,
@item @code{enlightenment-desktop-service-type} adds Enlightenment,
@item @code{lxqt-desktop-service-type} adds LXQt,
@item @code{mate-desktop-service-type} adds MATE, and
@item @code{xfce-desktop-service} adds Xfce.
@end itemize

These service types add ``metapackages'' such as @code{gnome} or
@code{plasma} to the system profile, but most of them also set up other useful
services that mere packages can't do.

For example, they may elevate privileges on a limited number of
special-purpose system interfaces and programs.  This allows backlight
adjustment helpers, power management utilities, screen lockers, and
other integrated functionality to work as expected.

The desktop environments in Guix use the Xorg display server by
default.  If you'd like to use the newer display server protocol
called Wayland, you need to enable Wayland support in GDM
(@pxref{wayland-gdm}).  Another solution is to use the
@code{sddm-service} instead of GDM as the graphical login manager.
You should then select the ``GNOME (Wayland)'' session in SDDM@.
Alternatively you can also try starting GNOME on Wayland manually from a
TTY with the command ``XDG_SESSION_TYPE=wayland exec dbus-run-session
gnome-session``.  Currently only GNOME has support for Wayland.

@defvar gnome-desktop-service-type
This is the type of the service that adds the @uref{https://www.gnome.org,
GNOME} desktop environment.  Its value is a @code{gnome-desktop-configuration}
object (see below).

This service adds the @code{gnome} package to the system profile, and extends
polkit with the actions from @code{gnome-settings-daemon}.
@end defvar

@deftp {Data Type} gnome-desktop-configuration
Configuration record for the GNOME desktop environment.
Available @code{gnome-desktop-configuration} fields are:

@table @asis
@item @code{core-services} (type: list-of-packages)
A list of packages that the GNOME Shell and applications may rely on.

@item @code{shell} (type: list-of-packages)
A list of packages that constitute the GNOME Shell, without
applications.

@item @code{utilities} (type: list-of-packages)
A list of packages that serve as applications to use on top of the GNOME Shell.

@item @code{gnome} (type: maybe-package)
This field used to be the only configuration point and specified
a GNOME meta-package to install system-wide.  Since the meta-package
itself provides neither sources nor the actual packages and is only
used to propagate them, this field is deprecated.

@item @code{extra-packages} (type: list-of-packages)
A list of GNOME-adjacent packages to also include.  This field is
intended for users to add their own packages to their GNOME experience.
Note, that it already includes some packages that are considered
essential by some (most?) GNOME users.

@item @code{udev-ignorelist} (default: @code{()}) (type: list-of-strings)
A list of regular expressions denoting udev rules or hardware file names
provided by any package that should not be installed.  By default, every
udev rule and hardware file specified by any package referenced in the
other fields are installed.

@item @code{polkit-ignorelist} (default: @code{()}) (type: list-of-strings)
A list of regular expressions denoting polkit rules provided by any
package that should not be installed.  By default, every polkit rule
added by any package referenced in the other fields are installed.

@end table
@end deftp

@defvar plasma-desktop-service-type
This is the type of the service that adds the @uref{https://kde.org/plasma-desktop/,
Plasma} desktop environment.  Its value is a @code{plasma-desktop-configuration}
object (see below).

This service adds the @code{plasma} package to the system profile.
@end defvar

@deftp {Data Type} plasma-desktop-configuration
Configuration record for the Plasma desktop environment.

@table @asis
@item @code{plasma} (default: @code{plasma})
The Plasma package to use.
@end table
@end deftp

@defvar xfce-desktop-service-type
This is the type of a service to run the @uref{Xfce, https://xfce.org/}
desktop environment.  Its value is an @code{xfce-desktop-configuration} object
(see below).

This service adds the @code{xfce} package to the system profile, and
extends polkit with the ability for @code{thunar} to manipulate the file
system as root from within a user session, after the user has authenticated
with the administrator's password.

Note that @code{xfce4-panel} and its plugin packages should be installed in
the same profile to ensure compatibility.  When using this service, you should
add extra plugins (@code{xfce4-whiskermenu-plugin},
@code{xfce4-weather-plugin}, etc.) to the @code{packages} field of your
@code{operating-system}.
@end defvar

@deftp {Data Type} xfce-desktop-configuration
Configuration record for the Xfce desktop environment.

@table @asis
@item @code{xfce} (default: @code{xfce})
The Xfce package to use.
@end table
@end deftp

@defvar mate-desktop-service-type
This is the type of the service that runs the @uref{https://mate-desktop.org/,
MATE desktop environment}.  Its value is a @code{mate-desktop-configuration}
object (see below).

This service adds the @code{mate} package to the system
profile, and extends polkit with the actions from
@code{mate-settings-daemon}.
@end defvar

@deftp {Data Type} mate-desktop-configuration
Configuration record for the MATE desktop environment.

@table @asis
@item @code{mate} (default: @code{mate})
The MATE package to use.
@end table
@end deftp

@defvar lxqt-desktop-service-type
This is the type of the service that runs the @uref{https://lxqt-project.org,
LXQt desktop environment}.  Its value is a @code{lxqt-desktop-configuration}
object (see below).

This service adds the @code{lxqt} package to the system
profile.
@end defvar

@deftp {Data Type} lxqt-desktop-configuration
Configuration record for the LXQt desktop environment.

@table @asis
@item @code{lxqt} (default: @code{lxqt})
The LXQT package to use.
@end table
@end deftp

@defvar sugar-desktop-service-type
This is the type of the service that runs the
@uref{https://www.sugarlabs.org, Sugar desktop environment}.  Its value
is a @code{sugar-desktop-configuration} object (see below).

This service adds the @code{sugar} package to the system profile, as
well as any selected Sugar activities.  By default it only includes a
minimal set of activities.
@end defvar

@deftp {Data Type} sugar-desktop-configuration
Configuration record for the Sugar desktop environment.

@table @asis
@item @code{sugar} (default: @code{sugar})
The Sugar package to use.
@item @code{gobject-introspection} (default: @code{gobject-introspection})
The @code{gobject-introspection} package to use.  This package is used
to access libraries installed as dependencies of Sugar activities.
@item @code{activities} (default: @code{(list sugar-help-activity)})
A list of Sugar activities to install.
@end table
@end deftp

The following example configures the Sugar desktop environment with a
number of useful activities:

@lisp
(use-modules (gnu))
(use-package-modules sugar)
(use-service-modules desktop)
(operating-system
  ...
  (services (cons* (service sugar-desktop-service-type
                            (sugar-desktop-configuration
                              (activities (list sugar-browse-activity
                                                sugar-help-activity
                                                sugar-jukebox-activity
                                                sugar-typing-turtle-activity))))
                   %desktop-services))
  ...)
@end lisp

@defvar enlightenment-desktop-service-type
Return a service that adds the @code{enlightenment} package to the system
profile, and extends dbus with actions from @code{efl}.
@end defvar

@deftp {Data Type} enlightenment-desktop-service-configuration
@table @asis
@item @code{enlightenment} (default: @code{enlightenment})
The enlightenment package to use.
@end table
@end deftp

Because the GNOME, Xfce and MATE desktop services pull in so many packages,
the default @code{%desktop-services} variable doesn't include any of
them by default.  To add GNOME, Xfce or MATE, just @code{cons} them onto
@code{%desktop-services} in the @code{services} field of your
@code{operating-system}:

@lisp
(use-modules (gnu))
(use-service-modules desktop)
(operating-system
  ...
  ;; cons* adds items to the list given as its last argument.
  (services (cons* (service gnome-desktop-service-type)
                   (service xfce-desktop-service)
                   %desktop-services))
  ...)
@end lisp

These desktop environments will then be available as options in the
graphical login window.

The actual service definitions included in @code{%desktop-services} and
provided by @code{(gnu services dbus)} and @code{(gnu services desktop)}
are described below.

@defvar dbus-root-service-type
Type for a service that runs the D-Bus ``system bus''.
@footnote{@uref{https://dbus.freedesktop.org/, D-Bus} is an inter-process
communication facility.  Its system bus is used to allow system services
to communicate and to be notified of system-wide events.}

The value for this service type is a @code{<dbus-configuration>} record.
@end defvar

@deftp {Data Type} dbus-configuration
Data type representing the configuration for @code{dbus-root-service-type}.

@table @asis
@item @code{dbus} (default: @code{dbus}) (type: file-like)
Package object for dbus.

@item @code{services} (default: @code{'()}) (type: list)
List of packages that provide an @file{etc/dbus-1/system.d} directory
containing additional D-Bus configuration and policy files.
For example, to allow avahi-daemon to use the system bus, @var{services}
must be equal to @code{(list avahi)}.

@item @code{verbose?} (default: @code{#f}) (type: boolean)
When @code{#t}, D-Bus is launched with environment variable
@samp{DBUS_VERBOSE} set to @samp{1}.  A verbose-enabled D-Bus package
such as @code{dbus-verbose} should be provided to @var{dbus} in this
scenario. The verbose output is logged to
@file{/var/log/dbus-daemon.log}.

@end table
@end deftp

@subsubheading Elogind

@uref{https://github.com/elogind/elogind, Elogind} is a login and seat
management daemon that also handles most system-level power events for a
computer, for example suspending the system when a lid is closed, or
shutting it down when the power button is pressed.

It also provides a D-Bus interface that can be used to know which users
are logged in, know what kind of sessions they have open, suspend the
system, inhibit system suspend, reboot the system, and other tasks.

@defvar elogind-service-type
Type of the service that runs @command{elogind}, a login and
seat management daemon.  The value for this service is a
@code{<elogind-configuration>} object.
@end defvar

@c TODO: field descriptions. This is best done by refactoring
@c elogind-configuration to use define-configuration which embeds the
@c descriptions in the code and then use configuration->documentation.
@deftp {Data Type} elogind-configuration
Data type representing the configuration of @command{elogind}.

@table @asis
@item @code{elogind} (default: @code{elogind}) (type: file-like)
...

@item @code{kill-user-processes?} (default: @code{#f}) (type: boolean)
...

@item @code{kill-only-users} (default: @code{'()}) (type: list)
...

@item @code{kill-exclude-users} (default: @code{'("root")}) (type: list-of-string)
...

@item @code{inhibit-delay-max-seconds} (default: @code{5}) (type: integer)
...

@item @code{handle-power-key} (default: @code{'poweroff}) (type: symbol)
...

@item @code{handle-suspend-key} (default: @code{'suspend}) (type: symbol)
...

@item @code{handle-hibernate-key} (default: @code{'hibernate}) (type: symbol)
...

@item @code{handle-lid-switch} (default: @code{'suspend}) (type: symbol)
...

@item @code{handle-lid-switch-docked} (default: @code{'ignore}) (type: symbol)
...

@item @code{handle-lid-switch-external-power} (default: @code{*unspecified*}) (type: symbol)
...

@item @code{power-key-ignore-inhibited?} (default: @code{#f}) (type: boolean)
...

@item @code{suspend-key-ignore-inhibited?} (default: @code{#f}) (type: boolean)
...

@item @code{hibernate-key-ignore-inhibited?} (default: @code{#f}) (type: boolean)
...

@item @code{lid-switch-ignore-inhibited?} (default: @code{#t}) (type: boolean)
...

@item @code{holdoff-timeout-seconds} (default: @code{30}) (type: integer)
...

@item @code{idle-action} (default: @code{'ignore}) (type: symbol)
...

@item @code{idle-action-seconds} (default: @code{(* 30 60)}) (type: integer)
...

@item @code{runtime-directory-size-percent} (default: @code{10}) (type: integer)
...

@item @code{runtime-directory-size} (default: @code{#f}) (type: integer)
...

@item @code{remove-ipc?} (default: @code{#t}) (type: boolean)
...

@item @code{suspend-state} (default: @code{'("mem" "standby" "freeze")}) (type: list)
...

@item @code{suspend-mode} (default: @code{'()}) (type: list)
...

@item @code{hibernate-state} (default: @code{'("disk")}) (type: list)
...

@item @code{hibernate-mode} (default: @code{'("platform" "shutdown")}) (type: list)
...

@item @code{hybrid-sleep-state} (default: @code{'("disk")}) (type: list)
...

@item @code{hybrid-sleep-mode} (default: @code{'("suspend" "platform" "shutdown")}) (type: list)
...

@item @code{hibernate-delay-seconds} (default: @code{*unspecified*}) (type: integer)
...

@item @code{suspend-estimation-seconds} (default: @code{*unspecified*}) (type: integer)
...

@end table
@end deftp

@defvar accountsservice-service-type
Type for the service that runs AccountsService, a system service that can
list available accounts, change their passwords, and so on.
AccountsService integrates with PolicyKit to enable unprivileged users
to acquire the capability to modify their system configuration.
See @url{https://www.freedesktop.org/wiki/Software/AccountsService/,
AccountsService} for more information.

The value for this service is a file-like object, by default it is
set to @code{accountsservice} (the package object for AccountsService).
@end defvar

@defvar polkit-service-type
Type for the service that runs the
@url{https://www.freedesktop.org/wiki/Software/polkit/, Polkit privilege
management service}, which allows system administrators to grant access to
privileged operations in a structured way.  By querying the Polkit service, a
privileged system component can know when it should grant additional
capabilities to ordinary users.  For example, an ordinary user can be granted
the capability to suspend the system if the user is logged in locally.

The value for this service is a @code{<polkit-configuration>} object.
@end defvar

@c TODO: Document <polkit-configuration>, preferably by refactoring this to use
@c       define-configuration and generating documentation from it.

@defvar polkit-wheel-service
Service that adds the @code{wheel} group as admins to the Polkit
service.  This makes it so that users in the @code{wheel} group are queried
for their own passwords when performing administrative actions instead of
@code{root}'s, similar to the behaviour used by @code{sudo}.
@end defvar

@defvar upower-service-type
Service that runs @uref{https://upower.freedesktop.org/, @command{upowerd}}, a
system-wide monitor for power consumption and battery levels, with the given
configuration settings.

It implements the @code{org.freedesktop.UPower} D-Bus interface, and is
notably used by GNOME.
@end defvar

@deftp {Data Type} upower-configuration
Data type representation the configuration for UPower.

@table @asis

@item @code{upower} (default: @var{upower})
Package to use for @code{upower}.

@item @code{watts-up-pro?} (default: @code{#f})
Enable the Watts Up Pro device.

@item @code{poll-batteries?} (default: @code{#t})
Enable polling the kernel for battery level changes.

@item @code{ignore-lid?} (default: @code{#f})
Ignore the lid state, this can be useful if it's incorrect on a device.

@item @code{use-percentage-for-policy?} (default: @code{#t})
Whether to use a policy based on battery percentage rather than on
estimated time left.  A policy based on battery percentage is usually
more reliable.

@item @code{percentage-low} (default: @code{20})
When @code{use-percentage-for-policy?} is @code{#t}, this sets the percentage
at which the battery is considered low.

@item @code{percentage-critical} (default: @code{5})
When @code{use-percentage-for-policy?} is @code{#t}, this sets the percentage
at which the battery is considered critical.

@item @code{percentage-action} (default: @code{2})
When @code{use-percentage-for-policy?} is @code{#t}, this sets the percentage
at which action will be taken.

@item @code{time-low} (default: @code{1200})
When @code{use-time-for-policy?} is @code{#f}, this sets the time remaining in
seconds at which the battery is considered low.

@item @code{time-critical} (default: @code{300})
When @code{use-time-for-policy?} is @code{#f}, this sets the time remaining in
seconds at which the battery is considered critical.

@item @code{time-action} (default: @code{120})
When @code{use-time-for-policy?} is @code{#f}, this sets the time remaining in
seconds at which action will be taken.

@item @code{critical-power-action} (default: @code{'hybrid-sleep})
The action taken when @code{percentage-action} or @code{time-action} is
reached (depending on the configuration of @code{use-percentage-for-policy?}).

Possible values are:

@itemize @bullet
@item
@code{'power-off}

@item
@code{'hibernate}

@item
@code{'hybrid-sleep}.
@end itemize

@end table
@end deftp

@defvar udisks-service-type
Type for the service that runs
@uref{https://udisks.freedesktop.org/docs/latest/, UDisks},
a @dfn{disk management} daemon that provides user interfaces
with notifications and ways to mount/unmount disks.  Programs that talk
to UDisks include the @command{udisksctl} command, part of UDisks, and
GNOME Disks.  Note that Udisks relies on the @command{mount} command, so
it will only be able to use the file-system utilities installed in the
system profile.  For example if you want to be able to mount NTFS
file-systems in read and write fashion, you'll need to have
@code{ntfs-3g} installed system-wide.

The value for this service is a @code{<udisks-configuration>} object.
@end defvar

@deftp {Data Type} udisks-configuration
Data type representing the configuration for @code{udisks-service-type}.

@table @asis
@item @code{udisks} (default: @code{udisks}) (type: file-like)
Package object for UDisks.

@end table
@end deftp

@defvar gvfs-service-type
Type for the service that provides virtual file systems for GIO
applicaitons, which enables support for @code{trash:///}, @code{ftp://},
@code{sftp://} and many other location schemas in file managers like
Nautilus (GNOME Files) and Thunar.

The value for this service is a @code{<gvfs-configuration>} object.
@end defvar

@deftp {Data Type} gvfs-configuration
Data type representing the configuration for @code{gvfs-service-type}.

@table @asis
@item @code{gvfs} (default: @code{gvfs}) (type: file-like)
Package object for GVfs.

@end table
@end deftp

@defvar colord-service-type
This is the type of the service that runs @command{colord}, a system
service with a D-Bus
interface to manage the color profiles of input and output devices such as
screens and scanners.  It is notably used by the GNOME Color Manager graphical
tool.  See @uref{https://www.freedesktop.org/software/colord/, the colord web
site} for more information.
@end defvar

@cindex scanner access
@defvar sane-service-type
This service provides access to scanners @i{via}
@uref{http://www.sane-project.org, SANE} by installing the necessary
udev rules.  It is included in @code{%desktop-services} (@pxref{Desktop
Services}) and relies by default on @code{sane-backends-minimal} package
(see below) for hardware support.
@end defvar

@defvar sane-backends-minimal
The default package which the @code{sane-service-type} installs.  It
supports many recent scanners.
@end defvar

@defvar sane-backends
This package includes support for all scanners that
@code{sane-backends-minimal} supports, plus older Hewlett-Packard
scanners supported by @code{hplip} package.  In order to use this on
a system which relies on @code{%desktop-services}, you may use
@code{modify-services} (@pxref{Service Reference,
@code{modify-services}}) as illustrated below:

@lisp
(use-modules (gnu))
(use-service-modules
  @dots{}
  desktop)
(use-package-modules
  @dots{}
  scanner)

(define %my-desktop-services
  ;; List of desktop services that supports a broader range of scanners.
  (modify-services %desktop-services
    (sane-service-type _ => sane-backends)))

(operating-system
  @dots{}
  (services %my-desktop-services))
@end lisp
@end defvar

@deffn {Procedure} geoclue-application name [#:allowed? #t] [#:system? #f] [#:users '()]
Return a configuration allowing an application to access GeoClue
location data.  @var{name} is the Desktop ID of the application, without
the @code{.desktop} part.  If @var{allowed?} is true, the application
will have access to location information by default.  The boolean
@var{system?}  value indicates whether an application is a system component
or not.  Finally @var{users} is a list of UIDs of all users for which
this application is allowed location info access.  An empty users list
means that all users are allowed.
@end deffn

@defvar %standard-geoclue-applications
The standard list of well-known GeoClue application configurations,
granting authority to the GNOME date-and-time utility to ask for the
current location in order to set the time zone, and allowing the
IceCat and Epiphany web browsers to request location information.
IceCat and Epiphany both query the user before allowing a web page to
know the user's location.
@end defvar

@defvar geoclue-service-type
Type for the service that runs the
@url{https://wiki.freedesktop.org/www/Software/GeoClue/, GeoClue}
location service.  This service provides a D-Bus interface to allow
applications to request access to a user's physical location, and
optionally to add information to online location databases.

The value for this service is a @code{<geoclue-configuration>} object.
@end defvar

@c TODO: Document <geoclue-configuration>, preferably by refactoring this to use
@c       define-configuration and generating documentation from it.

@defvar bluetooth-service-type
This is the type for the @uref{https://bluez.org/, Linux Bluetooth Protocol
Stack} (BlueZ) system, which generates the @file{/etc/bluetooth/main.conf}
configuration file.  The value for this type is a @command{bluetooth-configuration}
record as in this example:

@lisp
(service bluetooth-service-type)
@end lisp

See below for details about @code{bluetooth-configuration}.
@end defvar

@deftp {Data Type} bluetooth-configuration
Data type representing the configuration for @code{bluetooth-service}.

@table @asis
@item @code{bluez} (default: @code{bluez})
@code{bluez} package to use.

@item @code{name} (default: @code{"BlueZ"})
Default adapter name.

@item @code{class} (default: @code{#x000000})
Default device class. Only the major and minor device class bits are considered.

@item @code{discoverable-timeout} (default: @code{180})
How long to stay in discoverable mode before going back to non-discoverable. The
value is in seconds.

@item @code{always-pairable?} (default: @code{#f})
Always allow pairing even if there are no agents registered.

@item @code{pairable-timeout} (default: @code{0})
How long to stay in pairable mode before going back to non-discoverable. The
value is in seconds.

@item @code{device-id} (default: @code{#f})
Use vendor id source (assigner), vendor, product and version information for
DID profile support. The values are separated by ":" and @var{assigner}, @var{VID},
@var{PID} and @var{version}.

Possible values are:

@itemize @bullet
@item
@code{#f} to disable it,

@item
@code{"assigner:1234:5678:abcd"}, where @var{assigner} is either @code{usb} (default)
or @code{bluetooth}.

@end itemize

@item @code{reverse-service-discovery?} (default: @code{#t})
Do reverse service discovery for previously unknown devices that connect to
us. For BR/EDR this option is really only needed for qualification since the
BITE tester doesn't like us doing reverse SDP for some test cases, for LE
this disables the GATT client functionally so it can be used in system which
can only operate as peripheral.

@item @code{name-resolving?} (default: @code{#t})
Enable name resolving after inquiry. Set it to @code{#f} if you don't need
remote devices name and want shorter discovery cycle.

@item @code{debug-keys?} (default: @code{#f})
Enable runtime persistency of debug link keys. Default is false which makes
debug link keys valid only for the duration of the connection that they were
created for.

@item @code{controller-mode} (default: @code{'dual})
Restricts all controllers to the specified transport. @code{'dual} means both
BR/EDR and LE are enabled (if supported by the hardware).

Possible values are:

@itemize @bullet
@item
@code{'dual}

@item
@code{'bredr}

@item
@code{'le}

@end itemize

@item @code{multi-profile} (default: @code{'off})
Enables Multi Profile Specification support. This allows to specify if system
supports only Multiple Profiles Single Device (MPSD) configuration or both
Multiple Profiles Single Device (MPSD) and Multiple Profiles Multiple Devices
(MPMD) configurations.

Possible values are:

@itemize @bullet
@item
@code{'off}

@item
@code{'single}

@item
@code{'multiple}

@end itemize

@item @code{fast-connectable?} (default: @code{#f})
Permanently enables the Fast Connectable setting for adapters that support
it. When enabled other devices can connect faster to us, however the
tradeoff is increased power consumptions. This feature will fully work only
on kernel version 4.1 and newer.

@item @code{privacy} (default: @code{'off})
Default privacy settings.

@itemize @bullet
@item
@code{'off}: Disable local privacy

@item
@code{'network/on}: A device will only accept advertising packets from peer
devices that contain private addresses. It may not be compatible with some
legacy devices since it requires the use of RPA(s) all the time

@item
@code{'device}: A device in device privacy mode is only concerned about the
privacy of the device and will accept advertising packets from peer devices
that contain their Identity Address as well as ones that contain a private
address, even if the peer device has distributed its IRK in the past

@end itemize

and additionally, if @var{controller-mode} is set to @code{'dual}:

@itemize @bullet
@item
@code{'limited-network}: Apply Limited Discoverable Mode to advertising, which
follows the same policy as to BR/EDR that publishes the identity address when
discoverable, and Network Privacy Mode for scanning

@item
@code{'limited-device}: Apply Limited Discoverable Mode to advertising, which
follows the same policy as to BR/EDR that publishes the identity address when
discoverable, and Device Privacy Mode for scanning.

@end itemize

@item @code{just-works-repairing} (default: @code{'never})
Specify the policy to the JUST-WORKS repairing initiated by peer.

Possible values:
@itemize @bullet
@item
@code{'never}

@item
@code{'confirm}

@item
@code{'always}

@end itemize

@item @code{temporary-timeout} (default: @code{30})
How long to keep temporary devices around. The value is in seconds. @code{0}
disables the timer completely.

@item @code{refresh-discovery?} (default: @code{#t})
Enables the device to issue an SDP request to update known services when
profile is connected.

@item @code{experimental} (default: @code{#f})
Enables experimental features and interfaces, alternatively a list of UUIDs
can be given.

Possible values:

@itemize @bullet
@item
@code{#t}

@item
@code{#f}

@item
@code{(list (uuid <uuid-1>) (uuid <uuid-2>) ...)}.
@end itemize

List of possible UUIDs:
@itemize @bullet
@item
@code{d4992530-b9ec-469f-ab01-6c481c47da1c}: BlueZ Experimental Debug,

@item
@code{671b10b5-42c0-4696-9227-eb28d1b049d6}: BlueZ Experimental Simultaneous Central and Peripheral,

@item
@code{15c0a148-c273-11ea-b3de-0242ac130004}: BlueZ Experimental LL privacy,

@item
@code{330859bc-7506-492d-9370-9a6f0614037f}: BlueZ Experimental Bluetooth Quality Report,

@item
@code{a6695ace-ee7f-4fb9-881a-5fac66c629af}: BlueZ Experimental Offload Codecs.
@end itemize

@item @code{remote-name-request-retry-delay} (default: @code{300})
The duration to avoid retrying to resolve a peer's name, if the previous
try failed.

@item @code{page-scan-type} (default: @code{#f})
BR/EDR Page scan activity type.

@item @code{page-scan-interval} (default: @code{#f})
BR/EDR Page scan activity interval.

@item @code{page-scan-window} (default: @code{#f})
BR/EDR Page scan activity window.

@item @code{inquiry-scan-type} (default: @code{#f})
BR/EDR Inquiry scan activity type.

@item @code{inquiry-scan-interval} (default: @code{#f})
BR/EDR Inquiry scan activity interval.

@item @code{inquiry-scan-window} (default: @code{#f})
BR/EDR Inquiry scan activity window.

@item @code{link-supervision-timeout} (default: @code{#f})
BR/EDR Link supervision timeout.

@item @code{page-timeout} (default: @code{#f})
BR/EDR Page timeout.

@item @code{min-sniff-interval} (default: @code{#f})
BR/EDR minimum sniff interval.

@item @code{max-sniff-interval} (default: @code{#f})
BR/EDR maximum sniff interval.

@item @code{min-advertisement-interval} (default: @code{#f})
LE minimum advertisement interval (used for legacy advertisement only).

@item @code{max-advertisement-interval} (default: @code{#f})
LE maximum advertisement interval (used for legacy advertisement only).

@item @code{multi-advertisement-rotation-interval} (default: @code{#f})
LE multiple advertisement rotation interval.

@item @code{scan-interval-auto-connect} (default: @code{#f})
LE scanning interval used for passive scanning supporting auto connect.

@item @code{scan-window-auto-connect} (default: @code{#f})
LE scanning window used for passive scanning supporting auto connect.

@item @code{scan-interval-suspend} (default: @code{#f})
LE scanning interval used for active scanning supporting wake from suspend.

@item @code{scan-window-suspend} (default: @code{#f})
LE scanning window used for active scanning supporting wake from suspend.

@item @code{scan-interval-discovery} (default: @code{#f})
LE scanning interval used for active scanning supporting discovery.

@item @code{scan-window-discovery} (default: @code{#f})
LE scanning window used for active scanning supporting discovery.

@item @code{scan-interval-adv-monitor} (default: @code{#f})
LE scanning interval used for passive scanning supporting the advertisement monitor APIs.

@item @code{scan-window-adv-monitor} (default: @code{#f})
LE scanning window used for passive scanning supporting the advertisement monitor APIs.

@item @code{scan-interval-connect} (default: @code{#f})
LE scanning interval used for connection establishment.

@item @code{scan-window-connect} (default: @code{#f})
LE scanning window used for connection establishment.

@item @code{min-connection-interval} (default: @code{#f})
LE default minimum connection interval. This value is superseded by any specific
value provided via the Load Connection Parameters interface.

@item @code{max-connection-interval} (default: @code{#f})
LE default maximum connection interval. This value is superseded by any specific
value provided via the Load Connection Parameters interface.

@item @code{connection-latency} (default: @code{#f})
LE default connection latency. This value is superseded by any specific
value provided via the Load Connection Parameters interface.

@item @code{connection-supervision-timeout} (default: @code{#f})
LE default connection supervision timeout. This value is superseded by any specific
value provided via the Load Connection Parameters interface.

@item @code{autoconnect-timeout} (default: @code{#f})
LE default autoconnect timeout. This value is superseded by any specific
value provided via the Load Connection Parameters interface.

@item @code{adv-mon-allowlist-scan-duration} (default: @code{300})
Allowlist scan duration during interleaving scan. Only used when scanning for ADV
monitors. The units are msec.

@item @code{adv-mon-no-filter-scan-duration} (default: @code{500})
No filter scan duration during interleaving scan. Only used when scanning for ADV
monitors. The units are msec.

@item @code{enable-adv-mon-interleave-scan?} (default: @code{#t})
Enable/Disable Advertisement Monitor interleave scan for power saving.

@item @code{cache} (default: @code{'always})
GATT attribute cache.

Possible values are:
@itemize @bullet
@item
@code{'always}: Always cache attributes even for devices not paired, this is
recommended as it is best for interoperability, with more consistent
reconnection times and enables proper tracking of notifications for all
devices

@item
@code{'yes}: Only cache attributes of paired devices

@item
@code{'no}: Never cache attributes.
@end itemize

@item @code{key-size} (default: @code{0})
Minimum required Encryption Key Size for accessing secured characteristics.

Possible values are:
@itemize @bullet
@item
@code{0}: Don't care

@item
@code{7 <= N <= 16}
@end itemize

@item @code{exchange-mtu} (default: @code{517})
Exchange MTU size. Possible values are:

@itemize @bullet
@item
@code{23 <= N <= 517}
@end itemize

@item @code{att-channels} (default: @code{3})
Number of ATT channels. Possible values are:

@itemize @bullet
@item
@code{1}: Disables EATT

@item
@code{2 <= N <= 5}
@end itemize

@item @code{session-mode} (default: @code{'basic})
AVDTP L2CAP signalling channel mode.

Possible values are:

@itemize @bullet
@item
@code{'basic}: Use L2CAP basic mode

@item
@code{'ertm}: Use L2CAP enhanced retransmission mode.
@end itemize

@item @code{stream-mode} (default: @code{'basic})
AVDTP L2CAP transport channel mode.

Possible values are:

@itemize @bullet
@item
@code{'basic}: Use L2CAP basic mode

@item
@code{'streaming}: Use L2CAP streaming mode.
@end itemize

@item @code{reconnect-uuids} (default: @code{'()})
The ReconnectUUIDs defines the set of remote services that should try
to be reconnected to in case of a link loss (link supervision
timeout). The policy plugin should contain a sane set of values by
default, but this list can be overridden here. By setting the list to
empty the reconnection feature gets disabled.

Possible values:

@itemize @bullet
@item
@code{'()}

@item
@code{(list (uuid <uuid-1>) (uuid <uuid-2>) ...)}.
@end itemize

@item @code{reconnect-attempts} (default: @code{7})
Defines the number of attempts to reconnect after a link lost. Setting
the value to 0 disables reconnecting feature.

@item @code{reconnect-intervals} (default: @code{'(1 2 4 8 16 32 64)})
Defines a list of intervals in seconds to use in between attempts. If
the number of attempts defined in @var{reconnect-attempts} is bigger than
the list of intervals the last interval is repeated until the last attempt.

@item @code{auto-enable?} (default: @code{#f})
Defines option to enable all controllers when they are found. This includes
adapters present on start as well as adapters that are plugged in later on.

@item @code{resume-delay} (default: @code{2})
Audio devices that were disconnected due to suspend will be reconnected on
resume. @var{resume-delay} determines the delay between when the controller
resumes from suspend and a connection attempt is made. A longer delay is
better for better co-existence with Wi-Fi. The value is in seconds.

@item @code{rssi-sampling-period} (default: @code{#xFF})
Default RSSI Sampling Period. This is used when a client registers an
advertisement monitor and leaves the RSSISamplingPeriod unset.

Possible values are:
@itemize @bullet
@item
@code{#x0}: Report all advertisements

@item
@code{N = #xXX}: Report advertisements every N x 100 msec (range: #x01 to #xFE)

@item
@code{#xFF}: Report only one advertisement per device during monitoring period.
@end itemize

@end table
@end deftp

@defvar gnome-keyring-service-type
This is the type of the service that adds the
@uref{https://wiki.gnome.org/Projects/GnomeKeyring, GNOME Keyring}.  Its
value is a @code{gnome-keyring-configuration} object (see below).

This service adds the @code{gnome-keyring} package to the system profile
and extends PAM with entries using @code{pam_gnome_keyring.so}, unlocking
a user's login keyring when they log in or setting its password with passwd.
@end defvar

@deftp {Data Type} gnome-keyring-configuration
Configuration record for the GNOME Keyring service.

@table @asis
@item @code{keyring} (default: @code{gnome-keyring})
The GNOME keyring package to use.

@item @code{pam-services}
A list of @code{(@var{service} . @var{kind})} pairs denoting PAM
services to extend, where @var{service} is the name of an existing
service to extend and @var{kind} is one of @code{login} or
@code{passwd}.

If @code{login} is given, it adds an optional
@code{pam_gnome_keyring.so} to the auth block without arguments and to
the session block with @code{auto_start}.  If @code{passwd} is given, it
adds an optional @code{pam_gnome_keyring.so} to the password block
without arguments.

By default, this field contains ``gdm-password'' with the value @code{login}
and ``passwd'' is with the value @code{passwd}.
@end table
@end deftp

@defvar seatd-service-type
@uref{https://sr.ht/~kennylevinsen/seatd/, seatd} is a minimal seat
management daemon.

Seat management takes care of mediating access to shared devices (graphics,
input), without requiring the applications needing access to be root.

@lisp
(append
  (list
   ;; make sure seatd is running
   (service seatd-service-type))

  ;; normally one would want %base-services
  %base-services)

@end lisp

@code{seatd} operates over a UNIX domain socket, with @code{libseat}
providing the client side of the protocol.  Applications that acquire
access to the shared resources via @code{seatd} (e.g. @code{sway})
need to be able to talk to this socket.
This can be achieved by adding the user they run under to the group
owning @code{seatd}'s socket (usually ``seat''), like so:

@lisp
(user-account
  (name "alice")
  (group "users")
  (supplementary-groups '("wheel"   ; allow use of sudo, etc.
                          "seat"    ; seat management
                          "audio"   ; sound card
                          "video"   ; video devices such as webcams
                          "cdrom")) ; the good ol' CD-ROM
  (comment "Bob's sister"))
@end lisp

Depending on your setup, you will have to not only add regular users,
but also system users to this group.  For instance, some greetd greeters
require graphics and therefore also need to negotiate with seatd.

@end defvar

@deftp {Data Type} seatd-configuration
Configuration record for the seatd daemon service.

@table @asis
@item @code{seatd} (default: @code{seatd})
The seatd package to use.

@item @code{group} (default: @samp{"seat"})
Group to own the seatd socket.

@item @code{socket} (default: @samp{"/run/seatd.sock"})
Where to create the seatd socket.

@item @code{logfile} (default: @samp{"/var/log/seatd.log"})
Log file to write to.

@item @code{loglevel} (default: @samp{"error"})
Log level to output logs. Possible values: @samp{"silent"}, @samp{"error"},
@samp{"info"} and @samp{"debug"}.

@end table
@end deftp


@node Sound Services
@subsection Sound Services

@cindex sound support
@cindex ALSA
@cindex PulseAudio, sound support

The @code{(gnu services sound)} module provides a service to configure the
Advanced Linux Sound Architecture (ALSA) system, which makes PulseAudio the
preferred ALSA output driver.

@defvar alsa-service-type
This is the type for the @uref{https://alsa-project.org/, Advanced Linux Sound
Architecture} (ALSA) system, which generates the @file{/etc/asound.conf}
configuration file.  The value for this type is a @command{alsa-configuration}
record as in this example:

@lisp
(service alsa-service-type)
@end lisp

See below for details about @code{alsa-configuration}.
@end defvar

@deftp {Data Type} alsa-configuration
Data type representing the configuration for @code{alsa-service}.

@table @asis
@item @code{alsa-plugins} (default: @var{alsa-plugins})
@code{alsa-plugins} package to use.

@item @code{pulseaudio?} (default: @var{#t})
Whether ALSA applications should transparently be made to use the
@uref{https://www.pulseaudio.org/, PulseAudio} sound server.

Using PulseAudio allows you to run several sound-producing applications
at the same time and to individual control them @i{via}
@command{pavucontrol}, among other things.

@item @code{extra-options} (default: @var{""})
String to append to the @file{/etc/asound.conf} file.

@end table
@end deftp

Individual users who want to override the system configuration of ALSA can do
it with the @file{~/.asoundrc} file:

@example
# In guix, we have to specify the absolute path for plugins.
pcm_type.jack @{
  lib "/home/alice/.guix-profile/lib/alsa-lib/libasound_module_pcm_jack.so"
@}

# Routing ALSA to jack:
# <http://jackaudio.org/faq/routing_alsa.html>.
pcm.rawjack @{
  type jack
  playback_ports @{
    0 system:playback_1
    1 system:playback_2
  @}

  capture_ports @{
    0 system:capture_1
    1 system:capture_2
  @}
@}

pcm.!default @{
  type plug
  slave @{
    pcm "rawjack"
  @}
@}
@end example

See @uref{https://www.alsa-project.org/main/index.php/Asoundrc} for the
details.

@defvar pulseaudio-service-type
This is the type for the  @uref{https://www.pulseaudio.org/, PulseAudio}
sound server.  It exists to allow system overrides of the default settings
via @code{pulseaudio-configuration}, see below.

@quotation Warning
This service overrides per-user configuration files.  If you want
PulseAudio to honor configuration files in @file{~/.config/pulse} you
have to unset the environment variables @env{PULSE_CONFIG} and
@env{PULSE_CLIENTCONFIG} in your @file{~/.bash_profile}.
@end quotation

@quotation Warning
This service on its own does not ensure, that the @code{pulseaudio} package
exists on your machine.  It merely adds configuration files for it, as
detailed below.  In the (admittedly unlikely) case, that you find yourself
without a @code{pulseaudio} package, consider enabling it through the
@code{alsa-service-type} above.
@end quotation
@end defvar

@deftp {Data Type} pulseaudio-configuration
Data type representing the configuration for @code{pulseaudio-service}.

@table @asis
@item @code{client-conf} (default: @code{'()})
List of settings to set in @file{client.conf}.
Accepts a list of strings or symbol-value pairs.  A string will be
inserted as-is with a newline added.  A pair will be formatted as
``key = value'', again with a newline added.

@item @code{daemon-conf} (default: @code{'((flat-volumes . no))})
List of settings to set in @file{daemon.conf}, formatted just like
@var{client-conf}.

@item @code{script-file} (default: @code{(file-append pulseaudio "/etc/pulse/default.pa")})
Script file to use as @file{default.pa}.  In case the
@code{extra-script-files} field below is used, an @code{.include}
directive pointing to @file{/etc/pulse/default.pa.d} is appended to the
provided script.

@item @code{extra-script-files} (default: @code{'()})
A list of file-like objects defining extra PulseAudio scripts to run at
the initialization of the @command{pulseaudio} daemon, after the main
@code{script-file}.  The scripts are deployed to the
@file{/etc/pulse/default.pa.d} directory; they should have the
@samp{.pa} file name extension.  For a reference of the available
commands, refer to @command{man pulse-cli-syntax}.

@item @code{system-script-file} (default: @code{(file-append pulseaudio "/etc/pulse/system.pa")})
Script file to use as @file{system.pa}.
@end table

The example below sets the default PulseAudio card profile, the default
sink and the default source to use for a old SoundBlaster Audigy sound
card:
@lisp
(pulseaudio-configuration
 (extra-script-files
  (list (plain-file "audigy.pa"
                    (string-append "\
set-card-profile alsa_card.pci-0000_01_01.0 \
  output:analog-surround-40+input:analog-mono
set-default-source alsa_input.pci-0000_01_01.0.analog-mono
set-default-sink alsa_output.pci-0000_01_01.0.analog-surround-40\n")))))
@end lisp

Note that @code{pulseaudio-service-type} is part of
@code{%desktop-services}; if your operating system declaration was
derived from one of the desktop templates, you'll want to adjust the
above example to modify the existing @code{pulseaudio-service-type} via
@code{modify-services} (@pxref{Service Reference,
@code{modify-services}}), instead of defining a new one.

@end deftp

@defvar ladspa-service-type
This service sets the @var{LADSPA_PATH} variable, so that programs, which
respect it, e.g. PulseAudio, can load LADSPA plugins.

The following example will setup the service to enable modules from the
@code{swh-plugins} package:

@lisp
(service ladspa-service-type
         (ladspa-configuration (plugins (list swh-plugins))))
@end lisp

See @uref{http://plugin.org.uk/ladspa-swh/docs/ladspa-swh.html} for the
details.

@end defvar

@node File Search Services
@subsection File Search Services

@cindex file search
@cindex searching for a file
The services in this section populate @dfn{file databases} that let you
search for files on your machine.  These services are provided by the
@code{(gnu services admin)} module.

The first one, @code{file-database-service-type}, periodically runs the
venerable @command{updatedb} command (@pxref{Invoking updatedb,,, find,
GNU Findutils}).  That command populates a database of file names that
you can then search with the @command{locate} command (@pxref{Invoing
locate,,, find, GNU Findutils}), as in this example:

@example
locate important-notes.txt
@end example

You can enable this service with its default settings by adding this
snippet to your operating system services:

@lisp
(service file-database-service-type)
@end lisp

This updates the database once a week, excluding files from
@file{/gnu/store}---these are more usefully handled by @command{guix
locate} (@pxref{Invoking guix locate}).  You can of course provide a
custom configuration, as described below.

@defvar file-database-service-type
This is the type of the file database service, which runs
@command{updatedb} periodically.  Its associated value must be a
@code{file-database-configuration} record, as described below.
@end defvar

@deftp {Data Type} file-database-configuration
Record type for the @code{file-database-service-type} configuration,
with the following fields:

@table @asis
@item @code{package} (default: @code{findutils})
The GNU@tie{}Findutils package from which the @command{updatedb} command
is taken.

@item @code{schedule} (default: @code{%default-file-database-update-schedule})
String or G-exp denoting an mcron schedule for the periodic
@command{updatedb} job (@pxref{Guile Syntax,,, mcron, GNU@tie{}mcron}).

@item @code{excluded-directories} (default @code{%default-file-database-excluded-directories})
List of regular expressions of directories to ignore when building the
file database.  By default, this includes @file{/tmp} and @file{/gnu/store};
the latter should instead be indexed by @command{guix locate} (@pxref{Invoking
guix locate}).  This list is passed to the @option{--prunepaths} option of
@command{updatedb} (@pxref{Invoking updatedb,,, find, GNU@tie{}Findutils}).
@end table
@end deftp

The second service, @code{package-database-service-type}, builds the
database used by @command{guix locate}, which lets you search for
packages that contain a given file (@pxref{Invoking guix locate}).  The
service periodically updates a system-wide database, which will be
readily available to anyone running @command{guix locate} on the system.
To use this service with its default settings, add this snippet to your
service list:

@lisp
(service package-database-service-type)
@end lisp

This will run @command{guix locate --update} once a week.

@defvar package-database-service-type
This is the service type for periodic @command{guix locate} updates
(@pxref{Invoking guix locate}).  Its value must be a
@code{package-database-configuration} record, as shown below.
@end defvar

@deftp {Data Type} package-database-configuration
Data type to configure periodic package database updates.  It has the
following fields:

@table @asis
@item @code{package} (default: @code{guix})
The Guix package to use.

@item @code{schedule} (default: @code{%default-package-database-update-schedule})
String or G-exp denoting an mcron schedule for the periodic
@command{guix locate --update} job (@pxref{Guile Syntax,,, mcron,
GNU@tie{}mcron}).

@item @code{method} (default: @code{'store})
Indexing method for @command{guix locate}.  The default value,
@code{'store}, yields a more complete database but is relatively
expensive in terms of CPU and input/output.

@item @code{channels} (default: @code{#~%default-channels})
G-exp denoting the channels to use when updating the database
(@pxref{Channels}).
@end table
@end deftp


@node Database Services
@subsection Database Services

@cindex database
@cindex SQL
The @code{(gnu services databases)} module provides the following services.

@subsubheading PostgreSQL

@defvar postgresql-service-type
The service type for the PostgreSQL database server.  Its value should
be a valid @code{postgresql-configuration} object, documented below.
The following example describes a PostgreSQL service with the default
configuration.

@lisp
(service postgresql-service-type
         (postgresql-configuration
          (postgresql postgresql-10)))
@end lisp

If the services fails to start, it may be due to an incompatible
cluster already present in @var{data-directory}.  Adjust it (or, if you
don't need the cluster anymore, delete @var{data-directory}), then
restart the service.

Peer authentication is used by default and the @code{postgres} user
account has no shell, which prevents the direct execution of @code{psql}
commands as this user.  To use @code{psql}, you can temporarily log in
as @code{postgres} using a shell, create a PostgreSQL superuser with the
same name as one of the system users and then create the associated
database.

@example
sudo -u postgres -s /bin/sh
createuser --interactive
createdb $MY_USER_LOGIN      # Replace appropriately.
@end example
@end defvar

@deftp {Data Type} postgresql-configuration
Data type representing the configuration for the
@code{postgresql-service-type}.

@table @asis
@item @code{postgresql} (default: @code{postgresql-10})
PostgreSQL package to use for the service.

@item @code{port} (default: @code{5432})
Port on which PostgreSQL should listen.

@item @code{locale} (default: @code{"en_US.utf8"})
Locale to use as the default when creating the database cluster.

@item @code{config-file} (default: @code{(postgresql-config-file)})
The configuration file to use when running PostgreSQL@.  The default
behaviour uses the postgresql-config-file record with the default values
for the fields.

@item @code{log-directory} (default: @code{"/var/log/postgresql"})
The directory where @command{pg_ctl} output will be written in a file
named @code{"pg_ctl.log"}.  This file can be useful to debug PostgreSQL
configuration errors for instance.

@item @code{data-directory} (default: @code{"/var/lib/postgresql/data"})
Directory in which to store the data.

@item @code{extension-packages} (default: @code{'()})
@cindex postgresql extension-packages
Additional extensions are loaded from packages listed in
@var{extension-packages}.  Extensions are available at runtime.  For instance,
to create a geographic database using the @code{postgis} extension, a user can
configure the postgresql-service as in this example:

@cindex postgis
@lisp
(use-package-modules databases geo)

(operating-system
  ...
  ;; postgresql is required to run `psql' but postgis is not required for
  ;; proper operation.
  (packages (cons* postgresql %base-packages))
  (services
    (cons*
      (service postgresql-service-type
               (postgresql-configuration
                (postgresql postgresql-10)
                (extension-packages (list postgis))))
      %base-services)))
@end lisp

Then the extension becomes visible and you can initialise an empty geographic
database in this way:

@example
psql -U postgres
> create database postgistest;
> \connect postgistest;
> create extension postgis;
> create extension postgis_topology;
@end example

There is no need to add this field for contrib extensions such as hstore or
dblink as they are already loadable by postgresql.  This field is only
required to add extensions provided by other packages.

@item @code{create-account?} (default: @code{#t})
Whether or not the @code{postgres} user and group should be created.

@item @code{uid} (default: @code{#f})
Explicitly specify the UID of the @code{postgres} daemon account.
You normally do not need to specify this, in which case a free UID will
be automatically assigned.

One situation where this option might be useful is if the @var{data-directory}
is located on a mounted network share.

@item @code{gid} (default: @code{#f})
Explicitly specify the GID of the @code{postgres} group.

@end table
@end deftp

@deftp {Data Type} postgresql-config-file
Data type representing the PostgreSQL configuration file.  As shown in
the following example, this can be used to customize the configuration
of PostgreSQL@.  Note that you can use any G-expression or filename in
place of this record, if you already have a configuration file you'd
like to use for example.

@lisp
(service postgresql-service-type
         (postgresql-configuration
          (config-file
           (postgresql-config-file
            (log-destination "stderr")
            (hba-file
             (plain-file "pg_hba.conf"
                         "
local	all	all			trust
host	all	all	127.0.0.1/32 	md5
host	all	all	::1/128 	md5"))
            (extra-config
             '(("session_preload_libraries"     "auto_explain")
               ("random_page_cost"              2)
               ("auto_explain.log_min_duration" "100 ms")
               ("work_mem"                      "500 MB")
               ("logging_collector"             #t)
               ("log_directory"                 "/var/log/postgresql")))))))
@end lisp

@table @asis
@item @code{log-destination} (default: @code{"syslog"})
The logging method to use for PostgreSQL@.  Multiple values are accepted,
separated by commas.

@item @code{hba-file} (default: @code{%default-postgres-hba})
Filename or G-expression for the host-based authentication
configuration.

@item @code{ident-file} (default: @code{%default-postgres-ident})
Filename or G-expression for the user name mapping configuration.

@item @code{socket-directory} (default: @code{"/var/run/postgresql"})
Specifies the directory of the Unix-domain socket(s) on which PostgreSQL
is to listen for connections from client applications. If set to
@code{""} PostgreSQL does not listen on any Unix-domain sockets, in
which case only TCP/IP sockets can be used to connect to the server.

By default, the @code{#false} value means the PostgreSQL default value
will be used, which is currently @samp{/tmp}.

@item @code{extra-config} (default: @code{'()})
List of additional keys and values to include in the PostgreSQL config
file.  Each entry in the list should be a list where the first element
is the key, and the remaining elements are the values.

The values can be numbers, booleans or strings and will be mapped to
PostgreSQL parameters types @code{Boolean}, @code{String},
@code{Numeric}, @code{Numeric with Unit} and @code{Enumerated} described
@uref{https://www.postgresql.org/docs/current/config-setting.html,
here}.

@end table
@end deftp

@defvar postgresql-role-service-type
This service allows to create PostgreSQL roles and databases after
PostgreSQL service start.  Here is an example of its use.

@lisp
(service postgresql-role-service-type
            (postgresql-role-configuration
             (roles
              (list (postgresql-role
                     (name "test")
                     (create-database? #t))))))
@end lisp

This service can be extended with extra roles, as in this
example:

@lisp
(service-extension postgresql-role-service-type
                   (const (postgresql-role
                           (name "alice")
                           (create-database? #t))))
@end lisp
@end defvar

@deftp {Data Type} postgresql-role
PostgreSQL manages database access permissions using the concept of
roles.  A role can be thought of as either a database user, or a group
of database users, depending on how the role is set up.  Roles can own
database objects (for example, tables) and can assign privileges on
those objects to other roles to control who has access to which objects.

@table @asis
@item @code{name}
The role name.

@item @code{permissions} (default: @code{'(createdb login)})
The role permissions list.  Supported permissions are @code{bypassrls},
@code{createdb}, @code{createrole}, @code{login}, @code{replication} and
@code{superuser}.

@item @code{create-database?} (default: @code{#f})
whether to create a database with the same name as the role.

@item @code{encoding} (default: @code{"UTF8"})
The character set to use for storing text in the database.

@item @code{collation} (default: @code{"en_US.utf8"})
The string sort order locale setting.

@item @code{ctype} (default: @code{"en_US.utf8"})
The character classification locale setting.

@item @code{template} (default: @code{"template1"})
The default template to copy the new database from when creating it.
Use @code{"template0"} for a pristine database with no system-local
modifications.

@end table
@end deftp

@deftp {Data Type} postgresql-role-configuration
Data type representing the configuration of
@var{postgresql-role-service-type}.

@table @asis
@item @code{host} (default: @code{"/var/run/postgresql"})
The PostgreSQL host to connect to.

@item @code{log} (default: @code{"/var/log/postgresql_roles.log"})
File name of the log file.

@item @code{roles} (default: @code{'()})
The initial PostgreSQL roles to create.
@end table
@end deftp

@subsubheading MariaDB/MySQL

@defvar mysql-service-type
This is the service type for a MySQL or MariaDB database server.  Its value
is a @code{mysql-configuration} object that specifies which package to use,
as well as various settings for the @command{mysqld} daemon.
@end defvar

@deftp {Data Type} mysql-configuration
Data type representing the configuration of @var{mysql-service-type}.

@table @asis
@item @code{mysql} (default: @var{mariadb})
Package object of the MySQL database server, can be either @var{mariadb}
or @var{mysql}.

For MySQL, a temporary root password will be displayed at activation time.
For MariaDB, the root password is empty.

@item @code{bind-address} (default: @code{"127.0.0.1"})
The IP on which to listen for network connections.  Use @code{"0.0.0.0"}
to bind to all available network interfaces.

@item @code{port} (default: @code{3306})
TCP port on which the database server listens for incoming connections.

@item @code{socket} (default: @code{"/run/mysqld/mysqld.sock"})
Socket file to use for local (non-network) connections.

@item @code{extra-content} (default: @code{""})
Additional settings for the @file{my.cnf} configuration file.

@item @code{extra-environment} (default: @code{#~'()})
List of environment variables passed to the @command{mysqld} process.

@item @code{auto-upgrade?} (default: @code{#t})
Whether to automatically run @command{mysql_upgrade} after starting the
service.  This is necessary to upgrade the @dfn{system schema} after
``major'' updates (such as switching from MariaDB 10.4 to 10.5), but can
be disabled if you would rather do that manually.

@end table
@end deftp

@subsubheading Memcached

@defvar memcached-service-type
This is the service type for the @uref{https://memcached.org/,
Memcached} service, which provides a distributed in memory cache.  The
value for the service type is a @code{memcached-configuration} object.
@end defvar

@lisp
(service memcached-service-type)
@end lisp

@deftp {Data Type} memcached-configuration
Data type representing the configuration of memcached.

@table @asis
@item @code{memcached} (default: @code{memcached})
The Memcached package to use.

@item @code{interfaces} (default: @code{'("0.0.0.0")})
Network interfaces on which to listen.

@item @code{tcp-port} (default: @code{11211})
Port on which to accept connections.

@item @code{udp-port} (default: @code{11211})
Port on which to accept UDP connections on, a value of 0 will disable
listening on a UDP socket.

@item @code{additional-options} (default: @code{'()})
Additional command line options to pass to @code{memcached}.
@end table
@end deftp

@subsubheading Redis

@defvar redis-service-type
This is the service type for the @uref{https://redis.io/, Redis}
key/value store, whose value is a @code{redis-configuration} object.
@end defvar

@deftp {Data Type} redis-configuration
Data type representing the configuration of redis.

@table @asis
@item @code{redis} (default: @code{redis})
The Redis package to use.

@item @code{bind} (default: @code{"127.0.0.1"})
Network interface on which to listen.

@item @code{port} (default: @code{6379})
Port on which to accept connections on, a value of 0 will disable
listening on a TCP socket.

@item @code{working-directory} (default: @code{"/var/lib/redis"})
Directory in which to store the database and related files.
@end table
@end deftp

@node Mail Services
@subsection Mail Services

@cindex mail
@cindex email
The @code{(gnu services mail)} module provides Guix service definitions
for email services: IMAP, POP3, and LMTP servers, as well as mail
transport agents (MTAs).  Lots of acronyms!  These services are detailed
in the subsections below.

@subsubheading Dovecot Service

@defvar dovecot-service-type
Type for the service that runs the Dovecot IMAP/POP3/LMTP mail server,
whose value is a @code{<dovecot-configuration>} object.
@end defvar

By default, Dovecot does not need much configuration; the default
configuration object created by @code{(dovecot-configuration)} will
suffice if your mail is delivered to @code{~/Maildir}.  A self-signed
certificate will be generated for TLS-protected connections, though
Dovecot will also listen on cleartext ports by default.  There are a
number of options, though, which mail administrators might need to change,
and as is the case with other services, Guix allows the system
administrator to specify these parameters via a uniform Scheme interface.

For example, to specify that mail is located at @code{maildir~/.mail},
one would instantiate the Dovecot service like this:

@lisp
(service dovecot-service-type
         (dovecot-configuration
           (mail-location "maildir:~/.mail")))
@end lisp

The available configuration parameters follow.  Each parameter
definition is preceded by its type; for example, @samp{string-list foo}
indicates that the @code{foo} parameter should be specified as a list of
strings.  There is also a way to specify the configuration as a string,
if you have an old @code{dovecot.conf} file that you want to port over
from some other system; see the end for more details.

@c The following documentation was initially generated by
@c (generate-documentation) in (gnu services mail).  Manually maintained
@c documentation is better, so we shouldn't hesitate to edit below as
@c needed.  However if the change you want to make to this documentation
@c can be done in an automated way, it's probably easier to change
@c (generate-documentation) than to make it below and have to deal with
@c the churn as dovecot updates.

Available @code{dovecot-configuration} fields are:

@deftypevr {@code{dovecot-configuration} parameter} package dovecot
The dovecot package.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} comma-separated-string-list listen
A list of IPs or hosts where to listen for connections.  @samp{*}
listens on all IPv4 interfaces, @samp{::} listens on all IPv6
interfaces.  If you want to specify non-default ports or anything more
complex, customize the address and port fields of the
@samp{inet-listener} of the specific services you are interested in.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} protocol-configuration-list protocols
List of protocols we want to serve.  Available protocols include
@samp{imap}, @samp{pop3}, and @samp{lmtp}.

Available @code{protocol-configuration} fields are:

@deftypevr {@code{protocol-configuration} parameter} string name
The name of the protocol.
@end deftypevr

@deftypevr {@code{protocol-configuration} parameter} string auth-socket-path
UNIX socket path to the master authentication server to find users.
This is used by imap (for shared users) and lda.
It defaults to @samp{"/var/run/dovecot/auth-userdb"}.
@end deftypevr

@deftypevr {@code{protocol-configuration} parameter} boolean imap-metadata?
Whether to enable the @code{IMAP METADATA} extension as defined in
@uref{https://tools.ietf.org/html/rfc5464,RFC@tie{}5464}, which provides
a means for clients to set and retrieve per-mailbox, per-user metadata
and annotations over IMAP.

If this is @samp{#t}, you must also specify a dictionary @i{via} the
@code{mail-attribute-dict} setting.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{protocol-configuration} parameter} space-separated-string-list managesieve-notify-capabilities
Which NOTIFY capabilities to report to clients that first connect to
the ManageSieve service, before authentication.  These may differ from the
capabilities offered to authenticated users.  If this field is left empty,
report what the Sieve interpreter supports by default.

Defaults to @samp{'()}.
@end deftypevr

@deftypevr {@code{protocol-configuration} parameter} space-separated-string-list managesieve-sieve-capability
Which SIEVE capabilities to report to clients that first connect to
the ManageSieve service, before authentication.  These may differ from the
capabilities offered to authenticated users.  If this field is left empty,
report what the Sieve interpreter supports by default.

Defaults to @samp{'()}.

@end deftypevr

@deftypevr {@code{protocol-configuration} parameter} space-separated-string-list mail-plugins
Space separated list of plugins to load.
@end deftypevr

@deftypevr {@code{protocol-configuration} parameter} non-negative-integer mail-max-userip-connections
Maximum number of IMAP connections allowed for a user from each IP
address.  NOTE: The username is compared case-sensitively.
Defaults to @samp{10}.
@end deftypevr

@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} service-configuration-list services
List of services to enable.  Available services include @samp{imap},
@samp{imap-login}, @samp{pop3}, @samp{pop3-login}, @samp{auth}, and
@samp{lmtp}.

Available @code{service-configuration} fields are:

@deftypevr {@code{service-configuration} parameter} string kind
The service kind.  Valid values include @code{director},
@code{imap-login}, @code{pop3-login}, @code{lmtp}, @code{imap},
@code{pop3}, @code{auth}, @code{auth-worker}, @code{dict},
@code{tcpwrap}, @code{quota-warning}, or anything else.
@end deftypevr

@deftypevr {@code{service-configuration} parameter} listener-configuration-list listeners
Listeners for the service.  A listener is either a
@code{unix-listener-configuration}, a @code{fifo-listener-configuration}, or
an @code{inet-listener-configuration}.
Defaults to @samp{'()}.

Available @code{unix-listener-configuration} fields are:

@deftypevr {@code{unix-listener-configuration} parameter} string path
Path to the file, relative to @code{base-dir} field.  This is also used as
the section name.
@end deftypevr

@deftypevr {@code{unix-listener-configuration} parameter} string mode
The access mode for the socket.
Defaults to @samp{"0600"}.
@end deftypevr

@deftypevr {@code{unix-listener-configuration} parameter} string user
The user to own the socket.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{unix-listener-configuration} parameter} string group
The group to own the socket.
Defaults to @samp{""}.
@end deftypevr


Available @code{fifo-listener-configuration} fields are:

@deftypevr {@code{fifo-listener-configuration} parameter} string path
Path to the file, relative to @code{base-dir} field.  This is also used as
the section name.
@end deftypevr

@deftypevr {@code{fifo-listener-configuration} parameter} string mode
The access mode for the socket.
Defaults to @samp{"0600"}.
@end deftypevr

@deftypevr {@code{fifo-listener-configuration} parameter} string user
The user to own the socket.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{fifo-listener-configuration} parameter} string group
The group to own the socket.
Defaults to @samp{""}.
@end deftypevr


Available @code{inet-listener-configuration} fields are:

@deftypevr {@code{inet-listener-configuration} parameter} string protocol
The protocol to listen for.
@end deftypevr

@deftypevr {@code{inet-listener-configuration} parameter} string address
The address on which to listen, or empty for all addresses.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{inet-listener-configuration} parameter} non-negative-integer port
The port on which to listen.
@end deftypevr

@deftypevr {@code{inet-listener-configuration} parameter} boolean ssl?
Whether to use SSL for this service; @samp{yes}, @samp{no}, or
@samp{required}.
Defaults to @samp{#t}.
@end deftypevr

@end deftypevr

@deftypevr {@code{service-configuration} parameter} non-negative-integer client-limit
Maximum number of simultaneous client connections per process.  Once
this number of connections is received, the next incoming connection
will prompt Dovecot to spawn another process.  If set to 0,
@code{default-client-limit} is used instead.

Defaults to @samp{0}.

@end deftypevr

@deftypevr {@code{service-configuration} parameter} non-negative-integer service-count
Number of connections to handle before starting a new process.
Typically the only useful values are 0 (unlimited) or 1.  1 is more
secure, but 0 is faster.  <doc/wiki/LoginProcess.txt>.
Defaults to @samp{1}.

@end deftypevr

@deftypevr {@code{service-configuration} parameter} non-negative-integer process-limit
Maximum number of processes that can exist for this service.  If set to
0, @code{default-process-limit} is used instead.

Defaults to @samp{0}.

@end deftypevr

@deftypevr {@code{service-configuration} parameter} non-negative-integer process-min-avail
Number of processes to always keep waiting for more connections.
Defaults to @samp{0}.
@end deftypevr

@deftypevr {@code{service-configuration} parameter} non-negative-integer vsz-limit
If you set @samp{service-count 0}, you probably need to grow
this.
Defaults to @samp{256000000}.
@end deftypevr

@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} dict-configuration dict
Dict configuration, as created by the @code{dict-configuration}
constructor.

Available @code{dict-configuration} fields are:

@deftypevr {@code{dict-configuration} parameter} free-form-fields entries
A list of key-value pairs that this dict should hold.
Defaults to @samp{'()}.
@end deftypevr

@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} passdb-configuration-list passdbs
A list of passdb configurations, each one created by the
@code{passdb-configuration} constructor.

Available @code{passdb-configuration} fields are:

@deftypevr {@code{passdb-configuration} parameter} string driver
The driver that the passdb should use.  Valid values include
@samp{pam}, @samp{passwd}, @samp{shadow}, @samp{bsdauth}, and
@samp{static}.
Defaults to @samp{"pam"}.
@end deftypevr

@deftypevr {@code{passdb-configuration} parameter} space-separated-string-list args
Space separated list of arguments to the passdb driver.
Defaults to @samp{""}.
@end deftypevr

@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} userdb-configuration-list userdbs
List of userdb configurations, each one created by the
@code{userdb-configuration} constructor.

Available @code{userdb-configuration} fields are:

@deftypevr {@code{userdb-configuration} parameter} string driver
The driver that the userdb should use.  Valid values include
@samp{passwd} and @samp{static}.
Defaults to @samp{"passwd"}.
@end deftypevr

@deftypevr {@code{userdb-configuration} parameter} space-separated-string-list args
Space separated list of arguments to the userdb driver.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{userdb-configuration} parameter} free-form-args override-fields
Override fields from passwd.
Defaults to @samp{'()}.
@end deftypevr

@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} plugin-configuration plugin-configuration
Plug-in configuration, created by the @code{plugin-configuration}
constructor.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} list-of-namespace-configuration namespaces
List of namespaces.  Each item in the list is created by the
@code{namespace-configuration} constructor.

Available @code{namespace-configuration} fields are:

@deftypevr {@code{namespace-configuration} parameter} string name
Name for this namespace.
@end deftypevr

@deftypevr {@code{namespace-configuration} parameter} string type
Namespace type: @samp{private}, @samp{shared} or @samp{public}.
Defaults to @samp{"private"}.
@end deftypevr

@deftypevr {@code{namespace-configuration} parameter} string separator
Hierarchy separator to use.  You should use the same separator for
all namespaces or some clients get confused.  @samp{/} is usually a good
one.  The default however depends on the underlying mail storage
format.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{namespace-configuration} parameter} string prefix
Prefix required to access this namespace.  This needs to be
different for all namespaces.  For example @samp{Public/}.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{namespace-configuration} parameter} string location
Physical location of the mailbox. This is in the same format as
mail_location, which is also the default for it.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{namespace-configuration} parameter} boolean inbox?
There can be only one INBOX, and this setting defines which
namespace has it.
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{namespace-configuration} parameter} boolean hidden?
If namespace is hidden, it's not advertised to clients via NAMESPACE
extension.  You'll most likely also want to set @samp{list? #f}.  This is mostly
useful when converting from another server with different namespaces
which you want to deprecate but still keep working.  For example you can
create hidden namespaces with prefixes @samp{~/mail/}, @samp{~%u/mail/}
and @samp{mail/}.
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{namespace-configuration} parameter} boolean list?
Show the mailboxes under this namespace with the LIST command.  This
makes the namespace visible for clients that do not support the NAMESPACE
extension.  The special @code{children} value lists child mailboxes, but
hides the namespace prefix.
Defaults to @samp{#t}.
@end deftypevr

@deftypevr {@code{namespace-configuration} parameter} boolean subscriptions?
Namespace handles its own subscriptions.  If set to @code{#f}, the
parent namespace handles them.  The empty prefix should always have this
as @code{#t}).
Defaults to @samp{#t}.
@end deftypevr

@deftypevr {@code{namespace-configuration} parameter} mailbox-configuration-list mailboxes
List of predefined mailboxes in this namespace.
Defaults to @samp{'()}.

Available @code{mailbox-configuration} fields are:

@deftypevr {@code{mailbox-configuration} parameter} string name
Name for this mailbox.
@end deftypevr

@deftypevr {@code{mailbox-configuration} parameter} string auto
@samp{create} will automatically create this mailbox.
@samp{subscribe} will both create and subscribe to the mailbox.
Defaults to @samp{"no"}.
@end deftypevr

@deftypevr {@code{mailbox-configuration} parameter} space-separated-string-list special-use
List of IMAP @code{SPECIAL-USE} attributes as specified by RFC 6154.
Valid values are @code{\All}, @code{\Archive}, @code{\Drafts},
@code{\Flagged}, @code{\Junk}, @code{\Sent}, and @code{\Trash}.
Defaults to @samp{'()}.
@end deftypevr

@end deftypevr

@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} file-name base-dir
Base directory where to store runtime data.
Defaults to @samp{"/var/run/dovecot/"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string login-greeting
Greeting message for clients.
Defaults to @samp{"Dovecot ready."}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} space-separated-string-list login-trusted-networks
List of trusted network ranges.  Connections from these IPs are
allowed to override their IP addresses and ports (for logging and for
authentication checks).  @samp{disable-plaintext-auth} is also ignored
for these networks.  Typically you would specify your IMAP proxy servers
here.
Defaults to @samp{'()}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} space-separated-string-list login-access-sockets
List of login access check sockets (e.g.@: tcpwrap).
Defaults to @samp{'()}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean verbose-proctitle?
Show more verbose process titles (in ps).  Currently shows user name
and IP address.  Useful for seeing who is actually using the IMAP
processes (e.g.@: shared mailboxes or if the same uid is used for multiple
accounts).
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean shutdown-clients?
Should all processes be killed when Dovecot master process shuts down.
Setting this to @code{#f} means that Dovecot can be upgraded without
forcing existing client connections to close (although that could also
be a problem if the upgrade is e.g.@: due to a security fix).
Defaults to @samp{#t}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer doveadm-worker-count
If non-zero, run mail commands via this many connections to doveadm
server, instead of running them directly in the same process.
Defaults to @samp{0}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string doveadm-socket-path
UNIX socket or host:port used for connecting to doveadm server.
Defaults to @samp{"doveadm-server"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} space-separated-string-list import-environment
List of environment variables that are preserved on Dovecot startup
and passed down to all of its child processes.  You can also give
key=value pairs to always set specific settings.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean disable-plaintext-auth?
Disable LOGIN command and all other plaintext authentications unless
SSL/TLS is used (LOGINDISABLED capability).  Note that if the remote IP
matches the local IP (i.e.@: you're connecting from the same computer),
the connection is considered secure and plaintext authentication is
allowed.  See also the @samp{ssl=required} setting.
Defaults to @samp{#t}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer auth-cache-size
Authentication cache size (e.g.@: @samp{#e10e6}).  0 means it's disabled.
Note that bsdauth, PAM and vpopmail require @samp{cache-key} to be set
for caching to be used.
Defaults to @samp{0}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string auth-cache-ttl
Time to live for cached data.  After TTL expires the cached record
is no longer used, *except* if the main database lookup returns internal
failure.  We also try to handle password changes automatically: If
user's previous authentication was successful, but this one wasn't, the
cache isn't used.  For now this works only with plaintext
authentication.
Defaults to @samp{"1 hour"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string auth-cache-negative-ttl
TTL for negative hits (user not found, password mismatch).
0 disables caching them completely.
Defaults to @samp{"1 hour"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} space-separated-string-list auth-realms
List of realms for SASL authentication mechanisms that need them.
You can leave it empty if you don't want to support multiple realms.
Many clients simply use the first one listed here, so keep the default
realm first.
Defaults to @samp{'()}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string auth-default-realm
Default realm/domain to use if none was specified.  This is used for
both SASL realms and appending @@domain to username in plaintext
logins.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string auth-username-chars
List of allowed characters in username.  If the user-given username
contains a character not listed in here, the login automatically fails.
This is just an extra check to make sure user can't exploit any
potential quote escaping vulnerabilities with SQL/LDAP databases.  If
you want to allow all characters, set this value to empty.
Defaults to @samp{"abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ01234567890.-_@@"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string auth-username-translation
Username character translations before it's looked up from
databases.  The value contains series of from -> to characters.  For
example @samp{#@@/@@} means that @samp{#} and @samp{/} characters are
translated to @samp{@@}.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string auth-username-format
Username formatting before it's looked up from databases.  You can
use the standard variables here, e.g.@: %Lu would lowercase the username,
%n would drop away the domain if it was given, or @samp{%n-AT-%d} would
change the @samp{@@} into @samp{-AT-}.  This translation is done after
@samp{auth-username-translation} changes.
Defaults to @samp{"%Lu"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string auth-master-user-separator
If you want to allow master users to log in by specifying the master
username within the normal username string (i.e.@: not using SASL
mechanism's support for it), you can specify the separator character
here.  The format is then <username><separator><master username>.
UW-IMAP uses @samp{*} as the separator, so that could be a good
choice.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string auth-anonymous-username
Username to use for users logging in with ANONYMOUS SASL
mechanism.
Defaults to @samp{"anonymous"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer auth-worker-max-count
Maximum number of dovecot-auth worker processes.  They're used to
execute blocking passdb and userdb queries (e.g.@: MySQL and PAM).
They're automatically created and destroyed as needed.
Defaults to @samp{30}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string auth-gssapi-hostname
Host name to use in GSSAPI principal names.  The default is to use
the name returned by gethostname().  Use @samp{$ALL} (with quotes) to
allow all keytab entries.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string auth-krb5-keytab
Kerberos keytab to use for the GSSAPI mechanism.  Will use the
system default (usually @file{/etc/krb5.keytab}) if not specified.  You may
need to change the auth service to run as root to be able to read this
file.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean auth-use-winbind?
Do NTLM and GSS-SPNEGO authentication using Samba's winbind daemon
and @samp{ntlm-auth} helper.
<doc/wiki/Authentication/Mechanisms/Winbind.txt>.
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} file-name auth-winbind-helper-path
Path for Samba's @samp{ntlm-auth} helper binary.
Defaults to @samp{"/usr/bin/ntlm_auth"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string auth-failure-delay
Time to delay before replying to failed authentications.
Defaults to @samp{"2 secs"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean auth-ssl-require-client-cert?
Require a valid SSL client certificate or the authentication
fails.
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean auth-ssl-username-from-cert?
Take the username from client's SSL certificate, using
@code{X509_NAME_get_text_by_NID()} which returns the subject's DN's
CommonName.
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} space-separated-string-list auth-mechanisms
List of wanted authentication mechanisms.  Supported mechanisms are:
@samp{plain}, @samp{login}, @samp{digest-md5}, @samp{cram-md5},
@samp{ntlm}, @samp{rpa}, @samp{apop}, @samp{anonymous}, @samp{gssapi},
@samp{otp}, @samp{skey}, and @samp{gss-spnego}.  See also the
@samp{disable-plaintext-auth} setting.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} space-separated-string-list director-servers
List of IPs or hostnames to all director servers, including ourself.
Ports can be specified as ip:port.  The default port is the same as what
director service's @samp{inet-listener} is using.
Defaults to @samp{'()}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} space-separated-string-list director-mail-servers
List of IPs or hostnames to all backend mail servers.  Ranges are
allowed too, like 10.0.0.10-10.0.0.30.
Defaults to @samp{'()}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string director-user-expire
How long to redirect users to a specific server after it no longer
has any connections.
Defaults to @samp{"15 min"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string director-username-hash
How the username is translated before being hashed.  Useful values
include %Ln if user can log in with or without @@domain, %Ld if mailboxes
are shared within domain.
Defaults to @samp{"%Lu"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string log-path
Log file to use for error messages.  @samp{syslog} logs to syslog,
@samp{/dev/stderr} logs to stderr.
Defaults to @samp{"syslog"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string info-log-path
Log file to use for informational messages.  Defaults to
@samp{log-path}.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string debug-log-path
Log file to use for debug messages.  Defaults to
@samp{info-log-path}.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string syslog-facility
Syslog facility to use if you're logging to syslog.  Usually if you
don't want to use @samp{mail}, you'll use local0..local7.  Also other
standard facilities are supported.
Defaults to @samp{"mail"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean auth-verbose?
Log unsuccessful authentication attempts and the reasons why they
failed.
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string auth-verbose-passwords
In case of password mismatches, log the attempted password.  Valid
values are no, plain and sha1.  sha1 can be useful for detecting brute
force password attempts vs.  user simply trying the same password over
and over again.  You can also truncate the value to n chars by appending
":n" (e.g.@: sha1:6).
Defaults to @samp{"no"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean auth-debug?
Even more verbose logging for debugging purposes.  Shows for example
SQL queries.
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean auth-debug-passwords?
In case of password mismatches, log the passwords and used scheme so
the problem can be debugged.  Enabling this also enables
@samp{auth-debug}.
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean mail-debug?
Enable mail process debugging.  This can help you figure out why
Dovecot isn't finding your mails.
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean verbose-ssl?
Show protocol level SSL errors.
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string log-timestamp
Prefix for each line written to log file.  % codes are in
strftime(3) format.
Defaults to @samp{"\"%b %d %H:%M:%S \""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} space-separated-string-list login-log-format-elements
List of elements we want to log.  The elements which have a
non-empty variable value are joined together to form a comma-separated
string.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string login-log-format
Login log format.  %s contains @samp{login-log-format-elements}
string, %$ contains the data we want to log.
Defaults to @samp{"%$: %s"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mail-log-prefix
Log prefix for mail processes.  See doc/wiki/Variables.txt for list
of possible variables you can use.
Defaults to @samp{"\"%s(%u)<%@{pid@}><%@{session@}>: \""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string deliver-log-format
Format to use for logging mail deliveries.  You can use variables:
@table @code
@item %$
Delivery status message (e.g.@: @samp{saved to INBOX})
@item %m
Message-ID
@item %s
Subject
@item %f
From address
@item %p
Physical size
@item %w
Virtual size.
@end table
Defaults to @samp{"msgid=%m: %$"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mail-location
Location for users' mailboxes.  The default is empty, which means
that Dovecot tries to find the mailboxes automatically.  This won't work
if the user doesn't yet have any mail, so you should explicitly tell
Dovecot the full location.

If you're using mbox, giving a path to the INBOX
file (e.g.@: @file{/var/mail/%u}) isn't enough.  You'll also need to tell Dovecot
where the other mailboxes are kept.  This is called the @emph{root mail
directory}, and it must be the first path given in the
@samp{mail-location} setting.

There are a few special variables you can use, e.g.:

@table @samp
@item %u
username
@item %n
user part in user@@domain, same as %u if there's no domain
@item %d
domain part in user@@domain, empty if there's no domain
@item %h
home director
@end table

See doc/wiki/Variables.txt for full list.  Some examples:
@table @samp
@item maildir:~/Maildir
@item mbox:~/mail:INBOX=/var/mail/%u
@item mbox:/var/mail/%d/%1n/%n:INDEX=/var/indexes/%d/%1n/%
@end table
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mail-uid
System user and group used to access mails.  If you use multiple,
userdb can override these by returning uid or gid fields.  You can use
either numbers or names.  <doc/wiki/UserIds.txt>.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mail-gid

Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mail-privileged-group
Group to enable temporarily for privileged operations.  Currently
this is used only with INBOX when either its initial creation or
dotlocking fails.  Typically this is set to @samp{"mail"} to give access to
@file{/var/mail}.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mail-access-groups
Grant access to these supplementary groups for mail processes.
Typically these are used to set up access to shared mailboxes.  Note
that it may be dangerous to set these if users can create symlinks
(e.g.@: if @samp{mail} group is set here, @code{ln -s /var/mail ~/mail/var}
could allow a user to delete others' mailboxes, or @code{ln -s
/secret/shared/box ~/mail/mybox} would allow reading it).  Defaults to
@samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mail-attribute-dict
The location of a dictionary used to store @code{IMAP METADATA}
as defined by @uref{https://tools.ietf.org/html/rfc5464, RFC@tie{}5464}.

The IMAP METADATA commands are available only if the ``imap''
protocol configuration's @code{imap-metadata?} field is @samp{#t}.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean mail-full-filesystem-access?
Allow full file system access to clients.  There's no access checks
other than what the operating system does for the active UID/GID@.  It
works with both maildir and mboxes, allowing you to prefix mailboxes
names with e.g.@: @file{/path/} or @file{~user/}.
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean mmap-disable?
Don't use @code{mmap()} at all.  This is required if you store indexes to
shared file systems (NFS or clustered file system).
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean dotlock-use-excl?
Rely on @samp{O_EXCL} to work when creating dotlock files.  NFS
supports @samp{O_EXCL} since version 3, so this should be safe to use
nowadays by default.
Defaults to @samp{#t}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mail-fsync
When to use fsync() or fdatasync() calls:
@table @code
@item optimized
Whenever necessary to avoid losing important data
@item always
Useful with e.g.@: NFS when @code{write()}s are delayed
@item never
Never use it (best performance, but crashes can lose data).
@end table
Defaults to @samp{"optimized"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean mail-nfs-storage?
Mail storage exists in NFS@.  Set this to yes to make Dovecot flush
NFS caches whenever needed.  If you're using only a single mail server
this isn't needed.
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean mail-nfs-index?
Mail index files also exist in NFS@.  Setting this to yes requires
@samp{mmap-disable? #t} and @samp{fsync-disable? #f}.
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string lock-method
Locking method for index files.  Alternatives are fcntl, flock and
dotlock.  Dotlocking uses some tricks which may create more disk I/O
than other locking methods.  NFS users: flock doesn't work, remember to
change @samp{mmap-disable}.
Defaults to @samp{"fcntl"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} file-name mail-temp-dir
Directory in which LDA/LMTP temporarily stores incoming mails >128
kB.
Defaults to @samp{"/tmp"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer first-valid-uid
Valid UID range for users.  This is mostly to make sure that users can't
log in as daemons or other system users.  Note that denying root logins is
hardcoded to dovecot binary and can't be done even if @samp{first-valid-uid}
is set to 0.
Defaults to @samp{500}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer last-valid-uid

Defaults to @samp{0}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer first-valid-gid
Valid GID range for users.  Users having non-valid GID as primary group ID
aren't allowed to log in.  If user belongs to supplementary groups with
non-valid GIDs, those groups are not set.
Defaults to @samp{1}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer last-valid-gid

Defaults to @samp{0}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer mail-max-keyword-length
Maximum allowed length for mail keyword name.  It's only forced when
trying to create new keywords.
Defaults to @samp{50}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} colon-separated-file-name-list valid-chroot-dirs
List of directories under which chrooting is allowed for mail
processes (i.e.@: @file{/var/mail} will allow chrooting to @file{/var/mail/foo/bar}
too).  This setting doesn't affect @samp{login-chroot}
@samp{mail-chroot} or auth chroot settings.  If this setting is empty,
@samp{/./} in home dirs are ignored.  WARNING: Never add directories here
which local users can modify, that may lead to root exploit.  Usually
this should be done only if you don't allow shell access for users.
<doc/wiki/Chrooting.txt>.
Defaults to @samp{'()}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mail-chroot
Default chroot directory for mail processes.  This can be overridden
for specific users in user database by giving @samp{/./} in user's home
directory (e.g.@: @samp{/home/./user} chroots into @file{/home}).  Note that usually
there is no real need to do chrooting, Dovecot doesn't allow users to
access files outside their mail directory anyway.  If your home
directories are prefixed with the chroot directory, append @samp{/.} to
@samp{mail-chroot}.  <doc/wiki/Chrooting.txt>.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} file-name auth-socket-path
UNIX socket path to master authentication server to find users.
This is used by imap (for shared users) and lda.
Defaults to @samp{"/var/run/dovecot/auth-userdb"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} file-name mail-plugin-dir
Directory where to look up mail plugins.
Defaults to @samp{"/usr/lib/dovecot"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} space-separated-string-list mail-plugins
List of plugins to load for all services.  Plugins specific to IMAP,
LDA, etc.@: are added to this list in their own .conf files.
Defaults to @samp{'()}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer mail-cache-min-mail-count
The minimum number of mails in a mailbox before updates are done to
cache file.  This allows optimizing Dovecot's behavior to do less disk
writes at the cost of more disk reads.
Defaults to @samp{0}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mailbox-idle-check-interval
When IDLE command is running, mailbox is checked once in a while to
see if there are any new mails or other changes.  This setting defines
the minimum time to wait between those checks.  Dovecot can also use
dnotify, inotify and kqueue to find out immediately when changes
occur.
Defaults to @samp{"30 secs"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean mail-save-crlf?
Save mails with CR+LF instead of plain LF@.  This makes sending those
mails take less CPU, especially with sendfile() syscall with Linux and
FreeBSD@.  But it also creates a bit more disk I/O which may just make it
slower.  Also note that if other software reads the mboxes/maildirs,
they may handle the extra CRs wrong and cause problems.
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean maildir-stat-dirs?
By default LIST command returns all entries in maildir beginning
with a dot.  Enabling this option makes Dovecot return only entries
which are directories.  This is done by stat()ing each entry, so it
causes more disk I/O.
 (For systems setting struct @samp{dirent->d_type} this check is free
and it's done always regardless of this setting).
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean maildir-copy-with-hardlinks?
When copying a message, do it with hard links whenever possible.
This makes the performance much better, and it's unlikely to have any
side effects.
Defaults to @samp{#t}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean maildir-very-dirty-syncs?
Assume Dovecot is the only MUA accessing Maildir: Scan cur/
directory only when its mtime changes unexpectedly or when we can't find
the mail otherwise.
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} space-separated-string-list mbox-read-locks
Which locking methods to use for locking mbox.  There are four
available:

@table @code
@item dotlock
Create <mailbox>.lock file.  This is the oldest and most NFS-safe
solution.  If you want to use /var/mail/ like directory, the users will
need write access to that directory.
@item dotlock-try
Same as dotlock, but if it fails because of permissions or because there
isn't enough disk space, just skip it.
@item fcntl
Use this if possible.  Works with NFS too if lockd is used.
@item flock
May not exist in all systems.  Doesn't work with NFS.
@item lockf
May not exist in all systems.  Doesn't work with NFS.
@end table

You can use multiple locking methods; if you do the order they're declared
in is important to avoid deadlocks if other MTAs/MUAs are using multiple
locking methods as well.  Some operating systems don't allow using some of
them simultaneously.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} space-separated-string-list mbox-write-locks

@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mbox-lock-timeout
Maximum time to wait for lock (all of them) before aborting.
Defaults to @samp{"5 mins"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mbox-dotlock-change-timeout
If dotlock exists but the mailbox isn't modified in any way,
override the lock file after this much time.
Defaults to @samp{"2 mins"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean mbox-dirty-syncs?
When mbox changes unexpectedly we have to fully read it to find out
what changed.  If the mbox is large this can take a long time.  Since
the change is usually just a newly appended mail, it'd be faster to
simply read the new mails.  If this setting is enabled, Dovecot does
this but still safely fallbacks to re-reading the whole mbox file
whenever something in mbox isn't how it's expected to be.  The only real
downside to this setting is that if some other MUA changes message
flags, Dovecot doesn't notice it immediately.  Note that a full sync is
done with SELECT, EXAMINE, EXPUNGE and CHECK commands.
Defaults to @samp{#t}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean mbox-very-dirty-syncs?
Like @samp{mbox-dirty-syncs}, but don't do full syncs even with SELECT,
EXAMINE, EXPUNGE or CHECK commands.  If this is set,
@samp{mbox-dirty-syncs} is ignored.
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean mbox-lazy-writes?
Delay writing mbox headers until doing a full write sync (EXPUNGE
and CHECK commands and when closing the mailbox).  This is especially
useful for POP3 where clients often delete all mails.  The downside is
that our changes aren't immediately visible to other MUAs.
Defaults to @samp{#t}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer mbox-min-index-size
If mbox size is smaller than this (e.g.@: 100k), don't write index
files.  If an index file already exists it's still read, just not
updated.
Defaults to @samp{0}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer mdbox-rotate-size
Maximum dbox file size until it's rotated.
Defaults to @samp{10000000}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mdbox-rotate-interval
Maximum dbox file age until it's rotated.  Typically in days.  Day
begins from midnight, so 1d = today, 2d = yesterday, etc.  0 = check
disabled.
Defaults to @samp{"1d"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean mdbox-preallocate-space?
When creating new mdbox files, immediately preallocate their size to
@samp{mdbox-rotate-size}.  This setting currently works only in Linux
with some file systems (ext4, xfs).
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mail-attachment-dir
sdbox and mdbox support saving mail attachments to external files,
which also allows single instance storage for them.  Other backends
don't support this for now.

WARNING: This feature hasn't been tested much yet.  Use at your own risk.

Directory root where to store mail attachments.  Disabled, if empty.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer mail-attachment-min-size
Attachments smaller than this aren't saved externally.  It's also
possible to write a plugin to disable saving specific attachments
externally.
Defaults to @samp{128000}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mail-attachment-fs
File system backend to use for saving attachments:
@table @code
@item posix
No SiS done by Dovecot (but this might help FS's own deduplication)
@item sis posix
SiS with immediate byte-by-byte comparison during saving
@item sis-queue posix
SiS with delayed comparison and deduplication.
@end table
Defaults to @samp{"sis posix"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string mail-attachment-hash
Hash format to use in attachment filenames.  You can add any text and
variables: @code{%@{md4@}}, @code{%@{md5@}}, @code{%@{sha1@}},
@code{%@{sha256@}}, @code{%@{sha512@}}, @code{%@{size@}}.  Variables can be
truncated, e.g.@: @code{%@{sha256:80@}} returns only first 80 bits.
Defaults to @samp{"%@{sha1@}"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer default-process-limit

Defaults to @samp{100}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer default-client-limit

Defaults to @samp{1000}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer default-vsz-limit
Default VSZ (virtual memory size) limit for service processes.
This is mainly intended to catch and kill processes that leak memory
before they eat up everything.
Defaults to @samp{256000000}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string default-login-user
Login user is internally used by login processes.  This is the most
untrusted user in Dovecot system.  It shouldn't have access to anything
at all.
Defaults to @samp{"dovenull"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string default-internal-user
Internal user is used by unprivileged processes.  It should be
separate from login user, so that login processes can't disturb other
processes.
Defaults to @samp{"dovecot"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string ssl?
SSL/TLS support: yes, no, required.  <doc/wiki/SSL.txt>.
Defaults to @samp{"required"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string ssl-cert
PEM encoded X.509 SSL/TLS certificate (public key).
Defaults to @samp{"</etc/dovecot/default.pem"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string ssl-key
PEM encoded SSL/TLS private key.  The key is opened before
dropping root privileges, so keep the key file unreadable by anyone but
root.
Defaults to @samp{"</etc/dovecot/private/default.pem"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string ssl-key-password
If key file is password protected, give the password here.
Alternatively give it when starting dovecot with -p parameter.  Since
this file is often world-readable, you may want to place this setting
instead to a different.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string ssl-ca
PEM encoded trusted certificate authority.  Set this only if you
intend to use @samp{ssl-verify-client-cert? #t}.  The file should
contain the CA certificate(s) followed by the matching
CRL(s).  (e.g.@: @samp{ssl-ca </etc/ssl/certs/ca.pem}).
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean ssl-require-crl?
Require that CRL check succeeds for client certificates.
Defaults to @samp{#t}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean ssl-verify-client-cert?
Request client to send a certificate.  If you also want to require
it, set @samp{auth-ssl-require-client-cert? #t} in auth section.
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string ssl-cert-username-field
Which field from certificate to use for username.  commonName and
x500UniqueIdentifier are the usual choices.  You'll also need to set
@samp{auth-ssl-username-from-cert? #t}.
Defaults to @samp{"commonName"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string ssl-min-protocol
Minimum SSL protocol version to accept.
Defaults to @samp{"TLSv1"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string ssl-cipher-list
SSL ciphers to use.
Defaults to @samp{"ALL:!kRSA:!SRP:!kDHd:!DSS:!aNULL:!eNULL:!EXPORT:!DES:!3DES:!MD5:!PSK:!RC4:!ADH:!LOW@@STRENGTH"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string ssl-crypto-device
SSL crypto device to use, for valid values run "openssl engine".
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string postmaster-address
Address to use when sending rejection mails.
%d expands to recipient domain.
Defaults to @samp{"postmaster@@%d"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string hostname
Hostname to use in various parts of sent mails (e.g.@: in Message-Id)
and in LMTP replies.  Default is the system's real hostname@@domain.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean quota-full-tempfail?
If user is over quota, return with temporary failure instead of
bouncing the mail.
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} file-name sendmail-path
Binary to use for sending mails.
Defaults to @samp{"/usr/sbin/sendmail"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string submission-host
If non-empty, send mails via this SMTP host[:port] instead of
sendmail.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string rejection-subject
Subject: header to use for rejection mails.  You can use the same
variables as for @samp{rejection-reason} below.
Defaults to @samp{"Rejected: %s"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string rejection-reason
Human readable error message for rejection mails.  You can use
variables:

@table @code
@item %n
CRLF
@item %r
reason
@item %s
original subject
@item %t
recipient
@end table
Defaults to @samp{"Your message to <%t> was automatically rejected:%n%r"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string recipient-delimiter
Delimiter character between local-part and detail in email
address.
Defaults to @samp{"+"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string lda-original-recipient-header
Header where the original recipient address (SMTP's RCPT TO:
address) is taken from if not available elsewhere.  With dovecot-lda -a
parameter overrides this.  A commonly used header for this is
X-Original-To.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean lda-mailbox-autocreate?
Should saving a mail to a nonexistent mailbox automatically create
it?.
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} boolean lda-mailbox-autosubscribe?
Should automatically created mailboxes be also automatically
subscribed?.
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} non-negative-integer imap-max-line-length
Maximum IMAP command line length.  Some clients generate very long
command lines with huge mailboxes, so you may need to raise this if you
get "Too long argument" or "IMAP command line too large" errors
often.
Defaults to @samp{64000}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string imap-logout-format
IMAP logout format string:
@table @code
@item %i
total number of bytes read from client
@item %o
total number of bytes sent to client.
@end table
See @file{doc/wiki/Variables.txt} for a list of all the variables you can use.
Defaults to @samp{"in=%i out=%o deleted=%@{deleted@} expunged=%@{expunged@} trashed=%@{trashed@} hdr_count=%@{fetch_hdr_count@} hdr_bytes=%@{fetch_hdr_bytes@} body_count=%@{fetch_body_count@} body_bytes=%@{fetch_body_bytes@}"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string imap-capability
Override the IMAP CAPABILITY response.  If the value begins with '+',
add the given capabilities on top of the defaults (e.g.@: +XFOO XBAR).
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string imap-idle-notify-interval
How long to wait between "OK Still here" notifications when client
is IDLEing.
Defaults to @samp{"2 mins"}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string imap-id-send
ID field names and values to send to clients.  Using * as the value
makes Dovecot use the default value.  The following fields have default
values currently: name, version, os, os-version, support-url,
support-email.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string imap-id-log
ID fields sent by client to log.  * means everything.
Defaults to @samp{""}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} space-separated-string-list imap-client-workarounds
Workarounds for various client bugs:

@table @code
@item delay-newmail
Send EXISTS/RECENT new mail notifications only when replying to NOOP and
CHECK commands.  Some clients ignore them otherwise, for example OSX
Mail (<v2.1).  Outlook Express breaks more badly though, without this it
may show user "Message no longer in server" errors.  Note that OE6
still breaks even with this workaround if synchronization is set to
"Headers Only".

@item tb-extra-mailbox-sep
Thunderbird gets somehow confused with LAYOUT=fs (mbox and dbox) and
adds extra @samp{/} suffixes to mailbox names.  This option causes Dovecot to
ignore the extra @samp{/} instead of treating it as invalid mailbox name.

@item tb-lsub-flags
Show \Noselect flags for LSUB replies with LAYOUT=fs (e.g.@: mbox).
This makes Thunderbird realize they aren't selectable and show them
greyed out, instead of only later giving "not selectable" popup error.
@end table
Defaults to @samp{'()}.
@end deftypevr

@deftypevr {@code{dovecot-configuration} parameter} string imap-urlauth-host
Host allowed in URLAUTH URLs sent by client.  "*" allows all.
Defaults to @samp{""}.
@end deftypevr


Whew!  Lots of configuration options.  The nice thing about it though is
that Guix has a complete interface to Dovecot's configuration
language.  This allows not only a nice way to declare configurations,
but also offers reflective capabilities as well: users can write code to
inspect and transform configurations from within Scheme.

However, it could be that you just want to get a @code{dovecot.conf} up
and running.  In that case, you can pass an
@code{opaque-dovecot-configuration} as the @code{#:config} parameter to
@code{dovecot-service}.  As its name indicates, an opaque configuration
does not have easy reflective capabilities.

Available @code{opaque-dovecot-configuration} fields are:

@deftypevr {@code{opaque-dovecot-configuration} parameter} package dovecot
The dovecot package.
@end deftypevr

@deftypevr {@code{opaque-dovecot-configuration} parameter} string string
The contents of the @code{dovecot.conf}, as a string.
@end deftypevr

For example, if your @code{dovecot.conf} is just the empty string, you
could instantiate a dovecot service like this:

@lisp
(dovecot-service #:config
                 (opaque-dovecot-configuration
                  (string "")))
@end lisp

@subsubheading OpenSMTPD Service

@defvar opensmtpd-service-type
This is the type of the @uref{https://www.opensmtpd.org, OpenSMTPD}
service, whose value should be an @code{opensmtpd-configuration} object
as in this example:

@lisp
(service opensmtpd-service-type
         (opensmtpd-configuration
           (config-file (local-file "./my-smtpd.conf"))))
@end lisp
@end defvar

@deftp {Data Type} opensmtpd-configuration
Data type representing the configuration of opensmtpd.

@table @asis
@item @code{package} (default: @var{opensmtpd})
Package object of the OpenSMTPD SMTP server.

@item @code{shepherd-requirement} (default: @code{'()})
This option can be used to provide a list of symbols naming Shepherd services
that this service will depend on, such as @code{'networking}
if you want to configure OpenSMTPD to listen on non-loopback interfaces.

@item @code{config-file} (default: @code{%default-opensmtpd-config-file})
File-like object of the OpenSMTPD configuration file to use.  By default
it listens on the loopback network interface, and allows for mail from
users and daemons on the local machine, as well as permitting email to
remote servers.  Run @command{man smtpd.conf} for more information.

@item @code{setgid-commands?} (default: @code{#t})
Make the following commands setgid to @code{smtpq} so they can be
executed: @command{smtpctl}, @command{sendmail}, @command{send-mail},
@command{makemap}, @command{mailq}, and @command{newaliases}.
@xref{Privileged Programs}, for more information on setgid programs.
@end table
@end deftp

@subsubheading Exim Service

@cindex mail transfer agent (MTA)
@cindex MTA (mail transfer agent)
@cindex SMTP

@defvar exim-service-type
This is the type of the @uref{https://exim.org, Exim} mail transfer
agent (MTA), whose value should be an @code{exim-configuration} object
as in this example:

@lisp
(service exim-service-type
         (exim-configuration
           (config-file (local-file "./my-exim.conf"))))
@end lisp
@end defvar

In order to use an @code{exim-service-type} service you must also have a
@code{mail-aliases-service-type} service present in your
@code{operating-system} (even if it has no aliases).

@deftp {Data Type} exim-configuration
Data type representing the configuration of exim.

@table @asis
@item @code{package} (default: @var{exim})
Package object of the Exim server.

@item @code{config-file} (default: @code{#f})
File-like object of the Exim configuration file to use.  If its value is
@code{#f} then use the default configuration file from the package
provided in @code{package}.  The resulting configuration file is loaded
after setting the @code{exim_user} and @code{exim_group} configuration
variables.

@end table
@end deftp

@subsubheading Getmail service

@cindex IMAP
@cindex POP

@defvar getmail-service-type
This is the type of the @uref{http://pyropus.ca/software/getmail/, Getmail}
mail retriever, whose value should be a @code{getmail-configuration}.
@end defvar

Available @code{getmail-configuration} fields are:

@deftypevr {@code{getmail-configuration} parameter} symbol name
A symbol to identify the getmail service.

Defaults to @samp{"unset"}.

@end deftypevr

@deftypevr {@code{getmail-configuration} parameter} package package
The getmail package to use.

@end deftypevr

@deftypevr {@code{getmail-configuration} parameter} string user
The user to run getmail as.

Defaults to @samp{"getmail"}.

@end deftypevr

@deftypevr {@code{getmail-configuration} parameter} string group
The group to run getmail as.

Defaults to @samp{"getmail"}.

@end deftypevr

@deftypevr {@code{getmail-configuration} parameter} string directory
The getmail directory to use.

Defaults to @samp{"/var/lib/getmail/default"}.

@end deftypevr

@deftypevr {@code{getmail-configuration} parameter} getmail-configuration-file rcfile
The getmail configuration file to use.

Available @code{getmail-configuration-file} fields are:

@deftypevr {@code{getmail-configuration-file} parameter} getmail-retriever-configuration retriever
What mail account to retrieve mail from, and how to access that account.

Available @code{getmail-retriever-configuration} fields are:

@deftypevr {@code{getmail-retriever-configuration} parameter} string type
The type of mail retriever to use.  Valid values include @samp{passwd}
and @samp{static}.

Defaults to @samp{"SimpleIMAPSSLRetriever"}.

@end deftypevr

@deftypevr {@code{getmail-retriever-configuration} parameter} string server
Username to login to the mail server with.

Defaults to @samp{unset}.

@end deftypevr

@deftypevr {@code{getmail-retriever-configuration} parameter} string username
Username to login to the mail server with.

Defaults to @samp{unset}.

@end deftypevr

@deftypevr {@code{getmail-retriever-configuration} parameter} non-negative-integer port
Port number to connect to.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{getmail-retriever-configuration} parameter} string password
Override fields from passwd.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{getmail-retriever-configuration} parameter} list password-command
Override fields from passwd.

Defaults to @samp{'()}.

@end deftypevr

@deftypevr {@code{getmail-retriever-configuration} parameter} string keyfile
PEM-formatted key file to use for the TLS negotiation.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{getmail-retriever-configuration} parameter} string certfile
PEM-formatted certificate file to use for the TLS negotiation.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{getmail-retriever-configuration} parameter} string ca-certs
CA certificates to use.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{getmail-retriever-configuration} parameter} parameter-alist extra-parameters
Extra retriever parameters.

Defaults to @samp{'()}.

@end deftypevr

@end deftypevr

@deftypevr {@code{getmail-configuration-file} parameter} getmail-destination-configuration destination
What to do with retrieved messages.

Available @code{getmail-destination-configuration} fields are:

@deftypevr {@code{getmail-destination-configuration} parameter} string type
The type of mail destination.  Valid values include @samp{Maildir},
@samp{Mboxrd} and @samp{MDA_external}.

Defaults to @samp{unset}.

@end deftypevr

@deftypevr {@code{getmail-destination-configuration} parameter} string-or-filelike path
The path option for the mail destination.  The behaviour depends on the
chosen type.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{getmail-destination-configuration} parameter} parameter-alist extra-parameters
Extra destination parameters

Defaults to @samp{'()}.

@end deftypevr

@end deftypevr

@deftypevr {@code{getmail-configuration-file} parameter} getmail-options-configuration options
Configure getmail.

Available @code{getmail-options-configuration} fields are:

@deftypevr {@code{getmail-options-configuration} parameter} non-negative-integer verbose
If set to @samp{0}, getmail will only print warnings and errors.  A
value of @samp{1} means that messages will be printed about retrieving
and deleting messages.  If set to @samp{2}, getmail will print messages
about each of its actions.

Defaults to @samp{1}.

@end deftypevr

@deftypevr {@code{getmail-options-configuration} parameter} boolean read-all
If true, getmail will retrieve all available messages.  Otherwise it
will only retrieve messages it hasn't seen previously.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{getmail-options-configuration} parameter} boolean delete
If set to true, messages will be deleted from the server after
retrieving and successfully delivering them.  Otherwise, messages will
be left on the server.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{getmail-options-configuration} parameter} non-negative-integer delete-after
Getmail will delete messages this number of days after seeing them, if
they have been delivered.  This means messages will be left on the
server this number of days after delivering them.  A value of @samp{0}
disabled this feature.

Defaults to @samp{0}.

@end deftypevr

@deftypevr {@code{getmail-options-configuration} parameter} non-negative-integer delete-bigger-than
Delete messages larger than this of bytes after retrieving them, even if
the delete and delete-after options are disabled.  A value of @samp{0}
disables this feature.

Defaults to @samp{0}.

@end deftypevr

@deftypevr {@code{getmail-options-configuration} parameter} non-negative-integer max-bytes-per-session
Retrieve messages totalling up to this number of bytes before closing
the session with the server.  A value of @samp{0} disables this feature.

Defaults to @samp{0}.

@end deftypevr

@deftypevr {@code{getmail-options-configuration} parameter} non-negative-integer max-message-size
Don't retrieve messages larger than this number of bytes.  A value of
@samp{0} disables this feature.

Defaults to @samp{0}.

@end deftypevr

@deftypevr {@code{getmail-options-configuration} parameter} boolean delivered-to
If true, getmail will add a Delivered-To header to messages.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{getmail-options-configuration} parameter} boolean received
If set, getmail adds a Received header to the messages.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{getmail-options-configuration} parameter} string message-log
Getmail will record a log of its actions to the named file.  A value of
@samp{""} disables this feature.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{getmail-options-configuration} parameter} boolean message-log-syslog
If true, getmail will record a log of its actions using the system
logger.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{getmail-options-configuration} parameter} boolean message-log-verbose
If true, getmail will log information about messages not retrieved and
the reason for not retrieving them, as well as starting and ending
information lines.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{getmail-options-configuration} parameter} parameter-alist extra-parameters
Extra options to include.

Defaults to @samp{'()}.

@end deftypevr

@end deftypevr

@end deftypevr

@deftypevr {@code{getmail-configuration} parameter} list idle
A list of mailboxes that getmail should wait on the server for new mail
notifications.  This depends on the server supporting the IDLE
extension.

Defaults to @samp{'()}.

@end deftypevr

@deftypevr {@code{getmail-configuration} parameter} list environment-variables
Environment variables to set for getmail.

Defaults to @samp{'()}.

@end deftypevr

@subsubheading Mail Aliases Service

@cindex email aliases
@cindex aliases, for email addresses

@defvar mail-aliases-service-type
This is the type of the service which provides @code{/etc/aliases},
specifying how to deliver mail to users on this system.

@lisp
(service mail-aliases-service-type
         '(("postmaster" "bob")
           ("bob" "bob@@example.com" "bob@@example2.com")))
@end lisp
@end defvar

The configuration for a @code{mail-aliases-service-type} service is an
association list denoting how to deliver mail that comes to this
system.  Each entry is of the form @code{(alias addresses ...)}, with
@code{alias} specifying the local alias and @code{addresses} specifying
where to deliver this user's mail.

The aliases aren't required to exist as users on the local system.  In
the above example, there doesn't need to be a @code{postmaster} entry in
the @code{operating-system}'s @code{user-accounts} in order to deliver
the @code{postmaster} mail to @code{bob} (which subsequently would
deliver mail to @code{bob@@example.com} and @code{bob@@example2.com}).

@subsubheading GNU Mailutils IMAP4 Daemon
@cindex GNU Mailutils IMAP4 Daemon

@defvar imap4d-service-type
This is the type of the GNU Mailutils IMAP4 Daemon (@pxref{imap4d,,,
mailutils, GNU Mailutils Manual}), whose value should be an
@code{imap4d-configuration} object as in this example:

@lisp
(service imap4d-service-type
         (imap4d-configuration
           (config-file (local-file "imap4d.conf"))))
@end lisp
@end defvar

@deftp {Data Type} imap4d-configuration
Data type representing the configuration of @command{imap4d}.

@table @asis
@item @code{package} (default: @code{mailutils})
The package that provides @command{imap4d}.

@item @code{config-file} (default: @code{%default-imap4d-config-file})
File-like object of the configuration file to use, by default it will listen
on TCP port 143 of @code{localhost}.  @xref{Conf-imap4d,,, mailutils, GNU
Mailutils Manual}, for details.

@end table
@end deftp

@subsubheading Radicale Service
@cindex CalDAV
@cindex CardDAV

@defvar radicale-service-type
This is the type of the @uref{https://radicale.org, Radicale}
CalDAV/CardDAV server whose value should be a
@code{radicale-configuration}.  The default configuration matches the
@uref{https://radicale.org/v3.html#configuration, upstream
documentation}.
@end defvar

@deftp {Data Type} radicale-configuration
Data type representing the configuration of @command{radicale}.
Available @code{radicale-configuration} fields are:

@table @asis
@item @code{package} (default: @code{radicale}) (type: package)
Package that provides @command{radicale}.

@item @code{auth} (default: @code{'()}) (type: radicale-auth-configuration)
Configuration for auth-related variables.

@deftp {Data Type} radicale-auth-configuration
Data type representing the @code{auth} section of a @command{radicale}
configuration file.  Available @code{radicale-auth-configuration} fields
are:

@table @asis
@item @code{type} (default: @code{'none}) (type: symbol)
The method to verify usernames and passwords.  Options are @code{none},
@code{htpasswd}, @code{remote-user}, and @code{http-x-remote-user}.
This value is tied to @code{htpasswd-filename} and
@code{htpasswd-encryption}.

@item @code{htpasswd-filename} (default: @code{"/etc/radicale/users"}) (type: file-name)
Path to the htpasswd file.  Use htpasswd or similar to generate this
file.

@item @code{htpasswd-encryption} (default: @code{'md5}) (type: symbol)
Encryption method used in the htpasswd file.  Options are @code{plain},
@code{bcrypt}, and @code{md5}.

@item @code{delay} (default: @code{1}) (type: non-negative-integer)
Average delay after failed login attempts in seconds.

@item @code{realm} (default: @code{"Radicale - Password Required"}) (type: string)
Message displayed in the client when a password is needed.

@end table

@end deftp

@item @code{encoding} (default: @code{'()}) (type: radicale-encoding-configuration)
Configuration for encoding-related variables.

@deftp {Data Type} radicale-encoding-configuration
Data type representing the @code{encoding} section of a
@command{radicale} configuration file.  Available
@code{radicale-encoding-configuration} fields are:

@table @asis
@item @code{request} (default: @code{'utf-8}) (type: symbol)
Encoding for responding requests.

@item @code{stock} (default: @code{'utf-8}) (type: symbol)
Encoding for storing local collections.

@end table

@end deftp

@item @code{headers-file} (default: none) (type: file-like)
Custom HTTP headers.

@item @code{logging} (default: @code{'()}) (type: radicale-logging-configuration)
Configuration for logging-related variables.

@deftp {Data Type} radicale-logging-configuration
Data type representing the @code{logging} section of a
@command{radicale} configuration file.  Available
@code{radicale-logging-configuration} fields are:

@table @asis
@item @code{level} (default: @code{'warning}) (type: symbol)
Set the logging level.  One of @code{debug}, @code{info},
@code{warning}, @code{error}, or @code{critical}.

@item @code{mask-passwords?} (default: @code{#t}) (type: boolean)
Whether to include passwords in logs.

@end table

@end deftp

@item @code{rights} (default: @code{'()}) (type: radicale-rights-configuration)
Configuration for rights-related variables.  This should be a
@code{radicale-rights-configuration}.

@deftp {Data Type} radicale-rights-configuration
Data type representing the @code{rights} section of a @command{radicale}
configuration file.  Available @code{radicale-rights-configuration}
fields are:

@table @asis
@item @code{type} (default: @code{'owner-only}) (type: symbol)
Backend used to check collection access rights.  The recommended backend
is @code{owner-only}.  If access to calendars and address books outside
the home directory of users is granted, clients won't detect these
collections and will not show them to the user.  Choosing any other
method is only useful if you access calendars and address books directly
via URL.  Options are @code{authenticate}, @code{owner-only},
@code{owner-write}, and @code{from-file}.

@item @code{file} (default: @code{""}) (type: file-name)
File for the rights backend @code{from-file}.

@end table

@end deftp

@item @code{server} (default: @code{'()}) (type: radicale-server-configuration)
Configuration for server-related variables.  Ignored if WSGI is used.

@deftp {Data Type} radicale-server-configuration
Data type representing the @code{server} section of a @command{radicale}
configuration file.  Available @code{radicale-server-configuration}
fields are:

@table @asis
@item @code{hosts} (default: @code{(list "localhost:5232")}) (type: list-of-ip-addresses)
List of IP addresses that the server will bind to.

@item @code{max-connections} (default: @code{8}) (type: non-negative-integer)
Maximum number of parallel connections.  Set to 0 to disable the limit.

@item @code{max-content-length} (default: @code{100000000}) (type: non-negative-integer)
Maximum size of the request body in bytes.

@item @code{timeout} (default: @code{30}) (type: non-negative-integer)
Socket timeout in seconds.

@item @code{ssl?} (default: @code{#f}) (type: boolean)
Whether to enable transport layer encryption.

@item @code{certificate} (default: @code{"/etc/ssl/radicale.cert.pem"}) (type: file-name)
Path of the SSL certificate.

@item @code{key} (default: @code{"/etc/ssl/radicale.key.pem"}) (type: file-name)
Path to the private key for SSL.  Only effective if @code{ssl?} is
@code{#t}.

@item @code{certificate-authority} (default: @code{""}) (type: file-name)
Path to CA certificate for validating client certificates.  This can be
used to secure TCP traffic between Radicale and a reverse proxy.  If you
want to authenticate users with client-side certificates, you also have
to write an authentication plugin that extracts the username from the
certificate.

@end table

@end deftp

@item @code{storage} (default: @code{'()}) (type: radicale-storage-configuration)
Configuration for storage-related variables.

@deftp {Data Type} radicale-storage-configuration
Data type representing the @code{storage} section of a
@command{radicale} configuration file.  Available
@code{radicale-storage-configuration} fields are:

@table @asis
@item @code{type} (default: @code{'multifilesystem}) (type: symbol)
Backend used to store data.  Options are @code{multifilesystem} and
@code{multifilesystem-nolock}.

@item @code{filesystem-folder} (default: @code{"/var/lib/radicale/collections"}) (type: file-name)
Folder for storing local collections.  Created if not present.

@item @code{max-sync-token-age} (default: @code{2592000}) (type: non-negative-integer)
Delete sync-tokens that are older than the specified time in seconds.

@item @code{hook} (default: @code{""}) (type: string)
Command run after changes to storage.

@end table

@end deftp

@item @code{web-interface?} (default: @code{#t}) (type: boolean)
Whether to use Radicale's built-in web interface.

@end table

@end deftp

@subsubheading Rspamd Service
@cindex email
@cindex spam

@defvar rspamd-service-type
This is the type of the @uref{https://rspamd.com/, Rspamd} filtering
system whose value should be a @code{rspamd-configuration}.
@end defvar

@c %start of fragment

@deftp {Data Type} rspamd-configuration
Available @code{rspamd-configuration} fields are:

@table @asis
@item @code{package} (default: @code{rspamd}) (type: file-like)
The package that provides rspamd.

@item @code{config-file} (default: @code{%default-rspamd-config-file}) (type: file-like)
File-like object of the configuration file to use.  By default all
workers are enabled except fuzzy and they are binded to their usual
ports, e.g localhost:11334, localhost:11333 and so on

@item @code{local.d-files} (default: @code{()}) (type: directory-tree)
Configuration files in local.d, provided as a list of two element lists
where the first element is the filename and the second one is a
file-like object.  Settings in these files will be merged with the
defaults.

@item @code{override.d-files} (default: @code{()}) (type: directory-tree)
Configuration files in override.d, provided as a list of two element
lists where the first element is the filename and the second one is a
file-like object.  Settings in these files will override the defaults.

@item @code{user} (default: @code{%default-rspamd-account}) (type: user-account)
The user to run rspamd as.

@item @code{group} (default: @code{%default-rspamd-group}) (type: user-group)
The group to run rspamd as.

@item @code{debug?} (default: @code{#f}) (type: boolean)
Force debug output.

@item @code{insecure?} (default: @code{#f}) (type: boolean)
Ignore running workers as privileged users.

@item @code{skip-template?} (default: @code{#f}) (type: boolean)
Do not apply Jinja templates.

@item @code{shepherd-requirements} (default: @code{(loopback)}) (type: list-of-symbols)
This is a list of symbols naming Shepherd services that this service
will depend on.

@end table

@end deftp


@c %end of fragment

@node Messaging Services
@subsection Messaging Services

@cindex messaging
@cindex jabber
@cindex XMPP
The @code{(gnu services messaging)} module provides Guix service
definitions for messaging services.  Currently it provides the following
services:

@subsubheading Prosody Service

@defvar prosody-service-type
This is the type for the @uref{https://prosody.im, Prosody XMPP
communication server}.  Its value must be a @code{prosody-configuration}
record as in this example:

@lisp
(service prosody-service-type
         (prosody-configuration
          (modules-enabled (cons* "groups" "mam" %default-modules-enabled))
          (int-components
           (list
            (int-component-configuration
             (hostname "conference.example.net")
             (plugin "muc")
             (mod-muc (mod-muc-configuration)))))
          (virtualhosts
           (list
            (virtualhost-configuration
             (domain "example.net"))))))
@end lisp

See below for details about @code{prosody-configuration}.

@end defvar

By default, Prosody does not need much configuration.  Only one
@code{virtualhosts} field is needed: it specifies the domain you wish
Prosody to serve.

You can perform various sanity checks on the generated configuration
with the @code{prosodyctl check} command.

Prosodyctl will also help you to import certificates from the
@code{letsencrypt} directory so that the @code{prosody} user can access
them.  See @url{https://prosody.im/doc/letsencrypt}.

@example
prosodyctl --root cert import /etc/certs
@end example

The available configuration parameters follow.  Each parameter
definition is preceded by its type; for example, @samp{string-list foo}
indicates that the @code{foo} parameter should be specified as a list of
strings.  Types starting with @code{maybe-} denote parameters that won't
show up in @code{prosody.cfg.lua} when their value is left unspecified.

There is also a way to specify the configuration as a string, if you
have an old @code{prosody.cfg.lua} file that you want to port over from
some other system; see the end for more details.

The @code{file-object} type designates either a file-like object
(@pxref{G-Expressions, file-like objects}) or a file name.

@c The following documentation was initially generated by
@c (generate-documentation) in (gnu services messaging).  Manually maintained
@c documentation is better, so we shouldn't hesitate to edit below as
@c needed.  However if the change you want to make to this documentation
@c can be done in an automated way, it's probably easier to change
@c (generate-documentation) than to make it below and have to deal with
@c the churn as Prosody updates.

Available @code{prosody-configuration} fields are:

@deftypevr {@code{prosody-configuration} parameter} package prosody
The Prosody package.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} file-name data-path
Location of the Prosody data storage directory.  See
@url{https://prosody.im/doc/configure}.
Defaults to @samp{"/var/lib/prosody"}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} file-object-list plugin-paths
Additional plugin directories.  They are searched in all the specified
paths in order.  See @url{https://prosody.im/doc/plugins_directory}.
Defaults to @samp{'()}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} file-name certificates
Every virtual host and component needs a certificate so that clients and
servers can securely verify its identity.  Prosody will automatically load
certificates/keys from the directory specified here.
Defaults to @samp{"/etc/prosody/certs"}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} string-list admins
This is a list of accounts that are admins for the server.  Note that you
must create the accounts separately.  See @url{https://prosody.im/doc/admins} and
@url{https://prosody.im/doc/creating_accounts}.
Example: @code{(admins '("user1@@example.com" "user2@@example.net"))}
Defaults to @samp{'()}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} boolean use-libevent?
Enable use of libevent for better performance under high load.  See
@url{https://prosody.im/doc/libevent}.
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} module-list modules-enabled
This is the list of modules Prosody will load on startup.  It looks for
@code{mod_modulename.lua} in the plugins folder, so make sure that exists too.
Documentation on modules can be found at:
@url{https://prosody.im/doc/modules}.
Defaults to @samp{'("roster" "saslauth" "tls" "dialback" "disco" "carbons" "private" "blocklist" "vcard" "version" "uptime" "time" "ping" "pep" "register" "admin_adhoc")}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} string-list modules-disabled
@samp{"offline"}, @samp{"c2s"} and @samp{"s2s"} are auto-loaded, but
should you want to disable them then add them to this list.
Defaults to @samp{'()}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} file-object groups-file
Path to a text file where the shared groups are defined.  If this path is
empty then @samp{mod_groups} does nothing.  See
@url{https://prosody.im/doc/modules/mod_groups}.
Defaults to @samp{"/var/lib/prosody/sharedgroups.txt"}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} boolean allow-registration?
Disable account creation by default, for security.  See
@url{https://prosody.im/doc/creating_accounts}.
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} maybe-ssl-configuration ssl
These are the SSL/TLS-related settings.  Most of them are disabled so to
use Prosody's defaults.  If you do not completely understand these options, do
not add them to your config, it is easy to lower the security of your server
using them.  See @url{https://prosody.im/doc/advanced_ssl_config}.

Available @code{ssl-configuration} fields are:

@deftypevr {@code{ssl-configuration} parameter} maybe-string protocol
This determines what handshake to use.
@end deftypevr

@deftypevr {@code{ssl-configuration} parameter} maybe-file-name key
Path to your private key file.
@end deftypevr

@deftypevr {@code{ssl-configuration} parameter} maybe-file-name certificate
Path to your certificate file.
@end deftypevr

@deftypevr {@code{ssl-configuration} parameter} file-object capath
Path to directory containing root certificates that you wish Prosody to
trust when verifying the certificates of remote servers.
Defaults to @samp{"/etc/ssl/certs"}.
@end deftypevr

@deftypevr {@code{ssl-configuration} parameter} maybe-file-object cafile
Path to a file containing root certificates that you wish Prosody to trust.
Similar to @code{capath} but with all certificates concatenated together.
@end deftypevr

@deftypevr {@code{ssl-configuration} parameter} maybe-string-list verify
A list of verification options (these mostly map to OpenSSL's
@code{set_verify()} flags).
@end deftypevr

@deftypevr {@code{ssl-configuration} parameter} maybe-string-list options
A list of general options relating to SSL/TLS@.  These map to OpenSSL's
@code{set_options()}.  For a full list of options available in LuaSec, see the
LuaSec source.
@end deftypevr

@deftypevr {@code{ssl-configuration} parameter} maybe-non-negative-integer depth
How long a chain of certificate authorities to check when looking for a
trusted root certificate.
@end deftypevr

@deftypevr {@code{ssl-configuration} parameter} maybe-string ciphers
An OpenSSL cipher string.  This selects what ciphers Prosody will offer to
clients, and in what order.
@end deftypevr

@deftypevr {@code{ssl-configuration} parameter} maybe-file-name dhparam
A path to a file containing parameters for Diffie-Hellman key exchange.  You
can create such a file with:
@code{openssl dhparam -out /etc/prosody/certs/dh-2048.pem 2048}
@end deftypevr

@deftypevr {@code{ssl-configuration} parameter} maybe-string curve
Curve for Elliptic curve Diffie-Hellman.  Prosody's default is
@samp{"secp384r1"}.
@end deftypevr

@deftypevr {@code{ssl-configuration} parameter} maybe-string-list verifyext
A list of ``extra'' verification options.
@end deftypevr

@deftypevr {@code{ssl-configuration} parameter} maybe-string password
Password for encrypted private keys.
@end deftypevr

@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} boolean c2s-require-encryption?
Whether to force all client-to-server connections to be encrypted or not.
See @url{https://prosody.im/doc/modules/mod_tls}.
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} string-list disable-sasl-mechanisms
Set of mechanisms that will never be offered.  See
@url{https://prosody.im/doc/modules/mod_saslauth}.
Defaults to @samp{'("DIGEST-MD5")}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} string-list insecure-sasl-mechanisms
Set of mechanisms that will not be offered on unencrypted connections.
See @url{https://prosody.im/doc/modules/mod_saslauth}.
Defaults to @samp{'("PLAIN" "LOGIN")}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} boolean s2s-require-encryption?
Whether to force all server-to-server connections to be encrypted or not.
See @url{https://prosody.im/doc/modules/mod_tls}.
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} boolean s2s-secure-auth?
Whether to require encryption and certificate authentication.  This
provides ideal security, but requires servers you communicate with to support
encryption AND present valid, trusted certificates.  See
@url{https://prosody.im/doc/s2s#security}.
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} string-list s2s-insecure-domains
Many servers don't support encryption or have invalid or self-signed
certificates.  You can list domains here that will not be required to
authenticate using certificates.  They will be authenticated using DNS@.  See
@url{https://prosody.im/doc/s2s#security}.
Defaults to @samp{'()}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} string-list s2s-secure-domains
Even if you leave @code{s2s-secure-auth?} disabled, you can still require
valid certificates for some domains by specifying a list here.  See
@url{https://prosody.im/doc/s2s#security}.
Defaults to @samp{'()}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} string authentication
Select the authentication backend to use.  The default provider stores
passwords in plaintext and uses Prosody's configured data storage to store the
authentication data.  If you do not trust your server please see
@url{https://prosody.im/doc/modules/mod_auth_internal_hashed} for information
about using the hashed backend.  See also
@url{https://prosody.im/doc/authentication}
Defaults to @samp{"internal_plain"}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} maybe-string log
Set logging options.  Advanced logging configuration is not yet supported
by the Prosody service.  See @url{https://prosody.im/doc/logging}.
Defaults to @samp{"*syslog"}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} file-name pidfile
File to write pid in.  See @url{https://prosody.im/doc/modules/mod_posix}.
Defaults to @samp{"/var/run/prosody/prosody.pid"}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} maybe-non-negative-integer http-max-content-size
Maximum allowed size of the HTTP body (in bytes).
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} maybe-string http-external-url
Some modules expose their own URL in various ways.  This URL is built
from the protocol, host and port used.  If Prosody sits behind a proxy, the
public URL will be @code{http-external-url} instead.  See
@url{https://prosody.im/doc/http#external_url}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} virtualhost-configuration-list virtualhosts
A host in Prosody is a domain on which user accounts can be created.  For
example if you want your users to have addresses like
@samp{"john.smith@@example.com"} then you need to add a host
@samp{"example.com"}.  All options in this list will apply only to this host.

@quotation Note
The name @emph{virtual} host is used in configuration to avoid confusion with
the actual physical host that Prosody is installed on.  A single Prosody
instance can serve many domains, each one defined as a VirtualHost entry in
Prosody's configuration.  Conversely a server that hosts a single domain would
have just one VirtualHost entry.

See @url{https://prosody.im/doc/configure#virtual_host_settings}.
@end quotation

Available @code{virtualhost-configuration} fields are:

all these @code{prosody-configuration} fields: @code{admins}, @code{use-libevent?}, @code{modules-enabled}, @code{modules-disabled}, @code{groups-file}, @code{allow-registration?}, @code{ssl}, @code{c2s-require-encryption?}, @code{disable-sasl-mechanisms}, @code{insecure-sasl-mechanisms}, @code{s2s-require-encryption?}, @code{s2s-secure-auth?}, @code{s2s-insecure-domains}, @code{s2s-secure-domains}, @code{authentication}, @code{log}, @code{http-max-content-size}, @code{http-external-url}, @code{raw-content}, plus:
@deftypevr {@code{virtualhost-configuration} parameter} string domain
Domain you wish Prosody to serve.
@end deftypevr

@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} int-component-configuration-list int-components
Components are extra services on a server which are available to clients,
usually on a subdomain of the main server (such as
@samp{"mycomponent.example.com"}).  Example components might be chatroom
servers, user directories, or gateways to other protocols.

Internal components are implemented with Prosody-specific plugins.  To add an
internal component, you simply fill the hostname field, and the plugin you wish
to use for the component.

See @url{https://prosody.im/doc/components}.
Defaults to @samp{'()}.

Available @code{int-component-configuration} fields are:

all these @code{prosody-configuration} fields: @code{admins}, @code{use-libevent?}, @code{modules-enabled}, @code{modules-disabled}, @code{groups-file}, @code{allow-registration?}, @code{ssl}, @code{c2s-require-encryption?}, @code{disable-sasl-mechanisms}, @code{insecure-sasl-mechanisms}, @code{s2s-require-encryption?}, @code{s2s-secure-auth?}, @code{s2s-insecure-domains}, @code{s2s-secure-domains}, @code{authentication}, @code{log}, @code{http-max-content-size}, @code{http-external-url}, @code{raw-content}, plus:
@deftypevr {@code{int-component-configuration} parameter} string hostname
Hostname of the component.
@end deftypevr

@deftypevr {@code{int-component-configuration} parameter} string plugin
Plugin you wish to use for the component.
@end deftypevr

@deftypevr {@code{int-component-configuration} parameter} maybe-mod-muc-configuration mod-muc
Multi-user chat (MUC) is Prosody's module for allowing you to create
hosted chatrooms/conferences for XMPP users.

General information on setting up and using multi-user chatrooms can be found
in the ``Chatrooms'' documentation (@url{https://prosody.im/doc/chatrooms}),
which you should read if you are new to XMPP chatrooms.

See also @url{https://prosody.im/doc/modules/mod_muc}.

Available @code{mod-muc-configuration} fields are:

@deftypevr {@code{mod-muc-configuration} parameter} string name
The name to return in service discovery responses.
Defaults to @samp{"Prosody Chatrooms"}.
@end deftypevr

@deftypevr {@code{mod-muc-configuration} parameter} string-or-boolean restrict-room-creation
If @samp{#t}, this will only allow admins to create new chatrooms.
Otherwise anyone can create a room.  The value @samp{"local"} restricts room
creation to users on the service's parent domain.  E.g.@: @samp{user@@example.com}
can create rooms on @samp{rooms.example.com}.  The value @samp{"admin"}
restricts to service administrators only.
Defaults to @samp{#f}.
@end deftypevr

@deftypevr {@code{mod-muc-configuration} parameter} non-negative-integer max-history-messages
Maximum number of history messages that will be sent to the member that has
just joined the room.
Defaults to @samp{20}.
@end deftypevr

@end deftypevr

@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} ext-component-configuration-list ext-components
External components use XEP-0114, which most standalone components
support.  To add an external component, you simply fill the hostname field.  See
@url{https://prosody.im/doc/components}.
Defaults to @samp{'()}.

Available @code{ext-component-configuration} fields are:

all these @code{prosody-configuration} fields: @code{admins}, @code{use-libevent?}, @code{modules-enabled}, @code{modules-disabled}, @code{groups-file}, @code{allow-registration?}, @code{ssl}, @code{c2s-require-encryption?}, @code{disable-sasl-mechanisms}, @code{insecure-sasl-mechanisms}, @code{s2s-require-encryption?}, @code{s2s-secure-auth?}, @code{s2s-insecure-domains}, @code{s2s-secure-domains}, @code{authentication}, @code{log}, @code{http-max-content-size}, @code{http-external-url}, @code{raw-content}, plus:
@deftypevr {@code{ext-component-configuration} parameter} string component-secret
Password which the component will use to log in.
@end deftypevr

@deftypevr {@code{ext-component-configuration} parameter} string hostname
Hostname of the component.
@end deftypevr

@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} non-negative-integer-list component-ports
Port(s) Prosody listens on for component connections.
Defaults to @samp{'(5347)}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} string component-interface
Interface Prosody listens on for component connections.
Defaults to @samp{"127.0.0.1"}.
@end deftypevr

@deftypevr {@code{prosody-configuration} parameter} maybe-raw-content raw-content
Raw content that will be added to the configuration file.
@end deftypevr

It could be that you just want to get a @code{prosody.cfg.lua}
up and running.  In that case, you can pass an
@code{opaque-prosody-configuration} record as the value of
@code{prosody-service-type}.  As its name indicates, an opaque configuration
does not have easy reflective capabilities.
Available @code{opaque-prosody-configuration} fields are:

@deftypevr {@code{opaque-prosody-configuration} parameter} package prosody
The prosody package.
@end deftypevr

@deftypevr {@code{opaque-prosody-configuration} parameter} string prosody.cfg.lua
The contents of the @code{prosody.cfg.lua} to use.
@end deftypevr

For example, if your @code{prosody.cfg.lua} is just the empty
string, you could instantiate a prosody service like this:

@lisp
(service prosody-service-type
         (opaque-prosody-configuration
          (prosody.cfg.lua "")))
@end lisp

@c end of Prosody auto-generated documentation

@subsubheading BitlBee Service

@cindex IRC (Internet Relay Chat)
@cindex IRC gateway
@url{https://bitlbee.org,BitlBee} is a gateway that provides an IRC
interface to a variety of messaging protocols such as XMPP.

@defvar bitlbee-service-type
This is the service type for the @url{https://bitlbee.org,BitlBee} IRC
gateway daemon.  Its value is a @code{bitlbee-configuration} (see
below).

To have BitlBee listen on port 6667 on localhost, add this line to your
services:

@lisp
(service bitlbee-service-type)
@end lisp
@end defvar

@deftp {Data Type} bitlbee-configuration
This is the configuration for BitlBee, with the following fields:

@table @asis
@item @code{interface} (default: @code{"127.0.0.1"})
@itemx @code{port} (default: @code{6667})
Listen on the network interface corresponding to the IP address
specified in @var{interface}, on @var{port}.

When @var{interface} is @code{127.0.0.1}, only local clients can
connect; when it is @code{0.0.0.0}, connections can come from any
networking interface.

@item @code{bitlbee} (default: @code{bitlbee})
The BitlBee package to use.

@item @code{plugins} (default: @code{'()})
List of plugin packages to use---e.g., @code{bitlbee-discord}.

@item @code{extra-settings} (default: @code{""})
Configuration snippet added as-is to the BitlBee configuration file.
@end table
@end deftp

@subsubheading Quassel Service

@cindex IRC (Internet Relay Chat)
@url{https://quassel-irc.org/,Quassel} is a distributed IRC client,
meaning that one or more clients can attach to and detach from the
central core.

@defvar quassel-service-type
This is the service type for the @url{https://quassel-irc.org/,Quassel}
IRC backend daemon.  Its value is a @code{quassel-configuration}
(see below).
@end defvar

@deftp {Data Type} quassel-configuration
This is the configuration for Quassel, with the following fields:

@table @asis
@item @code{quassel} (default: @code{quassel})
The Quassel package to use.

@item @code{interface} (default: @code{"::,0.0.0.0"})
@item @code{port} (default: @code{4242})
Listen on the network interface(s) corresponding to the IPv4 or IPv6
interfaces specified in the comma delimited @var{interface}, on
@var{port}.

@item @code{loglevel} (default: @code{"Info"})
The level of logging desired.  Accepted values are Debug, Info, Warning
and Error.
@end table
@end deftp

@node Telephony Services
@subsection Telephony Services

@cindex telephony, services
The @code{(gnu services telephony)} module contains Guix service
definitions for telephony services.  Currently it provides the following
services:

@subsubheading Jami

@defvar jami-service-type
The service type for running Jami as a service.  It takes a
@code{jami-configuration} object as a value, documented below.  This
section describes how to configure a Jami server that can be used to
host video (or audio) conferences, among other uses.  The following
example demonstrates how to specify Jami account archives (backups) to
be provisioned automatically:

@lisp
(service jami-service-type
         (jami-configuration
          (accounts
           (list (jami-account
                  (archive "/etc/jami/unencrypted-account-1.gz"))
                 (jami-account
                  (archive "/etc/jami/unencrypted-account-2.gz"))))))
@end lisp

When the accounts field is specified, the Jami account files of the
service found under @file{/var/lib/jami} are recreated every time the
service starts.

Jami accounts and their corresponding backup archives can be generated
using the @code{jami} or @code{jami-gnome} Jami clients.  The accounts
should not be password-protected, but it is wise to ensure their files
are only readable by @samp{root}.

The next example shows how to declare that only some contacts should be
allowed to communicate with a given account:

@lisp
(service jami-service-type
         (jami-configuration
          (accounts
           (list (jami-account
                  (archive "/etc/jami/unencrypted-account-1.gz")
                  (peer-discovery? #t)
                  (rendezvous-point? #t)
                  (allowed-contacts
                   '("1dbcb0f5f37324228235564b79f2b9737e9a008f"
                     "2dbcb0f5f37324228235564b79f2b9737e9a008f")))))))
@end lisp

In this mode, only the declared @code{allowed-contacts} can initiate
communication with the Jami account.  This can be used, for example,
with rendezvous point accounts to create a private video conferencing
space.

To put the system administrator in full control of the conferences
hosted on their system, the Jami service supports the following actions:

@example sh
# herd doc jami list-actions
(list-accounts
 list-account-details
 list-banned-contacts
 list-contacts
 list-moderators
 add-moderator
 ban-contact
 enable-account
 disable-account)
@end example

The above actions aim to provide the most valuable actions for
moderation purposes, not to cover the whole Jami API.  Users wanting to
interact with the Jami daemon from Guile may be interested in
experimenting with the @code{(gnu build jami-service)} module, which
powers the above Shepherd actions.

@c TODO: This should be auto-generated from the doc already defined on
@c the shepherd-actions themselves in (gnu services telephony).
The @code{add-moderator} and @code{ban-contact} actions accept a contact
@emph{fingerprint} (40 characters long hash) as first argument and an
account fingerprint or username as second argument:

@example sh
# herd add-moderator jami 1dbcb0f5f37324228235564b79f2b9737e9a008f \
  f3345f2775ddfe07a4b0d95daea111d15fbc1199

# herd list-moderators jami
Moderators for account f3345f2775ddfe07a4b0d95daea111d15fbc1199:
  - 1dbcb0f5f37324228235564b79f2b9737e9a008f

@end example

In the case of @code{ban-contact}, the second username argument is
optional; when omitted, the account is banned from all Jami accounts:

@example sh
# herd ban-contact jami 1dbcb0f5f37324228235564b79f2b9737e9a008f

# herd list-banned-contacts jami
Banned contacts for account f3345f2775ddfe07a4b0d95daea111d15fbc1199:
  - 1dbcb0f5f37324228235564b79f2b9737e9a008f

@end example

Banned contacts are also stripped from their moderation privileges.

The @code{disable-account} action allows to completely disconnect an
account from the network, making it unreachable, while
@code{enable-account} does the inverse.  They accept a single account
username or fingerprint as first argument:

@example sh
# herd disable-account jami f3345f2775ddfe07a4b0d95daea111d15fbc1199

# herd list-accounts jami
The following Jami accounts are available:
  - f3345f2775ddfe07a4b0d95daea111d15fbc1199 (dummy) [disabled]

@end example

The @code{list-account-details} action prints the detailed parameters of
each accounts in the Recutils format, which means the @command{recsel}
command can be used to select accounts of interest (@pxref{Selection
Expressions,,,recutils, GNU recutils manual}).  Note that period
characters (@samp{.}) found in the account parameter keys are mapped to
underscores (@samp{_}) in the output, to meet the requirements of the
Recutils format.  The following example shows how to print the account
fingerprints for all accounts operating in the rendezvous point mode:

@example sh
# herd list-account-details jami | \
  recsel -p Account.username -e 'Account.rendezVous ~ "true"'
Account_username: f3345f2775ddfe07a4b0d95daea111d15fbc1199
@end example

The remaining actions should be self-explanatory.

The complete set of available configuration options is detailed below.
@end defvar

@c TODO: Ideally, the following fragments would be auto-generated at
@c build time, so that they needn't be manually duplicated.
@c Auto-generated via (configuration->documentation 'jami-configuration)
@deftp {Data Type} jami-configuration
Available @code{jami-configuration} fields are:

@table @asis
@item @code{libjami} (default: @code{libjami}) (type: package)
The Jami daemon package to use.

@item @code{dbus} (default: @code{dbus-for-jami}) (type: package)
The D-Bus package to use to start the required D-Bus session.

@item @code{nss-certs} (default: @code{nss-certs}) (type: package)
The nss-certs package to use to provide TLS certificates.

@item @code{enable-logging?} (default: @code{#t}) (type: boolean)
Whether to enable logging to syslog.

@item @code{debug?} (default: @code{#f}) (type: boolean)
Whether to enable debug level messages.

@item @code{auto-answer?} (default: @code{#f}) (type: boolean)
Whether to force automatic answer to incoming calls.

@item @code{accounts} (type: maybe-jami-account-list)
A list of Jami accounts to be (re-)provisioned every time the Jami
daemon service starts.  When providing this field, the account
directories under @file{/var/lib/jami/} are recreated every time the
service starts, ensuring a consistent state.

@end table

@end deftp

@c Auto-generated via (configuration->documentation 'jami-account)
@deftp {Data Type} jami-account
Available @code{jami-account} fields are:

@table @asis
@item @code{archive} (type: string-or-computed-file)
The account archive (backup) file name of the account.  This is used to
provision the account when the service starts.  The account archive
should @emph{not} be encrypted.  It is highly recommended to make it
readable only to the @samp{root} user (i.e., not in the store), to guard
against leaking the secret key material of the Jami account it contains.

@item @code{allowed-contacts} (type: maybe-account-fingerprint-list)
The list of allowed contacts for the account, entered as their 40
characters long fingerprint.  Messages or calls from accounts not in
that list will be rejected.  When left specified, the configuration of
the account archive is used as-is with respect to contacts and public
inbound calls/messaging allowance, which typically defaults to allow any
contact to communicate with the account.

@item @code{moderators} (type: maybe-account-fingerprint-list)
The list of contacts that should have moderation privileges (to ban,
mute, etc.  other users) in rendezvous conferences, entered as their 40
characters long fingerprint.  When left unspecified, the configuration
of the account archive is used as-is with respect to moderation, which
typically defaults to allow anyone to moderate.

@item @code{rendezvous-point?} (type: maybe-boolean)
Whether the account should operate in the rendezvous mode.  In this
mode, all the incoming audio/video calls are mixed into a conference.
When left unspecified, the value from the account archive prevails.

@item @code{peer-discovery?} (type: maybe-boolean)
Whether peer discovery should be enabled.  Peer discovery is used to
discover other OpenDHT nodes on the local network, which can be useful
to maintain communication between devices on such network even when the
connection to the Internet has been lost.  When left unspecified,
the value from the account archive prevails.

@item @code{bootstrap-hostnames} (type: maybe-list-of-strings)
A list of hostnames or IPs pointing to OpenDHT nodes, that should be
used to initially join the OpenDHT network.  When left unspecified, the
value from the account archive prevails.

@item @code{name-server-uri} (type: maybe-string)
The URI of the name server to use, that can be used to retrieve the
account fingerprint for a registered username.

@end table

@end deftp

@subsubheading Mumble server

@cindex Mumble
@cindex Murmur
@cindex VoIP server
This section describes how to set up and run a
@uref{https://mumble.info, Mumble} server (formerly known as Murmur).

@defvar mumble-server-service-type

This is the service to run a Mumble server.  It takes a
@code{mumble-server-configuration} object as its value, defined below.
@end defvar

@deftp {Data Type} mumble-server-configuration
The service type for the Mumble server.  An example configuration can
look like this:

@lisp
(service mumble-server-service-type
         (mumble-server-configuration
          (welcome-text
            "Welcome to this Mumble server running on Guix!")
          (cert-required? #t) ;disallow text password logins
          (ssl-cert "/etc/certs/mumble.example.com/fullchain.pem")
          (ssl-key "/etc/certs/mumble.example.com/privkey.pem")))
@end lisp

After reconfiguring your system, you can manually set the mumble-server
@code{SuperUser}
password with the command that is printed during the activation phase.

It is recommended to register a normal Mumble user account
and grant it admin or moderator rights.
You can use the @code{mumble} client to
login as new normal user, register yourself, and log out.
For the next step login with the name @code{SuperUser} use
the @code{SuperUser} password that you set previously,
and grant your newly registered mumble user administrator or moderator
rights and create some channels.

Available @code{mumble-server-configuration} fields are:

@table @asis
@item @code{package} (default: @code{mumble})
Package that contains @code{bin/mumble-server}.

@item @code{user} (default: @code{"mumble-server"})
User who will run the Mumble-Server server.

@item @code{group} (default: @code{"mumble-server"})
Group of the user who will run the mumble-server server.

@item @code{port} (default: @code{64738})
Port on which the server will listen.

@item @code{welcome-text} (default: @code{""})
Welcome text sent to clients when they connect.

@item @code{server-password} (default: @code{""})
Password the clients have to enter in order to connect.

@item @code{max-users} (default: @code{100})
Maximum of users that can be connected to the server at once.

@item @code{max-user-bandwidth} (default: @code{#f})
Maximum voice traffic a user can send per second.

@item @code{database-file} (default: @code{"/var/lib/mumble-server/db.sqlite"})
File name of the sqlite database.
The service's user will become the owner of the directory.

@item @code{log-file} (default: @code{"/var/log/mumble-server/mumble-server.log"})
File name of the log file.
The service's user will become the owner of the directory.

@item @code{autoban-attempts} (default: @code{10})
Maximum number of logins a user can make in @code{autoban-timeframe}
without getting auto banned for @code{autoban-time}.

@item @code{autoban-timeframe} (default: @code{120})
Timeframe for autoban in seconds.

@item @code{autoban-time} (default: @code{300})
Amount of time in seconds for which a client gets banned
when violating the autoban limits.

@item @code{opus-threshold} (default: @code{100})
Percentage of clients that need to support opus
before switching over to opus audio codec.

@item @code{channel-nesting-limit} (default: @code{10})
How deep channels can be nested at maximum.

@item @code{channelname-regex} (default: @code{#f})
A string in form of a Qt regular expression that channel names must conform to.

@item @code{username-regex} (default: @code{#f})
A string in form of a Qt regular expression that user names must conform to.

@item @code{text-message-length} (default: @code{5000})
Maximum size in bytes that a user can send in one text chat message.

@item @code{image-message-length} (default: @code{(* 128 1024)})
Maximum size in bytes that a user can send in one image message.

@item @code{cert-required?} (default: @code{#f})
If it is set to @code{#t} clients that use weak password authentication
will not be accepted.  Users must have completed the certificate wizard to join.

@item @code{remember-channel?} (default: @code{#f})
Should mumble-server remember the last channel each user was in when
they disconnected and put them into the remembered channel when they
rejoin.

@item @code{allow-html?} (default: @code{#f})
Should html be allowed in text messages, user comments, and channel descriptions.

@item @code{allow-ping?} (default: @code{#f})
Setting to true exposes the current user count, the maximum user count, and
the server's maximum bandwidth per client to unauthenticated users.  In the
Mumble client, this information is shown in the Connect dialog.

Disabling this setting will prevent public listing of the server.

@item @code{bonjour?} (default: @code{#f})
Should the server advertise itself in the local network through the bonjour protocol.

@item @code{send-version?} (default: @code{#f})
Should the mumble-server server version be exposed in ping requests.

@item @code{log-days} (default: @code{31})
Mumble also stores logs in the database, which are accessible via RPC.
The default is 31 days of months, but you can set this setting to 0 to keep logs forever,
or -1 to disable logging to the database.

@item @code{obfuscate-ips?} (default: @code{#t})
Should logged ips be obfuscated to protect the privacy of users.

@item @code{ssl-cert} (default: @code{#f})
File name of the SSL/TLS certificate used for encrypted connections.

@lisp
(ssl-cert "/etc/certs/example.com/fullchain.pem")
@end lisp
@item @code{ssl-key} (default: @code{#f})
Filepath to the ssl private key used for encrypted connections.
@lisp
(ssl-key "/etc/certs/example.com/privkey.pem")
@end lisp

@item @code{ssl-dh-params} (default: @code{#f})
File name of a PEM-encoded file with Diffie-Hellman parameters
for the SSL/TLS encryption.  Alternatively you set it to
@code{"@@ffdhe2048"}, @code{"@@ffdhe3072"}, @code{"@@ffdhe4096"}, @code{"@@ffdhe6144"}
or @code{"@@ffdhe8192"} to use bundled parameters from RFC 7919.

@item @code{ssl-ciphers} (default: @code{#f})
The @code{ssl-ciphers} option chooses the cipher suites to make available for use
in SSL/TLS.

This option is specified using
@uref{https://www.openssl.org/docs/apps/ciphers.html#CIPHER-LIST-FORMAT,
OpenSSL cipher list notation}.

It is recommended that you try your cipher string using
'openssl ciphers <string>' before setting it here, to get a feel for
which cipher suites you will get.
After setting this option, it is recommend that you inspect your Mumble
server log to ensure that Mumble is using the cipher suites that you
expected it to.

@quotation Note
Changing this option may impact the backwards compatibility of your
Mumble-Server server, and can remove the ability for older Mumble clients to be able to connect to it.
@end quotation

@item @code{public-registration} (default: @code{#f})
Must be a @code{<mumble-server-public-registration-configuration>}
record or @code{#f}.

You can optionally register your server in the public server list that the
@code{mumble} client shows on startup.
You cannot register your server if you have set a @code{server-password},
or set @code{allow-ping} to @code{#f}.

It might take a few hours until it shows up in the public list.

@item @code{file} (default: @code{#f})
Optional alternative override for this configuration.
@end table
@end deftp

@deftp {Data Type} mumble-server-public-registration-configuration
Configuration for public registration of a mumble-server service.

@table @asis
@item @code{name}
This is a display name for your server.  Not to be confused with the hostname.

@item @code{password}
A password to identify your registration.
Subsequent updates will need the same password.  Don't lose your password.

@item @code{url}
This should be a @code{http://} or @code{https://} link to your web
site.

@item @code{hostname} (default: @code{#f})
By default your server will be listed by its IP address.
If it is set your server will be linked by this host name instead.
@end table
@end deftp

@quotation Deprecation notice
Due to historical reasons, all of the above @code{mumble-server-}
procedures are also exported with the @code{murmur-} prefix.
It is recommended that you switch to using @code{mumble-server-}
going forward.
@end quotation

@node File-Sharing Services
@subsection File-Sharing Services

The @code{(gnu services file-sharing)} module provides services that
assist with transferring files over peer-to-peer file-sharing networks.

@subsubheading Transmission Daemon Service

@uref{https://transmissionbt.com/, Transmission} is a flexible
BitTorrent client that offers a variety of graphical and command-line
interfaces.  A @code{transmission-daemon-service-type} service provides
Transmission's headless variant, @command{transmission-daemon}, as a
system service, allowing users to share files via BitTorrent even when
they are not logged in.

@defvar transmission-daemon-service-type
The service type for the Transmission Daemon BitTorrent client. Its
value must be a @code{transmission-daemon-configuration} object as in
this example:

@lisp
(service transmission-daemon-service-type
         (transmission-daemon-configuration
          ;; Restrict access to the RPC ("control") interface
          (rpc-authentication-required? #t)
          (rpc-username "transmission")
          (rpc-password
           (transmission-password-hash
            "transmission" ; desired password
            "uKd1uMs9"))   ; arbitrary salt value

          ;; Accept requests from this and other hosts on the
          ;; local network
          (rpc-whitelist-enabled? #t)
          (rpc-whitelist '("::1" "127.0.0.1" "192.168.0.*"))

          ;; Limit bandwidth use during work hours
          (alt-speed-down (* 1024 2)) ;   2 MB/s
          (alt-speed-up 512)          ; 512 kB/s

          (alt-speed-time-enabled? #t)
          (alt-speed-time-day 'weekdays)
          (alt-speed-time-begin
           (+ (* 60 8) 30))           ; 8:30 am
          (alt-speed-time-end
           (+ (* 60 (+ 12 5)) 30))))  ; 5:30 pm
@end lisp
@end defvar

Once the service is started, users can interact with the daemon through
its Web interface (at @code{http://localhost:9091/}) or by using the
@command{transmission-remote} command-line tool, available in the
@code{transmission} package.  (Emacs users may want to also consider the
@code{emacs-transmission} package.)  Both communicate with the daemon
through its remote procedure call (RPC) interface, which by default is
available to all users on the system; you may wish to change this by
assigning values to the @code{rpc-authentication-required?},
@code{rpc-username} and @code{rpc-password} settings, as shown in the
example above and documented further below.

The value for @code{rpc-password} must be a password hash of the type
generated and used by Transmission clients.  This can be copied verbatim
from an existing @file{settings.json} file, if another Transmission
client is already being used.  Otherwise, the
@code{transmission-password-hash} and @code{transmission-random-salt}
procedures provided by this module can be used to obtain a suitable hash
value.

@deffn {Procedure} transmission-password-hash password salt
Returns a string containing the result of hashing @var{password}
together with @var{salt}, in the format recognized by Transmission
clients for their @code{rpc-password} configuration setting.

@var{salt} must be an eight-character string.  The
@code{transmission-random-salt} procedure can be used to generate a
suitable salt value at random.
@end deffn

@deffn {Procedure} transmission-random-salt
Returns a string containing a random, eight-character salt value of the
type generated and used by Transmission clients, suitable for passing to
the @code{transmission-password-hash} procedure.
@end deffn

These procedures are accessible from within a Guile REPL started with
the @command{guix repl} command (@pxref{Invoking guix repl}).  This is
useful for obtaining a random salt value to provide as the second
parameter to `transmission-password-hash`, as in this example session:

@example
$ guix repl
scheme@@(guix-user)> ,use (gnu services file-sharing)
scheme@@(guix-user)> (transmission-random-salt)
$1 = "uKd1uMs9"
@end example

Alternatively, a complete password hash can generated in a single step:

@example
scheme@@(guix-user)> (transmission-password-hash "transmission"
(transmission-random-salt))
$2 = "@{c8bbc6d1740cd8dc819a6e25563b67812c1c19c9VtFPfdsX"
@end example

The resulting string can be used as-is for the value of
@code{rpc-password}, allowing the password to be kept hidden even in the
operating-system configuration.

Torrent files downloaded by the daemon are directly accessible only to
users in the ``transmission'' user group, who receive read-only access
to the directory specified by the @code{download-dir} configuration
setting (and also the directory specified by @code{incomplete-dir}, if
@code{incomplete-dir-enabled?} is @code{#t}).  Downloaded files can be
moved to another directory or deleted altogether using
@command{transmission-remote} with its @code{--move} and
@code{--remove-and-delete} options.

If the @code{watch-dir-enabled?} setting is set to @code{#t}, users in
the ``transmission'' group are able also to place @file{.torrent} files
in the directory specified by @code{watch-dir} to have the corresponding
torrents added by the daemon.  (The @code{trash-original-torrent-files?}
setting controls whether the daemon deletes these files after processing
them.)

Some of the daemon's configuration settings can be changed temporarily
by @command{transmission-remote} and similar tools. To undo these
changes, use the service's @code{reload} action to have the daemon
reload its settings from disk:

@example
# herd reload transmission-daemon
@end example

The full set of available configuration settings is defined by the
@code{transmission-daemon-configuration} data type.

@deftp {Data Type} transmission-daemon-configuration
The data type representing configuration settings for Transmission
Daemon.  These correspond directly to the settings recognized by
Transmission clients in their @file{settings.json} file.
@end deftp

@c The following documentation was initially generated by
@c (generate-transmission-daemon-documentation) in (gnu services
@c file-sharing).  Manually maintained documentation is better, so we
@c shouldn't hesitate to edit below as needed.  However if the change
@c you want to make to this documentation can be done in an automated
@c way, it's probably easier to change (generate-documentation) than to
@c make it below and have to deal with the churn as Transmission Daemon
@c updates.

@c %start of fragment

Available @code{transmission-daemon-configuration} fields are:

@deftypevr {@code{transmission-daemon-configuration} parameter} package transmission
The Transmission package to use.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} non-negative-integer stop-wait-period
The period, in seconds, to wait when stopping the service for
@command{transmission-daemon} to exit before killing its process.  This
allows the daemon time to complete its housekeeping and send a final
update to trackers as it shuts down.  On slow hosts, or hosts with a
slow network connection, this value may need to be increased.

Defaults to @samp{10}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} string download-dir
The directory to which torrent files are downloaded.

Defaults to @samp{"/var/lib/transmission-daemon/downloads"}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean incomplete-dir-enabled?
If @code{#t}, files will be held in @code{incomplete-dir} while their
torrent is being downloaded, then moved to @code{download-dir} once the
torrent is complete.  Otherwise, files for all torrents (including those
still being downloaded) will be placed in @code{download-dir}.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} maybe-string incomplete-dir
The directory in which files from incompletely downloaded torrents will
be held when @code{incomplete-dir-enabled?} is @code{#t}.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} umask umask
The file mode creation mask used for downloaded files.  (See the
@command{umask} man page for more information.)

Defaults to @samp{18}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean rename-partial-files?
When @code{#t}, ``.part'' is appended to the name of partially
downloaded files.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} preallocation-mode preallocation
The mode by which space should be preallocated for downloaded files, one
of @code{none}, @code{fast} (or @code{sparse}) and @code{full}.
Specifying @code{full} will minimize disk fragmentation at a cost to
file-creation speed.

Defaults to @samp{fast}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean watch-dir-enabled?
If @code{#t}, the directory specified by @code{watch-dir} will be
watched for new @file{.torrent} files and the torrents they describe
added automatically (and the original files removed, if
@code{trash-original-torrent-files?} is @code{#t}).

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} maybe-string watch-dir
The directory to be watched for @file{.torrent} files indicating new
torrents to be added, when @code{watch-dir-enabled} is @code{#t}.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean trash-original-torrent-files?
When @code{#t}, @file{.torrent} files will be deleted from the watch
directory once their torrent has been added (see
@code{watch-directory-enabled?}).

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean speed-limit-down-enabled?
When @code{#t}, the daemon's download speed will be limited to the rate
specified by @code{speed-limit-down}.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} non-negative-integer speed-limit-down
The default global-maximum download speed, in kilobytes per second.

Defaults to @samp{100}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean speed-limit-up-enabled?
When @code{#t}, the daemon's upload speed will be limited to the rate
specified by @code{speed-limit-up}.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} non-negative-integer speed-limit-up
The default global-maximum upload speed, in kilobytes per second.

Defaults to @samp{100}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean alt-speed-enabled?
When @code{#t}, the alternate speed limits @code{alt-speed-down} and
@code{alt-speed-up} are used (in place of @code{speed-limit-down} and
@code{speed-limit-up}, if they are enabled) to constrain the daemon's
bandwidth usage.  This can be scheduled to occur automatically at
certain times during the week; see @code{alt-speed-time-enabled?}.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} non-negative-integer alt-speed-down
The alternate global-maximum download speed, in kilobytes per second.

Defaults to @samp{50}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} non-negative-integer alt-speed-up
The alternate global-maximum upload speed, in kilobytes per second.

Defaults to @samp{50}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean alt-speed-time-enabled?
When @code{#t}, the alternate speed limits @code{alt-speed-down} and
@code{alt-speed-up} will be enabled automatically during the periods
specified by @code{alt-speed-time-day}, @code{alt-speed-time-begin} and
@code{alt-time-speed-end}.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} day-list alt-speed-time-day
The days of the week on which the alternate-speed schedule should be
used, specified either as a list of days (@code{sunday}, @code{monday},
and so on) or using one of the symbols @code{weekdays}, @code{weekends}
or @code{all}.

Defaults to @samp{all}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} non-negative-integer alt-speed-time-begin
The time of day at which to enable the alternate speed limits, expressed
as a number of minutes since midnight.

Defaults to @samp{540}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} non-negative-integer alt-speed-time-end
The time of day at which to disable the alternate speed limits,
expressed as a number of minutes since midnight.

Defaults to @samp{1020}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} string bind-address-ipv4
The IP address at which to listen for peer connections, or ``0.0.0.0''
to listen at all available IP addresses.

Defaults to @samp{"0.0.0.0"}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} string bind-address-ipv6
The IPv6 address at which to listen for peer connections, or ``::'' to
listen at all available IPv6 addresses.

Defaults to @samp{"::"}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean peer-port-random-on-start?
If @code{#t}, when the daemon starts it will select a port at random on
which to listen for peer connections, from the range specified
(inclusively) by @code{peer-port-random-low} and
@code{peer-port-random-high}.  Otherwise, it listens on the port
specified by @code{peer-port}.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} port-number peer-port-random-low
The lowest selectable port number when @code{peer-port-random-on-start?}
is @code{#t}.

Defaults to @samp{49152}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} port-number peer-port-random-high
The highest selectable port number when @code{peer-port-random-on-start}
is @code{#t}.

Defaults to @samp{65535}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} port-number peer-port
The port on which to listen for peer connections when
@code{peer-port-random-on-start?} is @code{#f}.

Defaults to @samp{51413}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean port-forwarding-enabled?
If @code{#t}, the daemon will attempt to configure port-forwarding on an
upstream gateway automatically using @acronym{UPnP} and
@acronym{NAT-PMP}.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} encryption-mode encryption
The encryption preference for peer connections, one of
@code{prefer-unencrypted-connections},
@code{prefer-encrypted-connections} or
@code{require-encrypted-connections}.

Defaults to @samp{prefer-encrypted-connections}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} maybe-string peer-congestion-algorithm
The TCP congestion-control algorithm to use for peer connections,
specified using a string recognized by the operating system in calls to
@code{setsockopt}.  When left unspecified, the operating-system default
is used.

Note that on GNU/Linux systems, the kernel must be configured to allow
processes to use a congestion-control algorithm not in the default set;
otherwise, it will deny these requests with ``Operation not permitted''.
To see which algorithms are available on your system and which are
currently permitted for use, look at the contents of the files
@file{tcp_available_congestion_control} and
@file{tcp_allowed_congestion_control} in the @file{/proc/sys/net/ipv4}
directory.

As an example, to have Transmission Daemon use
@uref{http://www-ece.rice.edu/networks/TCP-LP/,the TCP Low Priority
congestion-control algorithm}, you'll need to modify your kernel
configuration to build in support for the algorithm, then update your
operating-system configuration to allow its use by adding a
@code{sysctl-service-type} service (or updating the existing one's
configuration) with lines like the following:

@lisp
(service sysctl-service-type
         (sysctl-configuration
          (settings
           ("net.ipv4.tcp_allowed_congestion_control" .
            "reno cubic lp"))))
@end lisp

The Transmission Daemon configuration can then be updated with

@lisp
(peer-congestion-algorithm "lp")
@end lisp

and the system reconfigured to have the changes take effect.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} tcp-type-of-service peer-socket-tos
The type of service to request in outgoing @acronym{TCP} packets, one of
@code{default}, @code{low-cost}, @code{throughput}, @code{low-delay} and
@code{reliability}.

Defaults to @samp{default}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} non-negative-integer peer-limit-global
The global limit on the number of connected peers.

Defaults to @samp{200}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} non-negative-integer peer-limit-per-torrent
The per-torrent limit on the number of connected peers.

Defaults to @samp{50}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} non-negative-integer upload-slots-per-torrent
The maximum number of peers to which the daemon will upload data
simultaneously for each torrent.

Defaults to @samp{14}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} non-negative-integer peer-id-ttl-hours
The maximum lifespan, in hours, of the peer ID associated with each
public torrent before it is regenerated.

Defaults to @samp{6}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean blocklist-enabled?
When @code{#t}, the daemon will ignore peers mentioned in the blocklist
it has most recently downloaded from @code{blocklist-url}.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} maybe-string blocklist-url
The URL of a peer blocklist (in @acronym{P2P}-plaintext or eMule
@file{.dat} format) to be periodically downloaded and applied when
@code{blocklist-enabled?} is @code{#t}.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean download-queue-enabled?
If @code{#t}, the daemon will be limited to downloading at most
@code{download-queue-size} non-stalled torrents simultaneously.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} non-negative-integer download-queue-size
The size of the daemon's download queue, which limits the number of
non-stalled torrents it will download at any one time when
@code{download-queue-enabled?} is @code{#t}.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean seed-queue-enabled?
If @code{#t}, the daemon will be limited to seeding at most
@code{seed-queue-size} non-stalled torrents simultaneously.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} non-negative-integer seed-queue-size
The size of the daemon's seed queue, which limits the number of
non-stalled torrents it will seed at any one time when
@code{seed-queue-enabled?} is @code{#t}.

Defaults to @samp{10}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean queue-stalled-enabled?
When @code{#t}, the daemon will consider torrents for which it has not
shared data in the past @code{queue-stalled-minutes} minutes to be
stalled and not count them against its @code{download-queue-size} and
@code{seed-queue-size} limits.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} non-negative-integer queue-stalled-minutes
The maximum period, in minutes, a torrent may be idle before it is
considered to be stalled, when @code{queue-stalled-enabled?} is
@code{#t}.

Defaults to @samp{30}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean ratio-limit-enabled?
When @code{#t}, a torrent being seeded will automatically be paused once
it reaches the ratio specified by @code{ratio-limit}.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} non-negative-rational ratio-limit
The ratio at which a torrent being seeded will be paused, when
@code{ratio-limit-enabled?} is @code{#t}.

Defaults to @samp{2.0}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean idle-seeding-limit-enabled?
When @code{#t}, a torrent being seeded will automatically be paused once
it has been idle for @code{idle-seeding-limit} minutes.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} non-negative-integer idle-seeding-limit
The maximum period, in minutes, a torrent being seeded may be idle
before it is paused, when @code{idle-seeding-limit-enabled?} is
@code{#t}.

Defaults to @samp{30}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean dht-enabled?
Enable @uref{http://bittorrent.org/beps/bep_0005.html,the distributed
hash table (@acronym{DHT}) protocol}, which supports the use of
trackerless torrents.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean lpd-enabled?
Enable @uref{https://en.wikipedia.org/wiki/Local_Peer_Discovery,local
peer discovery} (@acronym{LPD}), which allows the discovery of peers on
the local network and may reduce the amount of data sent over the public
Internet.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean pex-enabled?
Enable @uref{https://en.wikipedia.org/wiki/Peer_exchange,peer exchange}
(@acronym{PEX}), which reduces the daemon's reliance on external
trackers and may improve its performance.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean utp-enabled?
Enable @uref{http://bittorrent.org/beps/bep_0029.html,the micro
transport protocol} (@acronym{uTP}), which aims to reduce the impact of
BitTorrent traffic on other users of the local network while maintaining
full utilization of the available bandwidth.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean rpc-enabled?
If @code{#t}, enable the remote procedure call (@acronym{RPC})
interface, which allows remote control of the daemon via its Web
interface, the @command{transmission-remote} command-line client, and
similar tools.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} string rpc-bind-address
The IP address at which to listen for @acronym{RPC} connections, or
``0.0.0.0'' to listen at all available IP addresses.

Defaults to @samp{"0.0.0.0"}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} port-number rpc-port
The port on which to listen for @acronym{RPC} connections.

Defaults to @samp{9091}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} string rpc-url
The path prefix to use in the @acronym{RPC}-endpoint @acronym{URL}.

Defaults to @samp{"/transmission/"}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean rpc-authentication-required?
When @code{#t}, clients must authenticate (see @code{rpc-username} and
@code{rpc-password}) when using the @acronym{RPC} interface.  Note this
has the side effect of disabling host-name whitelisting (see
@code{rpc-host-whitelist-enabled?}.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} maybe-string rpc-username
The username required by clients to access the @acronym{RPC} interface
when @code{rpc-authentication-required?} is @code{#t}.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} maybe-transmission-password-hash rpc-password
The password required by clients to access the @acronym{RPC} interface
when @code{rpc-authentication-required?} is @code{#t}.  This must be
specified using a password hash in the format recognized by Transmission
clients, either copied from an existing @file{settings.json} file or
generated using the @code{transmission-password-hash} procedure.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean rpc-whitelist-enabled?
When @code{#t}, @acronym{RPC} requests will be accepted only when they
originate from an address specified in @code{rpc-whitelist}.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} string-list rpc-whitelist
The list of IP and IPv6 addresses from which @acronym{RPC} requests will
be accepted when @code{rpc-whitelist-enabled?} is @code{#t}.  Wildcards
may be specified using @samp{*}.

Defaults to @samp{'("127.0.0.1" "::1")}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean rpc-host-whitelist-enabled?
When @code{#t}, @acronym{RPC} requests will be accepted only when they
are addressed to a host named in @code{rpc-host-whitelist}.  Note that
requests to ``localhost'' or ``localhost.'', or to a numeric address,
are always accepted regardless of these settings.

Note also this functionality is disabled when
@code{rpc-authentication-required?} is @code{#t}.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} string-list rpc-host-whitelist
The list of host names recognized by the @acronym{RPC} server when
@code{rpc-host-whitelist-enabled?} is @code{#t}.

Defaults to @samp{'()}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} message-level message-level
The minimum severity level of messages to be logged (to
@file{/var/log/transmission.log}) by the daemon, one of @code{none} (no
logging), @code{error}, @code{info} and @code{debug}.

Defaults to @samp{info}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean start-added-torrents?
When @code{#t}, torrents are started as soon as they are added;
otherwise, they are added in ``paused'' state.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean script-torrent-done-enabled?
When @code{#t}, the script specified by
@code{script-torrent-done-filename} will be invoked each time a torrent
completes.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} maybe-file-object script-torrent-done-filename
A file name or file-like object specifying a script to run each time a
torrent completes, when @code{script-torrent-done-enabled?} is
@code{#t}.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean scrape-paused-torrents-enabled?
When @code{#t}, the daemon will scrape trackers for a torrent even when
the torrent is paused.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} non-negative-integer cache-size-mb
The amount of memory, in megabytes, to allocate for the daemon's
in-memory cache.  A larger value may increase performance by reducing
the frequency of disk I/O.

Defaults to @samp{4}.

@end deftypevr

@deftypevr {@code{transmission-daemon-configuration} parameter} boolean prefetch-enabled?
When @code{#t}, the daemon will try to improve I/O performance by
hinting to the operating system which data is likely to be read next
from disk to satisfy requests from peers.

Defaults to @samp{#t}.

@end deftypevr


@c %end of fragment



@node Monitoring Services
@subsection Monitoring Services

@subsubheading Tailon Service

@uref{https://tailon.readthedocs.io/, Tailon} is a web application for
viewing and searching log files.

The following example will configure the service with default values.
By default, Tailon can be accessed on port 8080 (@code{http://localhost:8080}).

@lisp
(service tailon-service-type)
@end lisp

The following example customises more of the Tailon configuration,
adding @command{sed} to the list of allowed commands.

@lisp
(service tailon-service-type
         (tailon-configuration
           (config-file
             (tailon-configuration-file
               (allowed-commands '("tail" "grep" "awk" "sed"))))))
@end lisp


@deftp {Data Type} tailon-configuration
Data type representing the configuration of Tailon.
This type has the following parameters:

@table @asis
@item @code{config-file} (default: @code{(tailon-configuration-file)})
The configuration file to use for Tailon.  This can be set to a
@dfn{tailon-configuration-file} record value, or any gexp
(@pxref{G-Expressions}).

For example, to instead use a local file, the @code{local-file} function
can be used:

@lisp
(service tailon-service-type
         (tailon-configuration
           (config-file (local-file "./my-tailon.conf"))))
@end lisp

@item @code{package} (default: @code{tailon})
The tailon package to use.

@end table
@end deftp

@deftp {Data Type} tailon-configuration-file
Data type representing the configuration options for Tailon.
This type has the following parameters:

@table @asis
@item @code{files} (default: @code{(list "/var/log")})
List of files to display.  The list can include strings for a single file
or directory, or a list, where the first item is the name of a
subsection, and the remaining items are the files or directories in that
subsection.

@item @code{bind} (default: @code{"localhost:8080"})
Address and port to which Tailon should bind on.

@item @code{relative-root} (default: @code{#f})
URL path to use for Tailon, set to @code{#f} to not use a path.

@item @code{allow-transfers?} (default: @code{#t})
Allow downloading the log files in the web interface.

@item @code{follow-names?} (default: @code{#t})
Allow tailing of not-yet existent files.

@item @code{tail-lines} (default: @code{200})
Number of lines to read initially from each file.

@item @code{allowed-commands} (default: @code{(list "tail" "grep" "awk")})
Commands to allow running.  By default, @code{sed} is disabled.

@item @code{debug?} (default: @code{#f})
Set @code{debug?} to @code{#t} to show debug messages.

@item @code{wrap-lines} (default: @code{#t})
Initial line wrapping state in the web interface.  Set to @code{#t} to
initially wrap lines (the default), or to @code{#f} to initially not
wrap lines.

@item @code{http-auth} (default: @code{#f})
HTTP authentication type to use.   Set to @code{#f} to disable
authentication (the default).  Supported values are @code{"digest"} or
@code{"basic"}.

@item @code{users} (default: @code{#f})
If HTTP authentication is enabled (see @code{http-auth}), access will be
restricted to the credentials provided here.  To configure users, use a
list of pairs, where the first element of the pair is the username, and
the 2nd element of the pair is the password.

@lisp
(tailon-configuration-file
  (http-auth "basic")
  (users     '(("user1" . "password1")
               ("user2" . "password2"))))
@end lisp

@end table
@end deftp


@subsubheading Darkstat Service
@cindex darkstat
Darkstat is a packet sniffer that captures network traffic, calculates
statistics about usage, and serves reports over HTTP.

@defvar darkstat-service-type
This is the service type for the
@uref{https://unix4lyfe.org/darkstat/, darkstat}
service,  its value must be a @code{darkstat-configuration} record as in
this example:

@lisp
(service darkstat-service-type
         (darkstat-configuration
           (interface "eno1")))
@end lisp
@end defvar

@deftp {Data Type} darkstat-configuration
Data type representing the configuration of @command{darkstat}.

@table @asis
@item @code{package} (default: @code{darkstat})
The darkstat package to use.

@item @code{interface}
Capture traffic on the specified network interface.

@item @code{port} (default: @code{"667"})
Bind the web interface to the specified port.

@item @code{bind-address} (default: @code{"127.0.0.1"})
Bind the web interface to the specified address.

@item @code{base} (default: @code{"/"})
Specify the path of the base URL@.  This can be useful if
@command{darkstat} is accessed via a reverse proxy.

@end table
@end deftp

@anchor{prometheus-node-exporter}
@subsubheading Prometheus Node Exporter Service
@cindex prometheus-node-exporter

The Prometheus ``node exporter'' makes hardware and operating system statistics
provided by the Linux kernel available for the Prometheus monitoring system.
This service should be deployed on all physical nodes and virtual machines,
where monitoring these statistics is desirable.

@defvar prometheus-node-exporter-service-type
This is the service type for the
@uref{https://github.com/prometheus/node_exporter/, prometheus-node-exporter}
service, its value must be a @code{prometheus-node-exporter-configuration}.

@lisp
(service prometheus-node-exporter-service-type)
@end lisp
@end defvar

@deftp {Data Type} prometheus-node-exporter-configuration
Data type representing the configuration of @command{node_exporter}.

@table @asis
@item @code{package} (default: @code{go-github-com-prometheus-node-exporter})
The prometheus-node-exporter package to use.

@item @code{web-listen-address} (default: @code{":9100"})
Bind the web interface to the specified address.

@item @code{textfile-directory} (default: @code{"/var/lib/prometheus/node-exporter"})
This directory can be used to export metrics specific to this machine.
Files containing metrics in the text format, with the filename ending in
@code{.prom} should be placed in this directory.

@item @code{extra-options} (default: @code{'()})
Extra options to pass to the Prometheus node exporter.

@end table
@end deftp

@anchor{vnstat}
@subsubheading vnStat Network Traffic Monitor
@cindex vnstat

vnStat is a network traffic monitor that uses interface statistics provided
by the kernel rather than traffic sniffing.  This makes it a light resource
monitor, regardless of network traffic rate.

@defvar vnstat-service-type
This is the service type for the @uref{https://humdi.net/vnstat/,vnStat} daemon
and accepts a @code{vnstat-configuration} value.

The following example will configure the service with default values:

@lisp
(service vnstat-service-type)
@end lisp
@end defvar

@c %start of fragment
@deftp {Data Type} vnstat-configuration
Available @code{vnstat-configuration} fields are:

@table @asis
@item @code{package} (default: @code{vnstat}) (type: file-like)
The vnstat package.

@item @code{database-directory} (default: @code{"/var/lib/vnstat"}) (type: string)
Specifies the directory where the database is to be stored.  A full path
must be given and a leading '/' isn't required.

@item @code{5-minute-hours} (default: @code{48}) (type: maybe-integer)
Data retention duration for the 5 minute resolution entries.  The
configuration defines for how many past hours entries will be stored.
Set to @code{-1} for unlimited entries or to @code{0} to disable the
data collection of this resolution.

@item @code{64bit-interface-counters} (default: @code{-2}) (type: maybe-integer)
Select interface counter handling.  Set to @code{1} for defining that
all interfaces use 64-bit counters on the kernel side and @code{0} for
defining 32-bit counter.  Set to @code{-1} for using the old style logic
used in earlier versions where counter values within 32-bits are assumed
to be 32-bit and anything larger is assumed to be a 64-bit counter.  This
may produce false results if a 64-bit counter is reset within the
32-bits.  Set to @code{-2} for using automatic detection based on
available kernel datastructures.

@item @code{always-add-new-interfaces?} (default: @code{#t}) (type: maybe-boolean)
Enable or disable automatic creation of new database entries for
interfaces not currently in the database even if the database file
already exists when the daemon is started.  New database entries will
also get created for new interfaces seen while the daemon is running.
Pseudo interfaces @samp{lo}, @samp{lo0} and @samp{sit0} are always excluded from getting
added.

@item @code{bandwidth-detection?} (default: @code{#t}) (type: maybe-boolean)
Try to automatically detect @var{max-bandwidth} value for each monitored
interface.  Mostly only ethernet interfaces support this feature.
@var{max-bandwidth} will be used as fallback value if detection fails.
Any interface specific @var{max-BW} configuration will disable the
detection for the specified interface.  In Linux, the detection is
disabled for tun interfaces due to the Linux kernel always reporting 10
Mbit regardless of the used real interface.

@item @code{bandwidth-detection-interval} (default: @code{5}) (type: maybe-integer)
How often in minutes interface specific detection of @var{max-bandwidth}
is done for detecting possible changes when @var{bandwidth-detection} is
enabled.  Can be disabled by setting to @code{0}.  Value range:
@samp{0}..@samp{30}

@item @code{boot-variation} (default: @code{15}) (type: maybe-integer)
Time in seconds how much the boot time reported by system kernel can
variate between updates.  Value range: @samp{0}..@samp{300}

@item @code{check-disk-space?} (default: @code{#t}) (type: maybe-boolean)
Enable or disable the availability check of at least some free disk
space before a database write.

@item @code{create-directories?} (default: @code{#t}) (type: maybe-boolean)
Enable or disable the creation of directories when a configured path
doesn't exist.  This includes @var{database-directory}.

@item @code{daemon-group} (type: maybe-user-group)
Specify the group to which the daemon process should switch during
startup.  Set to @code{%unset-value} to disable group switching.

@item @code{daemon-user} (type: maybe-user-account)
Specify the user to which the daemon process should switch during
startup.  Set to @code{%unset-value} to disable user switching.

@item @code{daily-days} (default: @code{62}) (type: maybe-integer)
Data retention duration for the one day resolution entries.  The
configuration defines for how many past days entries will be stored.  Set
to @code{-1} for unlimited entries or to @code{0} to disable the data
collection of this resolution.

@item @code{database-synchronous} (default: @code{-1}) (type: maybe-integer)
Change the setting of the SQLite "synchronous" flag which controls how
much care is taken to ensure disk writes have fully completed when
writing data to the database before continuing other actions.  Higher
values take extra steps to ensure data safety at the cost of slower
performance.  A value of @code{0} will result in all handling being left
to the filesystem itself.  Set to @code{-1} to select the default value
according to database mode controlled by
@var{database-write-ahead-logging} setting.  See SQLite documentation
for more details regarding values from @code{1} to @code{3}.  Value
range: @samp{-1}..@samp{3}

@item @code{database-write-ahead-logging?} (default: @code{#f}) (type: maybe-boolean)
Enable or disable SQLite Write-Ahead Logging mode for the database.  See
SQLite documentation for more details and note that support for
read-only operations isn't available in older SQLite versions.

@item @code{hourly-days} (default: @code{4}) (type: maybe-integer)
Data retention duration for the one hour resolution entries.  The
configuration defines for how many past days entries will be stored.  Set
to @code{-1} for unlimited entries or to @code{0} to disable the data
collection of this resolution.

@item @code{log-file} (type: maybe-string)
Specify log file path and name to be used if @var{use-logging} is set to
@code{1}.

@item @code{max-bandwidth} (type: maybe-integer)
Maximum bandwidth for all interfaces.  If the interface specific traffic
exceeds the given value then the data is assumed to be invalid and
rejected.  Set to 0 in order to disable the feature.  Value range:
@samp{0}..@samp{50000}

@item @code{max-bw} (type: maybe-alist)
Same as @var{max-bandwidth} but can be used for setting individual
limits for selected interfaces.  This is an association list of
interfaces as strings to integer values.  For example,
@lisp
(max-bw `(("eth0" .  15000)
          ("ppp0" .  10000)))
@end lisp
@var{bandwidth-detection} is disabled on an interface specific level for
each @var{max-bw} configuration.  Value range: @samp{0}..@samp{50000}

@item @code{monthly-months} (default: @code{25}) (type: maybe-integer)
Data retention duration for the one month resolution entries.  The
configuration defines for how many past months entries will be stored.
Set to @code{-1} for unlimited entries or to @code{0} to disable the
data collection of this resolution.

@item @code{month-rotate} (default: @code{1}) (type: maybe-integer)
Day of month that months are expected to change.  Usually set to 1 but
can be set to alternative values for example for tracking monthly billed
traffic where the billing period doesn't start on the first day.  For
example, if set to 7, days of February up to and including the 6th will
count for January.  Changing this option will not cause existing data to
be recalculated.  Value range: @samp{1}..@samp{28}

@item @code{month-rotate-affects-years?} (default: @code{#f}) (type: maybe-boolean)
Enable or disable @var{month-rotate} also affecting yearly data.
Applicable only when @var{month-rotate} has a value greater than one.

@item @code{offline-save-interval} (default: @code{30}) (type: maybe-integer)
How often in minutes cached interface data is saved to file when all
monitored interfaces are offline.  Value range:
@var{save-interval}..@samp{60}

@item @code{pid-file} (default: @code{"/var/run/vnstatd.pid"}) (type: maybe-string)
Specify pid file path and name to be used.

@item @code{poll-interval} (default: @code{5}) (type: maybe-integer)
How often in seconds interfaces are checked for status changes.  Value
range: @samp{2}..@samp{60}

@item @code{rescan-database-on-save?} (type: maybe-boolean)
Automatically discover added interfaces from the database and start
monitoring.  The rescan is done every @var{save-interval} or
@var{offline-save-interval} minutes depending on the current activity
state.

@item @code{save-interval} (default: @code{5}) (type: maybe-integer)
How often in minutes cached interface data is saved to file.  Value
range: ( @var{update-interval} / 60 )..@samp{60}

@item @code{save-on-status-change?} (default: @code{#t}) (type: maybe-boolean)
Enable or disable the additional saving to file of cached interface data
when the availability of an interface changes, i.e., when an interface
goes offline or comes online.

@item @code{time-sync-wait} (default: @code{5}) (type: maybe-integer)
How many minutes to wait during daemon startup for system clock to sync
if most recent database update appears to be in the future.  This may be
needed in systems without a real-time clock (RTC) which require some
time after boot to query and set the correct time.  @code{0} = wait
disabled.  Value range: @samp{0}..@samp{60}

@item @code{top-day-entries} (default: @code{20}) (type: maybe-integer)
Data retention duration for the top day entries.  The configuration
defines how many of the past top day entries will be stored.  Set to
@code{-1} for unlimited entries or to @code{0} to disable the data
collection of this resolution.

@item @code{trafficless-entries?} (default: @code{#t}) (type: maybe-boolean)
Create database entries even when there is no traffic during the entry's
time period.

@item @code{update-file-owner?} (default: @code{#t}) (type: maybe-boolean)
Enable or disable the update of file ownership during daemon process
startup.  During daemon startup, only database, log and pid files will
be modified if the user or group change feature ( @var{daemon-user} or
@var{daemon-group} ) is enabled and the files don't match the requested
user or group.  During manual database creation, this option will cause
file ownership to be inherited from the database directory if the
directory already exists.  This option only has effect when the process
is started as root or via sudo.

@item @code{update-interval} (default: @code{20}) (type: maybe-integer)
How often in seconds the interface data is updated.  Value range:
@var{poll-interval}..@samp{300}

@item @code{use-logging} (default: @code{2}) (type: maybe-integer)
Enable or disable logging.  Accepted values are: @code{0} = disabled,
@code{1} = logfile and @code{2} = syslog.

@item @code{use-utc?} (type: maybe-boolean)
Enable or disable using UTC as timezone in the database for all entries.
When enabled, all entries added to the database will use UTC regardless
of the configured system timezone.  When disabled, the configured system
timezone will be used.  Changing this setting will not result in already
existing data to be modified.

@item @code{yearly-years} (default: @code{-1}) (type: maybe-integer)
Data retention duration for the one year resolution entries.  The
configuration defines for how many past years entries will be stored.
Set to @code{-1} for unlimited entries or to @code{0} to disable the
data collection of this resolution.

@end table
@end deftp
@c %end of fragment

@subsubheading Zabbix server
@cindex zabbix zabbix-server
Zabbix is a high performance monitoring system that can collect data from a
variety of sources and provide the results in a web-based interface.  Alerting
and reporting is built-in, as well as @dfn{templates} for common operating
system metrics such as network utilization, CPU load, and disk space consumption.

This service provides the central Zabbix monitoring service; you also need
@ref{zabbix-front-end,@code{zabbix-front-end-service-type}} to configure Zabbix
and display results, and optionally @ref{zabbix-agent,
@code{zabbix-agent-service-type}} on machines that should be monitored (other
data sources are supported, such as @ref{prometheus-node-exporter,
Prometheus Node Exporter}).

@defvar zabbix-server-service-type
This is the service type for the Zabbix server service.  Its value must be a
@code{zabbix-server-configuration} record, shown below.
@end defvar

@c %start of fragment

@deftp {Data Type} zabbix-server-configuration
Available @code{zabbix-server-configuration} fields are:

@table @asis
@item @code{zabbix-server} (default: @code{zabbix-server}) (type: file-like)
The zabbix-server package.

@item @code{user} (default: @code{"zabbix"}) (type: string)
User who will run the Zabbix server.

@item @code{group} (default: @code{"zabbix"}) (type: string)
Group who will run the Zabbix server.

@item @code{db-host} (default: @code{"127.0.0.1"}) (type: string)
Database host name.

@item @code{db-name} (default: @code{"zabbix"}) (type: string)
Database name.

@item @code{db-user} (default: @code{"zabbix"}) (type: string)
Database user.

@item @code{db-password} (default: @code{""}) (type: string)
Database password.  Please, use @code{include-files} with
@code{DBPassword=SECRET} inside a specified file instead.

@item @code{db-port} (default: @code{5432}) (type: number)
Database port.

@item @code{log-type} (default: @code{""}) (type: string)
Specifies where log messages are written to:

@itemize @bullet

@item @code{system} - syslog.

@item @code{file} - file specified with @code{log-file} parameter.

@item @code{console} - standard output.

@end itemize

@item @code{log-file} (default: @code{"/var/log/zabbix/server.log"}) (type: string)
Log file name for @code{log-type} @code{file} parameter.

@item @code{pid-file} (default: @code{"/var/run/zabbix/zabbix_server.pid"}) (type: string)
Name of PID file.

@item @code{ssl-ca-location} (default: @code{"/etc/ssl/certs/ca-certificates.crt"}) (type: string)
The location of certificate authority (CA) files for SSL server
certificate verification.

@item @code{ssl-cert-location} (default: @code{"/etc/ssl/certs"}) (type: string)
Location of SSL client certificates.

@item @code{extra-options} (default: @code{""}) (type: extra-options)
Extra options will be appended to Zabbix server configuration file.

@item @code{include-files} (default: @code{'()}) (type: include-files)
You may include individual files or all files in a directory in the
configuration file.

@end table

@end deftp


@c %end of fragment

@anchor{zabbix-agent}
@subsubheading Zabbix agent
@cindex zabbix zabbix-agent

The Zabbix agent gathers information about the running system for the Zabbix
monitoring server.  It has a variety of built-in checks, and can be extended
with custom
@uref{https://www.zabbix.com/documentation/current/en/manual/config/items/userparameters,
@dfn{user parameters}}.

@defvar zabbix-agent-service-type
This is the service type for the Zabbix agent service.  Its value must be a
@code{zabbix-agent-configuration} record, shown below.
@end defvar

@c %start of fragment

@deftp {Data Type} zabbix-agent-configuration
Available @code{zabbix-agent-configuration} fields are:

@table @asis
@item @code{zabbix-agent} (default: @code{zabbix-agentd}) (type: file-like)
The zabbix-agent package.

@item @code{user} (default: @code{"zabbix"}) (type: string)
User who will run the Zabbix agent.

@item @code{group} (default: @code{"zabbix"}) (type: string)
Group who will run the Zabbix agent.

@item @code{hostname} (default: @code{""}) (type: string)
Unique, case sensitive hostname which is required for active checks and
must match hostname as configured on the server.

@item @code{log-type} (default: @code{""}) (type: string)
Specifies where log messages are written to:

@itemize @bullet
@item
@code{system} - syslog.

@item @code{file} - file specified with
@code{log-file} parameter.

@item @code{console} - standard output.

@end itemize

@item @code{log-file} (default: @code{"/var/log/zabbix/agent.log"}) (type: string)
Log file name for @code{log-type} @code{file} parameter.

@item @code{pid-file} (default: @code{"/var/run/zabbix/zabbix_agent.pid"}) (type: string)
Name of PID file.

@item @code{server} (default: @code{'("127.0.0.1")}) (type: list)
List of IP addresses, optionally in CIDR notation, or hostnames of
Zabbix servers and Zabbix proxies.  Incoming connections will be
accepted only from the hosts listed here.

@item @code{server-active} (default: @code{'("127.0.0.1")}) (type: list)
List of IP:port (or hostname:port) pairs of Zabbix servers and Zabbix
proxies for active checks.  If port is not specified, default port is
used.  If this parameter is not specified, active checks are disabled.

@item @code{extra-options} (default: @code{""}) (type: extra-options)
Extra options will be appended to Zabbix server configuration file.

@item @code{include-files} (default: @code{'()}) (type: include-files)
You may include individual files or all files in a directory in the
configuration file.

@end table

@end deftp


@c %end of fragment

@anchor{zabbix-front-end}
@subsubheading Zabbix front-end
@cindex zabbix zabbix-front-end

The Zabbix front-end provides a web interface to Zabbix.  It does not need
to run on the same machine as the Zabbix server.  This service works by
extending the @ref{PHP-FPM} and @ref{NGINX} services with the configuration
necessary for loading the Zabbix user interface.

@defvar zabbix-front-end-service-type
This is the service type for the Zabbix web frontend.  Its value must be a
@code{zabbix-front-end-configuration} record, shown below.
@end defvar

@c %start of fragment

@deftp {Data Type} zabbix-front-end-configuration
Available @code{zabbix-front-end-configuration} fields are:

@table @asis
@item @code{zabbix-server} (default: @code{zabbix-server}) (type: file-like)
The Zabbix server package to use.

@item @code{nginx} (default: @code{'()}) (type: list)
List of @ref{nginx-server-configuration,@code{nginx-server-configuration}}
blocks for the Zabbix front-end.  When empty, a default that listens on
port 80 is used.

@item @code{db-host} (default: @code{"localhost"}) (type: string)
Database host name.

@item @code{db-port} (default: @code{5432}) (type: number)
Database port.

@item @code{db-name} (default: @code{"zabbix"}) (type: string)
Database name.

@item @code{db-user} (default: @code{"zabbix"}) (type: string)
Database user.

@item @code{db-password} (default: @code{""}) (type: string)
Database password.  Please, use @code{db-secret-file} instead.

@item @code{db-secret-file} (default: @code{""}) (type: string)
Secret file which will be appended to @file{zabbix.conf.php} file.  This
file contains credentials for use by Zabbix front-end.  You are expected
to create it manually.

@item @code{zabbix-host} (default: @code{"localhost"}) (type: string)
Zabbix server hostname.

@item @code{zabbix-port} (default: @code{10051}) (type: number)
Zabbix server port.

@end table

@end deftp


@c %end of fragment

@node Kerberos Services
@subsection Kerberos Services
@cindex Kerberos

The @code{(gnu services kerberos)} module provides services relating to
the authentication protocol @dfn{Kerberos}.

@subsubheading Krb5 Service

Programs using a Kerberos client library normally
expect a configuration file in @file{/etc/krb5.conf}.
This service generates such a file from a definition provided in the
operating system declaration.
It does not cause any daemon to be started.

No ``keytab'' files are provided by this service---you must explicitly create them.
This service is known to work with the MIT client library, @code{mit-krb5}.
Other implementations have not been tested.

@defvar krb5-service-type
A service type for Kerberos 5 clients.
@end defvar

@noindent
Here is an example of its use:
@lisp
(service krb5-service-type
         (krb5-configuration
          (default-realm "EXAMPLE.COM")
          (allow-weak-crypto? #t)
          (realms (list
                   (krb5-realm
                    (name "EXAMPLE.COM")
                    (admin-server "groucho.example.com")
                    (kdc "karl.example.com"))
                   (krb5-realm
                    (name "ARGRX.EDU")
                    (admin-server "kerb-admin.argrx.edu")
                    (kdc "keys.argrx.edu"))))))
@end lisp

@noindent
This example provides a Kerberos@tie{}5 client configuration which:
@itemize
@item Recognizes two realms, @i{viz:} ``EXAMPLE.COM'' and ``ARGRX.EDU'', both
of which have distinct administration servers and key distribution centers;
@item Will default to the realm ``EXAMPLE.COM'' if the realm is not explicitly
specified by clients;
@item Accepts services which only support encryption types known to be weak.
@end itemize

The @code{krb5-realm} and @code{krb5-configuration} types have many fields.
Only the most commonly used ones are described here.
For a full list, and more detailed explanation of each, see the MIT
@uref{https://web.mit.edu/kerberos/krb5-devel/doc/admin/conf_files/krb5_conf.html,,krb5.conf}
documentation.


@deftp {Data Type} krb5-realm
@cindex realm, kerberos
@table @asis
@item @code{name}
This field is a string identifying the name of the realm.
A common convention is to use the fully qualified DNS name of your organization,
converted to upper case.

@item @code{admin-server}
This field is a string identifying the host where the administration server is
running.

@item @code{kdc}
This field is a string identifying the key distribution center
for the realm.
@end table
@end deftp

@deftp {Data Type} krb5-configuration

@table @asis
@item @code{allow-weak-crypto?} (default: @code{#f})
If this flag is @code{#t} then services which only offer encryption algorithms
known to be weak will be accepted.

@item @code{default-realm} (default: @code{#f})
This field should be a string identifying the default Kerberos
realm for the client.
You should set this field to the name of your Kerberos realm.
If this value is @code{#f}
then a realm must be specified with every Kerberos principal when invoking programs
such as @command{kinit}.

@item @code{realms}
This should be a non-empty list of @code{krb5-realm} objects, which clients may
access.
Normally, one of them will have a @code{name} field matching the @code{default-realm}
field.
@end table
@end deftp


@subsubheading PAM krb5 Service
@cindex pam-krb5

The @code{pam-krb5} service allows for login authentication and password
management via Kerberos.
You will need this service if you want PAM enabled applications to authenticate
users using Kerberos.

@defvar pam-krb5-service-type
A service type for the Kerberos 5 PAM module.
@end defvar

@deftp {Data Type} pam-krb5-configuration
Data type representing the configuration of the Kerberos 5 PAM module.
This type has the following parameters:
@table @asis
@item @code{pam-krb5} (default: @code{pam-krb5})
The pam-krb5 package to use.

@item @code{minimum-uid} (default: @code{1000})
The smallest user ID for which Kerberos authentications should be attempted.
Local accounts with lower values will silently fail to authenticate.
@end table
@end deftp


@node LDAP Services
@subsection LDAP Services
@cindex LDAP

@subsubheading Authentication against LDAP with nslcd
@cindex nslcd, LDAP service

The @code{(gnu services authentication)} module provides the
@code{nslcd-service-type}, which can be used to authenticate against an LDAP
server.  In addition to configuring the service itself, you may want to add
@code{ldap} as a name service to the Name Service Switch. @xref{Name Service
Switch} for detailed information.

Here is a simple operating system declaration with a default configuration of
the @code{nslcd-service-type} and a Name Service Switch configuration that
consults the @code{ldap} name service last:

@lisp
(use-service-modules authentication)
(use-modules (gnu system nss))
...
(operating-system
  ...
  (services
    (cons*
      (service nslcd-service-type)
      (service dhcp-client-service-type)
      %base-services))
  (name-service-switch
   (let ((services (list (name-service (name "db"))
                         (name-service (name "files"))
                         (name-service (name "ldap")))))
     (name-service-switch
      (inherit %mdns-host-lookup-nss)
      (password services)
      (shadow   services)
      (group    services)
      (netgroup services)
      (gshadow  services)))))
@end lisp

@c %start of generated documentation for nslcd-configuration

Available @code{nslcd-configuration} fields are:

@deftypevr {@code{nslcd-configuration} parameter} package nss-pam-ldapd
The @code{nss-pam-ldapd} package to use.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-number threads
The number of threads to start that can handle requests and perform LDAP
queries.  Each thread opens a separate connection to the LDAP server.
The default is to start 5 threads.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} string uid
This specifies the user id with which the daemon should be run.

Defaults to @samp{"nslcd"}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} string gid
This specifies the group id with which the daemon should be run.

Defaults to @samp{"nslcd"}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} log-option log
This option controls the way logging is done via a list containing
SCHEME and LEVEL@.  The SCHEME argument may either be the symbols
@samp{none} or @samp{syslog}, or an absolute file name.  The LEVEL
argument is optional and specifies the log level.  The log level may be
one of the following symbols: @samp{crit}, @samp{error}, @samp{warning},
@samp{notice}, @samp{info} or @samp{debug}.  All messages with the
specified log level or higher are logged.

Defaults to @samp{'("/var/log/nslcd" info)}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} list uri
The list of LDAP server URIs.  Normally, only the first server will be
used with the following servers as fall-back.

Defaults to @samp{'("ldap://localhost:389/")}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-string ldap-version
The version of the LDAP protocol to use.  The default is to use the
maximum version supported by the LDAP library.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-string binddn
Specifies the distinguished name with which to bind to the directory
server for lookups.  The default is to bind anonymously.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-string bindpw
Specifies the credentials with which to bind.  This option is only
applicable when used with binddn.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-string rootpwmoddn
Specifies the distinguished name to use when the root user tries to
modify a user's password using the PAM module.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-string rootpwmodpw
Specifies the credentials with which to bind if the root user tries to
change a user's password.  This option is only applicable when used with
rootpwmoddn

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-string sasl-mech
Specifies the SASL mechanism to be used when performing SASL
authentication.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-string sasl-realm
Specifies the SASL realm to be used when performing SASL authentication.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-string sasl-authcid
Specifies the authentication identity to be used when performing SASL
authentication.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-string sasl-authzid
Specifies the authorization identity to be used when performing SASL
authentication.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-boolean sasl-canonicalize?
Determines whether the LDAP server host name should be canonicalised.  If
this is enabled the LDAP library will do a reverse host name lookup.  By
default, it is left up to the LDAP library whether this check is
performed or not.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-string krb5-ccname
Set the name for the GSS-API Kerberos credentials cache.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} string base
The directory search base.

Defaults to @samp{"dc=example,dc=com"}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} scope-option scope
Specifies the search scope (subtree, onelevel, base or children).  The
default scope is subtree; base scope is almost never useful for name
service lookups; children scope is not supported on all servers.

Defaults to @samp{'(subtree)}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-deref-option deref
Specifies the policy for dereferencing aliases.  The default policy is
to never dereference aliases.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-boolean referrals
Specifies whether automatic referral chasing should be enabled.  The
default behaviour is to chase referrals.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} list-of-map-entries maps
This option allows for custom attributes to be looked up instead of the
default RFC 2307 attributes.  It is a list of maps, each consisting of
the name of a map, the RFC 2307 attribute to match and the query
expression for the attribute as it is available in the directory.

Defaults to @samp{'()}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} list-of-filter-entries filters
A list of filters consisting of the name of a map to which the filter
applies and an LDAP search filter expression.

Defaults to @samp{'()}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-number bind-timelimit
Specifies the time limit in seconds to use when connecting to the
directory server.  The default value is 10 seconds.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-number timelimit
Specifies the time limit (in seconds) to wait for a response from the
LDAP server.  A value of zero, which is the default, is to wait
indefinitely for searches to be completed.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-number idle-timelimit
Specifies the period if inactivity (in seconds) after which the con‐
nection to the LDAP server will be closed.  The default is not to time
out connections.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-number reconnect-sleeptime
Specifies the number of seconds to sleep when connecting to all LDAP
servers fails.  By default one second is waited between the first
failure and the first retry.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-number reconnect-retrytime
Specifies the time after which the LDAP server is considered to be
permanently unavailable.  Once this time is reached retries will be done
only once per this time period.  The default value is 10 seconds.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-ssl-option ssl
Specifies whether to use SSL/TLS or not (the default is not to).  If
'start-tls is specified then StartTLS is used rather than raw LDAP over
SSL.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-tls-reqcert-option tls-reqcert
Specifies what checks to perform on a server-supplied certificate.  The
meaning of the values is described in the ldap.conf(5) manual page.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-string tls-cacertdir
Specifies the directory containing X.509 certificates for peer authen‐
tication.  This parameter is ignored when using GnuTLS.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-string tls-cacertfile
Specifies the path to the X.509 certificate for peer authentication.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-string tls-randfile
Specifies the path to an entropy source.  This parameter is ignored when
using GnuTLS.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-string tls-ciphers
Specifies the ciphers to use for TLS as a string.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-string tls-cert
Specifies the path to the file containing the local certificate for
client TLS authentication.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-string tls-key
Specifies the path to the file containing the private key for client TLS
authentication.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-number pagesize
Set this to a number greater than 0 to request paged results from the
LDAP server in accordance with RFC2696.  The default (0) is to not
request paged results.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-ignore-users-option nss-initgroups-ignoreusers
This option prevents group membership lookups through LDAP for the
specified users.  Alternatively, the value 'all-local may be used.  With
that value nslcd builds a full list of non-LDAP users on startup.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-number nss-min-uid
This option ensures that LDAP users with a numeric user id lower than
the specified value are ignored.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-number nss-uid-offset
This option specifies an offset that is added to all LDAP numeric user
ids.  This can be used to avoid user id collisions with local users.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-number nss-gid-offset
This option specifies an offset that is added to all LDAP numeric group
ids.  This can be used to avoid user id collisions with local groups.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-boolean nss-nested-groups
If this option is set, the member attribute of a group may point to
another group.  Members of nested groups are also returned in the higher
level group and parent groups are returned when finding groups for a
specific user.  The default is not to perform extra searches for nested
groups.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-boolean nss-getgrent-skipmembers
If this option is set, the group member list is not retrieved when
looking up groups.  Lookups for finding which groups a user belongs to
will remain functional so the user will likely still get the correct
groups assigned on login.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-boolean nss-disable-enumeration
If this option is set, functions which cause all user/group entries to
be loaded from the directory will not succeed in doing so.  This can
dramatically reduce LDAP server load in situations where there are a
great number of users and/or groups.  This option is not recommended for
most configurations.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-string validnames
This option can be used to specify how user and group names are verified
within the system.  This pattern is used to check all user and group
names that are requested and returned from LDAP.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-boolean ignorecase
This specifies whether or not to perform searches using case-insensitive
matching.  Enabling this could open up the system to authorization
bypass vulnerabilities and introduce nscd cache poisoning
vulnerabilities which allow denial of service.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-boolean pam-authc-ppolicy
This option specifies whether password policy controls are requested and
handled from the LDAP server when performing user authentication.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-string pam-authc-search
By default nslcd performs an LDAP search with the user's credentials
after BIND (authentication) to ensure that the BIND operation was
successful.  The default search is a simple check to see if the user's
DN exists.  A search filter can be specified that will be used instead.
It should return at least one entry.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-string pam-authz-search
This option allows flexible fine tuning of the authorisation check that
should be performed.  The search filter specified is executed and if any
entries match, access is granted, otherwise access is denied.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} maybe-string pam-password-prohibit-message
If this option is set password modification using pam_ldap will be
denied and the specified message will be presented to the user instead.
The message can be used to direct the user to an alternative means of
changing their password.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{nslcd-configuration} parameter} list pam-services
List of pam service names for which LDAP authentication should suffice.

Defaults to @samp{'()}.

@end deftypevr

@c %end of generated documentation for nslcd-configuration


@subsubheading LDAP Directory Server
@cindex LDAP, server

The @code{(gnu services ldap)} module provides the
@code{directory-server-service-type}, which can be used to create and
launch an LDAP server instance.

Here is an example configuration of the
@code{directory-server-service-type}:

@lisp
(use-service-modules ldap)

...
(operating-system
  ...
  (services
    (cons
      (service directory-server-service-type
               (directory-server-instance-configuration
                (slapd
                 (slapd-configuration
                  (root-password "@{PBKDF2_SHA256@}AAAgAG@dots{}ABSOLUTELYSECRET")))))
      %base-services)))
@end lisp

The root password should be generated with the @command{pwdhash} utility
that is provided by the @code{389-ds-base} package.

Note that changes to the directory server configuration will not be
applied to existing instances.  You will need to back up and restore
server data manually.  Only new directory server instances will be
created upon system reconfiguration.

@c %start of generated documentation for directory-server-instance-configuration
@deftp {Data Type} directory-server-instance-configuration
Available @code{directory-server-instance-configuration} fields are:

@table @asis
@item @code{package} (default: @code{389-ds-base}) (type: file-like)
The @code{389-ds-base} package.

@item @code{config-version} (default: @code{2}) (type: number)
Sets the format version of the configuration file.  To use the INF file
with @command{dscreate}, this parameter must be 2.

@item @code{full-machine-name} (default: @code{"localhost"}) (type: string)
Sets the fully qualified hostname (FQDN) of this system.

@item @code{selinux} (default: @code{#false}) (type: boolean)
Enables SELinux detection and integration during the installation of
this instance.  If set to @code{#true}, @command{dscreate} auto-detects
whether SELinux is enabled.

@item @code{strict-host-checking} (default: @code{#true}) (type: boolean)
Sets whether the server verifies the forward and reverse record set in
the @code{full-machine-name} parameter.  When installing this instance with
GSSAPI authentication behind a load balancer, set this parameter to
@code{#false}.

@item @code{systemd} (default: @code{#false}) (type: boolean)
Enables systemd platform features.  If set to @code{#true},
@command{dscreate} auto-detects whether systemd is installed.

@item @code{slapd} (type: slapd-configuration)
Configuration of slapd.

@deftp {Data Type} slapd-configuration
Available @code{slapd-configuration} fields are:

@table @asis
@item @code{instance-name} (default: @code{"localhost"}) (type: string)
Sets the name of the instance.  You can refer to this value in other
parameters of this INF file using the @code{@{instance_name@}} variable.
Note that this name cannot be changed after the installation!

@item @code{user} (default: @code{"dirsrv"}) (type: string)
Sets the user name the ns-slapd process will use after the service
started.

@item @code{group} (default: @code{"dirsrv"}) (type: string)
Sets the group name the ns-slapd process will use after the service
started.

@item @code{port} (default: @code{389}) (type: number)
Sets the TCP port the instance uses for LDAP connections.

@item @code{secure-port} (default: @code{636}) (type: number)
Sets the TCP port the instance uses for TLS-secured LDAP connections
(LDAPS).

@item @code{root-dn} (default: @code{"cn=Directory Manager"}) (type: string)
Sets the @dfn{Distinquished Name} (DN) of the administrator account for this
instance.

@item @code{root-password} (default: @code{"@{invalid@}YOU-SHOULD-CHANGE-THIS"}) (type: string)
Sets the password of the account specified in the @code{root-dn}
parameter.  You can either set this parameter to a plain text password
@command{dscreate} hashes during the installation or to a
"@{algorithm@}hash" string generated by the @command{pwdhash} utility.
Note that setting a plain text password can be a security risk if
unprivileged users can read this INF file!

@item @code{self-sign-cert} (default: @code{#true}) (type: boolean)
Sets whether the setup creates a self-signed certificate and enables TLS
encryption during the installation.  This is not suitable for
production, but it enables administrators to use TLS right after the
installation.  You can replace the self-signed certificate with a
certificate issued by a certificate authority.

@item @code{self-sign-cert-valid-months} (default: @code{24}) (type: number)
Set the number of months the issued self-signed certificate will be
valid.

@item @code{backup-dir} (default: @code{"/var/lib/dirsrv/slapd-@{instance_name@}/bak"}) (type: string)
Set the backup directory of the instance.

@item @code{cert-dir} (default: @code{"/etc/dirsrv/slapd-@{instance_name@}"}) (type: string)
Sets the directory of the instance's Network Security Services (NSS)
database.

@item @code{config-dir} (default: @code{"/etc/dirsrv/slapd-@{instance_name@}"}) (type: string)
Sets the configuration directory of the instance.

@item @code{db-dir} (default: @code{"/var/lib/dirsrv/slapd-@{instance_name@}/db"}) (type: string)
Sets the database directory of the instance.

@item @code{initconfig-dir} (default: @code{"/etc/dirsrv/registry"}) (type: string)
Sets the directory of the operating system's rc configuration directory.

@item @code{ldif-dir} (default: @code{"/var/lib/dirsrv/slapd-@{instance_name@}/ldif"}) (type: string)
Sets the LDIF export and import directory of the instance.

@item @code{lock-dir} (default: @code{"/var/lock/dirsrv/slapd-@{instance_name@}"}) (type: string)
Sets the lock directory of the instance.

@item @code{log-dir} (default: @code{"/var/log/dirsrv/slapd-@{instance_name@}"}) (type: string)
Sets the log directory of the instance.

@item @code{run-dir} (default: @code{"/run/dirsrv"}) (type: string)
Sets PID directory of the instance.

@item @code{schema-dir} (default: @code{"/etc/dirsrv/slapd-@{instance_name@}/schema"}) (type: string)
Sets schema directory of the instance.

@item @code{tmp-dir} (default: @code{"/tmp"}) (type: string)
Sets the temporary directory of the instance.
@end table
@end deftp

@item @code{backend-userroot} (type: backend-userroot-configuration)
Configuration of the userroot backend.

@deftp {Data Type} backend-userroot-configuration
Available @code{backend-userroot-configuration} fields are:

@table @asis
@item @code{create-suffix-entry?} (default: @code{#false}) (type: boolean)
Set this parameter to @code{#true} to create a generic root node entry
for the suffix in the database.

@item @code{require-index?} (default: @code{#false}) (type: boolean)
Set this parameter to @code{#true} to refuse unindexed searches in this
database.

@item @code{sample-entries} (default: @code{"no"}) (type: string)
Set this parameter to @code{"yes"} to add latest version of sample
entries to this database.  Or, use @code{"001003006"} to use the 1.3.6
version sample entries.  Use this option, for example, to create a
database for testing purposes.

@item @code{suffix} (type: maybe-string)
Sets the root suffix stored in this database.  If you do not set the
suffix attribute the install process will not create the backend/suffix.
You can also create multiple backends/suffixes by duplicating this
section.

@end table
@end deftp
@end table
@end deftp
@c end of generated documentation for directory-server

@node Web Services
@subsection Web Services

@cindex web
@cindex www
@cindex HTTP
The @code{(gnu services web)} module provides the Apache HTTP Server,
the nginx web server, and also a fastcgi wrapper daemon.

@subsubheading Apache HTTP Server

@defvar httpd-service-type
Service type for the @uref{https://httpd.apache.org/,Apache HTTP} server
(@dfn{httpd}).  The value for this service type is a
@code{httpd-configuration} record.

A simple example configuration is given below.

@lisp
(service httpd-service-type
         (httpd-configuration
           (config
             (httpd-config-file
               (server-name "www.example.com")
               (document-root "/srv/http/www.example.com")))))
@end lisp

Other services can also extend the @code{httpd-service-type} to add to
the configuration.

@lisp
(simple-service 'www.example.com-server httpd-service-type
                (list
                  (httpd-virtualhost
                    "*:80"
                    (list (string-join '("ServerName www.example.com"
                                         "DocumentRoot /srv/http/www.example.com")
                                       "\n")))))
@end lisp
@end defvar

The details for the @code{httpd-configuration}, @code{httpd-module},
@code{httpd-config-file} and @code{httpd-virtualhost} record types are
given below.

@deftp {Data Type} httpd-configuration
This data type represents the configuration for the httpd service.

@table @asis
@item @code{package} (default: @code{httpd})
The httpd package to use.

@item @code{pid-file} (default: @code{"/var/run/httpd"})
The pid file used by the shepherd-service.

@item @code{config} (default: @code{(httpd-config-file)})
The configuration file to use with the httpd service.  The default value
is a @code{httpd-config-file} record, but this can also be a different
G-expression that generates a file, for example a @code{plain-file}.  A
file outside of the store can also be specified through a string.

@end table
@end deftp

@deftp {Data Type} httpd-module
This data type represents a module for the httpd service.

@table @asis
@item @code{name}
The name of the module.

@item @code{file}
The file for the module.  This can be relative to the httpd package being
used, the absolute location of a file, or a G-expression for a file
within the store, for example @code{(file-append mod-wsgi
"/modules/mod_wsgi.so")}.

@end table
@end deftp

@defvar %default-httpd-modules
A default list of @code{httpd-module} objects.
@end defvar

@deftp {Data Type} httpd-config-file
This data type represents a configuration file for the httpd service.

@table @asis
@item @code{modules} (default: @code{%default-httpd-modules})
The modules to load.  Additional modules can be added here, or loaded by
additional configuration.

For example, in order to handle requests for PHP files, you can use Apache’s
@code{mod_proxy_fcgi} module along with @code{php-fpm-service-type}:

@lisp
(service httpd-service-type
         (httpd-configuration
          (config
           (httpd-config-file
            (modules (cons*
                      (httpd-module
                       (name "proxy_module")
                       (file "modules/mod_proxy.so"))
                      (httpd-module
                       (name "proxy_fcgi_module")
                       (file "modules/mod_proxy_fcgi.so"))
                      %default-httpd-modules))
            (extra-config (list "\
<FilesMatch \\.php$>
    SetHandler \"proxy:unix:/var/run/php-fpm.sock|fcgi://localhost/\"
</FilesMatch>"))))))
(service php-fpm-service-type
         (php-fpm-configuration
          (socket "/var/run/php-fpm.sock")
          (socket-group "httpd")))
@end lisp

@item @code{server-root} (default: @code{httpd})
The @code{ServerRoot} in the configuration file, defaults to the httpd
package.  Directives including @code{Include} and @code{LoadModule} are
taken as relative to the server root.

@item @code{server-name} (default: @code{#f})
The @code{ServerName} in the configuration file, used to specify the
request scheme, hostname and port that the server uses to identify
itself.

This doesn't need to be set in the server config, and can be specified
in virtual hosts.  The default is @code{#f} to not specify a
@code{ServerName}.

@item @code{document-root} (default: @code{"/srv/http"})
The @code{DocumentRoot} from which files will be served.

@item @code{listen} (default: @code{'("80")})
The list of values for the @code{Listen} directives in the config
file.  The value should be a list of strings, when each string can
specify the port number to listen on, and optionally the IP address and
protocol to use.

@item @code{pid-file} (default: @code{"/var/run/httpd"})
The @code{PidFile} to use.  This should match the @code{pid-file} set in
the @code{httpd-configuration} so that the Shepherd service is
configured correctly.

@item @code{error-log} (default: @code{"/var/log/httpd/error_log"})
The @code{ErrorLog} to which the server will log errors.

@item @code{user} (default: @code{"httpd"})
The @code{User} which the server will answer requests as.

@item @code{group} (default: @code{"httpd"})
The @code{Group} which the server will answer requests as.

@item @code{extra-config} (default: @code{(list "TypesConfig etc/httpd/mime.types")})
A flat list of strings and G-expressions which will be added to the end
of the configuration file.

Any values which the service is extended with will be appended to this
list.

@end table
@end deftp

@deftp {Data Type} httpd-virtualhost
This data type represents a virtualhost configuration block for the httpd service.

These should be added to the extra-config for the httpd-service.

@lisp
(simple-service 'www.example.com-server httpd-service-type
                (list
                  (httpd-virtualhost
                    "*:80"
                    (list (string-join '("ServerName www.example.com"
                                          "DocumentRoot /srv/http/www.example.com")
                                       "\n")))))
@end lisp

@table @asis
@item @code{addresses-and-ports}
The addresses and ports for the @code{VirtualHost} directive.

@item @code{contents}
The contents of the @code{VirtualHost} directive, this should be a list
of strings and G-expressions.

@end table
@end deftp

@anchor{NGINX}
@subsubheading NGINX

@defvar nginx-service-type
Service type for the @uref{https://nginx.org/,NGinx} web server.  The
value for this service type is a @code{<nginx-configuration>} record.

A simple example configuration is given below.

@lisp
(service nginx-service-type
         (nginx-configuration
           (server-blocks
             (list (nginx-server-configuration
                     (server-name '("www.example.com"))
                     (root "/srv/http/www.example.com"))))))
@end lisp

In addition to adding server blocks to the service configuration
directly, this service can be extended by other services to add server
blocks, as in this example:

@lisp
(simple-service 'my-extra-server nginx-service-type
                (list (nginx-server-configuration
                        (root "/srv/http/extra-website")
                        (try-files (list "$uri" "$uri/index.html")))))
@end lisp
@end defvar

At startup, @command{nginx} has not yet read its configuration file, so
it uses a default file to log error messages.  If it fails to load its
configuration file, that is where error messages are logged.  After the
configuration file is loaded, the default error log file changes as per
configuration.  In our case, startup error messages can be found in
@file{/var/run/nginx/logs/error.log}, and after configuration in
@file{/var/log/nginx/error.log}.  The second location can be changed
with the @var{log-directory} configuration option.

@deftp {Data Type} nginx-configuration
This data type represents the configuration for NGinx.  Some
configuration can be done through this and the other provided record
types, or alternatively, a config file can be provided.

@table @asis
@item @code{nginx} (default: @code{nginx})
The nginx package to use.

@item @code{shepherd-requirement} (default: @code{'()})
This is a list of symbols naming Shepherd services the nginx service
will depend on.

This is useful if you would like @command{nginx} to be started after a
back-end web server or a logging service such as Anonip has been
started.

@item @code{log-directory} (default: @code{"/var/log/nginx"})
The directory to which NGinx will write log files.

@item @code{log-level} (default: @code{'error}) (type: symbol)
Logging level, which can be any of the following values: @code{'debug},
@code{'info}, @code{'notice}, @code{'warn}, @code{'error}, @code{'crit},
@code{'alert}, or @code{'emerg}.

@item @code{run-directory} (default: @code{"/var/run/nginx"})
The directory in which NGinx will create a pid file, and write temporary
files.

@item @code{server-blocks} (default: @code{'()})
A list of @dfn{server blocks} to create in the generated configuration
file, the elements should be of type
@code{<nginx-server-configuration>}.

The following example would setup NGinx to serve @code{www.example.com}
from the @code{/srv/http/www.example.com} directory, without using
HTTPS.
@lisp
(service nginx-service-type
         (nginx-configuration
           (server-blocks
             (list (nginx-server-configuration
                     (server-name '("www.example.com"))
                     (root "/srv/http/www.example.com"))))))
@end lisp

@item @code{upstream-blocks} (default: @code{'()})
A list of @dfn{upstream blocks} to create in the generated configuration
file, the elements should be of type
@code{<nginx-upstream-configuration>}.

Configuring upstreams through the @code{upstream-blocks} can be useful
when combined with @code{locations} in the
@code{<nginx-server-configuration>} records.  The following example
creates a server configuration with one location configuration, that
will proxy requests to a upstream configuration, which will handle
requests with two servers.

@lisp
(service
  nginx-service-type
  (nginx-configuration
    (server-blocks
      (list (nginx-server-configuration
              (server-name '("www.example.com"))
              (root "/srv/http/www.example.com")
              (locations
                (list
                  (nginx-location-configuration
                  (uri "/path1")
                  (body '("proxy_pass http://server-proxy;"))))))))
    (upstream-blocks
      (list (nginx-upstream-configuration
              (name "server-proxy")
              (servers (list "server1.example.com"
                             "server2.example.com")))))))
@end lisp

@item @code{file} (default: @code{#f})
If a configuration @var{file} is provided, this will be used, rather than
generating a configuration file from the provided @code{log-directory},
@code{run-directory}, @code{server-blocks} and @code{upstream-blocks}.  For
proper operation, these arguments should match what is in @var{file} to ensure
that the directories are created when the service is activated.

This can be useful if you have an existing configuration file, or it's
not possible to do what is required through the other parts of the
nginx-configuration record.

@item @code{server-names-hash-bucket-size} (default: @code{#f})
Bucket size for the server names hash tables, defaults to @code{#f} to
use the size of the processors cache line.

@item @code{server-names-hash-bucket-max-size} (default: @code{#f})
Maximum bucket size for the server names hash tables.

@item @code{modules} (default: @code{'()})
List of nginx dynamic modules to load.  This should be a list of file
names of loadable modules, as in this example:

@lisp
(modules
 (list
  (file-append nginx-accept-language-module "\
/etc/nginx/modules/ngx_http_accept_language_module.so")
  (file-append nginx-lua-module "\
/etc/nginx/modules/ngx_http_lua_module.so")))
@end lisp

@item @code{lua-package-path} (default: @code{'()})
List of nginx lua packages to load.  This should be a list of package
names of loadable lua modules, as in this example:

@lisp
(lua-package-path (list lua-resty-core
                        lua-resty-lrucache
                        lua-resty-signal
                        lua-tablepool
                        lua-resty-shell))
@end lisp

@item @code{lua-package-cpath} (default: @code{'()})
List of nginx lua C packages to load.  This should be a list of package
names of loadable lua C modules, as in this example:

@lisp
(lua-package-cpath (list lua-resty-signal))
@end lisp

@item @code{global-directives} (default: @code{'((events . ()))})
Association list of global directives for the top level of the nginx
configuration.  Values may themselves be association lists.

@lisp
(global-directives
 `((worker_processes . 16)
   (pcre_jit . on)
   (events . ((worker_connections . 1024)))))
@end lisp

@item @code{extra-content} (default: @code{""})
Additional content to be appended to the @code{http} block.  Can either
be a value that can be lowered into a string or a list of such values.
In the former case, it is inserted directly.  In the latter, it is
prefixed with indentation and suffixed with a newline.  Nested lists are
flattened into one line.

@lisp
(extra-content "include /etc/nginx/custom-config.conf;")
(extra-content `("include /etc/nginx/custom-config.conf;"
                 ("include " ,%custom-config.conf ";")))
@end lisp

@end table
@end deftp

@anchor{nginx-server-configuration}
@deftp {Data Type} nginx-server-configuration
Data type representing the configuration of an nginx server block.
This type has the following parameters:

@table @asis
@item @code{listen} (default: @code{'("80" "443 ssl")})
Each @code{listen} directive sets the address and port for IP, or the
path for a UNIX-domain socket on which the server will accept requests.
Both address and port, or only address or only port can be specified.
An address may also be a hostname, for example:

@lisp
'("127.0.0.1:8000" "127.0.0.1" "8000" "*:8000" "localhost:8000")
@end lisp

@item @code{server-name} (default: @code{(list 'default)})
A list of server names this server represents. @code{'default} represents the
default server for connections matching no other server.

@item @code{root} (default: @code{"/srv/http"})
Root of the website nginx will serve.

@item @code{locations} (default: @code{'()})
A list of @dfn{nginx-location-configuration} or
@dfn{nginx-named-location-configuration} records to use within this
server block.

@item @code{index} (default: @code{(list "index.html")})
Index files to look for when clients ask for a directory.  If it cannot be found,
Nginx will send the list of files in the directory.

@item @code{try-files} (default: @code{'()})
A list of files whose existence is checked in the specified order.
@code{nginx} will use the first file it finds to process the request.

@item @code{ssl-certificate} (default: @code{#f})
Where to find the certificate for secure connections.  Set it to @code{#f} if
you don't have a certificate or you don't want to use HTTPS.

@item @code{ssl-certificate-key} (default: @code{#f})
Where to find the private key for secure connections.  Set it to @code{#f} if
you don't have a key or you don't want to use HTTPS.

@item @code{server-tokens?} (default: @code{#f})
Whether the server should add its configuration to response.

@item @code{raw-content} (default: @code{'()})
A list of strings or file-like objects to be appended to the server
block.  Each item is prefixed with indentation and suffixed with a new
line.  Nested lists are flattened.

@end table
@end deftp

@deftp {Data Type} nginx-upstream-configuration
Data type representing the configuration of an nginx @code{upstream}
block.  This type has the following parameters:

@table @asis
@item @code{name}
Name for this group of servers.

@item @code{servers}
Specify the addresses of the servers in the group.  The address can be
specified as a IP address (e.g.@: @samp{127.0.0.1}), domain name
(e.g.@: @samp{backend1.example.com}) or a path to a UNIX socket using the
prefix @samp{unix:}.  For addresses using an IP address or domain name,
the default port is 80, and a different port can be specified
explicitly.

@item @code{extra-content}
A string or list of strings to add to the upstream block.

@end table
@end deftp

@deftp {Data Type} nginx-location-configuration
Data type representing the configuration of an nginx @code{location}
block.  This type has the following parameters:

@table @asis
@item @code{uri}
URI which this location block matches.

@anchor{nginx-location-configuration body}
@item @code{body}
Body of the location block, specified as a list of strings or file-like
objects.  Each item is prefixed with indentation and suffixed with a new
line.  Nested lists are flattened.

For example, to pass requests to a upstream server group defined using
an @code{nginx-upstream-configuration} block, the following directive
would be specified in the body @samp{(list "proxy_pass
http://upstream-name;")}.

@end table
@end deftp

@deftp {Data Type} nginx-named-location-configuration
Data type representing the configuration of an nginx named location
block.  Named location blocks are used for request redirection, and not
used for regular request processing.  This type has the following
parameters:

@table @asis
@item @code{name}
Name to identify this location block.

@item @code{body}
@xref{nginx-location-configuration body}, as the body for named location
blocks can be used in a similar way to the
@code{nginx-location-configuration body}.  One restriction is that the
body of a named location block cannot contain location blocks.

@end table
@end deftp

@subsubheading Varnish Cache
@cindex Varnish
Varnish is a fast cache server that sits in between web applications
and end users.  It proxies requests from clients and caches the
accessed URLs such that multiple requests for the same resource only
creates one request to the back-end.

@defvar varnish-service-type
Service type for the Varnish daemon.
@end defvar

@deftp {Data Type} varnish-configuration
Data type representing the @code{varnish} service configuration.
This type has the following parameters:

@table @asis
@item @code{package} (default: @code{varnish})
The Varnish package to use.

@item @code{name} (default: @code{"default"})
A name for this Varnish instance.  Varnish will create a directory in
@file{/var/varnish/} with this name and keep temporary files there.  If
the name starts with a forward slash, it is interpreted as an absolute
directory name.

Pass the @code{-n} argument to other Varnish programs to connect to the
named instance, e.g.@: @command{varnishncsa -n default}.

@item @code{backend} (default: @code{"localhost:8080"})
The backend to use.  This option has no effect if @code{vcl} is set.

@item @code{vcl} (default: #f)
The @dfn{VCL} (Varnish Configuration Language) program to run.  If this
is @code{#f}, Varnish will proxy @code{backend} using the default
configuration.  Otherwise this must be a file-like object with valid
VCL syntax.

@c Varnish does not support HTTPS, so keep this URL to avoid confusion.
For example, to mirror @url{https://www.gnu.org,www.gnu.org} with VCL you
can do something along these lines:

@lisp
(define %gnu-mirror
  (plain-file "gnu.vcl"
              "vcl 4.1;
backend gnu @{ .host = \"www.gnu.org\"; @}"))

(operating-system
  ;; @dots{}
  (services (cons (service varnish-service-type
                           (varnish-configuration
                            (listen '(":80"))
                            (vcl %gnu-mirror)))
                  %base-services)))
@end lisp

The configuration of an already running Varnish instance can be inspected
and changed using the @command{varnishadm} program.

Consult the @url{https://varnish-cache.org/docs/,Varnish User Guide} and
@url{https://book.varnish-software.com/4.0/,Varnish Book} for
comprehensive documentation on Varnish and its configuration language.

@item @code{listen} (default: @code{'("localhost:80")})
List of addresses Varnish will listen on.

@item @code{storage} (default: @code{'("malloc,128m")})
List of storage backends that will be available in VCL.

@item @code{parameters} (default: @code{'()})
List of run-time parameters in the form @code{'(("parameter" . "value"))}.

@item @code{extra-options} (default: @code{'()})
Additional arguments to pass to the @command{varnishd} process.

@end table
@end deftp

@subheading Whoogle Search
@cindex Whoogle Search

@uref{https://github.com/benbusby/whoogle-search, Whoogle Search} is a
self-hosted, ad-free, privacy-respecting meta search engine that collects
and displays Google search results.  By default, you can configure it by
adding this line to the @code{services} field of your operating system
declaration:

@lisp
(service whoogle-service-type)
@end lisp

As a result, Whoogle Search runs as local Web server, which you can
access by opening @indicateurl{http://localhost:5000} in your browser.
The configuration reference is given below.

@defvar whoogle-service-type
Service type for Whoogle Search.  Its value must be a
@code{whoogle-configuration} record---see below.
@end defvar

@deftp {Data Type} whoogle-configuration
Data type representing Whoogle Search service configuration.

@table @asis
@item @code{package} (default: @code{whoogle-search})
The Whoogle Search package to use.

@item @code{host} (default: @code{"127.0.0.1"})
The host address to run Whoogle on.

@item @code{port} (default: @code{5000})
The port where Whoogle will be exposed.

@item @code{environment-variables} (default: @code{'()})
A list of strings with the environment variables to configure Whoogle.
You can consult
@uref{https://github.com/benbusby/whoogle-search/blob/main/whoogle.template.env,
its environment variables template} for the list of available options.

@end table
@end deftp

@subsubheading Patchwork
@cindex Patchwork
Patchwork is a patch tracking system.  It can collect patches sent to a
mailing list, and display them in a web interface.

@defvar patchwork-service-type
Service type for Patchwork.
@end defvar

The following example is an example of a minimal service for Patchwork, for
the @code{patchwork.example.com} domain.

@lisp
(service patchwork-service-type
         (patchwork-configuration
          (domain "patchwork.example.com")
          (settings-module
           (patchwork-settings-module
            (allowed-hosts (list domain))
            (default-from-email "patchwork@@patchwork.example.com")))
          (getmail-retriever-config
           (getmail-retriever-configuration
            (type "SimpleIMAPSSLRetriever")
            (server "imap.example.com")
            (port 993)
            (username "patchwork")
            (password-command
             (list (file-append coreutils "/bin/cat")
                   "/etc/getmail-patchwork-imap-password"))
            (extra-parameters
            '((mailboxes . ("Patches"))))))))

@end lisp

There are three records for configuring the Patchwork service.  The
@code{<patchwork-configuration>} relates to the configuration for Patchwork
within the HTTPD service.

The @code{settings-module} field within the @code{<patchwork-configuration>}
record can be populated with the @code{<patchwork-settings-module>} record,
which describes a settings module that is generated within the Guix store.

For the @code{database-configuration} field within the
@code{<patchwork-settings-module>}, the
@code{<patchwork-database-configuration>} must be used.

@deftp {Data Type} patchwork-configuration
Data type representing the Patchwork service configuration.  This type has the
following parameters:

@table @asis
@item @code{patchwork} (default: @code{patchwork})
The Patchwork package to use.

@item @code{domain}
The domain to use for Patchwork, this is used in the HTTPD service virtual
host.

@item @code{settings-module}
The settings module to use for Patchwork.  As a Django application, Patchwork
is configured with a Python module containing the settings.  This can either be
an instance of the @code{<patchwork-settings-module>} record, any other record
that represents the settings in the store, or a directory outside of the
store.

@item @code{static-path}  (default: @code{"/static/"})
The path under which the HTTPD service should serve the static files.

@item @code{getmail-retriever-config}
The getmail-retriever-configuration record value to use with
Patchwork.  Getmail will be configured with this value, the messages will be
delivered to Patchwork.

@end table
@end deftp

@deftp {Data Type} patchwork-settings-module
Data type representing a settings module for Patchwork.  Some of these
settings relate directly to Patchwork, but others relate to Django, the web
framework used by Patchwork, or the Django Rest Framework library.  This type
has the following parameters:

@table @asis
@item @code{database-configuration} (default: @code{(patchwork-database-configuration)})
The database connection settings used for Patchwork.  See the
@code{<patchwork-database-configuration>} record type for more information.

@item @code{secret-key-file} (default: @code{"/etc/patchwork/django-secret-key"})
Patchwork, as a Django web application uses a secret key for cryptographically
signing values.  This file should contain a unique unpredictable value.

If this file does not exist, it will be created and populated with a random
value by the patchwork-setup shepherd service.

This setting relates to Django.

@item @code{allowed-hosts}
A list of valid hosts for this Patchwork service.  This should at least include
the domain specified in the @code{<patchwork-configuration>} record.

This is a Django setting.

@item @code{default-from-email}
The email address from which Patchwork should send email by default.

This is a Patchwork setting.

@item @code{static-url} (default: @code{#f})
The URL to use when serving static assets.  It can be part of a URL, or a full
URL, but must end in a @code{/}.

If the default value is used, the @code{static-path} value from the
@code{<patchwork-configuration>} record will be used.

This is a Django setting.

@item @code{admins} (default: @code{'()})
Email addresses to send the details of errors that occur.  Each value should
be a list containing two elements, the name and then the email address.

This is a Django setting.

@item @code{debug?} (default: @code{#f})
Whether to run Patchwork in debug mode.  If set to @code{#t}, detailed error
messages will be shown.

This is a Django setting.

@item @code{enable-rest-api?} (default: @code{#t})
Whether to enable the Patchwork REST API.

This is a Patchwork setting.

@item @code{enable-xmlrpc?} (default: @code{#t})
Whether to enable the XML RPC API.

This is a Patchwork setting.

@item @code{force-https-links?} (default: @code{#t})
Whether to use HTTPS links on Patchwork pages.

This is a Patchwork setting.

@item @code{extra-settings} (default: @code{""})
Extra code to place at the end of the Patchwork settings module.

@end table
@end deftp

@deftp {Data Type} patchwork-database-configuration
Data type representing the database configuration for Patchwork.

@table @asis
@item @code{engine} (default: @code{"django.db.backends.postgresql_psycopg2"})
The database engine to use.

@item @code{name} (default: @code{"patchwork"})
The name of the database to use.

@item @code{user} (default: @code{"httpd"})
The user to connect to the database as.

@item @code{password} (default: @code{""})
The password to use when connecting to the database.

@item @code{host} (default: @code{""})
The host to make the database connection to.

@item @code{port} (default: @code{""})
The port on which to connect to the database.

@end table
@end deftp

@subsubheading Mumi

@cindex Mumi, Debbugs Web interface
@cindex Debbugs, Mumi Web interface
@uref{https://git.savannah.gnu.org/cgit/guix/mumi.git/, Mumi} is a
Web interface to the Debbugs bug tracker, by default for
@uref{https://bugs.gnu.org, the GNU instance}.  Mumi is a Web server,
but it also fetches and indexes mail retrieved from Debbugs.

@defvar mumi-service-type
This is the service type for Mumi.
@end defvar

@deftp {Data Type} mumi-configuration
Data type representing the Mumi service configuration.  This type has the
following fields:

@table @asis
@item @code{mumi} (default: @code{mumi})
The Mumi package to use.

@item @code{mailer?} (default: @code{#true})
Whether to enable or disable the mailer component.

@item @code{mumi-configuration-sender}
The email address used as the sender for comments.

@item @code{mumi-configuration-smtp}
A URI to configure the SMTP settings for Mailutils.  This could be
something like @code{sendmail:///path/to/bin/msmtp} or any other URI
supported by Mailutils.  @xref{SMTP Mailboxes, SMTP Mailboxes,,
mailutils, GNU@tie{}Mailutils}.

@end table
@end deftp


@subsubheading FastCGI
@cindex fastcgi
@cindex fcgiwrap
FastCGI is an interface between the front-end and the back-end of a web
service.  It is a somewhat legacy facility; new web services should
generally just talk HTTP between the front-end and the back-end.
However there are a number of back-end services such as PHP or the
optimized HTTP Git repository access that use FastCGI, so we have
support for it in Guix.

To use FastCGI, you configure the front-end web server (e.g., nginx) to
dispatch some subset of its requests to the fastcgi backend, which
listens on a local TCP or UNIX socket.  There is an intermediary
@code{fcgiwrap} program that sits between the actual backend process and
the web server.  The front-end indicates which backend program to run,
passing that information to the @code{fcgiwrap} process.

@defvar fcgiwrap-service-type
A service type for the @code{fcgiwrap} FastCGI proxy.
@end defvar

@deftp {Data Type} fcgiwrap-configuration
Data type representing the configuration of the @code{fcgiwrap} service.
This type has the following parameters:
@table @asis
@item @code{package} (default: @code{fcgiwrap})
The fcgiwrap package to use.

@item @code{socket} (default: @code{tcp:127.0.0.1:9000})
The socket on which the @code{fcgiwrap} process should listen, as a
string.  Valid @var{socket} values include
@code{unix:@var{/path/to/unix/socket}},
@code{tcp:@var{dot.ted.qu.ad}:@var{port}} and
@code{tcp6:[@var{ipv6_addr}]:port}.

@item @code{user} (default: @code{fcgiwrap})
@itemx @code{group} (default: @code{fcgiwrap})
The user and group names, as strings, under which to run the
@code{fcgiwrap} process.  The @code{fastcgi} service will ensure that if
the user asks for the specific user or group names @code{fcgiwrap} that
the corresponding user and/or group is present on the system.

It is possible to configure a FastCGI-backed web service to pass HTTP
authentication information from the front-end to the back-end, and to
allow @code{fcgiwrap} to run the back-end process as a corresponding
local user.  To enable this capability on the back-end, run
@code{fcgiwrap} as the @code{root} user and group.  Note that this
capability also has to be configured on the front-end as well.
@end table
@end deftp

@anchor{PHP-FPM}
@subsubheading PHP-FPM
@cindex php-fpm
PHP-FPM (FastCGI Process Manager) is an alternative PHP FastCGI implementation
with some additional features useful for sites of any size.

These features include:
@itemize @bullet
@item Adaptive process spawning
@item Basic statistics (similar to Apache's mod_status)
@item Advanced process management with graceful stop/start
@item Ability to start workers with different uid/gid/chroot/environment
and different php.ini (replaces safe_mode)
@item Stdout & stderr logging
@item Emergency restart in case of accidental opcode cache destruction
@item Accelerated upload support
@item Support for a "slowlog"
@item Enhancements to FastCGI, such as fastcgi_finish_request() -
a special function to finish request & flush all data while continuing to do
something time-consuming (video converting, stats processing, etc.)
@end itemize
...@: and much more.

@defvar php-fpm-service-type
A Service type for @code{php-fpm}.
@end defvar

@deftp {Data Type} php-fpm-configuration
Data Type for php-fpm service configuration.
@table @asis
@item @code{php} (default: @code{php})
The php package to use.
@item @code{socket} (default: @code{(string-append "/var/run/php" (version-major (package-version php)) "-fpm.sock")})
The address on which to accept FastCGI requests.  Valid syntaxes are:
@table @asis
@item @code{"ip.add.re.ss:port"}
Listen on a TCP socket to a specific address on a specific port.
@item @code{"port"}
Listen on a TCP socket to all addresses on a specific port.
@item @code{"/path/to/unix/socket"}
Listen on a unix socket.
@end table

@item @code{user} (default: @code{php-fpm})
User who will own the php worker processes.
@item @code{group} (default: @code{php-fpm})
Group of the worker processes.
@item @code{socket-user} (default: @code{php-fpm})
User who can speak to the php-fpm socket.
@item @code{socket-group} (default: @code{nginx})
Group that can speak to the php-fpm socket.
@item @code{pid-file} (default: @code{(string-append "/var/run/php" (version-major (package-version php)) "-fpm.pid")})
The process id of the php-fpm process is written to this file
once the service has started.
@item @code{log-file} (default: @code{(string-append "/var/log/php" (version-major (package-version php)) "-fpm.log")})
Log for the php-fpm master process.
@item @code{process-manager} (default: @code{(php-fpm-dynamic-process-manager-configuration)})
Detailed settings for the php-fpm process manager.
Must be one of:
@table @asis
@item @code{<php-fpm-dynamic-process-manager-configuration>}
@item @code{<php-fpm-static-process-manager-configuration>}
@item @code{<php-fpm-on-demand-process-manager-configuration>}
@end table
@item @code{display-errors} (default @code{#f})
Determines whether php errors and warning should be sent to clients
and displayed in their browsers.
This is useful for local php development, but a security risk for public sites,
as error messages can reveal passwords and personal data.
@item @code{timezone} (default @code{#f})
Specifies @code{php_admin_value[date.timezone]} parameter.
@item @code{workers-logfile} (default @code{(string-append "/var/log/php" (version-major (package-version php)) "-fpm.www.log")})
This file will log the @code{stderr} outputs of php worker processes.
Can be set to @code{#f} to disable logging.
@item @code{file} (default @code{#f})
An optional override of the whole configuration.
You can use the @code{mixed-text-file} function or an absolute filepath for it.
@item @code{php-ini-file} (default @code{#f})
An optional override of the default php settings.
It may be any ``file-like'' object (@pxref{G-Expressions, file-like objects}).
You can use the @code{mixed-text-file} function or an absolute filepath for it.

For local development it is useful to set a higher timeout and memory
limit for spawned php processes.  This be accomplished with the
following operating system configuration snippet:
@lisp
(define %local-php-ini
  (plain-file "php.ini"
              "memory_limit = 2G
max_execution_time = 1800"))

(operating-system
  ;; @dots{}
  (services (cons (service php-fpm-service-type
                           (php-fpm-configuration
                            (php-ini-file %local-php-ini)))
                  %base-services)))
@end lisp

Consult the @url{https://www.php.net/manual/en/ini.core.php,core php.ini
directives} for comprehensive documentation on the acceptable
@file{php.ini} directives.
@end table
@end deftp

@deftp {Data type} php-fpm-dynamic-process-manager-configuration
Data Type for the @code{dynamic} php-fpm process manager.  With the
@code{dynamic} process manager, spare worker processes are kept around
based on its configured limits.
@table @asis
@item @code{max-children} (default: @code{5})
Maximum of worker processes.
@item @code{start-servers} (default: @code{2})
How many worker processes should be started on start-up.
@item @code{min-spare-servers} (default: @code{1})
How many spare worker processes should be kept around at minimum.
@item @code{max-spare-servers} (default: @code{3})
How many spare worker processes should be kept around at maximum.
@end table
@end deftp

@deftp {Data type} php-fpm-static-process-manager-configuration
Data Type for the @code{static} php-fpm process manager.  With the
@code{static} process manager, an unchanging number of worker processes
are created.
@table @asis
@item @code{max-children} (default: @code{5})
Maximum of worker processes.
@end table
@end deftp

@deftp {Data type} php-fpm-on-demand-process-manager-configuration
Data Type for the @code{on-demand} php-fpm process manager.  With the
@code{on-demand} process manager, worker processes are only created as
requests arrive.
@table @asis
@item @code{max-children} (default: @code{5})
Maximum of worker processes.
@item @code{process-idle-timeout} (default: @code{10})
The time in seconds after which a process with no requests is killed.
@end table
@end deftp


@deffn {Procedure} nginx-php-location [#:nginx-package nginx] @
  [socket (string-append "/var/run/php" @
  (version-major (package-version php)) "-fpm.sock")]
A helper function to quickly add php to an @code{nginx-server-configuration}.
@end deffn

A simple services setup for nginx with php can look like this:
@lisp
(services (cons* (service dhcp-client-service-type)
                 (service php-fpm-service-type)
                 (service nginx-service-type
                          (nginx-server-configuration
                           (server-name '("example.com"))
                           (root "/srv/http/")
                           (locations
                            (list (nginx-php-location)))
                           (listen '("80"))
                           (ssl-certificate #f)
                           (ssl-certificate-key #f)))
                 %base-services))
@end lisp

@cindex cat-avatar-generator
The cat avatar generator is a simple service to demonstrate the use of php-fpm
in @code{Nginx}.  It is used to generate cat avatar from a seed, for instance
the hash of a user's email address.

@deffn {Procedure} cat-avatar-generator-service @
       [#:cache-dir "/var/cache/cat-avatar-generator"] @
       [#:package cat-avatar-generator] @
       [#:configuration (nginx-server-configuration)]
Returns an nginx-server-configuration that inherits @code{configuration}.  It
extends the nginx configuration to add a server block that serves @code{package},
a version of cat-avatar-generator.  During execution, cat-avatar-generator will
be able to use @code{cache-dir} as its cache directory.
@end deffn

A simple setup for cat-avatar-generator can look like this:
@lisp
(services (cons* (cat-avatar-generator-service
                  #:configuration
                  (nginx-server-configuration
                    (server-name '("example.com"))))
                 ...
                 %base-services))
@end lisp

@subsubheading Hpcguix-web

@cindex hpcguix-web
The @uref{https://github.com/UMCUGenetics/hpcguix-web/, hpcguix-web}
program is a customizable web interface to browse Guix packages,
initially designed for users of high-performance computing (HPC)
clusters.

@defvar hpcguix-web-service-type
The service type for @code{hpcguix-web}.
@end defvar

@deftp {Data Type} hpcguix-web-configuration
Data type for the hpcguix-web service configuration.

@table @asis
@item @code{specs} (default: @code{#f})
Either @code{#f} or a gexp (@pxref{G-Expressions}) specifying the
hpcguix-web service configuration as an @code{hpcguix-web-configuration}
record.  The main fields of that record type are:

@table @asis
@item @code{title-prefix} (default: @code{"hpcguix | "})
The page title prefix.

@item @code{guix-command} (default: @code{"guix"})
The @command{guix} command to use in examples that appear on HTML pages.

@item @code{package-filter-proc} (default: @code{(const #t)})
A procedure specifying how to filter packages that are displayed.

@item @code{package-page-extension-proc} (default: @code{(const '())})
Extension package for @code{hpcguix-web}.

@item @code{menu} (default: @code{'()})
Additional entry in page @code{menu}.

@item @code{channels} (default: @code{%default-channels})
List of channels from which the package list is built (@pxref{Channels}).

@item @code{package-list-expiration} (default: @code{(* 12 3600)})
The expiration time, in seconds, after which the package list is rebuilt from
the latest instances of the given channels.
@end table

See the hpcguix-web repository for a
@uref{https://github.com/UMCUGenetics/hpcguix-web/blob/master/hpcweb-configuration.scm,
complete example}.

@item @code{package} (default: @code{hpcguix-web})
The hpcguix-web package to use.

@item @code{address} (default: @code{"127.0.0.1"})
The IP address to listen to.

@item @code{port} (default: @code{5000})
The port number to listen to.
@end table
@end deftp

A typical hpcguix-web service declaration looks like this:

@lisp
(service hpcguix-web-service-type
         (hpcguix-web-configuration
          (specs
           #~(hpcweb-configuration
              (title-prefix "Guix-HPC - ")
              (menu '(("/about" "ABOUT")))))))
@end lisp

@quotation Note
The hpcguix-web service periodically updates the package list it publishes by
pulling channels from Git.  To that end, it needs to access X.509 certificates
so that it can authenticate Git servers when communicating over HTTPS, and it
assumes that @file{/etc/ssl/certs} contains those certificates.

A certificate package, @code{nss-certs}, is provided by default as
part of @code{%base-packages}.  @ref{X.509 Certificates}, for more
information on X.509 certificates.
@end quotation

@subsubheading gmnisrv

@cindex gmnisrv
The @uref{https://git.sr.ht/~sircmpwn/gmnisrv, gmnisrv} program is a
simple @uref{https://gemini.circumlunar.space/, Gemini} protocol server.

@defvar gmnisrv-service-type
This is the type of the gmnisrv service, whose value should be a
@code{gmnisrv-configuration} object, as in this example:

@lisp
(service gmnisrv-service-type
         (gmnisrv-configuration
           (config-file (local-file "./my-gmnisrv.ini"))))
@end lisp
@end defvar

@deftp {Data Type} gmnisrv-configuration
Data type representing the configuration of gmnisrv.

@table @asis
@item @code{package} (default: @var{gmnisrv})
Package object of the gmnisrv server.

@item @code{config-file} (default: @code{%default-gmnisrv-config-file})
File-like object of the gmnisrv configuration file to use.  The default
configuration listens on port 1965 and serves files from
@file{/srv/gemini}.  Certificates are stored in
@file{/var/lib/gemini/certs}.  For more information, run @command{man
gmnisrv} and @command{man gmnisrv.ini}.

@end table
@end deftp

@subsubheading Agate

@cindex agate
The @uref{gemini://qwertqwefsday.eu/agate.gmi, Agate}
(@uref{https://github.com/mbrubeck/agate, GitHub page over HTTPS})
program is a simple @uref{https://gemini.circumlunar.space/, Gemini}
protocol server written in Rust.

@defvar agate-service-type
This is the type of the agate service, whose value should be an
@code{agate-service-type} object, as in this example:

@lisp
(service agate-service-type
	 (agate-configuration
	   (content "/srv/gemini")
	   (certs "/srv/gemini-certs")))
@end lisp

The example above represents the minimal tweaking necessary to get Agate
up and running.  Specifying the path to the certificate and key directory is
always necessary, as the Gemini protocol requires TLS by default.

If specified path is writable by Agate, and contains no valid key
and certificate, the Agate will try to generate them on the first start.
If specified directory is read-only - key and certificate should be pre-generated by user.

To obtain a certificate and a key in a DER format, you could, for example,
use OpenSSL, running a commands similar to the following example:

@example
openssl genpkey -out key.der -outform DER -algorithm RSA \
    -pkeyopt rsa_keygen_bits:4096
openssl req -x509 -key key.der -outform DER -days 3650 -out cert.der \
    -subj "/CN=example.com"
@end example

Of course, you'll have to replace @i{example.com} with your own domain
name, and then point the Agate configuration towards the path of the
directory with the generated key and certificate using the @code{certs} option.

@end defvar

@deftp {Data Type} agate-configuration
Data type representing the configuration of Agate.

@table @asis
@item @code{package} (default: @code{agate})
The package object of the Agate server.

@item @code{content} (default: @file{"/srv/gemini"})
The directory from which Agate will serve files.

@item @code{certs} (default: @file{"/srv/gemini-certs"})
Root of the certificate directory. Must be filled in with a value from the user.

@item @code{addr} (default: @code{'("0.0.0.0:1965" "[::]:1965")})
A list of the addresses to listen on.

@item @code{hostnames} (default: @code{'()})
Virtual hosts for the Gemini server. If multiple values are
specified, corresponding directory names should be present in the @code{content}
directory. Optional.

@item @code{lang} (default: @code{#f})
RFC 4646 language code(s) for text/gemini documents.  Optional.

@item @code{only-tls13?} (default: @code{#f})
Set to @code{#t} to disable support for TLSv1.2.

@item @code{serve-secret?} (default: @code{#f})
Set to @code{#t} to serve secret files (files/directories starting with
a dot).

@item @code{central-conf?} (default: @code{#f})
Set to @code{#t} to look for the .meta configuration file in the @code{content}
root directory and will ignore @code{.meta} files in other directories

@item @code{ed25519?} (default: @code{#f})
Set to @code{#t} to generate keys using the Ed25519 signature algorithm
instead of the default ECDSA.

@item @code{skip-port-check?} (default: @code{#f})
Set to @code{#t} to skip URL port check even when a @code{hostname} is specified.

@item @code{log-ip?} (default: @code{#t})
Whether or not to output IP addresses when logging.

@item @code{user} (default: @code{"agate"})
Owner of the @code{agate} process.

@item @code{group} (default: @code{"agate"})
Owner's group of the @code{agate} process.

@item @code{log-file} (default: @file{"/var/log/agate.log"})
The file which should store the logging output of Agate.

@end table
@end deftp

@node Certificate Services
@subsection Certificate Services

@cindex Web
@cindex HTTP, HTTPS
@cindex Let's Encrypt
@cindex TLS certificates
The @code{(gnu services certbot)} module provides a service to
automatically obtain a valid TLS certificate from the Let's Encrypt
certificate authority.  These certificates can then be used to serve
content securely over HTTPS or other TLS-based protocols, with the
knowledge that the client will be able to verify the server's
authenticity.

@url{https://letsencrypt.org/, Let's Encrypt} provides the
@code{certbot} tool to automate the certification process.  This tool
first securely generates a key on the server.  It then makes a request
to the Let's Encrypt certificate authority (CA) to sign the key.  The CA
checks that the request originates from the host in question by using a
challenge-response protocol, requiring the server to provide its
response over HTTP@.  If that protocol completes successfully, the CA
signs the key, resulting in a certificate.  That certificate is valid
for a limited period of time, and therefore to continue to provide TLS
services, the server needs to periodically ask the CA to renew its
signature.

The certbot service automates this process: the initial key
generation, the initial certification request to the Let's Encrypt
service, the web server challenge/response integration, writing the
certificate to disk, the automated periodic renewals, and the deployment
tasks associated with the renewal (e.g.@: reloading services, copying keys
with different permissions).

Certbot is run twice a day, at a random minute within the hour.  It
won't do anything until your certificates are due for renewal or
revoked, but running it regularly would give your service a chance of
staying online in case a Let's Encrypt-initiated revocation happened for
some reason.

By using this service, you agree to the ACME Subscriber Agreement, which
can be found there:
@url{https://acme-v01.api.letsencrypt.org/directory}.

@defvar certbot-service-type
A service type for the @code{certbot} Let's Encrypt client.  Its value
must be a @code{certbot-configuration} record as in this example:

@lisp
(service certbot-service-type
         (certbot-configuration
          (email "foo@@example.net")
          (certificates
           (list
            (certificate-configuration
             (domains '("example.net" "www.example.net")))
            (certificate-configuration
             (domains '("bar.example.net")))))))
@end lisp

See below for details about @code{certbot-configuration}.
@end defvar

@deftp {Data Type} certbot-configuration
Data type representing the configuration of the @code{certbot} service.
This type has the following parameters:

@table @asis
@item @code{package} (default: @code{certbot})
The certbot package to use.

@item @code{webroot} (default: @code{/var/www})
The directory from which to serve the Let's Encrypt challenge/response
files.

@item @code{certificates} (default: @code{'()})
A list of @code{certificates-configuration}s for which to generate
certificates and request signatures.  Each certificate has a @code{name}
and several @code{domains}.

@item @code{email} (default: @code{#f})
Optional email address used for registration and recovery contact.
Setting this is encouraged as it allows you to receive important
notifications about the account and issued certificates.

@item @code{server} (default: @code{#f})
Optional URL of ACME server.  Setting this overrides certbot's default,
which is the Let's Encrypt server.

@item @code{rsa-key-size} (default: @code{2048})
Size of the RSA key.

@item @code{default-location} (default: @i{see below})
The default @code{nginx-location-configuration}.  Because @code{certbot}
needs to be able to serve challenges and responses, it needs to be able
to run a web server.  It does so by extending the @code{nginx} web
service with an @code{nginx-server-configuration} listening on the
@var{domains} on port 80, and which has a
@code{nginx-location-configuration} for the @code{/.well-known/} URI
path subspace used by Let's Encrypt.  @xref{Web Services}, for more on
these nginx configuration data types.

Requests to other URL paths will be matched by the
@code{default-location}, which if present is added to all
@code{nginx-server-configuration}s.

By default, the @code{default-location} will issue a redirect from
@code{http://@var{domain}/...} to @code{https://@var{domain}/...}, leaving
you to define what to serve on your site via @code{https}.

Pass @code{#f} to not issue a default location.
@end table
@end deftp

@deftp {Data Type} certificate-configuration
Data type representing the configuration of a certificate.
This type has the following parameters:

@table @asis
@item @code{name} (default: @i{see below})
This name is used by Certbot for housekeeping and in file paths; it
doesn't affect the content of the certificate itself.  To see
certificate names, run @code{certbot certificates}.

Its default is the first provided domain.

@item @code{domains} (default: @code{'()})
The first domain provided will be the subject CN of the certificate, and
all domains will be Subject Alternative Names on the certificate.

@item @code{challenge} (default: @code{#f})
The challenge type that has to be run by certbot.  If @code{#f} is specified,
default to the HTTP challenge.  If a value is specified, defaults to the
manual plugin (see @code{authentication-hook}, @code{cleanup-hook} and
the documentation at @url{https://certbot.eff.org/docs/using.html#hooks}),
and gives Let's Encrypt permission to log the public IP address of the
requesting machine.

@item @code{csr} (default: @code{#f})
File name of Certificate Signing Request (CSR) in DER or PEM format.
If @code{#f} is specified, this argument will not be passed to certbot.
If a value is specified, certbot will use it to obtain a certificate, instead of
using a self-generated CSR.
The domain-name(s) mentioned in @code{domains}, must be consistent with the
domain-name(s) mentioned in CSR file.

@item @code{authentication-hook} (default: @code{#f})
Command to be run in a shell once for each certificate challenge to be
answered.  For this command, the shell variable @code{$CERTBOT_DOMAIN}
will contain the domain being authenticated, @code{$CERTBOT_VALIDATION}
contains the validation string and @code{$CERTBOT_TOKEN} contains the
file name of the resource requested when performing an HTTP-01 challenge.

@item @code{cleanup-hook} (default: @code{#f})
Command to be run in a shell once for each certificate challenge that
have been answered by the @code{auth-hook}.  For this command, the shell
variables available in the @code{auth-hook} script are still available, and
additionally @code{$CERTBOT_AUTH_OUTPUT} will contain the standard output
of the @code{auth-hook} script.

@item @code{deploy-hook} (default: @code{#f})
Command to be run in a shell once for each successfully issued
certificate.  For this command, the shell variable
@code{$RENEWED_LINEAGE} will point to the config live subdirectory (for
example, @samp{"/etc/letsencrypt/live/example.com"}) containing the new
certificates and keys; the shell variable @code{$RENEWED_DOMAINS} will
contain a space-delimited list of renewed certificate domains (for
example, @samp{"example.com www.example.com"}.

@item @code{start-self-signed?} (default: @code{#t})
Whether to generate an initial self-signed certificate during system
activation.  This option is particularly useful to allow @code{nginx} to
start before @code{certbot} has run, because @code{certbot} relies on
@code{nginx} running to perform HTTP challenges.

@end table
@end deftp

For each @code{certificate-configuration}, the certificate is saved to
@code{/etc/certs/@var{name}/fullchain.pem} and the key is
saved to @code{/etc/certs/@var{name}/privkey.pem}.
@node DNS Services
@subsection DNS Services
@cindex DNS (domain name system)
@cindex domain name system (DNS)

The @code{(gnu services dns)} module provides services related to the
@dfn{domain name system} (DNS).  It provides a server service for hosting
an @emph{authoritative} DNS server for multiple zones, slave or master.
This service uses @uref{https://www.knot-dns.cz/, Knot DNS}.  And also a
caching and forwarding DNS server for the LAN, which uses
@uref{http://www.thekelleys.org.uk/dnsmasq/doc.html, dnsmasq}.

@subsubheading Knot Service

An example configuration of an authoritative server for two zones, one master
and one slave, is:

@lisp
(define-zone-entries example.org.zone
;; Name TTL Class Type Data
  ("@@"  ""  "IN"  "A"  "127.0.0.1")
  ("@@"  ""  "IN"  "NS" "ns")
  ("ns" ""  "IN"  "A"  "127.0.0.1"))

(define master-zone
  (knot-zone-configuration
    (domain "example.org")
    (zone (zone-file
            (origin "example.org")
            (entries example.org.zone)))))

(define slave-zone
  (knot-zone-configuration
    (domain "plop.org")
    (dnssec-policy "default")
    (master (list "plop-master"))))

(define plop-master
  (knot-remote-configuration
    (id "plop-master")
    (address (list "208.76.58.171"))))

(operating-system
  ;; ...
  (services (cons* (service knot-service-type
                     (knot-configuration
                       (remotes (list plop-master))
                       (zones (list master-zone slave-zone))))
                   ;; ...
                   %base-services)))
@end lisp

@defvar knot-service-type
This is the type for the Knot DNS server.

Knot DNS is an authoritative DNS server, meaning that it can serve multiple
zones, that is to say domain names you would buy from a registrar.  This server
is not a resolver, meaning that it can only resolve names for which it is
authoritative.  This server can be configured to serve zones as a master server
or a slave server as a per-zone basis.  Slave zones will get their data from
masters, and will serve it as an authoritative server.  From the point of view
of a resolver, there is no difference between master and slave.

The following data types are used to configure the Knot DNS server:
@end defvar

@deftp {Data Type} knot-key-configuration
Data type representing a key.
This type has the following parameters:

@table @asis
@item @code{id} (default: @code{""})
An identifier for other configuration fields to refer to this key.  IDs must
be unique and must not be empty.

@item @code{algorithm} (default: @code{#f})
The algorithm to use.  Choose between @code{#f}, @code{'hmac-md5},
@code{'hmac-sha1}, @code{'hmac-sha224}, @code{'hmac-sha256}, @code{'hmac-sha384}
and @code{'hmac-sha512}.

@item @code{secret} (default: @code{""})
The secret key itself.

@end table
@end deftp

@deftp {Data Type} knot-acl-configuration
Data type representing an Access Control List (ACL) configuration.
This type has the following parameters:

@table @asis
@item @code{id} (default: @code{""})
An identifier for other configuration fields to refer to this key.  IDs must be
unique and must not be empty.

@item @code{address} (default: @code{'()})
An ordered list of IP addresses, network subnets, or network ranges represented
with strings.  The query must match one of them.  Empty value means that
address match is not required.

@item @code{key} (default: @code{'()})
An ordered list of references to keys represented with strings.  The string
must match a key ID defined in a @code{knot-key-configuration}.  No key means
that a key is not require to match that ACL.

@item @code{action} (default: @code{'()})
An ordered list of actions that are permitted or forbidden by this ACL@.  Possible
values are lists of zero or more elements from @code{'transfer}, @code{'notify}
and @code{'update}.

@item @code{deny?} (default: @code{#f})
When true, the ACL defines restrictions.  Listed actions are forbidden.  When
false, listed actions are allowed.

@end table
@end deftp

@deftp {Data Type} zone-entry
Data type representing a record entry in a zone file.
This type has the following parameters:

@table @asis
@item @code{name} (default: @code{"@@"})
The name of the record.  @code{"@@"} refers to the origin of the zone.  Names
are relative to the origin of the zone.  For example, in the @code{example.org}
zone, @code{"ns.example.org"} actually refers to @code{ns.example.org.example.org}.
Names ending with a dot are absolute, which means that @code{"ns.example.org."}
refers to @code{ns.example.org}.

@item @code{ttl} (default: @code{""})
The Time-To-Live (TTL) of this record.  If not set, the default TTL is used.

@item @code{class} (default: @code{"IN"})
The class of the record.  Knot currently supports only @code{"IN"} and
partially @code{"CH"}.

@item @code{type} (default: @code{"A"})
The type of the record.  Common types include A (IPv4 address), AAAA (IPv6
address), NS (Name Server) and MX (Mail eXchange).  Many other types are
defined.

@item @code{data} (default: @code{""})
The data contained in the record.  For instance an IP address associated with
an A record, or a domain name associated with an NS record.  Remember that
domain names are relative to the origin unless they end with a dot.

@end table
@end deftp

@deftp {Data Type} zone-file
Data type representing the content of a zone file.
This type has the following parameters:

@table @asis
@item @code{entries} (default: @code{'()})
The list of entries.  The SOA record is taken care of, so you don't need to
put it in the list of entries.  This list should probably contain an entry
for your primary authoritative DNS server.  Other than using a list of entries
directly, you can use @code{define-zone-entries} to define a object containing
the list of entries more easily, that you can later pass to the @code{entries}
field of the @code{zone-file}.

@item @code{origin} (default: @code{""})
The name of your zone.  This parameter cannot be empty.

@item @code{ns} (default: @code{"ns"})
The domain of your primary authoritative DNS server.  The name is relative to
the origin, unless it ends with a dot.  It is mandatory that this primary
DNS server corresponds to an NS record in the zone and that it is associated
to an IP address in the list of entries.

@item @code{mail} (default: @code{"hostmaster"})
An email address people can contact you at, as the owner of the zone.  This
is translated as @code{<mail>@@<origin>}.

@item @code{serial} (default: @code{1})
The serial number of the zone.  As this is used to keep track of changes by
both slaves and resolvers, it is mandatory that it @emph{never} decreases.
Always increment it when you make a change in your zone.

@item @code{refresh} (default: @code{(* 2 24 3600)})
The frequency at which slaves will do a zone transfer.  This value is a number
of seconds.  It can be computed by multiplications or with
@code{(string->duration)}.

@item @code{retry} (default: @code{(* 15 60)})
The period after which a slave will retry to contact its master when it fails
to do so a first time.

@item @code{expiry} (default: @code{(* 14 24 3600)})
Default TTL of records.  Existing records are considered correct for at most
this amount of time.  After this period, resolvers will invalidate their cache
and check again that it still exists.

@item @code{nx} (default: @code{3600})
Default TTL of inexistent records.  This delay is usually short because you want
your new domains to reach everyone quickly.

@end table
@end deftp

@deftp {Data Type} knot-remote-configuration
Data type representing a remote configuration.
This type has the following parameters:

@table @asis
@item @code{id} (default: @code{""})
An identifier for other configuration fields to refer to this remote.  IDs must
be unique and must not be empty.

@item @code{address} (default: @code{'()})
An ordered list of destination IP addresses.  Addresses are tried in sequence.
An optional port can be given with the @@ separator.  For instance:
@code{(list "1.2.3.4" "2.3.4.5@@53")}.  Default port is 53.

@item @code{via} (default: @code{'()})
An ordered list of source IP addresses.  An empty list will have Knot choose
an appropriate source IP@.  An optional port can be given with the @@ separator.
The default is to choose at random.

@item @code{key} (default: @code{#f})
A reference to a key, that is a string containing the identifier of a key
defined in a @code{knot-key-configuration} field.

@end table
@end deftp

@deftp {Data Type} knot-keystore-configuration
Data type representing a keystore to hold dnssec keys.
This type has the following parameters:

@table @asis
@item @code{id} (default: @code{""})
The id of the keystore.  It must not be empty.

@item @code{backend} (default: @code{'pem})
The backend to store the keys in.  Can be @code{'pem} or @code{'pkcs11}.

@item @code{config} (default: @code{"/var/lib/knot/keys/keys"})
The configuration string of the backend.  An example for the PKCS#11 is:
@code{"pkcs11:token=knot;pin-value=1234 /gnu/store/.../lib/pkcs11/libsofthsm2.so"}.
For the pem backend, the string represents a path in the file system.

@end table
@end deftp

@deftp {Data Type} knot-policy-configuration
Data type representing a dnssec policy.  Knot DNS is able to automatically
sign your zones.  It can either generate and manage your keys automatically or
use keys that you generate.

Dnssec is usually implemented using two keys: a Key Signing Key (KSK) that is
used to sign the second, and a Zone Signing Key (ZSK) that is used to sign the
zone.  In order to be trusted, the KSK needs to be present in the parent zone
(usually a top-level domain).  If your registrar supports dnssec, you will
have to send them your KSK's hash so they can add a DS record in their zone.
This is not automated and need to be done each time you change your KSK.

The policy also defines the lifetime of keys.  Usually, ZSK can be changed
easily and use weaker cryptographic functions (they use lower parameters) in
order to sign records quickly, so they are changed often.  The KSK however
requires manual interaction with the registrar, so they are changed less often
and use stronger parameters because they sign only one record.

This type has the following parameters:

@table @asis
@item @code{id} (default: @code{""})
The id of the policy.  It must not be empty.

@item @code{keystore} (default: @code{"default"})
A reference to a keystore, that is a string containing the identifier of a
keystore defined in a @code{knot-keystore-configuration} field.  The
@code{"default"} identifier means the default keystore (a kasp database that
was setup by this service).

@item @code{manual?} (default: @code{#f})
Whether the key management is manual or automatic.

@item @code{single-type-signing?} (default: @code{#f})
When @code{#t}, use the Single-Type Signing Scheme.

@item @code{algorithm} (default: @code{"ecdsap256sha256"})
An algorithm of signing keys and issued signatures.

@item @code{ksk-size} (default: @code{256})
The length of the KSK@.  Note that this value is correct for the default
algorithm, but would be unsecure for other algorithms.

@item @code{zsk-size} (default: @code{256})
The length of the ZSK@.  Note that this value is correct for the default
algorithm, but would be unsecure for other algorithms.

@item @code{dnskey-ttl} (default: @code{'default})
The TTL value for DNSKEY records added into zone apex.  The special
@code{'default} value means same as the zone SOA TTL.

@item @code{zsk-lifetime} (default: @code{(* 30 24 3600)})
The period between ZSK publication and the next rollover initiation.

@item @code{propagation-delay} (default: @code{(* 24 3600)})
An extra delay added for each key rollover step.  This value should be high
enough to cover propagation of data from the master server to all slaves.

@item @code{rrsig-lifetime} (default: @code{(* 14 24 3600)})
A validity period of newly issued signatures.

@item @code{rrsig-refresh} (default: @code{(* 7 24 3600)})
A period how long before a signature expiration the signature will be refreshed.

@item @code{nsec3?} (default: @code{#f})
When @code{#t}, NSEC3 will be used instead of NSEC.

@item @code{nsec3-iterations} (default: @code{5})
The number of additional times the hashing is performed.

@item @code{nsec3-salt-length} (default: @code{8})
The length of a salt field in octets, which is appended to the original owner
name before hashing.

@item @code{nsec3-salt-lifetime} (default: @code{(* 30 24 3600)})
The validity period of newly issued salt field.

@end table
@end deftp

@deftp {Data Type} knot-zone-configuration
Data type representing a zone served by Knot.
This type has the following parameters:

@table @asis
@item @code{domain} (default: @code{""})
The domain served by this configuration.  It must not be empty.

@item @code{file} (default: @code{""})
The file where this zone is saved.  This parameter is ignored by master zones.
Empty means default location that depends on the domain name.

@item @code{zone} (default: @code{(zone-file)})
The content of the zone file.  This parameter is ignored by slave zones.  It
must contain a zone-file record.

@item @code{master} (default: @code{'()})
A list of master remotes.  When empty, this zone is a master.  When set, this
zone is a slave.  This is a list of remotes identifiers.

@item @code{ddns-master} (default: @code{#f})
The main master.  When empty, it defaults to the first master in the list of
masters.

@item @code{notify} (default: @code{'()})
A list of slave remote identifiers.

@item @code{acl} (default: @code{'()})
A list of acl identifiers.

@item @code{semantic-checks?} (default: @code{#f})
When set, this adds more semantic checks to the zone.

@item @code{zonefile-sync} (default: @code{0})
The delay between a modification in memory and on disk.  0 means immediate
synchronization.

@item @code{zonefile-load} (default: @code{#f})
The way the zone file contents are applied during zone load.  Possible values
are:

@itemize
@item @code{#f} for using the default value from Knot,
@item @code{'none} for not using the zone file at all,
@item @code{'difference} for computing the difference between already available
contents and zone contents and applying it to the current zone contents,
@item @code{'difference-no-serial} for the same as @code{'difference}, but
ignoring the SOA serial in the zone file, while the server takes care of it
automatically.
@item @code{'whole} for loading zone contents from the zone file.
@end itemize

@item @code{journal-content} (default: @code{#f})
The way the journal is used to store zone and its changes.  Possible values
are @code{'none} to not use it at all, @code{'changes} to store changes and
@code{'all} to store contents.  @code{#f} does not set this option, so the
default value from Knot is used.

@item @code{max-journal-usage} (default: @code{#f})
The maximum size for the journal on disk.  @code{#f} does not set this option,
so the default value from Knot is used.

@item @code{max-journal-depth} (default: @code{#f})
The maximum size of the history.  @code{#f} does not set this option, so the
default value from Knot is used.

@item @code{max-zone-size} (default: @code{#f})
The maximum size of the zone file.  This limit is enforced for incoming
transfer and updates.  @code{#f} does not set this option, so the default
value from Knot is used.

@item @code{dnssec-policy} (default: @code{#f})
A reference to a @code{knot-policy-configuration} record, or the special
name @code{"default"}.  If the value is @code{#f}, there is no dnssec signing
on this zone.

@item @code{serial-policy} (default: @code{'increment})
A policy between @code{'increment} and @code{'unixtime}.

@end table
@end deftp

@deftp {Data Type} knot-configuration
Data type representing the Knot configuration.
This type has the following parameters:

@table @asis
@item @code{knot} (default: @code{knot})
The Knot package.

@item @code{run-directory} (default: @code{"/var/run/knot"})
The run directory.  This directory will be used for pid file and sockets.

@item @code{includes} (default: @code{'()})
A list of strings or file-like objects denoting other files that must be
included at the top of the configuration file.

@cindex secrets, Knot service
This can be used to manage secrets out-of-band.  For example, secret
keys may be stored in an out-of-band file not managed by Guix, and
thus not visible in @file{/gnu/store}---e.g., you could store secret
key configuration in @file{/etc/knot/secrets.conf} and add this file
to the @code{includes} list.

One can generate a secret tsig key (for nsupdate and zone transfers with the
keymgr command from the knot package.  Note that the package is not automatically
installed by the service.  The following example shows how to generate a new
tsig key:

@example
keymgr -t mysecret > /etc/knot/secrets.conf
chmod 600 /etc/knot/secrets.conf
@end example

Also note that the generated key will be named @var{mysecret}, so it is the
name that needs to be used in the @var{key} field of the
@code{knot-acl-configuration} record and in other places that need to refer
to that key.

It can also be used to add configuration not supported by this interface.

@item @code{listen-v4} (default: @code{"0.0.0.0"})
An ip address on which to listen.

@item @code{listen-v6} (default: @code{"::"})
An ip address on which to listen.

@item @code{listen-port} (default: @code{53})
A port on which to listen.

@item @code{keys} (default: @code{'()})
The list of knot-key-configuration used by this configuration.

@item @code{acls} (default: @code{'()})
The list of knot-acl-configuration used by this configuration.

@item @code{remotes} (default: @code{'()})
The list of knot-remote-configuration used by this configuration.

@item @code{zones} (default: @code{'()})
The list of knot-zone-configuration used by this configuration.

@end table
@end deftp

@subsubheading Knot Resolver Service

@defvar knot-resolver-service-type
This is the type of the knot resolver service, whose value should be
a @code{knot-resolver-configuration} object as in this example:

@lisp
(service knot-resolver-service-type
         (knot-resolver-configuration
           (kresd-config-file (plain-file "kresd.conf" "
net.listen('192.168.0.1', 5353)
user('knot-resolver', 'knot-resolver')
modules = @{ 'hints > iterate', 'stats', 'predict' @}
cache.size = 100 * MB
"))))
@end lisp

For more information, refer its @url{https://knot-resolver.readthedocs.io/en/stable/config-overview.html, manual}.
@end defvar

@deftp {Data Type} knot-resolver-configuration
Data type representing the configuration of knot-resolver.

@table @asis
@item @code{package} (default: @var{knot-resolver})
Package object of the knot DNS resolver.

@item @code{kresd-config-file} (default: %kresd.conf)
File-like object of the kresd configuration file to use, by default it
will listen on @code{127.0.0.1} and @code{::1}.

@item @code{garbage-collection-interval} (default: 1000)
Number of milliseconds for @code{kres-cache-gc} to periodically trim the cache.

@end table
@end deftp


@subsubheading Dnsmasq Service

@defvar dnsmasq-service-type
This is the type of the dnsmasq service, whose value should be a
@code{dnsmasq-configuration} object as in this example:

@lisp
(service dnsmasq-service-type
         (dnsmasq-configuration
           (no-resolv? #t)
           (servers '("192.168.1.1"))))
@end lisp
@end defvar

@deftp {Data Type} dnsmasq-configuration
Data type representing the configuration of dnsmasq.

@table @asis
@item @code{package} (default: @var{dnsmasq})
Package object of the dnsmasq server.

@item @code{no-hosts?} (default: @code{#f})
When true, don't read the hostnames in /etc/hosts.

@item @code{port} (default: @code{53})
The port to listen on.  Setting this to zero completely disables DNS
responses, leaving only DHCP and/or TFTP functions.

@item @code{local-service?} (default: @code{#t})
Accept DNS queries only from hosts whose address is on a local subnet,
ie a subnet for which an interface exists on the server.

@item @code{listen-addresses} (default: @code{'()})
Listen on the given IP addresses.

@item @code{resolv-file} (default: @code{"/etc/resolv.conf"})
The file to read the IP address of the upstream nameservers from.

@item @code{no-resolv?} (default: @code{#f})
When true, don't read @var{resolv-file}.

@item @code{forward-private-reverse-lookup?} (default: @code{#t})
When false, all reverse lookups for private IP ranges are answered with
"no such domain" rather than being forwarded upstream.

@item @code{query-servers-in-order?} (default: @code{#f})
When true, dnsmasq queries the servers in the same order as they appear
in @var{servers}.

@item @code{servers} (default: @code{'()})
Specify IP address of upstream servers directly.

@item @code{servers-file} (default: @code{#f})
Specify file containing upstream servers. This file is re-read when dnsmasq receives SIGHUP.
Could be either a string or a file-like object.

@item @code{addresses} (default: @code{'()})
For each entry, specify an IP address to return for any host in the
given domains.  Queries in the domains are never forwarded and always
replied to with the specified IP address.

This is useful for redirecting hosts locally, for example:

@lisp
(service dnsmasq-service-type
         (dnsmasq-configuration
           (addresses
             '(; Redirect to a local web-server.
               "/example.org/127.0.0.1"
               ; Redirect subdomain to a specific IP.
               "/subdomain.example.org/192.168.1.42"))))
@end lisp

Note that rules in @file{/etc/hosts} take precedence over this.

@item @code{cache-size} (default: @code{150})
Set the size of dnsmasq's cache.  Setting the cache size to zero
disables caching.

@item @code{negative-cache?} (default: @code{#t})
When false, disable negative caching.

@item @code{cpe-id} (default: @code{#f})
If set, add a CPE (Customer-Premises Equipment) identifier to DNS
queries which are forwarded upstream.

@item @code{tftp-enable?} (default: @code{#f})
Whether to enable the built-in TFTP server.

@item @code{tftp-no-fail?} (default: @code{#f})
If true, does not fail dnsmasq if the TFTP server could not start up.

@item @code{tftp-single-port?} (default: @code{#f})
Whether to use only one single port for TFTP.

@item @code{tftp-secure?} (default: @code{#f})
If true, only files owned by the user running the dnsmasq process are accessible.

If dnsmasq is being run as root, different rules apply:
@code{tftp-secure?} has no effect, but only files which have the
world-readable bit set are accessible.

@item @code{tftp-max} (default: @code{#f})
If set, sets the maximal number of concurrent connections allowed.

@item @code{tftp-mtu} (default: @code{#f})
If set, sets the MTU for TFTP packets to that value.

@item @code{tftp-no-blocksize?} (default: @code{#f})
If true, stops the TFTP server from negotiating the blocksize with a client.

@item @code{tftp-lowercase?} (default: @code{#f})
Whether to convert all filenames in TFTP requests to lowercase.

@item @code{tftp-port-range} (default: @code{#f})
If set, fixes the dynamical ports (one per client) to the given range
(@code{"<start>,<end>"}).

@item @code{tftp-root} (default: @code{/var/empty,lo})
Look for files to transfer using TFTP relative to the given directory.
When this is set, TFTP paths which include @samp{..} are rejected, to stop clients
getting outside the specified root.  Absolute paths (starting with @samp{/}) are
allowed, but they must be within the TFTP-root.  If the optional interface
argument is given, the directory is only used for TFTP requests via that
interface.

@item @code{tftp-unique-root} (default: @code{#f})
If set, add the IP or hardware address of the TFTP client as a path component
on the end of the TFTP-root.  Only valid if a TFTP root is set and the
directory exists.  Defaults to adding IP address (in standard dotted-quad
format).

For instance, if @option{--tftp-root} is @samp{/tftp} and client
@samp{1.2.3.4} requests file @file{myfile} then the effective path will
be @file{/tftp/1.2.3.4/myfile} if @file{/tftp/1.2.3.4} exists or
@file{/tftp/myfile} otherwise.  When @samp{=mac} is specified it will
append the MAC address instead, using lowercase zero padded digits
separated by dashes, e.g.: @samp{01-02-03-04-aa-bb}.  Note that
resolving MAC addresses is only possible if the client is in the local
network or obtained a DHCP lease from dnsmasq.

@item @code{extra-options} (default: @code{'()})
This option provides an ``escape hatch'' for the user to provide arbitrary
command-line arguments to @command{dnsmasq} as a list of strings.

@end table
@end deftp

@node VNC Services
@subsection VNC Services
@cindex VNC (virtual network computing)
@cindex XDMCP (x display manager control protocol)

The @code{(gnu services vnc)} module provides services related to
@dfn{Virtual Network Computing} (VNC), which makes it possible to
locally use graphical Xorg applications running on a remote machine.
Combined with a graphical manager that supports the @dfn{X Display
Manager Control Protocol}, such as GDM (@pxref{gdm}) or LightDM
(@pxref{lightdm}), it is possible to remote an entire desktop for a
multi-user environment.

@subsubheading Xvnc

Xvnc is a VNC server that spawns its own X window server; which means it
can run on headless servers.  The Xvnc implementations provided by the
@code{tigervnc-server} and @code{turbovnc} aim to be fast and efficient.

@defvar xvnc-service-type

The @code{xvnc-service-type} service can be configured via the
@code{xvnc-configuration} record, documented below.  A second virtual
display could be made available on a remote machine via the
following configuration:
@end defvar

@lisp
(service xvnc-service-type
         (xvnc-configuration (display-number 10)))
@end lisp

As a demonstration, the @command{xclock} command could then be started
on the remote machine on display number 10, and it could be displayed
locally via the @command{vncviewer} command:
@example
# Start xclock on the remote machine.
ssh -L5910:localhost:5910 @var{your-host} -- guix shell xclock \
    -- env DISPLAY=:10 xclock
# Access it via VNC.
guix shell tigervnc-client -- vncviewer localhost:5910
@end example

The following configuration combines XDMCP and Inetd to allow multiple
users to concurrently use the remote system and login graphically via
the GDM display manager:

@lisp
(operating-system
  [...]
  (services (cons*
             [...]
             (service xvnc-service-type (xvnc-configuration
                                         (display-number 5)
                                         (localhost? #f)
                                         (xdmcp? #t)
                                         (inetd? #t)))
             (modify-services %desktop-services
               (gdm-service-type config => (gdm-configuration
                                            (inherit config)
                                            (auto-suspend? #f)
                                            (xdmcp? #t)))))))
@end lisp

A remote user could then connect to it by using the @command{vncviewer}
command or a compatible VNC client and start a desktop session of their
choosing:
@example
vncviewer remote-host:5905
@end example

@quotation Warning
Unless your machine is in a controlled environment, for security
reasons, the @code{localhost?} configuration of the
@code{xvnc-configuration} record should be left to its default @code{#t}
value and exposed via a secure means such as an SSH port forward.  The
XDMCP port, UDP 177 should also be blocked from the outside by a
firewall, as it is not a secure protocol and can expose login
credentials in clear.
@end quotation

@c Use (configuration->documentation 'xvnc-configuration) to regenerate
@c the documentation.
@c %start of fragment
@deftp {Data Type} xvnc-configuration
Available @code{xvnc-configuration} fields are:

@table @asis
@item @code{xvnc} (default: @code{tigervnc-server}) (type: file-like)
The package that provides the Xvnc binary.

@item @code{display-number} (default: @code{0}) (type: number)
The display number used by Xvnc.  You should set this to a number not
already used a Xorg server.

@item @code{geometry} (default: @code{"1024x768"}) (type: string)
The size of the desktop to be created.

@item @code{depth} (default: @code{24}) (type: color-depth)
The pixel depth in bits of the desktop to be created.  Accepted values
are 16, 24 or 32.

@item @code{port} (type: maybe-port)
The port on which to listen for connections from viewers.  When left
unspecified, it defaults to 5900 plus the display number.

@item @code{ipv4?} (default: @code{#t}) (type: boolean)
Use IPv4 for incoming and outgoing connections.

@item @code{ipv6?} (default: @code{#t}) (type: boolean)
Use IPv6 for incoming and outgoing connections.

@item @code{password-file} (type: maybe-string)
The password file to use, if any.  Refer to vncpasswd(1) to learn how to
generate such a file.

@item @code{xdmcp?} (default: @code{#f}) (type: boolean)
Query the XDMCP server for a session.  This enables users to log in a
desktop session from the login manager screen.  For a multiple users
scenario, you'll want to enable the @code{inetd?} option as well, so
that each connection to the VNC server is handled separately rather than
shared.

@item @code{inetd?} (default: @code{#f}) (type: boolean)
Use an Inetd-style service, which runs the Xvnc server on demand.

@item @code{frame-rate} (default: @code{60}) (type: number)
The maximum number of updates per second sent to each client.

@item @code{security-types} (default: @code{'("None")}) (type: security-types)
The allowed security schemes to use for incoming connections.  The
default is "None", which is safe given that Xvnc is configured to
authenticate the user via the display manager, and only for local
connections.  Accepted values are any of the following: ("None"
"VncAuth" "Plain" "TLSNone" "TLSVnc" "TLSPlain" "X509None" "X509Vnc")

@item @code{localhost?} (default: @code{#t}) (type: boolean)
Only allow connections from the same machine.  It is set to #true by
default for security, which means SSH or another secure means should be
used to expose the remote port.

@item @code{log-level} (default: @code{30}) (type: log-level)
The log level, a number between 0 and 100, 100 meaning most verbose
output.  The log messages are output to syslog.

@item @code{extra-options} (default: @code{'()}) (type: strings)
This can be used to provide extra Xvnc options not exposed via this
<xvnc-configuration> record.

@end table

@end deftp
@c %end of fragment

@node VPN Services
@subsection VPN Services
@cindex VPN (virtual private network)
@cindex virtual private network (VPN)

The @code{(gnu services vpn)} module provides services related to
@dfn{virtual private networks} (VPNs).

@subsubheading Bitmask

@defvar bitmask-service-type
A service type for the @uref{https://bitmask.net, Bitmask} VPN client.  It makes
the client available in the system and loads its polkit policy.  Please note that
the client expects an active polkit-agent, which is either run by your
desktop-environment or should be run manually.
@end defvar

@subsubheading OpenVPN

It provides a @emph{client} service for your machine to connect to a
VPN, and a @emph{server} service for your machine to host a VPN@.
Both @code{openvpn-client-service-type} and
@code{openvpn-server-service-type} can be run simultaneously.

@defvar openvpn-client-service-type
Type of the service that runs @command{openvpn}, a VPN daemon, as a client.

The value for this service is a @code{<openvpn-client-configuration>}
object.
@end defvar

@defvar openvpn-server-service-type
Type of the service that runs @command{openvpn}, a VPN daemon, as a server.

The value for this service is a @code{<openvpn-server-configuration>}
object.
@end defvar

@c %automatically generated documentation

@deftp {Data Type} openvpn-client-configuration
Available @code{openvpn-client-configuration} fields are:

@table @asis
@item @code{openvpn} (default: @code{openvpn}) (type: file-like)
The OpenVPN package.

@item @code{pid-file} (default: @code{"/var/run/openvpn/openvpn.pid"}) (type: string)
The OpenVPN pid file.

@item @code{proto} (default: @code{udp}) (type: proto)
The protocol (UDP or TCP) used to open a channel between clients and
servers.

@item @code{dev} (default: @code{tun}) (type: dev)
The device type used to represent the VPN connection.

@item @code{ca} (default: @code{"/etc/openvpn/ca.crt"}) (type: maybe-string)
The certificate authority to check connections against.

@item @code{cert} (default: @code{"/etc/openvpn/client.crt"}) (type: maybe-string)
The certificate of the machine the daemon is running on.  It should be
signed by the authority given in @code{ca}.

@item @code{key} (default: @code{"/etc/openvpn/client.key"}) (type: maybe-string)
The key of the machine the daemon is running on.  It must be the key
whose certificate is @code{cert}.

@item @code{comp-lzo?} (default: @code{#t}) (type: boolean)
Whether to use the lzo compression algorithm.

@item @code{persist-key?} (default: @code{#t}) (type: boolean)
Don't re-read key files across SIGUSR1 or --ping-restart.

@item @code{persist-tun?} (default: @code{#t}) (type: boolean)
Don't close and reopen TUN/TAP device or run up/down scripts across
SIGUSR1 or --ping-restart restarts.

@item @code{fast-io?} (default: @code{#f}) (type: boolean)
(Experimental) Optimize TUN/TAP/UDP I/O writes by avoiding a call to
poll/epoll/select prior to the write operation.

@item @code{verbosity} (default: @code{3}) (type: number)
Verbosity level.

@item @code{tls-auth} (default: @code{#f}) (type: tls-auth-client)
Add an additional layer of HMAC authentication on top of the TLS control
channel to protect against DoS attacks.

@item @code{auth-user-pass} (type: maybe-string)
Authenticate with server using username/password.  The option is a file
containing username/password on 2 lines.  Do not use a file-like object
as it would be added to the store and readable by any user.

@item @code{verify-key-usage?} (default: @code{#t}) (type: key-usage)
Whether to check the server certificate has server usage extension.

@item @code{bind?} (default: @code{#f}) (type: bind)
Bind to a specific local port number.

@item @code{resolv-retry?} (default: @code{#t}) (type: resolv-retry)
Retry resolving server address.

@item @code{remote} (default: @code{'()}) (type: openvpn-remote-list)
A list of remote servers to connect to.

@deftp {Data Type} openvpn-remote-configuration
Available @code{openvpn-remote-configuration} fields are:

@table @asis
@item @code{name} (default: @code{"my-server"}) (type: string)
Server name.

@item @code{port} (default: @code{1194}) (type: number)
Port number the server listens to.

@end table

@end deftp

@end table

@end deftp

@c %end of automatic openvpn-client documentation

@c %automatically generated documentation

@deftp {Data Type} openvpn-server-configuration
Available @code{openvpn-server-configuration} fields are:

@table @asis
@item @code{openvpn} (default: @code{openvpn}) (type: file-like)
The OpenVPN package.

@item @code{pid-file} (default: @code{"/var/run/openvpn/openvpn.pid"}) (type: string)
The OpenVPN pid file.

@item @code{proto} (default: @code{udp}) (type: proto)
The protocol (UDP or TCP) used to open a channel between clients and
servers.

@item @code{dev} (default: @code{tun}) (type: dev)
The device type used to represent the VPN connection.

@item @code{ca} (default: @code{"/etc/openvpn/ca.crt"}) (type: maybe-string)
The certificate authority to check connections against.

@item @code{cert} (default: @code{"/etc/openvpn/client.crt"}) (type: maybe-string)
The certificate of the machine the daemon is running on.  It should be
signed by the authority given in @code{ca}.

@item @code{key} (default: @code{"/etc/openvpn/client.key"}) (type: maybe-string)
The key of the machine the daemon is running on.  It must be the key
whose certificate is @code{cert}.

@item @code{comp-lzo?} (default: @code{#t}) (type: boolean)
Whether to use the lzo compression algorithm.

@item @code{persist-key?} (default: @code{#t}) (type: boolean)
Don't re-read key files across SIGUSR1 or --ping-restart.

@item @code{persist-tun?} (default: @code{#t}) (type: boolean)
Don't close and reopen TUN/TAP device or run up/down scripts across
SIGUSR1 or --ping-restart restarts.

@item @code{fast-io?} (default: @code{#f}) (type: boolean)
(Experimental) Optimize TUN/TAP/UDP I/O writes by avoiding a call to
poll/epoll/select prior to the write operation.

@item @code{verbosity} (default: @code{3}) (type: number)
Verbosity level.

@item @code{tls-auth} (default: @code{#f}) (type: tls-auth-server)
Add an additional layer of HMAC authentication on top of the TLS control
channel to protect against DoS attacks.

@item @code{port} (default: @code{1194}) (type: number)
Specifies the port number on which the server listens.

@item @code{server} (default: @code{"10.8.0.0 255.255.255.0"}) (type: ip-mask)
An ip and mask specifying the subnet inside the virtual network.

@item @code{server-ipv6} (default: @code{#f}) (type: cidr6)
A CIDR notation specifying the IPv6 subnet inside the virtual network.

@item @code{dh} (default: @code{"/etc/openvpn/dh2048.pem"}) (type: string)
The Diffie-Hellman parameters file.

@item @code{ifconfig-pool-persist} (default: @code{"/etc/openvpn/ipp.txt"}) (type: string)
The file that records client IPs.

@item @code{redirect-gateway?} (default: @code{#f}) (type: gateway)
When true, the server will act as a gateway for its clients.

@item @code{client-to-client?} (default: @code{#f}) (type: boolean)
When true, clients are allowed to talk to each other inside the VPN.

@item @code{keepalive} (default: @code{(10 120)}) (type: keepalive)
Causes ping-like messages to be sent back and forth over the link so
that each side knows when the other side has gone down.  @code{keepalive}
requires a pair.  The first element is the period of the ping sending,
and the second element is the timeout before considering the other side
down.

@item @code{max-clients} (default: @code{100}) (type: number)
The maximum number of clients.

@item @code{status} (default: @code{"/var/run/openvpn/status"}) (type: string)
The status file.  This file shows a small report on current connection.
It is truncated and rewritten every minute.

@item @code{client-config-dir} (default: @code{'()}) (type: openvpn-ccd-list)
The list of configuration for some clients.

@end table

@end deftp

@c %end of automatic openvpn-server documentation

@subheading strongSwan

Currently, the strongSwan service only provides legacy-style configuration with
@file{ipsec.conf} and @file{ipsec.secrets} files.

@defvar strongswan-service-type
A service type for configuring strongSwan for IPsec @acronym{VPN,
Virtual Private Networking}.  Its value must be a
@code{strongswan-configuration} record as in this example:

@lisp
(service strongswan-service-type
         (strongswan-configuration
          (ipsec-conf "/etc/ipsec.conf")
          (ipsec-secrets "/etc/ipsec.secrets")))
@end lisp

@end defvar

@deftp {Data Type} strongswan-configuration
Data type representing the configuration of the StrongSwan service.

@table @asis
@item @code{strongswan}
The strongSwan package to use for this service.

@item @code{ipsec-conf} (default: @code{#f})
The file name of your @file{ipsec.conf}.  If not @code{#f}, then this and
@code{ipsec-secrets} must both be strings.

@item @code{ipsec-secrets} (default @code{#f})
The file name of your @file{ipsec.secrets}.  If not @code{#f}, then this and
@code{ipsec-conf} must both be strings.

@end table
@end deftp

@subsubheading Wireguard

@defvar wireguard-service-type
A service type for a Wireguard tunnel interface.  Its value must be a
@code{wireguard-configuration} record as in this example:

@lisp
(service wireguard-service-type
         (wireguard-configuration
          (peers
           (list
            (wireguard-peer
             (name "my-peer")
             (endpoint "my.wireguard.com:51820")
             (public-key "hzpKg9X1yqu1axN6iJp0mWf6BZGo8m1wteKwtTmDGF4=")
             (allowed-ips '("10.0.0.2/32")))))))
@end lisp

@end defvar

@deftp {Data Type} wireguard-configuration
Data type representing the configuration of the Wireguard service.

@table @asis
@item @code{wireguard}
The wireguard package to use for this service.

@item @code{interface} (default: @code{"wg0"})
The interface name for the VPN.

@item @code{addresses} (default: @code{'("10.0.0.1/32")})
The IP addresses to be assigned to the above interface.

@item @code{port} (default: @code{51820})
The port on which to listen for incoming connections.

@item @code{dns} (default: @code{'())})
The DNS server(s) to announce to VPN clients via DHCP.

@item @code{monitor-ips?} (default: @code{#f})
@cindex Dynamic IP, with Wireguard
@cindex dyndns, usage with Wireguard
Whether to monitor the resolved Internet addresses (IPs) of the
endpoints of the configured peers, resetting the peer endpoints using an
IP address that no longer correspond to their freshly resolved host
name.  Set this to @code{#t} if one or more endpoints use host names
provided by a dynamic DNS service to keep the sessions alive.

@item @code{monitor-ips-interval} (default: @code{'(next-minute (range 0 60 5))})
The time interval at which the IP monitoring job should run, provided as
an mcron time specification (@pxref{Guile Syntax,,,mcron}).

@item @code{private-key} (default: @code{"/etc/wireguard/private.key"})
The private key file for the interface.  It is automatically generated
if the file does not exist.

@item @code{peers} (default: @code{'()})
The authorized peers on this interface.  This is a list of
@var{wireguard-peer} records.

@item @code{pre-up} (default: @code{'()})
The script commands to be run before setting up the interface.

@item @code{post-up} (default: @code{'()})
The script commands to be run after setting up the interface.

@item @code{pre-down} (default: @code{'()})
The script commands to be run before tearing down the interface.

@item @code{post-down} (default: @code{'()})
The script commands to be run after tearing down the interface.

@item @code{table} (default: @code{"auto"})
The routing table to which routes are added, as a string.  There are two
special values: @code{"off"} that disables the creation of routes
altogether, and @code{"auto"} (the default) that adds routes to the
default table and enables special handling of default routes.

@end table
@end deftp

@deftp {Data Type} wireguard-peer
Data type representing a Wireguard peer attached to a given interface.

@table @asis
@item @code{name}
The peer name.

@item @code{endpoint} (default: @code{#f})
The optional endpoint for the peer, such as
@code{"demo.wireguard.com:51820"}.

@item @code{public-key}
The peer public-key represented as a base64 string.

@item @code{preshared-key} (default: @code{#f})
An optional pre-shared key file for this peer.  The given file will not
be autogenerated.

@item @code{allowed-ips}
A list of IP addresses from which incoming traffic for this peer is
allowed and to which incoming traffic for this peer is directed.

@item @code{keep-alive} (default: @code{#f})
An optional time interval in seconds.  A packet will be sent to the
server endpoint once per time interval.  This helps receiving
incoming connections from this peer when you are behind a NAT or
a firewall.

@end table
@end deftp

@node Network File System
@subsection Network File System
@cindex NFS

The @code{(gnu services nfs)} module provides the following services,
which are most commonly used in relation to mounting or exporting
directory trees as @dfn{network file systems} (NFS).

While it is possible to use the individual components that together make
up a Network File System service, we recommended to configure an NFS
server with the @code{nfs-service-type}.

@subsubheading NFS Service
@cindex NFS, server

The NFS service takes care of setting up all NFS component services,
kernel configuration file systems, and installs configuration files in
the locations that NFS expects.

@defvar nfs-service-type
A service type for a complete NFS server.
@end defvar

@deftp {Data Type} nfs-configuration
This data type represents the configuration of the NFS service and all
of its subsystems.

It has the following parameters:
@table @asis
@item @code{nfs-utils} (default: @code{nfs-utils})
The nfs-utils package to use.

@item @code{nfs-versions} (default: @code{'("4.2" "4.1" "4.0")})
If a list of string values is provided, the @command{rpc.nfsd} daemon
will be limited to supporting the given versions of the NFS protocol.

@item @code{exports} (default: @code{'()})
This is a list of directories the NFS server should export.  Each entry
is a list consisting of two elements: a directory name and a string
containing all options.  This is an example in which the directory
@file{/export} is served to all NFS clients as a read-only share:

@lisp
(nfs-configuration
 (exports
  '(("/export"
     "*(ro,insecure,no_subtree_check,crossmnt,fsid=0)"))))
@end lisp

@item @code{rpcmountd-port} (default: @code{#f})
The network port that the @command{rpc.mountd} daemon should use.

@item @code{rpcstatd-port} (default: @code{#f})
The network port that the @command{rpc.statd} daemon should use.

@item @code{rpcbind} (default: @code{rpcbind})
The rpcbind package to use.

@item @code{idmap-domain} (default: @code{"localdomain"})
The local NFSv4 domain name.

@item @code{nfsd-port} (default: @code{2049})
The network port that the @command{nfsd} daemon should use.

@item @code{nfsd-threads} (default: @code{8})
The number of threads used by the @command{nfsd} daemon.

@item @code{nfsd-tcp?} (default: @code{#t})
Whether the @command{nfsd} daemon should listen on a TCP socket.

@item @code{nfsd-udp?} (default: @code{#f})
Whether the @command{nfsd} daemon should listen on a UDP socket.

@item @code{pipefs-directory} (default: @code{"/var/lib/nfs/rpc_pipefs"})
The directory where the pipefs file system is mounted.

@item @code{debug} (default: @code{'()"})
A list of subsystems for which debugging output should be enabled.  This
is a list of symbols.  Any of these symbols are valid: @code{nfsd},
@code{nfs}, @code{rpc}, @code{idmap}, @code{statd}, or @code{mountd}.
@end table
@end deftp

If you don't need a complete NFS service or prefer to build it yourself
you can use the individual component services that are documented below.

@subsubheading RPC Bind Service
@cindex rpcbind

The RPC Bind service provides a facility to map program numbers into
universal addresses.
Many NFS related services use this facility.  Hence it is automatically
started when a dependent service starts.

@defvar rpcbind-service-type
A service type  for the RPC portmapper daemon.
@end defvar


@deftp {Data Type} rpcbind-configuration
Data type representing the configuration of the RPC Bind Service.
This type has the following parameters:
@table @asis
@item @code{rpcbind} (default: @code{rpcbind})
The rpcbind package to use.

@item @code{warm-start?} (default: @code{#t})
If this parameter is @code{#t}, then the daemon will read a
state file on startup thus reloading state information saved by a previous
instance.
@end table
@end deftp


@subsubheading Pipefs Pseudo File System
@cindex pipefs
@cindex rpc_pipefs

The pipefs file system is used to transfer NFS related data
between the kernel and user space programs.

@defvar pipefs-service-type
A service type for the pipefs pseudo file system.
@end defvar

@deftp {Data Type} pipefs-configuration
Data type representing the configuration of the pipefs pseudo file system service.
This type has the following parameters:
@table @asis
@item @code{mount-point} (default: @code{"/var/lib/nfs/rpc_pipefs"})
The directory to which the file system is to be attached.
@end table
@end deftp


@subsubheading GSS Daemon Service
@cindex GSSD
@cindex GSS
@cindex global security system

The @dfn{global security system} (GSS) daemon provides strong security for RPC
based protocols.
Before exchanging RPC requests an RPC client must establish a security
context.  Typically this is done using the Kerberos command @command{kinit}
or automatically at login time using PAM services (@pxref{Kerberos Services}).

@defvar gss-service-type
A service type for the Global Security System (GSS) daemon.
@end defvar

@deftp {Data Type} gss-configuration
Data type representing the configuration of the GSS daemon service.
This type has the following parameters:
@table @asis
@item @code{nfs-utils} (default: @code{nfs-utils})
The package in which the @command{rpc.gssd} command is to be found.

@item @code{pipefs-directory} (default: @code{"/var/lib/nfs/rpc_pipefs"})
The directory where the pipefs file system is mounted.

@end table
@end deftp


@subsubheading IDMAP Daemon Service
@cindex idmapd
@cindex name mapper

The idmap daemon service provides mapping between user IDs and user names.
Typically it is required in order to access file systems mounted via NFSv4.

@defvar idmap-service-type
A service type for the Identity Mapper (IDMAP) daemon.
@end defvar

@deftp {Data Type} idmap-configuration
Data type representing the configuration of the IDMAP daemon service.
This type has the following parameters:
@table @asis
@item @code{nfs-utils} (default: @code{nfs-utils})
The package in which the @command{rpc.idmapd} command is to be found.

@item @code{pipefs-directory} (default: @code{"/var/lib/nfs/rpc_pipefs"})
The directory where the pipefs file system is mounted.

@item @code{domain} (default: @code{#f})
The local NFSv4 domain name.
This must be a string or @code{#f}.
If it is @code{#f} then the daemon will use the host's fully qualified domain name.

@item @code{verbosity} (default: @code{0})
The verbosity level of the daemon.

@end table
@end deftp

@node Samba Services, Continuous Integration, Network File System, Services
@subsection Samba Services

@cindex Samba
@cindex SMB
The @code{(gnu services samba)} module provides service definitions for
Samba as well as additional helper services.  Currently it provides the
following services.

@subsubheading Samba

@uref{https://www.samba.org, Samba} provides network shares for folders
and printers using the SMB/CIFS protocol commonly used on Windows.  It
can also act as an Active Directory Domain Controller (AD DC) for other
hosts in an heterougenious network with different types of Computer
systems.

@defvar samba-service-type

The service type to enable the samba services @code{samba}, @code{nmbd},
@code{smbd} and @code{winbindd}.  By default this service type does not
run any of the Samba daemons; they must be enabled individually.

Below is a basic example that configures a simple, anonymous
(unauthenticated) Samba file share exposing the @file{/public}
directory.

@quotation Tip
The @file{/public} directory and its contents must be world
readable/writable, so you'll want to run @samp{chmod -R 777 /public} on
it.
@end quotation

@quotation Caution
Such a Samba configuration should only be used in controlled
environments, and you should not share any private files using it, as
anyone connecting to your network would be able to access them.
@end quotation

@lisp
(service samba-service-type (samba-configuration
                             (enable-smbd? #t)
                             (config-file (plain-file "smb.conf" "\
[global]
map to guest = Bad User
logging = syslog@@1

[public]
browsable = yes
path = /public
read only = no
guest ok = yes
guest only = yes\n"))))
@end lisp

@end defvar

@deftp {Data Type} samba-service-configuration
Configuration record for the Samba suite.

@table @asis
@item @code{package} (default: @code{samba})
The samba package to use.

@item @code{config-file} (default: @code{#f})
The config file to use.  To learn about its syntax, run @samp{man
smb.conf}.

@item @code{enable-samba?} (default: @code{#f})
Enable the @code{samba} daemon.

@item @code{enable-smbd?} (default: @code{#f})
Enable the @code{smbd} daemon.

@item @code{enable-nmbd?} (default: @code{#f})
Enable the @code{nmbd} daemon.

@item @code{enable-winbindd?} (default: @code{#f})
Enable the @code{winbindd} daemon.

@end table
@end deftp

@cindex wsdd, Web service discovery daemon
@subsubheading Web Service Discovery Daemon

The @acronym{WSDD, Web Service Discovery daemon} implements the
@uref{http://docs.oasis-open.org/ws-dd/discovery/1.1/os/wsdd-discovery-1.1-spec-os.html,
Web Services Dynamic Discovery} protocol that enables host discovery
over Multicast DNS, similar to what Avahi does.  It is a drop-in
replacement for SMB hosts that have had SMBv1 disabled for security
reasons.

@defvar wsdd-service-type
Service type for the WSD host daemon.  The value for
this service type is a @code{wsdd-configuration} record.  The details
for the @code{wsdd-configuration} record type are given below.
@end defvar

@deftp {Data Type} wsdd-configuration
This data type represents the configuration for the wsdd service.

@table @asis

@item @code{package} (default: @code{wsdd})
The wsdd package to use.

@item @code{ipv4only?} (default: @code{#f})
Only listen to IPv4 addresses.

@item @code{ipv6only} (default: @code{#f})
Only listen to IPv6 addresses.  Please note: Activating both options is
not possible, since there would be no IP versions to listen to.

@item @code{chroot} (default: @code{#f})
Chroot into a separate directory to prevent access to other directories.
This is to increase security in case there is a vulnerability in
@command{wsdd}.

@item @code{hop-limit} (default: @code{1})
Limit to the level of hops for multicast packets.  The default is
@var{1} which should prevent packets from leaving the local network.

@item @code{interface} (default: @code{'()})
Limit to the given list of interfaces to listen to.  By default wsdd
will listen to all interfaces.  Except the loopback interface is never
used.

@item @code{uuid-device} (default: @code{#f})
The WSD protocol requires a device to have a UUID.  Set this to manually
assign the service a UUID.

@item @code{domain} (default: @code{#f})
Notify this host is a member of an Active Directory.

@item @code{host-name} (default: @code{#f})
Manually set the hostname rather than letting @command{wsdd} inherit
this host's hostname.  Only the host name part of a possible FQDN will
be used in the default case.

@item @code{preserve-case?} (default: @code{#f})
By default @command{wsdd} will convert the hostname in workgroup to all
uppercase.  The opposite is true for hostnames in domains.  Setting this
parameter will preserve case.

@item @code{workgroup} (default: @var{"WORKGROUP"})
Change the name of the workgroup.  By default @command{wsdd} reports
this host being member of a workgroup.

@end table
@end deftp

@node Continuous Integration
@subsection Continuous Integration

@cindex continuous integration
@uref{https://guix.gnu.org/cuirass/, Cuirass} is a continuous
integration tool for Guix.  It can be used both for development and for
providing substitutes to others (@pxref{Substitutes}).

The @code{(gnu services cuirass)} module provides the following service.

@defvr {Procedure} cuirass-service-type
The type of the Cuirass service.  Its value must be a
@code{cuirass-configuration} object, as described below.
@end defvr

To add build jobs, you have to set the @code{specifications} field of
the configuration.  For instance, the following example will build all
the packages provided by the @code{my-channel} channel.

@lisp
(define %cuirass-specs
  #~(list (specification
           (name 'my-channel)
           (build '(channels my-channel))
           (channels
            (cons (channel
                   (name 'my-channel)
                   (url "https://my-channel.git"))
                  %default-channels)))))

(service cuirass-service-type
         (cuirass-configuration
          (specifications %cuirass-specs)))
@end lisp

To build the @code{linux-libre} package defined by the default Guix
channel, one can use the following configuration.

@lisp
(define %cuirass-specs
  #~(list (specification
           (name 'my-linux)
           (build '(packages "linux-libre")))))

(service cuirass-service-type
         (cuirass-configuration
          (specifications %cuirass-specs)))
@end lisp

The other configuration possibilities, as well as the specification
record itself are described in the Cuirass manual
(@pxref{Specifications,,, cuirass, Cuirass}).

While information related to build jobs is located directly in the
specifications, global settings for the @command{cuirass} process are
accessible in other @code{cuirass-configuration} fields.

@deftp {Data Type} cuirass-configuration
Data type representing the configuration of Cuirass.

@table @asis
@item @code{cuirass} (default: @code{cuirass})
The Cuirass package to use.

@item @code{log-file} (default: @code{"/var/log/cuirass.log"})
Location of the log file.

@item @code{web-log-file} (default: @code{"/var/log/cuirass-web.log"})
Location of the log file used by the web interface.

@item @code{cache-directory} (default: @code{"/var/cache/cuirass"})
Location of the repository cache.

@item @code{user} (default: @code{"cuirass"})
Owner of the @code{cuirass} process.

@item @code{group} (default: @code{"cuirass"})
Owner's group of the @code{cuirass} process.

@item @code{interval} (default: @code{60})
Number of seconds between the poll of the repositories followed by the
Cuirass jobs.

@item @code{ttl} (default: @code{2592000})
Duration to keep build results' GC roots alive, in seconds.

@item @code{threads} (default: @code{#f})
Number of kernel threads to use for Cuirass. The default value should be appropriate for most cases.

@item @code{parameters} (default: @code{#f})
Read parameters from the given @var{parameters} file.  The supported
parameters are described here (@pxref{Parameters,,, cuirass, Cuirass}).

@item @code{remote-server} (default: @code{#f})
A @code{cuirass-remote-server-configuration} record to use the build
remote mechanism or @code{#f} to use the default build mechanism.

@item @code{database} (default: @code{"dbname=cuirass host=/var/run/postgresql"})
Use @var{database} as the database containing the jobs and the past
build results. Since Cuirass uses PostgreSQL as a database engine,
@var{database} must be a string such as @code{"dbname=cuirass
host=localhost"}.

@item @code{port} (default: @code{8081})
Port number used by the HTTP server.

@item @code{host} (default: @code{"localhost"})
Listen on the network interface for @var{host}.  The default is to
accept connections from localhost.

@item @code{specifications} (default: @code{#~'()})
A gexp (@pxref{G-Expressions}) that evaluates to a list of
specifications records.  The specification record is described in the
Cuirass manual (@pxref{Specifications,,, cuirass, Cuirass}).

@item @code{one-shot?} (default: @code{#f})
Only evaluate specifications and build derivations once.

@item @code{fallback?} (default: @code{#f})
When substituting a pre-built binary fails, fall back to building
packages locally.

@item @code{extra-options} (default: @code{'()})
Extra options to pass when running the @code{cuirass register} process.

@item @code{web-extra-options} (default: @code{'()})
Extra options to pass when running the @code{cuirass web} process.

@end table
@end deftp

@cindex remote build
@subsubheading Cuirass remote building

Cuirass supports two mechanisms to build derivations.

@itemize
@item Using the local Guix daemon.
This is the default build mechanism.  Once the build jobs are
evaluated, they are sent to the local Guix daemon.  Cuirass then
listens to the Guix daemon output to detect the various build events.

@item Using the remote build mechanism.
The build jobs are not submitted to the local Guix daemon.  Instead, a
remote server dispatches build requests to the connect remote workers,
according to the build priorities.

@end itemize

To enable this build mode a @code{cuirass-remote-server-configuration}
record must be passed as @code{remote-server} argument of the
@code{cuirass-configuration} record.  The
@code{cuirass-remote-server-configuration} record is described below.

This build mode scales way better than the default build mode.  This is
the build mode that is used on the GNU Guix build farm at
@url{https://ci.guix.gnu.org}.  It should be preferred when using
Cuirass to build large amount of packages.

@deftp {Data Type} cuirass-remote-server-configuration
Data type representing the configuration of the Cuirass remote-server.

@table @asis
@item @code{backend-port} (default: @code{5555})
The TCP port for communicating with @code{remote-worker} processes
using ZMQ.  It defaults to @code{5555}.

@item @code{log-port} (default: @code{5556})
The TCP port of the log server.  It defaults to @code{5556}.

@item @code{publish-port} (default: @code{5557})
The TCP port of the publish server.  It defaults to @code{5557}.

@item @code{log-file} (default: @code{"/var/log/cuirass-remote-server.log"})
Location of the log file.

@item @code{cache} (default: @code{"/var/cache/cuirass/remote"})
Use @var{cache} directory to cache build log files.

@item @code{log-expiry} (default: 6 months)
The duration in seconds after which build logs collected by
@command{cuirass remote-worker} may be deleted.

@item @code{trigger-url} (default: @code{#f})
Once a substitute is successfully fetched, trigger substitute baking at
@var{trigger-url}.

@item @code{publish?} (default: @code{#t})
If set to false, do not start a publish server and ignore the
@code{publish-port} argument.  This can be useful if there is already a
standalone publish server standing next to the remote server.

@item @code{public-key}
@item @code{private-key}
Use the specific @var{file}s as the public/private key pair used to sign
the store items being published.

@end table
@end deftp

At least one remote worker must also be started on any machine of the
local network to actually perform the builds and report their status.

@deftp {Data Type} cuirass-remote-worker-configuration
Data type representing the configuration of the Cuirass remote-worker.

@table @asis
@item @code{cuirass} (default: @code{cuirass})
The Cuirass package to use.

@item @code{workers} (default: @code{1})
Start @var{workers} parallel workers.

@item @code{server} (default: @code{#f})
Do not use Avahi discovery and connect to the given @code{server} IP
address instead.

@item @code{systems} (default: @code{(list (%current-system))})
Only request builds for the given @var{systems}.

@item @code{log-file} (default: @code{"/var/log/cuirass-remote-worker.log"})
Location of the log file.

@item @code{publish-port} (default: @code{5558})
The TCP port of the publish server.  It defaults to @code{5558}.

@item @code{substitute-urls} (default: @code{%default-substitute-urls})
The list of URLs where to look for substitutes by default.

@item @code{public-key}
@item @code{private-key}
Use the specific @var{file}s as the public/private key pair used to sign
the store items being published.

@end table
@end deftp

@subsubheading Laminar

@uref{https://laminar.ohwg.net/, Laminar} is a lightweight and modular
Continuous Integration service.  It doesn't have a configuration web UI
instead uses version-controllable configuration files and scripts.

Laminar encourages the use of existing tools such as bash and cron
instead of reinventing them.

@defvar laminar-service-type
The type of the Laminar service.  Its value must be a
@code{laminar-configuration} object, as described below.

All configuration values have defaults, a minimal configuration to get
Laminar running is shown below. By default, the web interface is
available on port 8080.

@lisp
(service laminar-service-type)
@end lisp
@end defvar

@deftp {Data Type} laminar-configuration
Data type representing the configuration of Laminar.

@table @asis
@item @code{laminar} (default: @code{laminar})
The Laminar package to use.

@item @code{home-directory} (default: @code{"/var/lib/laminar"})
The directory for job configurations and run directories.

@item @code{supplementary-groups} (default: @code{()})
Supplementary groups for the Laminar user account.

@item @code{bind-http} (default: @code{"*:8080"})
The interface/port or unix socket on which laminard should listen for
incoming connections to the web frontend.

@item @code{bind-rpc} (default: @code{"unix-abstract:laminar"})
The interface/port or unix socket on which laminard should listen for
incoming commands such as build triggers.

@item @code{title} (default: @code{"Laminar"})
The page title to show in the web frontend.

@item @code{keep-rundirs} (default: @code{0})
Set to an integer defining how many rundirs to keep per job.  The
lowest-numbered ones will be deleted.  The default is 0, meaning all run
dirs will be immediately deleted.

@item @code{archive-url} (default: @code{#f})
The web frontend served by laminard will use this URL to form links to
artefacts archived jobs.

@item @code{base-url} (default: @code{#f})
Base URL to use for links to laminar itself.

@end table
@end deftp

@node Power Management Services
@subsection Power Management Services

@cindex power-profiles-daemon
@subsubheading Power Profiles Daemon

The @code{(gnu services pm)} module provides a Guix service definition for
the Linux Power Profiles Daemon, which makes power profiles handling
available over D-Bus.

The available profiles consist of the default @samp{balanced} mode, a @samp{power-saver} mode
and on supported systems a @samp{performance} mode.

@quotation Important
The @code{power-profiles-daemon} conflicts with other power management tools
like @code{tlp}. Using both together is not recommended.
@end quotation

@defvar power-profiles-daemon-service-type
This is the service type for the
@uref{https://gitlab.freedesktop.org/upower/power-profiles-daemon/, Power Profiles Daemon}.
The value for this service is a @code{power-profiles-daemon-configuration}.

To enable the Power Profiles Daemon with default configuration
add this line to your services:

@lisp
(service power-profiles-daemon-service-type)
@end lisp
@end defvar

@deftp {Data Type} power-profiles-daemon-configuration
Data type representing the configuration of @code{power-profiles-daemon-service-type}.

@table @asis
@item @code{power-profiles-daemon} (default: @code{power-profiles-daemon}) (type: file-like)
Package object of power-profiles-daemon.

@end table
@end deftp


@cindex tlp
@cindex power management with TLP
@subsubheading TLP daemon

The @code{(gnu services pm)} module provides a Guix service definition
for the Linux power management tool TLP.

TLP enables various powersaving modes in userspace and kernel.
Contrary to @code{upower-service}, it is not a passive,
monitoring tool, as it will apply custom settings each time a new power
source is detected.  More information can be found at
@uref{https://linrunner.de/en/tlp/tlp.html, TLP home page}.

@defvar tlp-service-type
The service type for the TLP tool.  The default settings are optimised
for battery life on most systems, but you can tweak them to your heart's
content by adding a valid @code{tlp-configuration}:
@lisp
(service tlp-service-type
         (tlp-configuration
          (cpu-scaling-governor-on-ac (list "performance"))
          (sched-powersave-on-bat? #t)))
@end lisp
@end defvar

Each parameter definition is preceded by its type; for example,
@samp{boolean foo} indicates that the @code{foo} parameter should be
specified as a boolean.  Types starting with @code{maybe-} denote
parameters that won't show up in TLP config file when their value is
left unset, or is explicitly set to the @code{%unset-value} value.

@c The following documentation was initially generated by
@c (generate-tlp-documentation) in (gnu services pm).  Manually maintained
@c documentation is better, so we shouldn't hesitate to edit below as
@c needed.  However if the change you want to make to this documentation
@c can be done in an automated way, it's probably easier to change
@c (generate-documentation) than to make it below and have to deal with
@c the churn as TLP updates.

Available @code{tlp-configuration} fields are:

@deftypevr {@code{tlp-configuration} parameter} package tlp
The TLP package.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} boolean tlp-enable?
Set to true if you wish to enable TLP.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string tlp-default-mode
Default mode when no power supply can be detected.  Alternatives are AC
and BAT.

Defaults to @samp{"AC"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} non-negative-integer disk-idle-secs-on-ac
Number of seconds Linux kernel has to wait after the disk goes idle,
before syncing on AC.

Defaults to @samp{0}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} non-negative-integer disk-idle-secs-on-bat
Same as @code{disk-idle-ac} but on BAT mode.

Defaults to @samp{2}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} non-negative-integer max-lost-work-secs-on-ac
Dirty pages flushing periodicity, expressed in seconds.

Defaults to @samp{15}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} non-negative-integer max-lost-work-secs-on-bat
Same as @code{max-lost-work-secs-on-ac} but on BAT mode.

Defaults to @samp{60}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-space-separated-string-list cpu-scaling-governor-on-ac
CPU frequency scaling governor on AC mode.  With intel_pstate driver,
alternatives are powersave and performance.  With acpi-cpufreq driver,
alternatives are ondemand, powersave, performance and conservative.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-space-separated-string-list cpu-scaling-governor-on-bat
Same as @code{cpu-scaling-governor-on-ac} but on BAT mode.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-non-negative-integer cpu-scaling-min-freq-on-ac
Set the min available frequency for the scaling governor on AC.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-non-negative-integer cpu-scaling-max-freq-on-ac
Set the max available frequency for the scaling governor on AC.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-non-negative-integer cpu-scaling-min-freq-on-bat
Set the min available frequency for the scaling governor on BAT.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-non-negative-integer cpu-scaling-max-freq-on-bat
Set the max available frequency for the scaling governor on BAT.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-non-negative-integer cpu-min-perf-on-ac
Limit the min P-state to control the power dissipation of the CPU, in AC
mode.  Values are stated as a percentage of the available performance.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-non-negative-integer cpu-max-perf-on-ac
Limit the max P-state to control the power dissipation of the CPU, in AC
mode.  Values are stated as a percentage of the available performance.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-non-negative-integer cpu-min-perf-on-bat
Same as @code{cpu-min-perf-on-ac} on BAT mode.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-non-negative-integer cpu-max-perf-on-bat
Same as @code{cpu-max-perf-on-ac} on BAT mode.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-boolean cpu-boost-on-ac?
Enable CPU turbo boost feature on AC mode.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-boolean cpu-boost-on-bat?
Same as @code{cpu-boost-on-ac?} on BAT mode.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} boolean sched-powersave-on-ac?
Allow Linux kernel to minimize the number of CPU cores/hyper-threads
used under light load conditions.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} boolean sched-powersave-on-bat?
Same as @code{sched-powersave-on-ac?} but on BAT mode.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} boolean nmi-watchdog?
Enable Linux kernel NMI watchdog.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-string phc-controls
For Linux kernels with PHC patch applied, change CPU voltages.  An
example value would be @samp{"F:V F:V F:V F:V"}.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string energy-perf-policy-on-ac
Set CPU performance versus energy saving policy on AC@.  Alternatives are
performance, normal, powersave.

Defaults to @samp{"performance"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string energy-perf-policy-on-bat
Same as @code{energy-perf-policy-ac} but on BAT mode.

Defaults to @samp{"powersave"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} space-separated-string-list disks-devices
Hard disk devices.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} space-separated-string-list disk-apm-level-on-ac
Hard disk advanced power management level.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} space-separated-string-list disk-apm-level-on-bat
Same as @code{disk-apm-bat} but on BAT mode.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-space-separated-string-list disk-spindown-timeout-on-ac
Hard disk spin down timeout.  One value has to be specified for each
declared hard disk.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-space-separated-string-list disk-spindown-timeout-on-bat
Same as @code{disk-spindown-timeout-on-ac} but on BAT mode.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-space-separated-string-list disk-iosched
Select IO scheduler for disk devices.  One value has to be specified for
each declared hard disk.  Example alternatives are cfq, deadline and
noop.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string sata-linkpwr-on-ac
SATA aggressive link power management (ALPM) level.  Alternatives are
min_power, medium_power, max_performance.

Defaults to @samp{"max_performance"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string sata-linkpwr-on-bat
Same as @code{sata-linkpwr-ac} but on BAT mode.

Defaults to @samp{"min_power"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-string sata-linkpwr-blacklist
Exclude specified SATA host devices for link power management.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-on-off-boolean ahci-runtime-pm-on-ac?
Enable Runtime Power Management for AHCI controller and disks on AC
mode.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-on-off-boolean ahci-runtime-pm-on-bat?
Same as @code{ahci-runtime-pm-on-ac} on BAT mode.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} non-negative-integer ahci-runtime-pm-timeout
Seconds of inactivity before disk is suspended.

Defaults to @samp{15}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string pcie-aspm-on-ac
PCI Express Active State Power Management level.  Alternatives are
default, performance, powersave.

Defaults to @samp{"performance"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string pcie-aspm-on-bat
Same as @code{pcie-aspm-ac} but on BAT mode.

Defaults to @samp{"powersave"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-non-negative-integer start-charge-thresh-bat0
Percentage when battery 0 should begin charging.  Only supported on some laptops.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-non-negative-integer stop-charge-thresh-bat0
Percentage when battery 0 should stop charging.  Only supported on some laptops.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-non-negative-integer start-charge-thresh-bat1
Percentage when battery 1 should begin charging.  Only supported on some laptops.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-non-negative-integer stop-charge-thresh-bat1
Percentage when battery 1 should stop charging.  Only supported on some laptops.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string radeon-power-profile-on-ac
Radeon graphics clock speed level.  Alternatives are low, mid, high,
auto, default.

Defaults to @samp{"high"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string radeon-power-profile-on-bat
Same as @code{radeon-power-ac} but on BAT mode.

Defaults to @samp{"low"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string radeon-dpm-state-on-ac
Radeon dynamic power management method (DPM).  Alternatives are battery,
performance.

Defaults to @samp{"performance"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string radeon-dpm-state-on-bat
Same as @code{radeon-dpm-state-ac} but on BAT mode.

Defaults to @samp{"battery"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string radeon-dpm-perf-level-on-ac
Radeon DPM performance level.  Alternatives are auto, low, high.

Defaults to @samp{"auto"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string radeon-dpm-perf-level-on-bat
Same as @code{radeon-dpm-perf-ac} but on BAT mode.

Defaults to @samp{"auto"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} on-off-boolean wifi-pwr-on-ac?
Wifi power saving mode.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} on-off-boolean wifi-pwr-on-bat?
Same as @code{wifi-power-ac?} but on BAT mode.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} y-n-boolean wol-disable?
Disable wake on LAN.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} non-negative-integer sound-power-save-on-ac
Timeout duration in seconds before activating audio power saving on
Intel HDA and AC97 devices.  A value of 0 disables power saving.

Defaults to @samp{0}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} non-negative-integer sound-power-save-on-bat
Same as @code{sound-powersave-ac} but on BAT mode.

Defaults to @samp{1}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} y-n-boolean sound-power-save-controller?
Disable controller in powersaving mode on Intel HDA devices.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} boolean bay-poweroff-on-bat?
Enable optical drive in UltraBay/MediaBay on BAT mode.  Drive can be
powered on again by releasing (and reinserting) the eject lever or by
pressing the disc eject button on newer models.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string bay-device
Name of the optical drive device to power off.

Defaults to @samp{"sr0"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string runtime-pm-on-ac
Runtime Power Management for PCI(e) bus devices.  Alternatives are on
and auto.

Defaults to @samp{"on"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} string runtime-pm-on-bat
Same as @code{runtime-pm-ac} but on BAT mode.

Defaults to @samp{"auto"}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} boolean runtime-pm-all?
Runtime Power Management for all PCI(e) bus devices, except blacklisted
ones.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-space-separated-string-list runtime-pm-blacklist
Exclude specified PCI(e) device addresses from Runtime Power Management.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} space-separated-string-list runtime-pm-driver-blacklist
Exclude PCI(e) devices assigned to the specified drivers from Runtime
Power Management.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} boolean usb-autosuspend?
Enable USB autosuspend feature.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-string usb-blacklist
Exclude specified devices from USB autosuspend.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} boolean usb-blacklist-wwan?
Exclude WWAN devices from USB autosuspend.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-string usb-whitelist
Include specified devices into USB autosuspend, even if they are already
excluded by the driver or via @code{usb-blacklist-wwan?}.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} maybe-boolean usb-autosuspend-disable-on-shutdown?
Enable USB autosuspend before shutdown.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{tlp-configuration} parameter} boolean restore-device-state-on-startup?
Restore radio device state (bluetooth, wifi, wwan) from previous
shutdown on system startup.

Defaults to @samp{#f}.

@end deftypevr

@cindex thermald
@cindex CPU frequency scaling with thermald
@subsubheading Thermald daemon

The @code{(gnu services pm)} module provides an interface to
thermald, a CPU frequency scaling service which helps prevent overheating.

@defvar thermald-service-type
This is the service type for
@uref{https://01.org/linux-thermal-daemon/, thermald}, the Linux
Thermal Daemon, which is responsible for controlling the thermal state
of processors and preventing overheating.
@end defvar

@deftp {Data Type} thermald-configuration
Data type representing the configuration of @code{thermald-service-type}.

@table @asis
@item @code{adaptive?} (default: @code{#f})
Use @acronym{DPTF, Dynamic Power and Thermal Framework} adaptive tables
when present.

@item @code{ignore-cpuid-check?} (default: @code{#f})
Ignore cpuid check for supported CPU models.

@item @code{thermald} (default: @var{thermald})
Package object of thermald.

@end table
@end deftp

@node Audio Services
@subsection Audio Services

The @code{(gnu services audio)} module provides a service to start MPD
(the Music Player Daemon).

@cindex mpd
@subsubheading Music Player Daemon

The Music Player Daemon (MPD) is a service that can play music while
being controlled from the local machine or over the network by a variety
of clients.

The following example shows the simplest configuration to locally
expose, via PulseAudio, a music collection kept at @file{/srv/music},
with @command{mpd} running as the default @samp{mpd} user.  This user
will spawn its own PulseAudio daemon, which may compete for the sound
card access with that of your own user.  In this configuration, you may
have to stop the playback of your user audio applications to hear MPD's
output and vice-versa.

@lisp
(service mpd-service-type
         (mpd-configuration
          (music-directory "/srv/music")))
@end lisp

@quotation Important
The music directory must be readable to the MPD user, by default,
@samp{mpd}.  Permission problems will be reported via @samp{Permission
denied} errors in the MPD logs, which appear in @file{/var/log/messages}
by default.
@end quotation

Most MPD clients will trigger a database update upon connecting, but you
can also use the @code{update} action do to so:

@example
herd update mpd
@end example

All the MPD configuration fields are documented below, and a more
complex example follows.

@defvar mpd-service-type
The service type for @command{mpd}
@end defvar

@c %start of fragment
@deftp {Data Type} mpd-configuration
Available @code{mpd-configuration} fields are:

@table @asis
@item @code{package} (default: @code{mpd}) (type: file-like)
The MPD package.

@item @code{user} (type: user-account)
The user to run mpd as.

@item @code{group} (type: user-group)
The group to run mpd as.

The default @code{%mpd-group} is a system group with name ``mpd''.

@item @code{shepherd-requirement} (default: @code{'()}) (type: list-of-symbols)
A list of symbols naming Shepherd services that this service
will depend on.

@item @code{environment-variables} (default: @code{'("PULSE_CLIENTCONFIG=/etc/pulse/client.conf" "PULSE_CONFIG=/etc/pulse/daemon.conf")}) (type: list-of-strings)
A list of strings specifying environment variables.

@item @code{log-file} (type: maybe-string)
The location of the log file.  Unless specified, logs are sent to the
local syslog daemon.  Alternatively, a log file name can be specified,
for example @file{/var/log/mpd.log}.

@item @code{log-level} (type: maybe-string)
Supress any messages below this threshold.  The available values, in
decreasing order of verbosity, are: @code{verbose}, @code{info},
@code{notice}, @code{warning} and @code{error}.

@item @code{music-directory} (type: maybe-string)
The directory to scan for music files.

@item @code{music-dir} (type: maybe-string)
The directory to scan for music files.

@item @code{playlist-directory} (type: maybe-string)
The directory to store playlists.

@item @code{playlist-dir} (type: maybe-string)
The directory to store playlists.

@item @code{db-file} (type: maybe-string)
The location of the music database.  When left unspecified,
@file{~/.cache/db} is used.

@item @code{state-file} (type: maybe-string)
The location of the file that stores current MPD's state.

@item @code{sticker-file} (type: maybe-string)
The location of the sticker database.

@item @code{default-port} (default: @code{6600}) (type: maybe-port)
The default port to run mpd on.

@item @code{endpoints} (type: maybe-list-of-strings)
The addresses that mpd will bind to.  A port different from
@var{default-port} may be specified, e.g.  @code{localhost:6602} and
IPv6 addresses must be enclosed in square brackets when a different port
is used.  To use a Unix domain socket, an absolute path or a path
starting with @code{~} can be specified here.

@item @code{address} (type: maybe-string)
The address that mpd will bind to.  To use a Unix domain socket, an
absolute path can be specified here.

@item @code{database} (type: maybe-mpd-plugin)
MPD database plugin configuration.

@item @code{partitions} (default: @code{'()}) (type: list-of-mpd-partition)
List of MPD "partitions".

@item @code{neighbors} (default: @code{'()}) (type: list-of-mpd-plugin)
List of MPD neighbor plugin configurations.

@item @code{inputs} (default: @code{'()}) (type: list-of-mpd-plugin)
List of MPD input plugin configurations.

@item @code{archive-plugins} (default: @code{'()}) (type: list-of-mpd-plugin)
List of MPD archive plugin configurations.

@item @code{auto-update?} (type: maybe-boolean)
Whether to automatically update the music database when files are
changed in the @var{music-directory}.

@item @code{input-cache-size} (type: maybe-string)
MPD input cache size.

@item @code{decoders} (default: @code{'()}) (type: list-of-mpd-plugin)
List of MPD decoder plugin configurations.

@item @code{resampler} (type: maybe-mpd-plugin)
MPD resampler plugin configuration.

@item @code{filters} (default: @code{'()}) (type: list-of-mpd-plugin)
List of MPD filter plugin configurations.

@item @code{outputs} (type: list-of-mpd-plugin-or-output)
The audio outputs that MPD can use.  By default this is a single output
using pulseaudio.

@item @code{playlist-plugins} (default: @code{'()}) (type: list-of-mpd-plugin)
List of MPD playlist plugin configurations.

@item @code{extra-options} (default: @code{'()}) (type: alist)
An association list of option symbols/strings to string values to be
appended to the configuration.

@end table
@end deftp
@c %end of fragment

@deftp {Data Type} mpd-plugin
Data type representing a @command{mpd} plugin.

@table @asis
@item @code{plugin} (type: maybe-string)
Plugin name.

@item @code{name} (type: maybe-string)
Name.

@item @code{enabled?} (type: maybe-boolean)
Whether the plugin is enabled/disabled.

@item @code{extra-options} (default: @code{'()}) (type: alist)
An association list of option symbols/strings to string values to be
appended to the plugin configuration.  See
@uref{https://mpd.readthedocs.io/en/latest/plugins.html,MPD plugin
reference} for available options.

@end table
@end deftp

@deftp {Data Type} mpd-partition
Data type representing a @command{mpd} partition.

@table @asis
@item @code{name} (type: string)
Partition name.

@item @code{extra-options} (default: @code{'()}) (type: alist)
An association list of option symbols/strings to string values to be
appended to the partition configuration.  See
@uref{https://mpd.readthedocs.io/en/latest/user.html#configuring-partitions,Configuring
Partitions} for available options.

@end table
@end deftp

@c %start of fragment
@deftp {Data Type} mpd-output
Available @code{mpd-output} fields are:

@table @asis
@item @code{name} (default: @code{"MPD"}) (type: string)
The name of the audio output.

@item @code{type} (default: @code{"pulse"}) (type: string)
The type of audio output.

@item @code{enabled?} (default: @code{#t}) (type: boolean)
Specifies whether this audio output is enabled when MPD is started.  By
default, all audio outputs are enabled.  This is just the default
setting when there is no state file; with a state file, the previous
state is restored.

@item @code{format} (type: maybe-string)
Force a specific audio format on output.  See
@uref{https://mpd.readthedocs.io/en/latest/user.html#audio-output-format,Global
Audio Format} for a more detailed description.

@item @code{tags?} (default: @code{#t}) (type: boolean)
If set to @code{#f}, then MPD will not send tags to this output.  This
is only useful for output plugins that can receive tags, for example the
@code{httpd} output plugin.

@item @code{always-on?} (default: @code{#f}) (type: boolean)
If set to @code{#t}, then MPD attempts to keep this audio output always
open.  This may be useful for streaming servers, when you don’t want to
disconnect all listeners even when playback is accidentally stopped.

@item @code{mixer-type} (type: maybe-string)
This field accepts a string that specifies which mixer should be used
for this audio output: the @code{hardware} mixer, the @code{software}
mixer, the @code{null} mixer (allows setting the volume, but with no
effect; this can be used as a trick to implement an external mixer
External Mixer) or no mixer (@code{none}).  When left unspecified, a
@code{hardware} mixer is used for devices that support it.

@item @code{replay-gain-handler} (type: maybe-string)
This field accepts a string that specifies how
@uref{https://mpd.readthedocs.io/en/latest/user.html#replay-gain,Replay
Gain} is to be applied.  @code{software} uses an internal software
volume control, @code{mixer} uses the configured (hardware) mixer
control and @code{none} disables replay gain on this audio output.

@item @code{extra-options} (default: @code{'()}) (type: alist)
An association list of option symbols/strings to string values to be
appended to the audio output configuration.

@end table
@end deftp
@c %end of fragment

The following example shows a configuration of @command{mpd} that
configures some of its plugins and provides a HTTP audio streaming output.

@lisp
(service mpd-service-type
         (mpd-configuration
           (outputs
             (list (mpd-output
                     (name "streaming")
                     (type "httpd")
                     (mixer-type 'null)
                     (extra-options
                      `((encoder . "vorbis")
                        (port    . "8080"))))))
           (decoders
             (list (mpd-plugin
                     (plugin "mikmod")
                     (enabled? #f))
                   (mpd-plugin
                     (plugin "openmpt")
                     (enabled? #t)
                     (extra-options `((repeat-count . -1)
                                      (interpolation-filter . 1))))))
           (resampler (mpd-plugin
                        (plugin "libsamplerate")
                        (extra-options `((type . 0)))))))
@end lisp

@subsubheading myMPD

@cindex MPD, web interface
@cindex myMPD service

@uref{https://jcorporation.github.io/myMPD/, myMPD} is a web server
frontend for MPD that provides a mobile friendly web client for MPD.

The following example shows a myMPD instance listening on port 80,
with album cover caching disabled.

@lisp
(service mympd-service-type
         (mympd-configuration
          (port 80)
          (covercache-ttl 0)))
@end lisp

@defvar mympd-service-type
The service type for @command{mympd}.
@end defvar

@c %start of fragment
@deftp {Data Type} mympd-configuration
Available @code{mympd-configuration} fields are:

@table @asis
@item @code{package} (default: @code{mympd}) (type: file-like)
The package object of the myMPD server.

@item @code{shepherd-requirement} (default: @code{'()}) (type: list-of-symbols)
This is a list of symbols naming Shepherd services that this service
will depend on.

@item @code{user} (default: @code{%mympd-user}) (type: user-account)
Owner of the @command{mympd} process.

The default @code{%mympd-user} is a system user with the name ``mympd'',
who is a part of the group @var{group} (see below).

@item @code{group} (default: @code{%mympd-group}) (type: user-group)
Owner group of the @command{mympd} process.

The default @code{%mympd-group} is a system group with name ``mympd''.
@item @code{work-directory} (default: @code{"/var/lib/mympd"}) (type: string)
Where myMPD will store its data.

@item @code{cache-directory} (default: @code{"/var/cache/mympd"}) (type: string)
Where myMPD will store its cache.

@item @code{acl} (type: maybe-mympd-ip-acl)
ACL to access the myMPD webserver.

@item @code{covercache-ttl} (default: @code{31}) (type: maybe-integer)
How long to keep cached covers, @code{0} disables cover caching.

@item @code{http?} (default: @code{#t}) (type: boolean)
HTTP support.

@item @code{host} (default: @code{"[::]"}) (type: string)
Host name to listen on.

@item @code{port} (default: @code{80}) (type: maybe-port)
HTTP port to listen on.

@item @code{log-level} (default: @code{5}) (type: integer)
How much detail to include in logs, possible values: @code{0} to
@code{7}.

@item @code{log-to} (type: maybe-string)
Where to send logs.  Unless specified, the service logs to the local
syslog service under the @samp{daemon} facility.  Alternatively, a log
file name can be specified, for example @file{/var/log/mympd.log}.

@item @code{lualibs} (default: @code{"all"}) (type: maybe-string)
See
@uref{https://jcorporation.github.io/myMPD/scripting/#lua-standard-libraries}.

@item @code{uri} (type: maybe-string)
Override URI to myMPD.  See
@uref{https://github.com/jcorporation/myMPD/issues/950}.

@item @code{script-acl} (default: @code{(mympd-ip-acl (allow '("127.0.0.1")))}) (type: maybe-mympd-ip-acl)
ACL to access the myMPD script backend.

@item @code{ssl?} (default: @code{#f}) (type: boolean)
SSL/TLS support.

@item @code{ssl-port} (default: @code{443}) (type: maybe-port)
Port to listen for HTTPS.

@item @code{ssl-cert} (type: maybe-string)
Path to PEM encoded X.509 SSL/TLS certificate (public key).

@item @code{ssl-key} (type: maybe-string)
Path to PEM encoded SSL/TLS private key.

@item @code{pin-hash} (type: maybe-string)
SHA-256 hashed pin used by myMPD to control settings access by prompting
a pin from the user.

@item @code{save-caches?} (type: maybe-boolean)
Whether to preserve caches between service restarts.

@end table
@end deftp
@c %end of fragment

@c %start of fragment
@deftp {Data Type} mympd-ip-acl
Available @code{mympd-ip-acl} fields are:

@table @asis
@item @code{allow} (default: @code{'()}) (type: list-of-strings)
Allowed IP addresses.

@item @code{deny} (default: @code{'()}) (type: list-of-strings)
Disallowed IP addresses.

@end table
@end deftp
@c %end of fragment

@node Virtualization Services
@subsection Virtualization Services

The @code{(gnu services virtualization)} module provides services for
the libvirt and virtlog daemons, as well as other virtualization-related
services.

@subsubheading Libvirt daemon

@code{libvirtd} is the server side daemon component of the libvirt
virtualization management system.  This daemon runs on host servers and
performs required management tasks for virtualized guests.  To connect
to the libvirt daemon as an unprivileged user, it must be added to the
@samp{libvirt} group, as shown in the example below.

@defvar libvirt-service-type
This is the type of the @uref{https://libvirt.org, libvirt daemon}.
Its value must be a @code{libvirt-configuration}.

@lisp
(users (cons (user-account
              (name "user")
              (group "users")
              (supplementary-groups '("libvirt"
                                      "audio" "video" "wheel")))
             %base-user-accounts))
(service libvirt-service-type
         (libvirt-configuration
          (tls-port "16555")))
@end lisp
@end defvar

@c Auto-generated with (generate-libvirt-documentation)
Available @code{libvirt-configuration} fields are:

@deftypevr {@code{libvirt-configuration} parameter} package libvirt
Libvirt package.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} boolean listen-tls?
Flag listening for secure TLS connections on the public TCP/IP port.
You must set @code{listen} for this to have any effect.

It is necessary to setup a CA and issue server certificates before using
this capability.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} boolean listen-tcp?
Listen for unencrypted TCP connections on the public TCP/IP port.  You must
set @code{listen} for this to have any effect.

Using the TCP socket requires SASL authentication by default.  Only SASL
mechanisms which support data encryption are allowed.  This is
DIGEST_MD5 and GSSAPI (Kerberos5).

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string tls-port
Port for accepting secure TLS connections.   This can be a port number,
or service name.

Defaults to @samp{"16514"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string tcp-port
Port for accepting insecure TCP connections.  This can be a port number,
or service name.

Defaults to @samp{"16509"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string listen-addr
IP address or hostname used for client connections.

Defaults to @samp{"0.0.0.0"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} boolean mdns-adv?
Flag toggling mDNS advertisement of the libvirt service.

Alternatively can disable for all services on a host by stopping the
Avahi daemon.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string mdns-name
Default mDNS advertisement name.  This must be unique on the immediate
broadcast network.

Defaults to @samp{"Virtualization Host <hostname>"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string unix-sock-group
UNIX domain socket group ownership.  This can be used to allow a
'trusted' set of users access to management capabilities without
becoming root.

Defaults to @samp{"libvirt"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string unix-sock-ro-perms
UNIX socket permissions for the R/O socket.  This is used for monitoring
VM status only.

Defaults to @samp{"0777"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string unix-sock-rw-perms
UNIX socket permissions for the R/W socket.  Default allows only root.
If PolicyKit is enabled on the socket, the default will change to allow
everyone (eg, 0777)

Defaults to @samp{"0770"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string unix-sock-admin-perms
UNIX socket permissions for the admin socket.  Default allows only owner
(root), do not change it unless you are sure to whom you are exposing
the access to.

Defaults to @samp{"0777"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string unix-sock-dir
The directory in which sockets will be found/created.

Defaults to @samp{"/var/run/libvirt"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string auth-unix-ro
Authentication scheme for UNIX read-only sockets.  By default socket
permissions allow anyone to connect

Defaults to @samp{"polkit"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string auth-unix-rw
Authentication scheme for UNIX read-write sockets.  By default socket
permissions only allow root.  If PolicyKit support was compiled into
libvirt, the default will be to use 'polkit' auth.

Defaults to @samp{"polkit"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string auth-tcp
Authentication scheme for TCP sockets.  If you don't enable SASL, then
all TCP traffic is cleartext.  Don't do this outside of a dev/test
scenario.

Defaults to @samp{"sasl"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string auth-tls
Authentication scheme for TLS sockets.  TLS sockets already have
encryption provided by the TLS layer, and limited authentication is done
by certificates.

It is possible to make use of any SASL authentication mechanism as well,
by using 'sasl' for this option

Defaults to @samp{"none"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} optional-list access-drivers
API access control scheme.

By default an authenticated user is allowed access to all APIs.  Access
drivers can place restrictions on this.

Defaults to @samp{'()}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string key-file
Server key file path.  If set to an empty string, then no private key is
loaded.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string cert-file
Server key file path.  If set to an empty string, then no certificate is
loaded.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string ca-file
Server key file path.  If set to an empty string, then no CA certificate
is loaded.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string crl-file
Certificate revocation list path.  If set to an empty string, then no
CRL is loaded.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} boolean tls-no-sanity-cert
Disable verification of our own server certificates.

When libvirtd starts it performs some sanity checks against its own
certificates.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} boolean tls-no-verify-cert
Disable verification of client certificates.

Client certificate verification is the primary authentication mechanism.
Any client which does not present a certificate signed by the CA will be
rejected.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} optional-list tls-allowed-dn-list
Whitelist of allowed x509 Distinguished Name.

Defaults to @samp{'()}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} optional-list sasl-allowed-usernames
Whitelist of allowed SASL usernames.  The format for username depends on
the SASL authentication mechanism.

Defaults to @samp{'()}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string tls-priority
Override the compile time default TLS priority string.  The default is
usually @samp{"NORMAL"} unless overridden at build time.  Only set this is it
is desired for libvirt to deviate from the global default settings.

Defaults to @samp{"NORMAL"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer max-clients
Maximum number of concurrent client connections to allow over all
sockets combined.

Defaults to @samp{5000}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer max-queued-clients
Maximum length of queue of connections waiting to be accepted by the
daemon.  Note, that some protocols supporting retransmission may obey
this so that a later reattempt at connection succeeds.

Defaults to @samp{1000}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer max-anonymous-clients
Maximum length of queue of accepted but not yet authenticated clients.
Set this to zero to turn this feature off

Defaults to @samp{20}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer min-workers
Number of workers to start up initially.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer max-workers
Maximum number of worker threads.

If the number of active clients exceeds @code{min-workers}, then more
threads are spawned, up to max_workers limit.  Typically you'd want
max_workers to equal maximum number of clients allowed.

Defaults to @samp{20}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer prio-workers
Number of priority workers.  If all workers from above pool are stuck,
some calls marked as high priority (notably domainDestroy) can be
executed in this pool.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer max-requests
Total global limit on concurrent RPC calls.

Defaults to @samp{20}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer max-client-requests
Limit on concurrent requests from a single client connection.  To avoid
one client monopolizing the server this should be a small fraction of
the global max_requests and max_workers parameter.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer admin-min-workers
Same as @code{min-workers} but for the admin interface.

Defaults to @samp{1}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer admin-max-workers
Same as @code{max-workers} but for the admin interface.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer admin-max-clients
Same as @code{max-clients} but for the admin interface.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer admin-max-queued-clients
Same as @code{max-queued-clients} but for the admin interface.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer admin-max-client-requests
Same as @code{max-client-requests} but for the admin interface.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer log-level
Logging level.  4 errors, 3 warnings, 2 information, 1 debug.

Defaults to @samp{3}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string log-filters
Logging filters.

A filter allows to select a different logging level for a given category
of logs.  The format for a filter is one of:

@itemize @bullet
@item
x:name

@item
x:+name

@end itemize

where @code{name} is a string which is matched against the category
given in the @code{VIR_LOG_INIT()} at the top of each libvirt source
file, e.g., @samp{"remote"}, @samp{"qemu"}, or @samp{"util.json"} (the
name in the filter can be a substring of the full category name, in
order to match multiple similar categories), the optional @samp{"+"}
prefix tells libvirt to log stack trace for each message matching name,
and @code{x} is the minimal level where matching messages should be
logged:

@itemize @bullet
@item
1: DEBUG

@item
2: INFO

@item
3: WARNING

@item
4: ERROR

@end itemize

Multiple filters can be defined in a single filters statement, they just
need to be separated by spaces.

Defaults to @samp{"3:remote 4:event"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string log-outputs
Logging outputs.

An output is one of the places to save logging information.  The format
for an output can be:

@table @code
@item x:stderr
output goes to stderr

@item x:syslog:name
use syslog for the output and use the given name as the ident

@item x:file:file_path
output to a file, with the given filepath

@item x:journald
output to journald logging system

@end table

In all case the x prefix is the minimal level, acting as a filter

@itemize @bullet
@item
1: DEBUG

@item
2: INFO

@item
3: WARNING

@item
4: ERROR

@end itemize

Multiple outputs can be defined, they just need to be separated by
spaces.

Defaults to @samp{"3:stderr"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer audit-level
Allows usage of the auditing subsystem to be altered

@itemize @bullet
@item
0: disable all auditing

@item
1: enable auditing, only if enabled on host

@item
2: enable auditing, and exit if disabled on host.

@end itemize

Defaults to @samp{1}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} boolean audit-logging
Send audit messages via libvirt logging infrastructure.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} optional-string host-uuid
Host UUID@.  UUID must not have all digits be the same.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} string host-uuid-source
Source to read host UUID.

@itemize @bullet
@item
@code{smbios}: fetch the UUID from @code{dmidecode -s system-uuid}

@item
@code{machine-id}: fetch the UUID from @code{/etc/machine-id}

@end itemize

If @code{dmidecode} does not provide a valid UUID a temporary UUID will
be generated.

Defaults to @samp{"smbios"}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer keepalive-interval
A keepalive message is sent to a client after @code{keepalive_interval}
seconds of inactivity to check if the client is still responding.  If
set to -1, libvirtd will never send keepalive requests; however clients
can still send them and the daemon will send responses.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer keepalive-count
Maximum number of keepalive messages that are allowed to be sent to the
client without getting any response before the connection is considered
broken.

In other words, the connection is automatically closed approximately
after @code{keepalive_interval * (keepalive_count + 1)} seconds since
the last message received from the client.  When @code{keepalive-count}
is set to 0, connections will be automatically closed after
@code{keepalive-interval} seconds of inactivity without sending any
keepalive messages.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer admin-keepalive-interval
Same as above but for admin interface.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer admin-keepalive-count
Same as above but for admin interface.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{libvirt-configuration} parameter} integer ovs-timeout
Timeout for Open vSwitch calls.

The @code{ovs-vsctl} utility is used for the configuration and its
timeout option is set by default to 5 seconds to avoid potential
infinite waits blocking libvirt.

Defaults to @samp{5}.

@end deftypevr

@c %end of autogenerated docs

@subsubheading Virtlog daemon
The virtlogd service is a server side daemon component of libvirt that is
used to manage logs from virtual machine consoles.

This daemon is not used directly by libvirt client applications, rather it
is called on their behalf by @code{libvirtd}.  By maintaining the logs in a
standalone daemon, the main @code{libvirtd} daemon can be restarted without
risk of losing logs.  The @code{virtlogd} daemon has the ability to re-exec()
itself upon receiving @code{SIGUSR1}, to allow live upgrades without downtime.

@defvar virtlog-service-type
This is the type of the virtlog daemon.
Its value must be a @code{virtlog-configuration}.

@lisp
(service virtlog-service-type
         (virtlog-configuration
          (max-clients 1000)))
@end lisp
@end defvar

@deftypevr {@code{libvirt} parameter} package libvirt
Libvirt package.
@end deftypevr

@deftypevr {@code{virtlog-configuration} parameter} integer log-level
Logging level.  4 errors, 3 warnings, 2 information, 1 debug.

Defaults to @samp{3}.

@end deftypevr

@deftypevr {@code{virtlog-configuration} parameter} string log-filters
Logging filters.

A filter allows to select a different logging level for a given category
of logs The format for a filter is one of:

@itemize @bullet
@item
x:name

@item
x:+name

@end itemize

where @code{name} is a string which is matched against the category
given in the @code{VIR_LOG_INIT()} at the top of each libvirt source
file, e.g., "remote", "qemu", or "util.json" (the name in the filter can
be a substring of the full category name, in order to match multiple
similar categories), the optional "+" prefix tells libvirt to log stack
trace for each message matching name, and @code{x} is the minimal level
where matching messages should be logged:

@itemize @bullet
@item
1: DEBUG

@item
2: INFO

@item
3: WARNING

@item
4: ERROR

@end itemize

Multiple filters can be defined in a single filters statement, they just
need to be separated by spaces.

Defaults to @samp{"3:remote 4:event"}.

@end deftypevr

@deftypevr {@code{virtlog-configuration} parameter} string log-outputs
Logging outputs.

An output is one of the places to save logging information The format
for an output can be:

@table @code
@item x:stderr
output goes to stderr

@item x:syslog:name
use syslog for the output and use the given name as the ident

@item x:file:file_path
output to a file, with the given filepath

@item x:journald
output to journald logging system

@end table

In all case the x prefix is the minimal level, acting as a filter

@itemize @bullet
@item
1: DEBUG

@item
2: INFO

@item
3: WARNING

@item
4: ERROR

@end itemize

Multiple outputs can be defined, they just need to be separated by
spaces.

Defaults to @samp{"3:stderr"}.

@end deftypevr

@deftypevr {@code{virtlog-configuration} parameter} integer max-clients
Maximum number of concurrent client connections to allow over all
sockets combined.

Defaults to @samp{1024}.

@end deftypevr

@deftypevr {@code{virtlog-configuration} parameter} integer max-size
Maximum file size before rolling over.

Defaults to @samp{2MB}

@end deftypevr

@deftypevr {@code{virtlog-configuration} parameter} integer max-backups
Maximum number of backup files to keep.

Defaults to @samp{3}

@end deftypevr

@anchor{transparent-emulation-qemu}
@subsubheading Transparent Emulation with QEMU

@cindex emulation
@cindex @code{binfmt_misc}
@code{qemu-binfmt-service-type} provides support for transparent
emulation of program binaries built for different architectures---e.g.,
it allows you to transparently execute an ARMv7 program on an x86_64
machine.  It achieves this by combining the @uref{https://www.qemu.org,
QEMU} emulator and the @code{binfmt_misc} feature of the kernel Linux.
This feature only allows you to emulate GNU/Linux on a different
architecture, but see below for GNU/Hurd support.

@defvar qemu-binfmt-service-type
This is the type of the QEMU/binfmt service for transparent emulation.
Its value must be a @code{qemu-binfmt-configuration} object, which
specifies the QEMU package to use as well as the architecture we want to
emulated:

@lisp
(service qemu-binfmt-service-type
         (qemu-binfmt-configuration
           (platforms (lookup-qemu-platforms "arm" "aarch64"))))
@end lisp

In this example, we enable transparent emulation for the ARM and aarch64
platforms.  Running @code{herd stop qemu-binfmt} turns it off, and
running @code{herd start qemu-binfmt} turns it back on (@pxref{Invoking
herd, the @command{herd} command,, shepherd, The GNU Shepherd Manual}).
@end defvar

@deftp {Data Type} qemu-binfmt-configuration
This is the configuration for the @code{qemu-binfmt} service.

@table @asis
@item @code{platforms} (default: @code{'()})
The list of emulated QEMU platforms.  Each item must be a @dfn{platform
object} as returned by @code{lookup-qemu-platforms} (see below).

For example, let's suppose you're on an x86_64 machine and you have this
service:

@lisp
(service qemu-binfmt-service-type
         (qemu-binfmt-configuration
           (platforms (lookup-qemu-platforms "arm"))))
@end lisp

You can run:

@example
guix build -s armhf-linux inkscape
@end example

@noindent
and it will build Inkscape for ARMv7 @emph{as if it were a native
build}, transparently using QEMU to emulate the ARMv7 CPU@.  Pretty handy
if you'd like to test a package build for an architecture you don't have
access to!

@item @code{qemu} (default: @code{qemu})
The QEMU package to use.
@end table
@end deftp

@deffn {Procedure} lookup-qemu-platforms platforms@dots{}
Return the list of QEMU platform objects corresponding to
@var{platforms}@dots{}.  @var{platforms} must be a list of strings
corresponding to platform names, such as @code{"arm"}, @code{"sparc"},
@code{"mips64el"}, and so on.
@end deffn

@deffn {Procedure} qemu-platform? obj
Return true if @var{obj} is a platform object.
@end deffn

@deffn {Procedure} qemu-platform-name platform
Return the name of @var{platform}---a string such as @code{"arm"}.
@end deffn


@subsubheading QEMU Guest Agent

@cindex emulation

The QEMU guest agent provides control over the emulated system to the
host.  The @code{qemu-guest-agent} service runs the agent on Guix
guests.  To control the agent from the host, open a socket by invoking
QEMU with the following arguments:

@example
qemu-system-x86_64 \
	-chardev socket,path=/tmp/qga.sock,server=on,wait=off,id=qga0 \
	-device virtio-serial \
	-device virtserialport,chardev=qga0,name=org.qemu.guest_agent.0 \
	...
@end example

This creates a socket at @file{/tmp/qga.sock} on the host.  Once the
guest agent is running, you can issue commands with @code{socat}:

@example
$ guix shell socat -- socat unix-connect:/tmp/qga.sock stdio
@{"execute": "guest-get-host-name"@}
@{"return": @{"host-name": "guix"@}@}
@end example

See @url{https://wiki.qemu.org/Features/GuestAgent,QEMU guest agent
documentation} for more options and commands.

@defvar qemu-guest-agent-service-type
Service type for the QEMU guest agent service.
@end defvar

@deftp {Data Type} qemu-guest-agent-configuration
Configuration for the @code{qemu-guest-agent} service.

@table @asis
@item @code{qemu} (default: @code{qemu-minimal})
The QEMU package to use.

@item @code{device} (default: @code{""})
File name of the device or socket the agent uses to communicate with the
host.  If empty, QEMU uses a default file name.
@end table
@end deftp


@anchor{build-vm}
@subsubheading Virtual Build Machines

@cindex virtual build machines
@cindex build VMs
@cindex VMs, for offloading
@dfn{Virtual build machines} or ``build VMs'' let you offload builds to
a fully controlled environment.  ``How can it be more controlled than
regular builds?  And why would it be useful?'', you ask.  Good
questions.

Builds spawned by @code{guix-daemon} indeed run in a controlled
environment; specifically the daemon spawns build processes in separate
namespaces and in a chroot, such as that build processes only see their
declared dependencies and a well-defined subset of the file system tree
(@pxref{Build Environment Setup}, for details).  A few aspects of the
environments are not controlled though: the operating system kernel, the
CPU model, and the date.  Most of the time, these aspects have no impact
on the build process: the level of isolation @code{guix-daemon} provides
is ``good enough''.

@cindex time traps
However, there are occasionally cases where those aspects @emph{do}
influence the build process.  A typical example is @dfn{time traps}:
build processes that stop working after a certain date@footnote{The most
widespread example of time traps is test suites that involve checking
the expiration date of a certificate.  Such tests exists in TLS
implementations such as OpenSSL and GnuTLS, but also in high-level
software such as Python.}.  Another one is software that optimizes for
the CPU microarchitecture it is built on or, worse, bugs that manifest
only on specific CPUs.

To address that, @code{virtual-build-machine-service-type} lets you add
a virtual build machine on your system, as in this example:

@lisp
(use-modules (gnu services virtualization))

(operating-system
  ;; @dots{}
  (services (append (list (service virtual-build-machine-service-type))
                    %base-services)))
@end lisp

By default, you have to explicitly start the build machine when you need
it, at which point builds may be offloaded to it (@pxref{Daemon Offload
Setup}):

@example
herd start build-vm
@end example

With the default setting shown above, the build VM runs with its clock
set to a date several years in the past, and on a CPU model that
corresponds to that date---a model possibly older than that of your
machine.  This lets you rebuild today software from the past that would
otherwise fail to build due to a time trap or other issues in its build
process.  You can view the VM's config like this:

@example
herd configuration build-vm
@end example

You can configure the build VM, as in this example:

@lisp
(service virtual-build-machine-service-type
         (virtual-build-machine
          (cpu "Westmere")
          (cpu-count 8)
          (memory-size (* 1 1024))
          (auto-start? #t)))
@end lisp

The available options are shown below.

@defvar virtual-build-machine-service-type
This is the service type to run @dfn{virtual build machines}.  Virtual
build machines are configured so that builds are offloaded to them when
they are running.
@end defvar

@deftp {Data Type} virtual-build-machine
This is the data type specifying the configuration of a build machine.
It contains the fields below:

@table @asis
@item @code{name} (default: @code{'build-vm})
The name of this build VM.  It is used to construct the name of its
Shepherd service.

@item @code{image}
The image of the virtual machine (@pxref{System Images}).  This notably
specifies the virtual disk size and the operating system running into it
(@pxref{operating-system Reference}).  The default value is a minimal
operating system image.

@item @code{qemu} (default: @code{qemu-minimal})
The QEMU package to run the image.

@item @code{cpu}
The CPU model being emulated as a string denoting a model known to QEMU.

The default value is a model that matches @code{date} (see below).  To
see what CPU models are available, run, for example:

@example
qemu-system-x86_64 -cpu help
@end example

@item @code{cpu-count} (default: @code{4})
The number of CPUs emulated by the virtual machine.

@item @code{memory-size} (default: @code{2048})
Size in mebibytes (MiB) of the virtual machine's main memory (RAM).

@item @code{date} (default: a few years ago)
Date inside the virtual machine when it starts; this must be a SRFI-19
date object (@pxref{SRFI-19 Date,,, guile, GNU Guile Reference Manual}).

@item @code{port-forwardings} (default: 11022 and 11004)
TCP ports of the virtual machine forwarded to the host.  By default, the
SSH and secrets ports are forwarded into the host.

@item @code{systems} (default: @code{(list (%current-system))})
List of system types supported by the build VM---e.g.,
@code{"x86_64-linux"}.

@item @code{auto-start?} (default: @code{#f})
Whether to start the virtual machine when the system boots.
@end table
@end deftp

In the next section, you'll find a variant on this theme: GNU/Hurd
virtual machines!

@anchor{hurd-vm}
@subsubheading The Hurd in a Virtual Machine

@cindex @code{hurd}
@cindex the Hurd
@cindex childhurd

Service @code{hurd-vm} provides support for running GNU/Hurd in a
virtual machine (VM), a so-called @dfn{childhurd}.  This service is meant
to be used on GNU/Linux and the given GNU/Hurd operating system
configuration is cross-compiled.  The virtual machine is a Shepherd
service that can be referred to by the names @code{hurd-vm} and
@code{childhurd} and be controlled with commands such as:

@example
herd start hurd-vm
herd stop childhurd
@end example

When the service is running, you can view its console by connecting to
it with a VNC client, for example with:

@example
guix shell tigervnc-client -- vncviewer localhost:5900
@end example

The default configuration (see @code{hurd-vm-configuration} below)
spawns a secure shell (SSH) server in your GNU/Hurd system, which QEMU
(the virtual machine emulator) redirects to port 10022 on the host.
By default, the service enables @dfn{offloading} such that the host
@code{guix-daemon} automatically offloads GNU/Hurd builds to the
childhurd (@pxref{Daemon Offload Setup}).  This is what happens when
running a command like the following one, where @code{i586-gnu} is the
system type of 32-bit GNU/Hurd:

@example
guix build emacs-minimal -s i586-gnu
@end example

The childhurd is volatile and stateless: it starts with a fresh root
file system every time you restart it.  By default though, all the files
under @file{/etc/childhurd} on the host are copied as is to the root
file system of the childhurd when it boots.  This allows you to
initialize ``secrets'' inside the VM: SSH host keys, authorized
substitute keys, and so on---see the explanation of @code{secret-root}
below.

You will probably find it useful to create an account for you in the
GNU/Hurd virtual machine and to authorize logins with your SSH key.  To
do that, you can define the GNU/Hurd system in the usual way
(@pxref{Using the Configuration System}), and then pass that operating
system as the @code{os} field of @code{hurd-vm-configuration}, as in
this example:

@lisp
(define childhurd-os
  ;; Definition of my GNU/Hurd system, derived from the default one.
  (operating-system
    (inherit %hurd-vm-operating-system)

    ;; Add a user account.
    (users (cons (user-account
                  (name "charlie")
                  (comment "This is me!")
                  (group "users")
                  (supplementary-groups '("wheel"))) ;for 'sudo'
                 %base-user-accounts))

    (services
     ;; Modify the SSH configuration to allow login as "root"
     ;; and as "charlie" using public key authentication.
     (modify-services (operating-system-user-services
                       %hurd-vm-operating-system)
       (openssh-service-type
        config => (openssh-configuration
                   (inherit config)
                   (authorized-keys
                    `(("root"
                       ,(local-file
                         "/home/charlie/.ssh/id_rsa.pub"))
                      ("charlie"
                       ,(local-file
                         "/home/charlie/.ssh/id_rsa.pub"))))))))))

(operating-system
  ;; @dots{}
  (services
    ;; Add the 'hurd-vm' service, configured to use the
    ;; operating system configuration above.
    (append (list (service hurd-vm-service-type
                           (hurd-vm-configuration
                             (os %childhurd-os))))
            %base-services)))
@end lisp

That's it!  The remainder of this section provides the reference of the
service configuration.

@defvar hurd-vm-service-type
This is the type of the Hurd in a Virtual Machine service.  Its value
must be a @code{hurd-vm-configuration} object, which specifies the
operating system (@pxref{operating-system Reference}) and the disk size
for the Hurd Virtual Machine, the QEMU package to use as well as the
options for running it.

For example:

@lisp
(service hurd-vm-service-type
         (hurd-vm-configuration
          (disk-size (* 5000 (expt 2 20))) ;5G
          (memory-size 1024)))             ;1024MiB
@end lisp

would create a disk image big enough to build GNU@tie{}Hello, with some
extra memory.
@end defvar

@deftp {Data Type} hurd-vm-configuration
The data type representing the configuration for
@code{hurd-vm-service-type}.

@table @asis
@item @code{os} (default: @var{%hurd-vm-operating-system})
The operating system to instantiate.  This default is bare-bones with a
permissive OpenSSH secure shell daemon listening on port 2222
(@pxref{Networking Services, @code{openssh-service-type}}).

@item @code{qemu} (default: @code{qemu-minimal})
The QEMU package to use.

@item @code{image} (default: @var{hurd-vm-disk-image})
The image object representing the disk image of this virtual machine
(@pxref{System Images}).

@item @code{disk-size} (default: @code{'guess})
The size of the disk image.

@item @code{memory-size} (default: @code{512})
The memory size of the Virtual Machine in mebibytes.

@item @code{options} (default: @code{'("--snapshot")})
The extra options for running QEMU.

@item @code{id} (default: @code{#f})
If set, a non-zero positive integer used to parameterize Childhurd
instances.  It is appended to the service's name,
e.g. @code{childhurd1}.

@item @code{net-options} (default: @var{hurd-vm-net-options})
The procedure used to produce the list of QEMU networking options.

By default, it produces

@lisp
'("--device" "rtl8139,netdev=net0"
  "--netdev" (string-append
              "user,id=net0,"
              "hostfwd=tcp:127.0.0.1:@var{secrets-port}-:1004,"
              "hostfwd=tcp:127.0.0.1:@var{ssh-port}-:2222,"
              "hostfwd=tcp:127.0.0.1:@var{vnc-port}-:5900"))
@end lisp

with forwarded ports:

@example
@var{secrets-port}: @code{(+ 11004 (* 1000 @var{ID}))}
@var{ssh-port}: @code{(+ 10022 (* 1000 @var{ID}))}
@var{vnc-port}: @code{(+ 15900 (* 1000 @var{ID}))}
@end example

@cindex childhurd, offloading
@cindex Hurd, offloading
@item @code{offloading?} (default: @code{#t})
Whether to automatically set up offloading of builds to the childhurd.

When enabled, this lets you run GNU/Hurd builds on the host and have
them transparently offloaded to the VM, for instance when running a
command like this:

@example
guix build coreutils -s i586-gnu
@end example

This option automatically sets up offloading like so:

@enumerate
@item
Authorizing the childhurd's key on the host so that the host accepts
build results coming from the childhurd, which can be done like so
(@pxref{Invoking guix archive, @command{guix archive --authorize}}, for
more on that).

@item
Creating a user account called @code{offloading} dedicated to offloading
in the childhurd.

@item
Creating an SSH key pair on the host and making it an authorized key of
the @code{offloading} account in the childhurd.

@item
Adding the childhurd to @file{/etc/guix/machines.scm} (@pxref{Daemon
Offload Setup}).
@end enumerate

@item @code{secret-root} (default: @file{/etc/childhurd})
The root directory with out-of-band secrets to be installed into the
childhurd once it runs.  Childhurds are volatile which means that on
every startup, secrets such as the SSH host keys and Guix signing key
are recreated.

If the @file{/etc/childhurd} directory does not exist, the
@code{secret-service} running in the Childhurd will be sent an empty
list of secrets.

By default, the service automatically populates @file{/etc/childhurd}
with the following non-volatile secrets, unless they already exist:

@example
/etc/childhurd/etc/guix/acl
/etc/childhurd/etc/guix/signing-key.pub
/etc/childhurd/etc/guix/signing-key.sec
/etc/childhurd/etc/ssh/authorized_keys.d/offloading
/etc/childhurd/etc/ssh/ssh_host_ed25519_key
/etc/childhurd/etc/ssh/ssh_host_ecdsa_key
/etc/childhurd/etc/ssh/ssh_host_ed25519_key.pub
/etc/childhurd/etc/ssh/ssh_host_ecdsa_key.pub
@end example

@end table
@end deftp

Note that by default the VM image is volatile, i.e., once stopped the
contents are lost.  If you want a stateful image instead, override the
configuration's @code{image} and @code{options} without
the @code{--snapshot} flag using something along these lines:

@lisp
(service hurd-vm-service-type
         (hurd-vm-configuration
          (image   (const "/out/of/store/writable/hurd.img"))
          (options '())))
@end lisp

@subsubheading Ganeti

@cindex ganeti

@quotation Note
This service is considered experimental.  Configuration options may be changed
in a backwards-incompatible manner, and not all features have been thorougly
tested.  Users of this service are encouraged to share their experience at
@email{guix-devel@@gnu.org}.
@end quotation

Ganeti is a virtual machine management system.  It is designed to keep virtual
machines running on a cluster of servers even in the event of hardware failures,
and to make maintenance and recovery tasks easy.  It consists of multiple
services which are described later in this section.  In addition to the Ganeti
service, you will need the OpenSSH service (@pxref{Networking Services,
@code{openssh-service-type}}), and update the @file{/etc/hosts} file
(@pxref{Service Reference, @code{hosts-service-type}}) with the cluster name
and address (or use a DNS server).

All nodes participating in a Ganeti cluster should have the same Ganeti and
@file{/etc/hosts} configuration.  Here is an example configuration for a Ganeti
cluster node that supports multiple storage backends, and installs the
@code{debootstrap} and @code{guix} @dfn{OS providers}:

@lisp
(use-package-modules virtualization)
(use-service-modules base ganeti networking ssh)
(operating-system
  ;; @dots{}
  (host-name "node1")

  ;; Install QEMU so we can use KVM-based instances, and LVM, DRBD and Ceph
  ;; in order to use the "plain", "drbd" and "rbd" storage backends.
  (packages (append (map specification->package
                         '("qemu" "lvm2" "drbd-utils" "ceph"
                           ;; Add the debootstrap and guix OS providers.
                           "ganeti-instance-guix" "ganeti-instance-debootstrap"))
                    %base-packages))
  (services
   (append (list (service static-networking-service-type
                          (list (static-networking
                                 (addresses
                                  (list (network-address
                                         (device "eth0")
                                         (value "192.168.1.201/24"))))
                                 (routes
                                  (list (network-route
                                         (destination "default")
                                         (gateway "192.168.1.254"))))
                                 (name-servers '("192.168.1.252"
                                                 "192.168.1.253")))))

                 ;; Ganeti uses SSH to communicate between nodes.
                 (service openssh-service-type
                          (openssh-configuration
                           (permit-root-login 'prohibit-password)))

                 (simple-service 'ganeti-hosts-entries hosts-service-type
                                 (list
                                   (host "192.168.1.200" "ganeti.example.com")
                                   (host "192.168.1.201" "node1.example.com"
                                         '("node1"))
                                   (host "192.168.1.202" "node2.example.com"
                                         '("node2"))))

                 (service ganeti-service-type
                          (ganeti-configuration
                           ;; This list specifies allowed file system paths
                           ;; for storing virtual machine images.
                           (file-storage-paths '("/srv/ganeti/file-storage"))
                           ;; This variable configures a single "variant" for
                           ;; both Debootstrap and Guix that works with KVM.
                           (os %default-ganeti-os))))
           %base-services)))
@end lisp

Users are advised to read the
@url{https://docs.ganeti.org/docs/ganeti/3.0/html/admin.html,Ganeti
administrators guide} to learn about the various cluster options and
day-to-day operations.  There is also a
@url{https://guix.gnu.org/blog/2020/running-a-ganeti-cluster-on-guix/,blog post}
describing how to configure and initialize a small cluster.

@defvar ganeti-service-type
This is a service type that includes all the various services that Ganeti
nodes should run.

Its value is a @code{ganeti-configuration} object that defines the package
to use for CLI operations, as well as configuration for the various daemons.
Allowed file storage paths and available guest operating systems are also
configured through this data type.
@end defvar

@deftp {Data Type} ganeti-configuration
The @code{ganeti} service takes the following configuration options:

@table @asis
@item @code{ganeti} (default: @code{ganeti})
The @code{ganeti} package to use.  It will be installed to the system profile
and make @command{gnt-cluster}, @command{gnt-instance}, etc available.  Note
that the value specified here does not affect the other services as each refer
to a specific @code{ganeti} package (see below).

@item @code{noded-configuration} (default: @code{(ganeti-noded-configuration)})
@itemx @code{confd-configuration} (default: @code{(ganeti-confd-configuration)})
@itemx @code{wconfd-configuration} (default: @code{(ganeti-wconfd-configuration)})
@itemx @code{luxid-configuration} (default: @code{(ganeti-luxid-configuration)})
@itemx @code{rapi-configuration} (default: @code{(ganeti-rapi-configuration)})
@itemx @code{kvmd-configuration} (default: @code{(ganeti-kvmd-configuration)})
@itemx @code{mond-configuration} (default: @code{(ganeti-mond-configuration)})
@itemx @code{metad-configuration} (default: @code{(ganeti-metad-configuration)})
@itemx @code{watcher-configuration} (default: @code{(ganeti-watcher-configuration)})
@itemx @code{cleaner-configuration} (default: @code{(ganeti-cleaner-configuration)})

These options control the various daemons and cron jobs that are distributed
with Ganeti.  The possible values for these are described in detail below.
To override a setting, you must use the configuration type for that service:

@lisp
(service ganeti-service-type
         (ganeti-configuration
          (rapi-configuration
           (ganeti-rapi-configuration
            (interface "eth1"))))
          (watcher-configuration
           (ganeti-watcher-configuration
            (rapi-ip "10.0.0.1"))))
@end lisp

@item @code{file-storage-paths} (default: @code{'()})
List of allowed directories for file storage backend.

@item @code{hooks} (default: @code{#f})
When set, this should be a file-like object containing a directory with
@url{https://docs.ganeti.org/docs/ganeti/3.0/html/hooks.html,cluster execution hooks}.

@item @code{os} (default: @code{%default-ganeti-os})
List of @code{<ganeti-os>} records.
@end table

In essence @code{ganeti-service-type} is shorthand for declaring each service
individually:

@lisp
(service ganeti-noded-service-type)
(service ganeti-confd-service-type)
(service ganeti-wconfd-service-type)
(service ganeti-luxid-service-type)
(service ganeti-kvmd-service-type)
(service ganeti-mond-service-type)
(service ganeti-metad-service-type)
(service ganeti-watcher-service-type)
(service ganeti-cleaner-service-type)
@end lisp

Plus a service extension for @code{etc-service-type} that configures the file
storage backend and OS variants.

@end deftp

@deftp {Data Type} ganeti-os
This data type is suitable for passing to the @code{os} parameter of
@code{ganeti-configuration}.  It takes the following parameters:

@table @asis
@item @code{name}
The name for this OS provider.  It is only used to specify where the
configuration ends up.  Setting it to ``debootstrap'' will create
@file{/etc/ganeti/instance-debootstrap}.

@item @code{extension} (default: @code{#f})
The file extension for variants of this OS type.  For example @file{.conf}
or @file{.scm}.  It will be appended to the variant file name if set.

@item @code{variants} (default: @code{'()})
This must be either a list of @code{ganeti-os-variant} objects for this OS,
or a ``file-like'' object (@pxref{G-Expressions, file-like objects})
representing the variants directory.

To use the Guix OS provider with variant definitions residing in a local
directory instead of declaring individual variants (see @var{guix-variants}
below), you can do:

@lisp
(ganeti-os
 (name "guix")
 (variants (local-file "ganeti-guix-variants"
                       #:recursive? #true)))
@end lisp

Note that you will need to maintain the @file{variants.list} file
(see @code{@url{https://docs.ganeti.org/docs/ganeti/3.0/man/ganeti-os-interface.html,
ganeti-os-interface(7)}})
manually in this case.

@end table
@end deftp

@deftp {Data Type} ganeti-os-variant
This is the data type for a Ganeti OS variant.  It takes the following
parameters:

@table @asis
@item @code{name}
The name of this variant.

@item @code{configuration}
A configuration file for this variant.
@end table
@end deftp

@defvar %default-debootstrap-hooks
This variable contains hooks to configure networking and the GRUB bootloader.
@end defvar

@defvar %default-debootstrap-extra-pkgs
This variable contains a list of packages suitable for a fully-virtualized guest.
@end defvar

@deftp {Data Type} debootstrap-configuration

This data type creates configuration files suitable for the debootstrap OS provider.

@table @asis
@item @code{hooks} (default: @code{%default-debootstrap-hooks})
When not @code{#f}, this must be a G-expression that specifies a directory with
scripts that will run when the OS is installed.  It can also be a list of
@code{(name . file-like)} pairs.  For example:

@lisp
`((99-hello-world . ,(plain-file "#!/bin/sh\necho Hello, World")))
@end lisp

That will create a directory with one executable named @code{99-hello-world}
and run it every time this variant is installed.  If set to @code{#f}, hooks
in @file{/etc/ganeti/instance-debootstrap/hooks} will be used, if any.
@item @code{proxy} (default: @code{#f})
Optional HTTP proxy to use.
@item @code{mirror} (default: @code{#f})
The Debian mirror.  Typically something like @code{http://ftp.no.debian.org/debian}.
The default varies depending on the distribution.
@item @code{arch} (default: @code{#f})
The dpkg architecture.  Set to @code{armhf} to debootstrap an ARMv7 instance
on an AArch64 host.  Default is to use the current system architecture.
@item @code{suite} (default: @code{"stable"})
When set, this must be a Debian distribution ``suite'' such as @code{buster}
or @code{focal}.  If set to @code{#f}, the default for the OS provider is used.
@item @code{extra-pkgs} (default: @code{%default-debootstrap-extra-pkgs})
List of extra packages that will get installed by dpkg in addition
to the minimal system.
@item @code{components} (default: @code{#f})
When set, must be a list of Debian repository ``components''.  For example
@code{'("main" "contrib")}.
@item @code{generate-cache?} (default: @code{#t})
Whether to automatically cache the generated debootstrap archive.
@item @code{clean-cache} (default: @code{14})
Discard the cache after this amount of days.  Use @code{#f} to never
clear the cache.
@item @code{partition-style} (default: @code{'msdos})
The type of partition to create.  When set, it must be one of
@code{'msdos}, @code{'none} or a string.
@item @code{partition-alignment} (default: @code{2048})
Alignment of the partition in sectors.
@end table
@end deftp

@deffn {Procedure} debootstrap-variant name configuration
This is a helper procedure that creates a @code{ganeti-os-variant} record.  It
takes two parameters: a name and a @code{debootstrap-configuration} object.
@end deffn

@deffn {Procedure} debootstrap-os variants@dots{}
This is a helper procedure that creates a @code{ganeti-os} record.  It takes
a list of variants created with @code{debootstrap-variant}.
@end deffn

@deffn {Procedure} guix-variant name configuration
This is a helper procedure that creates a @code{ganeti-os-variant} record for
use with the Guix OS provider.  It takes a name and a G-expression that returns
a ``file-like'' (@pxref{G-Expressions, file-like objects}) object containing a
Guix System configuration.
@end deffn

@deffn {Procedure} guix-os variants@dots{}
This is a helper procedure that creates a @code{ganeti-os} record.  It
takes a list of variants produced by @code{guix-variant}.
@end deffn

@defvar %default-debootstrap-variants
This is a convenience variable to make the debootstrap provider work
``out of the box'' without users having to declare variants manually.  It
contains a single debootstrap variant with the default configuration:

@lisp
(list (debootstrap-variant
       "default"
       (debootstrap-configuration)))
@end lisp
@end defvar

@defvar %default-guix-variants
This is a convenience variable to make the Guix OS provider work without
additional configuration.  It creates a virtual machine that has an SSH
server, a serial console, and authorizes the Ganeti hosts SSH keys.

@lisp
(list (guix-variant
       "default"
       (file-append ganeti-instance-guix
                    "/share/doc/ganeti-instance-guix/examples/dynamic.scm")))
@end lisp
@end defvar

Users can implement support for OS providers unbeknownst to Guix by extending
the @code{ganeti-os} and @code{ganeti-os-variant} records appropriately.
For example:

@lisp
(ganeti-os
 (name "custom")
 (extension ".conf")
 (variants
  (list (ganeti-os-variant
         (name "foo")
         (configuration (plain-file "bar" "this is fine"))))))
@end lisp

That creates @file{/etc/ganeti/instance-custom/variants/foo.conf} which points
to a file in the store with contents @code{this is fine}.  It also creates
@file{/etc/ganeti/instance-custom/variants/variants.list} with contents @code{foo}.

Obviously this may not work for all OS providers out there.  If you find the
interface limiting, please reach out to @email{guix-devel@@gnu.org}.

The rest of this section documents the various services that are included by
@code{ganeti-service-type}.

@defvar ganeti-noded-service-type
@command{ganeti-noded} is the daemon responsible for node-specific functions
within the Ganeti system.  The value of this service must be a
@code{ganeti-noded-configuration} object.
@end defvar

@deftp {Data Type} ganeti-noded-configuration
This is the configuration for the @code{ganeti-noded} service.

@table @asis
@item @code{ganeti} (default: @code{ganeti})
The @code{ganeti} package to use for this service.

@item @code{port} (default: @code{1811})
The TCP port on which the node daemon listens for network requests.

@item @code{address} (default: @code{"0.0.0.0"})
The network address that the daemon will bind to.  The default address means
bind to all available addresses.

@item @code{interface} (default: @code{#f})
When this is set, it must be a specific network interface (e.g.@: @code{eth0})
that the daemon will bind to.

@item @code{max-clients} (default: @code{20})
This sets a limit on the maximum number of simultaneous client connections
that the daemon will handle.  Connections above this count are accepted, but
no responses will be sent until enough connections have closed.

@item @code{ssl?} (default: @code{#t})
Whether to use SSL/TLS to encrypt network communications.  The certificate
is automatically provisioned by the cluster and can be rotated with
@command{gnt-cluster renew-crypto}.

@item @code{ssl-key} (default: @file{"/var/lib/ganeti/server.pem"})
This can be used to provide a specific encryption key for TLS communications.

@item @code{ssl-cert} (default: @file{"/var/lib/ganeti/server.pem"})
This can be used to provide a specific certificate for TLS communications.

@item @code{debug?} (default: @code{#f})
When true, the daemon performs additional logging for debugging purposes.
Note that this will leak encryption details to the log files, use with caution.

@end table
@end deftp

@defvar ganeti-confd-service-type
@command{ganeti-confd} answers queries related to the configuration of a
Ganeti cluster.  The purpose of this daemon is to have a highly available
and fast way to query cluster configuration values.  It is automatically
active on all @dfn{master candidates}.  The value of this service must be a
@code{ganeti-confd-configuration} object.

@end defvar

@deftp {Data Type} ganeti-confd-configuration
This is the configuration for the @code{ganeti-confd} service.

@table @asis
@item @code{ganeti} (default: @code{ganeti})
The @code{ganeti} package to use for this service.

@item @code{port} (default: @code{1814})
The UDP port on which to listen for network requests.

@item @code{address} (default: @code{"0.0.0.0"})
Network address that the daemon will bind to.

@item @code{debug?} (default: @code{#f})
When true, the daemon performs additional logging for debugging purposes.

@end table
@end deftp

@defvar ganeti-wconfd-service-type
@command{ganeti-wconfd} is the daemon that has authoritative knowledge
about the cluster configuration and is the only entity that can accept
changes to it.  All jobs that need to modify the configuration will do so
by sending appropriate requests to this daemon.  It only runs on the
@dfn{master node} and will automatically disable itself on other nodes.

The value of this service must be a
@code{ganeti-wconfd-configuration} object.
@end defvar

@deftp {Data Type} ganeti-wconfd-configuration
This is the configuration for the @code{ganeti-wconfd} service.

@table @asis
@item @code{ganeti} (default: @code{ganeti})
The @code{ganeti} package to use for this service.

@item @code{no-voting?} (default: @code{#f})
The daemon will refuse to start if the majority of cluster nodes does not
agree that it is running on the master node.  Set to @code{#t} to start
even if a quorum can not be reached (dangerous, use with caution).

@item @code{debug?} (default: @code{#f})
When true, the daemon performs additional logging for debugging purposes.

@end table
@end deftp

@defvar ganeti-luxid-service-type
@command{ganeti-luxid} is a daemon used to answer queries related to the
configuration and the current live state of a Ganeti cluster.  Additionally,
it is the authoritative daemon for the Ganeti job queue.   Jobs can be
submitted via this daemon and it schedules and starts them.

It takes a @code{ganeti-luxid-configuration} object.
@end defvar

@deftp {Data Type} ganeti-luxid-configuration
This is the configuration for the @code{ganeti-luxid} service.

@table @asis
@item @code{ganeti} (default: @code{ganeti})
The @code{ganeti} package to use for this service.

@item @code{no-voting?} (default: @code{#f})
The daemon will refuse to start if it cannot verify that the majority of
cluster nodes believes that it is running on the master node.  Set to
@code{#t} to ignore such checks and start anyway (this can be dangerous).

@item @code{debug?} (default: @code{#f})
When true, the daemon performs additional logging for debugging purposes.

@end table
@end deftp

@defvar ganeti-rapi-service-type
@command{ganeti-rapi} provides a remote API for Ganeti clusters.  It runs on
the master node and can be used to perform cluster actions programmatically
via a JSON-based RPC protocol.

Most query operations are allowed without authentication (unless
@var{require-authentication?} is set), whereas write operations require
explicit authorization via the @file{/var/lib/ganeti/rapi/users} file.  See
the @url{https://docs.ganeti.org/docs/ganeti/3.0/html/rapi.html, Ganeti Remote
API documentation} for more information.

The value of this service must be a @code{ganeti-rapi-configuration} object.
@end defvar

@deftp {Data Type} ganeti-rapi-configuration
This is the configuration for the @code{ganeti-rapi} service.

@table @asis
@item @code{ganeti} (default: @code{ganeti})
The @code{ganeti} package to use for this service.

@item @code{require-authentication?} (default: @code{#f})
Whether to require authentication even for read-only operations.

@item @code{port} (default: @code{5080})
The TCP port on which to listen to API requests.

@item @code{address} (default: @code{"0.0.0.0"})
The network address that the service will bind to.  By default it listens
on all configured addresses.

@item @code{interface} (default: @code{#f})
When set, it must specify a specific network interface such as @code{eth0}
that the daemon will bind to.

@item @code{max-clients} (default: @code{20})
The maximum number of simultaneous client requests to handle.  Further
connections are allowed, but no responses are sent until enough connections
have closed.

@item @code{ssl?} (default: @code{#t})
Whether to use SSL/TLS encryption on the RAPI port.

@item @code{ssl-key} (default: @file{"/var/lib/ganeti/server.pem"})
This can be used to provide a specific encryption key for TLS communications.

@item @code{ssl-cert} (default: @file{"/var/lib/ganeti/server.pem"})
This can be used to provide a specific certificate for TLS communications.

@item @code{debug?} (default: @code{#f})
When true, the daemon performs additional logging for debugging purposes.
Note that this will leak encryption details to the log files, use with caution.

@end table
@end deftp

@defvar ganeti-kvmd-service-type
@command{ganeti-kvmd} is responsible for determining whether a given KVM
instance was shut down by an administrator or a user.  Normally Ganeti will
restart an instance that was not stopped through Ganeti itself.  If the
cluster option @code{user_shutdown} is true, this daemon monitors the
@code{QMP} socket provided by QEMU and listens for shutdown events, and
marks the instance as @dfn{USER_down} instead of @dfn{ERROR_down} when
it shuts down gracefully by itself.

It takes a @code{ganeti-kvmd-configuration} object.
@end defvar

@deftp {Data Type} ganeti-kvmd-configuration

@table @asis
@item @code{ganeti} (default: @code{ganeti})
The @code{ganeti} package to use for this service.

@item @code{debug?} (default: @code{#f})
When true, the daemon performs additional logging for debugging purposes.

@end table
@end deftp

@defvar ganeti-mond-service-type
@command{ganeti-mond} is an optional daemon that provides Ganeti monitoring
functionality.  It is responsible for running data collectors and publish the
collected information through a HTTP interface.

It takes a @code{ganeti-mond-configuration} object.
@end defvar

@deftp {Data Type} ganeti-mond-configuration

@table @asis
@item @code{ganeti} (default: @code{ganeti})
The @code{ganeti} package to use for this service.

@item @code{port} (default: @code{1815})
The port on which the daemon will listen.

@item @code{address} (default: @code{"0.0.0.0"})
The network address that the daemon will bind to.  By default it binds to all
available interfaces.

@item @code{debug?} (default: @code{#f})
When true, the daemon performs additional logging for debugging purposes.

@end table
@end deftp

@defvar ganeti-metad-service-type
@command{ganeti-metad} is an optional daemon that can be used to provide
information about the cluster to instances or OS install scripts.

It takes a @code{ganeti-metad-configuration} object.
@end defvar

@deftp {Data Type} ganeti-metad-configuration

@table @asis
@item @code{ganeti} (default: @code{ganeti})
The @code{ganeti} package to use for this service.

@item @code{port} (default: @code{80})
The port on which the daemon will listen.

@item @code{address} (default: @code{#f})
If set, the daemon will bind to this address only.  If left unset, the behavior
depends on the cluster configuration.

@item @code{debug?} (default: @code{#f})
When true, the daemon performs additional logging for debugging purposes.

@end table
@end deftp

@defvar ganeti-watcher-service-type
@command{ganeti-watcher} is a script designed to run periodically and ensure
the health of a cluster.  It will automatically restart instances that have
stopped without Ganeti's consent, and repairs DRBD links in case a node has
rebooted.  It also archives old cluster jobs and restarts Ganeti daemons
that are not running.  If the cluster parameter @code{ensure_node_health}
is set, the watcher will also shutdown instances and DRBD devices if the
node it is running on is declared offline by known master candidates.

It can be paused on all nodes with @command{gnt-cluster watcher pause}.

The service takes a @code{ganeti-watcher-configuration} object.
@end defvar

@deftp {Data Type} ganeti-watcher-configuration

@table @asis
@item @code{ganeti} (default: @code{ganeti})
The @code{ganeti} package to use for this service.

@item @code{schedule} (default: @code{'(next-second-from (next-minute (range 0 60 5)))})
How often to run the script.  The default is every five minutes.

@item @code{rapi-ip} (default: @code{#f})
This option needs to be specified only if the RAPI daemon is configured to use
a particular interface or address.  By default the cluster address is used.

@item @code{job-age} (default: @code{(* 6 3600)})
Archive cluster jobs older than this age, specified in seconds.  The default
is 6 hours.  This keeps @command{gnt-job list} manageable.

@item @code{verify-disks?} (default: @code{#t})
If this is @code{#f}, the watcher will not try to repair broken DRBD links
automatically.  Administrators will need to use @command{gnt-cluster verify-disks}
manually instead.

@item @code{debug?} (default: @code{#f})
When @code{#t}, the script performs additional logging for debugging purposes.

@end table
@end deftp

@defvar ganeti-cleaner-service-type
@command{ganeti-cleaner} is a script designed to run periodically and remove
old files from the cluster.  This service type controls two @dfn{cron jobs}:
one intended for the master node that permanently purges old cluster jobs,
and one intended for every node that removes expired X509 certificates, keys,
and outdated @command{ganeti-watcher} information.  Like all Ganeti services,
it is safe to include even on non-master nodes as it will disable itself as
necessary.

It takes a @code{ganeti-cleaner-configuration} object.
@end defvar

@deftp {Data Type} ganeti-cleaner-configuration

@table @asis
@item @code{ganeti} (default: @code{ganeti})
The @code{ganeti} package to use for the @command{gnt-cleaner} command.

@item @code{master-schedule} (default: @code{"45 1 * * *"})
How often to run the master cleaning job.  The default is once per day, at
01:45:00.

@item @code{node-schedule} (default: @code{"45 2 * * *"})
How often to run the node cleaning job.  The default is once per day, at
02:45:00.

@end table
@end deftp

@node Version Control Services
@subsection Version Control Services

The @code{(gnu services version-control)} module provides a service to
allow remote access to local Git repositories.  There are three options:
the @code{git-daemon-service-type}, which provides access to repositories via
the @code{git://} unsecured TCP-based protocol, extending the
@code{nginx} web server to proxy some requests to
@code{git-http-backend}, or providing a web interface with
@code{cgit-service-type}.

@defvar git-daemon-service-type
Type for a service that runs @command{git daemon}, a simple TCP server to
expose repositories over the Git protocol for anonymous access.

The value for this service type is a @code{<git-daemon-configuration>}
record, by default it allows read-only access to exported@footnote{By
creating the magic file @file{git-daemon-export-ok} in the repository
directory.} repositories under @file{/srv/git}.
@end defvar

@deftp {Data Type} git-daemon-configuration
Data type representing the configuration for @code{git-daemon-service-type}.

@table @asis
@item @code{package} (default: @code{git})
Package object of the Git distributed version control system.

@item @code{export-all?} (default: @code{#f})
Whether to allow access for all Git repositories, even if they do not
have the @file{git-daemon-export-ok} file.

@item @code{base-path} (default: @file{/srv/git})
Whether to remap all the path requests as relative to the given path.
If you run @command{git daemon} with @code{(base-path "/srv/git")} on
@samp{example.com}, then if you later try to pull
@indicateurl{git://example.com/hello.git}, git daemon will interpret the
path as @file{/srv/git/hello.git}.

@item @code{user-path} (default: @code{#f})
Whether to allow @code{~user} notation to be used in requests.  When
specified with empty string, requests to
@indicateurl{git://host/~alice/foo} is taken as a request to access
@code{foo} repository in the home directory of user @code{alice}.  If
@code{(user-path "@var{path}")} is specified, the same request is taken
as a request to access @file{@var{path}/foo} repository in the home
directory of user @code{alice}.

@item @code{listen} (default: @code{'()})
Whether to listen on specific IP addresses or hostnames, defaults to
all.

@item @code{port} (default: @code{#f})
Whether to listen on an alternative port, which defaults to 9418.

@item @code{whitelist} (default: @code{'()})
If not empty, only allow access to this list of directories.

@item @code{extra-options} (default: @code{'()})
Extra options that will be passed to @command{git daemon}.@footnote{Run
@command{man git-daemon} for more information.}

@end table
@end deftp

The @code{git://} protocol lacks authentication.  When you pull from a
repository fetched via @code{git://}, you don't know whether the data you
receive was modified or is even coming from the specified host, and your
connection is subject to eavesdropping.  It's better to use an authenticated
and encrypted transport, such as @code{https}.  Although Git allows you
to serve repositories using unsophisticated file-based web servers,
there is a faster protocol implemented by the @code{git-http-backend}
program.  This program is the back-end of a proper Git web service.  It
is designed to sit behind a FastCGI proxy.  @xref{Web Services}, for more
on running the necessary @code{fcgiwrap} daemon.

Guix has a separate configuration data type for serving Git repositories
over HTTP.

@deftp {Data Type} git-http-configuration
Data type representing the configuration for a future
@code{git-http-service-type}; can currently be used to configure Nginx
through @code{git-http-nginx-location-configuration}.

@table @asis
@item @code{package} (default: @var{git})
Package object of the Git distributed version control system.

@item @code{git-root} (default: @file{/srv/git})
Directory containing the Git repositories to expose to the world.

@item @code{export-all?} (default: @code{#f})
Whether to expose access for all Git repositories in @var{git-root},
even if they do not have the @file{git-daemon-export-ok} file.

@item @code{uri-path} (default: @samp{/git/})
Path prefix for Git access.  With the default @samp{/git/} prefix, this
will map @indicateurl{http://@var{server}/git/@var{repo}.git} to
@file{/srv/git/@var{repo}.git}.  Requests whose URI paths do not begin
with this prefix are not passed on to this Git instance.

@item @code{fcgiwrap-socket} (default: @code{127.0.0.1:9000})
The socket on which the @code{fcgiwrap} daemon is listening.  @xref{Web
Services}.
@end table
@end deftp

There is no @code{git-http-service-type}, currently; instead you can
create an @code{nginx-location-configuration} from a
@code{git-http-configuration} and then add that location to a web
server.

@deffn {Procedure} git-http-nginx-location-configuration @
       [config=(git-http-configuration)]
Compute an @code{nginx-location-configuration} that corresponds to the
given Git http configuration.  An example nginx service definition to
serve the default @file{/srv/git} over HTTPS might be:

@lisp
(service nginx-service-type
         (nginx-configuration
          (server-blocks
           (list
            (nginx-server-configuration
             (listen '("443 ssl"))
             (server-name "git.my-host.org")
             (ssl-certificate
              "/etc/certs/git.my-host.org/fullchain.pem")
             (ssl-certificate-key
              "/etc/certs/git.my-host.org/privkey.pem")
             (locations
              (list
               (git-http-nginx-location-configuration
                (git-http-configuration (uri-path "/"))))))))))
@end lisp

This example assumes that you are using Let's Encrypt to get your TLS
certificate.  @xref{Certificate Services}.  The default @code{certbot}
service will redirect all HTTP traffic on @code{git.my-host.org} to
HTTPS@.  You will also need to add an @code{fcgiwrap} proxy to your
system services.  @xref{Web Services}.
@end deffn

@subsubheading Cgit Service

@cindex Cgit service
@cindex Git, web interface
@uref{https://git.zx2c4.com/cgit/, Cgit} is a web frontend for Git
repositories written in C.

The following example will configure the service with default values.
By default, Cgit can be accessed on port 80 (@code{http://localhost:80}).

@lisp
(service cgit-service-type)
@end lisp

The @code{file-object} type designates either a file-like object
(@pxref{G-Expressions, file-like objects}) or a string.

@c %start of fragment

Available @code{cgit-configuration} fields are:

@deftypevr {@code{cgit-configuration} parameter} package package
The CGIT package.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} nginx-server-configuration-list nginx
NGINX configuration.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} file-object about-filter
Specifies a command which will be invoked to format the content of about
pages (both top-level and for each repository).

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string agefile
Specifies a path, relative to each repository path, which can be used to
specify the date and time of the youngest commit in the repository.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} file-object auth-filter
Specifies a command that will be invoked for authenticating repository
access.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string branch-sort
Flag which, when set to @samp{age}, enables date ordering in the branch
ref list, and when set @samp{name} enables ordering by branch name.

Defaults to @samp{"name"}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string cache-root
Path used to store the cgit cache entries.

Defaults to @samp{"/var/cache/cgit"}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer cache-static-ttl
Number which specifies the time-to-live, in minutes, for the cached
version of repository pages accessed with a fixed SHA1.

Defaults to @samp{-1}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer cache-dynamic-ttl
Number which specifies the time-to-live, in minutes, for the cached
version of repository pages accessed without a fixed SHA1.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer cache-repo-ttl
Number which specifies the time-to-live, in minutes, for the cached
version of the repository summary page.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer cache-root-ttl
Number which specifies the time-to-live, in minutes, for the cached
version of the repository index page.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer cache-scanrc-ttl
Number which specifies the time-to-live, in minutes, for the result of
scanning a path for Git repositories.

Defaults to @samp{15}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer cache-about-ttl
Number which specifies the time-to-live, in minutes, for the cached
version of the repository about page.

Defaults to @samp{15}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer cache-snapshot-ttl
Number which specifies the time-to-live, in minutes, for the cached
version of snapshots.

Defaults to @samp{5}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer cache-size
The maximum number of entries in the cgit cache.  When set to @samp{0},
caching is disabled.

Defaults to @samp{0}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean case-sensitive-sort?
Sort items in the repo list case sensitively.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} list clone-prefix
List of common prefixes which, when combined with a repository URL,
generates valid clone URLs for the repository.

Defaults to @samp{'()}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} list clone-url
List of @code{clone-url} templates.

Defaults to @samp{'()}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} file-object commit-filter
Command which will be invoked to format commit messages.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string commit-sort
Flag which, when set to @samp{date}, enables strict date ordering in the
commit log, and when set to @samp{topo} enables strict topological
ordering.

Defaults to @samp{"git log"}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} file-object css
URL which specifies the css document to include in all cgit pages.

Defaults to @samp{"/share/cgit/cgit.css"}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} file-object email-filter
Specifies a command which will be invoked to format names and email
address of committers, authors, and taggers, as represented in various
places throughout the cgit interface.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean embedded?
Flag which, when set to @samp{#t}, will make cgit generate a HTML
fragment suitable for embedding in other HTML pages.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean enable-commit-graph?
Flag which, when set to @samp{#t}, will make cgit print an ASCII-art
commit history graph to the left of the commit messages in the
repository log page.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean enable-filter-overrides?
Flag which, when set to @samp{#t}, allows all filter settings to be
overridden in repository-specific cgitrc files.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean enable-follow-links?
Flag which, when set to @samp{#t}, allows users to follow a file in the
log view.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean enable-http-clone?
If set to @samp{#t}, cgit will act as an dumb HTTP endpoint for Git
clones.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean enable-index-links?
Flag which, when set to @samp{#t}, will make cgit generate extra links
"summary", "commit", "tree" for each repo in the repository index.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean enable-index-owner?
Flag which, when set to @samp{#t}, will make cgit display the owner of
each repo in the repository index.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean enable-log-filecount?
Flag which, when set to @samp{#t}, will make cgit print the number of
modified files for each commit on the repository log page.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean enable-log-linecount?
Flag which, when set to @samp{#t}, will make cgit print the number of
added and removed lines for each commit on the repository log page.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean enable-remote-branches?
Flag which, when set to @code{#t}, will make cgit display remote
branches in the summary and refs views.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean enable-subject-links?
Flag which, when set to @code{1}, will make cgit use the subject of the
parent commit as link text when generating links to parent commits in
commit view.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean enable-html-serving?
Flag which, when set to @samp{#t}, will make cgit use the subject of the
parent commit as link text when generating links to parent commits in
commit view.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean enable-tree-linenumbers?
Flag which, when set to @samp{#t}, will make cgit generate linenumber
links for plaintext blobs printed in the tree view.

Defaults to @samp{#t}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean enable-git-config?
Flag which, when set to @samp{#f}, will allow cgit to use Git config to
set any repo specific settings.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} file-object favicon
URL used as link to a shortcut icon for cgit.

Defaults to @samp{"/favicon.ico"}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string footer
The content of the file specified with this option will be included
verbatim at the bottom of all pages (i.e.@: it replaces the standard
"generated by..."@: message).

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string head-include
The content of the file specified with this option will be included
verbatim in the HTML HEAD section on all pages.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string header
The content of the file specified with this option will be included
verbatim at the top of all pages.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} file-object include
Name of a configfile to include before the rest of the current config-
file is parsed.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string index-header
The content of the file specified with this option will be included
verbatim above the repository index.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string index-info
The content of the file specified with this option will be included
verbatim below the heading on the repository index page.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean local-time?
Flag which, if set to @samp{#t}, makes cgit print commit and tag times
in the servers timezone.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} file-object logo
URL which specifies the source of an image which will be used as a logo
on all cgit pages.

Defaults to @samp{"/share/cgit/cgit.png"}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string logo-link
URL loaded when clicking on the cgit logo image.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} file-object owner-filter
Command which will be invoked to format the Owner column of the main
page.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer max-atom-items
Number of items to display in atom feeds view.

Defaults to @samp{10}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer max-commit-count
Number of entries to list per page in "log" view.

Defaults to @samp{50}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer max-message-length
Number of commit message characters to display in "log" view.

Defaults to @samp{80}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer max-repo-count
Specifies the number of entries to list per page on the repository index
page.

Defaults to @samp{50}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer max-repodesc-length
Specifies the maximum number of repo description characters to display
on the repository index page.

Defaults to @samp{80}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer max-blob-size
Specifies the maximum size of a blob to display HTML for in KBytes.

Defaults to @samp{0}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string max-stats
Maximum statistics period.  Valid values are @samp{week},@samp{month},
@samp{quarter} and @samp{year}.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} mimetype-alist mimetype
Mimetype for the specified filename extension.

Defaults to @samp{'((gif "image/gif") (html "text/html") (jpg
"image/jpeg") (jpeg "image/jpeg") (pdf "application/pdf") (png
"image/png") (svg "image/svg+xml"))}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} file-object mimetype-file
Specifies the file to use for automatic mimetype lookup.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string module-link
Text which will be used as the formatstring for a hyperlink when a
submodule is printed in a directory listing.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean nocache?
If set to the value @samp{#t} caching will be disabled.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean noplainemail?
If set to @samp{#t} showing full author email addresses will be
disabled.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean noheader?
Flag which, when set to @samp{#t}, will make cgit omit the standard
header on all pages.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} project-list project-list
A list of subdirectories inside of @code{repository-directory}, relative
to it, that should loaded as Git repositories.  An empty list means that
all subdirectories will be loaded.

Defaults to @samp{'()}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} file-object readme
Text which will be used as default @code{repository-cgit-configuration}
@code{readme}.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean remove-suffix?
If set to @code{#t} and @code{repository-directory} is enabled, if any
repositories are found with a suffix of @code{.git}, this suffix will be
removed for the URL and name.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer renamelimit
Maximum number of files to consider when detecting renames.

Defaults to @samp{-1}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string repository-sort
The way in which repositories in each section are sorted.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} robots-list robots
Text used as content for the @code{robots} meta-tag.

Defaults to @samp{'("noindex" "nofollow")}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string root-desc
Text printed below the heading on the repository index page.

Defaults to @samp{"a fast webinterface for the git dscm"}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string root-readme
The content of the file specified with this option will be included
verbatim below the ``about'' link on the repository index page.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string root-title
Text printed as heading on the repository index page.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean scan-hidden-path
If set to @samp{#t} and repository-directory is enabled,
repository-directory will recurse into directories whose name starts
with a period.  Otherwise, repository-directory will stay away from such
directories, considered as ``hidden''.  Note that this does not apply to
the @file{.git} directory in non-bare repos.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} list snapshots
Text which specifies the default set of snapshot formats that cgit
generates links for.

Defaults to @samp{'()}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} repository-directory repository-directory
Name of the directory to scan for repositories (represents
@code{scan-path}).

Defaults to @samp{"/srv/git"}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string section
The name of the current repository section - all repositories defined
after this option will inherit the current section name.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string section-sort
Flag which, when set to @samp{1}, will sort the sections on the
repository listing by name.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer section-from-path
A number which, if defined prior to repository-directory, specifies how
many path elements from each repo path to use as a default section name.

Defaults to @samp{0}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} boolean side-by-side-diffs?
If set to @samp{#t} shows side-by-side diffs instead of unidiffs per
default.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} file-object source-filter
Specifies a command which will be invoked to format plaintext blobs in
the tree view.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer summary-branches
Specifies the number of branches to display in the repository ``summary''
view.

Defaults to @samp{10}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer summary-log
Specifies the number of log entries to display in the repository
``summary'' view.

Defaults to @samp{10}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} integer summary-tags
Specifies the number of tags to display in the repository ``summary''
view.

Defaults to @samp{10}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string strict-export
Filename which, if specified, needs to be present within the repository
for cgit to allow access to that repository.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} string virtual-root
URL which, if specified, will be used as root for all cgit links.

Defaults to @samp{"/"}.

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} repository-cgit-configuration-list repositories
A list of @code{repository-cgit-configuration} records.

Defaults to @samp{'()}.

Available @code{repository-cgit-configuration} fields are:

@deftypevr {@code{repository-cgit-configuration} parameter} repo-list snapshots
A mask of snapshot formats for this repo that cgit generates links for,
restricted by the global @code{snapshots} setting.

Defaults to @samp{'()}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-file-object source-filter
Override the default @code{source-filter}.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string url
The relative URL used to access the repository.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-file-object about-filter
Override the default @code{about-filter}.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string branch-sort
Flag which, when set to @samp{age}, enables date ordering in the branch
ref list, and when set to @samp{name} enables ordering by branch name.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-list clone-url
A list of URLs which can be used to clone repo.

Defaults to @samp{'()}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-file-object commit-filter
Override the default @code{commit-filter}.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string commit-sort
Flag which, when set to @samp{date}, enables strict date ordering in the
commit log, and when set to @samp{topo} enables strict topological
ordering.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string defbranch
The name of the default branch for this repository.  If no such branch
exists in the repository, the first branch name (when sorted) is used as
default instead.  By default branch pointed to by HEAD, or ``master'' if
there is no suitable HEAD.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string desc
The value to show as repository description.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string homepage
The value to show as repository homepage.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-file-object email-filter
Override the default @code{email-filter}.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} maybe-repo-boolean enable-commit-graph?
A flag which can be used to disable the global setting
@code{enable-commit-graph?}.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} maybe-repo-boolean enable-log-filecount?
A flag which can be used to disable the global setting
@code{enable-log-filecount?}.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} maybe-repo-boolean enable-log-linecount?
A flag which can be used to disable the global setting
@code{enable-log-linecount?}.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} maybe-repo-boolean enable-remote-branches?
Flag which, when set to @code{#t}, will make cgit display remote
branches in the summary and refs views.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} maybe-repo-boolean enable-subject-links?
A flag which can be used to override the global setting
@code{enable-subject-links?}.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} maybe-repo-boolean enable-html-serving?
A flag which can be used to override the global setting
@code{enable-html-serving?}.

Defaults to @samp{disabled}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-boolean hide?
Flag which, when set to @code{#t}, hides the repository from the
repository index.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-boolean ignore?
Flag which, when set to @samp{#t}, ignores the repository.

Defaults to @samp{#f}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-file-object logo
URL which specifies the source of an image which will be used as a logo
on this repo’s pages.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string logo-link
URL loaded when clicking on the cgit logo image.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-file-object owner-filter
Override the default @code{owner-filter}.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string module-link
Text which will be used as the formatstring for a hyperlink when a
submodule is printed in a directory listing.  The arguments for the
formatstring are the path and SHA1 of the submodule commit.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} module-link-path module-link-path
Text which will be used as the formatstring for a hyperlink when a
submodule with the specified subdirectory path is printed in a directory
listing.

Defaults to @samp{'()}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string max-stats
Override the default maximum statistics period.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string name
The value to show as repository name.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string owner
A value used to identify the owner of the repository.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string path
An absolute path to the repository directory.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string readme
A path (relative to repo) which specifies a file to include verbatim as
the ``About'' page for this repo.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-string section
The name of the current repository section - all repositories defined
after this option will inherit the current section name.

Defaults to @samp{""}.

@end deftypevr

@deftypevr {@code{repository-cgit-configuration} parameter} repo-list extra-options
Extra options will be appended to cgitrc file.

Defaults to @samp{'()}.

@end deftypevr

@end deftypevr

@deftypevr {@code{cgit-configuration} parameter} list extra-options
Extra options will be appended to cgitrc file.

Defaults to @samp{'()}.

@end deftypevr


@c %end of fragment

However, it could be that you just want to get a @code{cgitrc} up and
running.  In that case, you can pass an @code{opaque-cgit-configuration}
as a record to @code{cgit-service-type}.  As its name indicates, an
opaque configuration does not have easy reflective capabilities.

Available @code{opaque-cgit-configuration} fields are:

@deftypevr {@code{opaque-cgit-configuration} parameter} package cgit
The cgit package.
@end deftypevr

@deftypevr {@code{opaque-cgit-configuration} parameter} string string
The contents of the @code{cgitrc}, as a string.
@end deftypevr

For example, if your @code{cgitrc} is just the empty string, you
could instantiate a cgit service like this:

@lisp
(service cgit-service-type
         (opaque-cgit-configuration
          (cgitrc "")))
@end lisp

@subsubheading Gitolite Service

@cindex Gitolite service
@cindex Git, hosting
@uref{https://gitolite.com/gitolite/, Gitolite} is a tool for hosting Git
repositories on a central server.

Gitolite can handle multiple repositories and users, and supports flexible
configuration of the permissions for the users on the repositories.

The following example will configure Gitolite using the default @code{git}
user, and the provided SSH public key.

@lisp
(service gitolite-service-type
         (gitolite-configuration
           (admin-pubkey (plain-file
                           "yourname.pub"
                           "ssh-rsa AAAA... guix@@example.com"))))
@end lisp

Gitolite is configured through a special admin repository which you can clone,
for example, if you setup Gitolite on @code{example.com}, you would run the
following command to clone the admin repository.

@example
git clone git@@example.com:gitolite-admin
@end example

When the Gitolite service is activated, the provided @code{admin-pubkey} will
be inserted in to the @file{keydir} directory in the gitolite-admin
repository.  If this results in a change in the repository, it will be
committed using the message ``gitolite setup by GNU Guix''.

@deftp {Data Type} gitolite-configuration
Data type representing the configuration for @code{gitolite-service-type}.

@table @asis
@item @code{package} (default: @var{gitolite})
Gitolite package to use.  There are optional Gitolite dependencies that
are not included in the default package, such as Redis and git-annex.
These features can be made available by using the @code{make-gitolite}
procedure in the @code{(gnu packages version-control}) module to produce
a variant of Gitolite with the desired additional dependencies.

The following code returns a package in which the Redis and git-annex
programs can be invoked by Gitolite's scripts:

@example
(use-modules (gnu packages databases)
             (gnu packages haskell-apps)
             (gnu packages version-control))
(make-gitolite (list redis git-annex))
@end example

@item @code{user} (default: @var{git})
User to use for Gitolite.  This will be user that you use when accessing
Gitolite over SSH.

@item @code{group} (default: @var{git})
Group to use for Gitolite.

@item @code{home-directory} (default: @var{"/var/lib/gitolite"})
Directory in which to store the Gitolite configuration and repositories.

@item @code{rc-file} (default: @var{(gitolite-rc-file)})
A ``file-like'' object (@pxref{G-Expressions, file-like objects}),
representing the configuration for Gitolite.

@item @code{admin-pubkey} (default: @var{#f})
A ``file-like'' object (@pxref{G-Expressions, file-like objects}) used to
setup Gitolite.  This will be inserted in to the @file{keydir} directory
within the gitolite-admin repository.

To specify the SSH key as a string, use the @code{plain-file} function.

@lisp
(plain-file "yourname.pub" "ssh-rsa AAAA... guix@@example.com")
@end lisp

@end table
@end deftp

@deftp {Data Type} gitolite-rc-file
Data type representing the Gitolite RC file.

@table @asis
@item @code{umask} (default: @code{#o0077})
This controls the permissions Gitolite sets on the repositories and their
contents.

A value like @code{#o0027} will give read access to the group used by Gitolite
(by default: @code{git}).  This is necessary when using Gitolite with software
like cgit or gitweb.

@item @code{local-code} (default: @code{"$rc@{GL_ADMIN_BASE@}/local"})
Allows you to add your own non-core programs, or even override the
shipped ones with your own.

Please supply the FULL path to this variable. By default, directory
called "local" in your gitolite clone is used, providing the benefits of
versioning them as well as making changes to them without having to log
on to the server.

@item @code{unsafe-pattern} (default: @code{#f})
An optional Perl regular expression for catching unsafe configurations in
the configuration file.  See
@uref{https://gitolite.com/gitolite/git-config.html#compensating-for-unsafe_patt,
Gitolite's documentation} for more information.

When the value is not @code{#f}, it should be a string containing a Perl
regular expression, such as @samp{"[`~#\$\&()|;<>]"}, which is the default
value used by gitolite.  It rejects any special character in configuration
that might be interpreted by a shell, which is useful when sharing the
administration burden with other people that do not otherwise have shell
access on the server.

@item @code{git-config-keys} (default: @code{""})
Gitolite allows you to set git config values using the @samp{config}
keyword.  This setting allows control over the config keys to accept.

@item @code{roles} (default: @code{'(("READERS" . 1) ("WRITERS" . ))})
Set the role names allowed to be used by users running the perms command.

@item @code{enable} (default: @code{'("help" "desc" "info" "perms" "writable" "ssh-authkeys" "git-config" "daemon" "gitweb")})
This setting controls the commands and features to enable within Gitolite.

@end table
@end deftp


@subsubheading Gitile Service

@cindex Gitile service
@cindex Git, forge
@uref{https://git.lepiller.eu/gitile, Gitile} is a Git forge for viewing
public git repository contents from a web browser.

Gitile works best in collaboration with Gitolite, and will serve the public
repositories from Gitolite by default.  The service should listen only on
a local port, and a webserver should be configured to serve static resources.
The gitile service provides an easy way to extend the Nginx service for
that purpose (@pxref{NGINX}).

The following example will configure Gitile to serve repositories from a
custom location, with some default messages for the home page and the
footers.

@lisp
(service gitile-service-type
         (gitile-configuration
           (repositories "/srv/git")
           (base-git-url "https://myweb.site/git")
           (index-title "My git repositories")
           (intro '((p "This is all my public work!")))
           (footer '((p "This is the end")))
           (nginx
             (nginx-server-configuration
               (ssl-certificate
                 "/etc/certs/myweb.site/fullchain.pem")
               (ssl-certificate-key
                 "/etc/certs/myweb.site/privkey.pem")
               (listen '("443 ssl http2" "[::]:443 ssl http2"))
               (locations
                 (list
                   ;; Allow for https anonymous fetch on /git/ urls.
                   (git-http-nginx-location-configuration
                     (git-http-configuration
                       (uri-path "/git/")
                       (git-root "/var/lib/gitolite/repositories")))))))))
@end lisp

In addition to the configuration record, you should configure your git
repositories to contain some optional information.  First, your public
repositories need to contain the @file{git-daemon-export-ok} magic file
that allows Git to export the repository.  Gitile uses the presence of this
file to detect public repositories it should make accessible.  To do so with
Gitolite for instance, modify your @file{conf/gitolite.conf} to include
this in the repositories you want to make public:

@example
repo foo
    R = daemon
@end example

In addition, Gitile can read the repository configuration to display more
information on the repository.  Gitile uses the gitweb namespace for its
configuration.  As an example, you can use the following in your
@file{conf/gitolite.conf}:

@example
repo foo
    R = daemon
    desc = A long description, optionally with <i>HTML</i>, shown on the index page
    config gitweb.name = The Foo Project
    config gitweb.synopsis = A short description, shown on the main page of the project
@end example

Do not forget to commit and push these changes once you are satisfied.  You
may need to change your gitolite configuration to allow the previous
configuration options to be set.  One way to do that is to add the
following service definition:

@lisp
(service gitolite-service-type
          (gitolite-configuration
            (admin-pubkey (local-file "key.pub"))
            (rc-file
              (gitolite-rc-file
                (umask #o0027)
                ;; Allow to set any configuration key
                (git-config-keys ".*")
                ;; Allow any text as a valid configuration value
                (unsafe-patt "^$")))))
@end lisp

@deftp {Data Type} gitile-configuration
Data type representing the configuration for @code{gitile-service-type}.

@table @asis
@item @code{package} (default: @var{gitile})
Gitile package to use.

@item @code{host} (default: @code{"localhost"})
The host on which gitile is listening.

@item @code{port} (default: @code{8080})
The port on which gitile is listening.

@item @code{database} (default: @code{"/var/lib/gitile/gitile-db.sql"})
The location of the database.

@item @code{repositories} (default: @code{"/var/lib/gitolite/repositories"})
The location of the repositories.  Note that only public repositories will
be shown by Gitile.  To make a repository public, add an empty
@file{git-daemon-export-ok} file at the root of that repository.

@item @code{base-git-url}
The base git url that will be used to show clone commands.

@item @code{index-title} (default: @code{"Index"})
The page title for the index page that lists all the available repositories.

@item @code{intro} (default: @code{'()})
The intro content, as a list of sxml expressions.  This is shown above the list
of repositories, on the index page.

@item @code{footer} (default: @code{'()})
The footer content, as a list of sxml expressions.  This is shown on every
page served by Gitile.

@item @code{nginx}
An nginx server block that will be extended and used as a reverse proxy by
Gitile to serve its pages, and as a normal web server to serve its assets.

You can use this block to add more custom URLs to your domain, such as a
@code{/git/} URL for anonymous clones, or serving any other files you would
like to serve.
@end table
@end deftp


@node Game Services
@subsection Game Services

@subsubheading Joycond service
@cindex joycond
The joycond service allows the pairing of Nintendo joycon game
controllers over Bluetooth. (@pxref{Desktop Services} for setting up
Bluetooth.)

@deftp {Data Type} joycond-configuration
Data type representing the configuration of @command{joycond}.

@table @asis
@item @code{package} (default: @code{joycond})
The joycond package to use.
@end table
@end deftp

@defvar joycond-service-type
Service type for the joycond service.
@end defvar

@subsubheading The Battle for Wesnoth Service
@cindex wesnothd
@uref{https://wesnoth.org, The Battle for Wesnoth} is a fantasy, turn
based tactical strategy game, with several single player campaigns, and
multiplayer games (both networked and local).

@defvar wesnothd-service-type
Service type for the wesnothd service.  Its value must be a
@code{wesnothd-configuration} object.  To run wesnothd in the default
configuration, instantiate it as:

@lisp
(service wesnothd-service-type)
@end lisp
@end defvar

@deftp {Data Type} wesnothd-configuration
Data type representing the configuration of @command{wesnothd}.

@table @asis
@item @code{package} (default: @code{wesnoth-server})
The wesnoth server package to use.

@item @code{port} (default: @code{15000})
The port to bind the server to.
@end table
@end deftp


@node PAM Mount Service
@subsection PAM Mount Service
@cindex pam-mount

The @code{(gnu services pam-mount)} module provides a service allowing
users to mount volumes when they log in.  It should be able to mount any
volume format supported by the system.

@defvar pam-mount-service-type
Service type for PAM Mount support.
@end defvar

@deftp {Data Type} pam-mount-configuration
Data type representing the configuration of PAM Mount.

It takes the following parameters:

@table @asis
@item @code{rules}
The configuration rules that will be used to generate
@file{/etc/security/pam_mount.conf.xml}.

The configuration rules are SXML elements (@pxref{SXML,,, guile, GNU
Guile Reference Manual}), and the default ones don't mount anything for
anyone at login:

@lisp
`((debug (@@ (enable "0")))
  (mntoptions (@@ (allow ,(string-join
                          '("nosuid" "nodev" "loop"
                            "encryption" "fsck" "nonempty"
                            "allow_root" "allow_other")
                          ","))))
  (mntoptions (@@ (require "nosuid,nodev")))
  (logout (@@ (wait "0")
             (hup "0")
             (term "no")
             (kill "no")))
  (mkmountpoint (@@ (enable "1")
                   (remove "true"))))
@end lisp

Some @code{volume} elements must be added to automatically mount volumes
at login.  Here's an example allowing the user @code{alice} to mount her
encrypted @env{HOME} directory and allowing the user @code{bob} to mount
the partition where he stores his data:

@lisp
(define pam-mount-rules
`((debug (@@ (enable "0")))
            (volume (@@ (user "alice")
                       (fstype "crypt")
                       (path "/dev/sda2")
                       (mountpoint "/home/alice")))
            (volume (@@ (user "bob")
                       (fstype "auto")
                       (path "/dev/sdb3")
                       (mountpoint "/home/bob/data")
                       (options "defaults,autodefrag,compress")))
            (mntoptions (@@ (allow ,(string-join
                                    '("nosuid" "nodev" "loop"
                                      "encryption" "fsck" "nonempty"
                                      "allow_root" "allow_other")
                                    ","))))
            (mntoptions (@@ (require "nosuid,nodev")))
            (logout (@@ (wait "0")
                       (hup "0")
                       (term "no")
                       (kill "no")))
            (mkmountpoint (@@ (enable "1")
                             (remove "true")))))

(service pam-mount-service-type
         (pam-mount-configuration
           (rules pam-mount-rules)))
@end lisp

The complete list of possible options can be found in the man page for
@uref{http://pam-mount.sourceforge.net/pam_mount.conf.5.html, pam_mount.conf}.
@end table
@end deftp

@subheading PAM Mount Volume Service
@cindex pam volume mounting

PAM mount volumes are automatically mounted at login by the PAM login
service according to a set of per-volume rules.  Because they are
mounted by PAM the password entered during login may be used directly to
mount authenticated volumes, such as @code{cifs}, using the same
credentials.

These volumes will be added in addition to any volumes directly
specified in @code{pam-mount-rules}.

Here is an example of a rule which will mount a remote CIFS share from
@file{//remote-server/share} into a sub-directory of @file{/shares}
named after the user logging in:

@lisp
(simple-service 'pam-mount-remote-share pam-mount-volume-service-type
                (list (pam-mount-volume
                       (secondary-group "users")
                       (file-system-type "cifs")
                       (server "remote-server")
                       (file-name "share")
                       (mount-point "/shares/%(USER)")
                       (options "nosuid,nodev,seal,cifsacl"))))
@end lisp

@deftp {Data Type} pam-mount-volume-service-type
Configuration for a single volume to be mounted.  Any fields not
specified will be omitted from the run-time PAM configuration.  See
@uref{http://pam-mount.sourceforge.net/pam_mount.conf.5.html,
the man page} for the default values when unspecified.

@table @asis
@item @code{user-name} (type: maybe-string)
Mount the volume for the given user.

@item @code{user-id} (type: maybe-integer-or-range)
Mount the volume for the user with this ID.  This field may also be
specified as a pair of @code{(start . end)} indicating a range of user
IDs for whom to mount the volume.

@item @code{primary-group} (type: maybe-string)
Mount the volume for users with this primary group name.

@item @code{group-id} (type: maybe-integer-or-range)
Mount the volume for the users with this primary group ID.  This field
may also be specified as a cons cell of @code{(start . end)} indicating
a range of group ids for whom to mount the volume.

@item @code{secondary-group} (type: maybe-string)
Mount the volume for users who are members of this group as either a
primary or secondary group.

@item @code{file-system-type} (type: maybe-string)
The file system type for the volume being mounted (e.g., @code{cifs})

@item @code{no-mount-as-root?} (type: maybe-boolean)
Whether or not to mount the volume with root privileges.  This is
normally disabled, but may be enabled for mounts of type @code{fuse}, or
other user-level mounts.

@item @code{server} (type: maybe-string)
The name of the remote server to mount the volume from, when necessary.

@item @code{file-name} (type: maybe-string)
The location of the volume, either local or remote, depending on the
@code{file-system-type}.

@item @code{mount-point} (type: maybe-string)
Where to mount the volume in the local file-system.  This may be set to
@file{~} to indicate the home directory of the user logging in.  If this
field is omitted then @file{/etc/fstab} is consulted for the mount
destination.

@item @code{options} (type: maybe-string)
The options to be passed as-is to the underlying mount program.

@item @code{ssh?} (type: maybe-boolean)
Enable this option to pass the login password to SSH for use with mounts
involving SSH (e.g., @code{sshfs}).

@item @code{cipher} (type: maybe-string)
Cryptsetup cipher name for the volume.  To be used with the @code{crypt}
@code{file-system-type}.

@item @code{file-system-key-cipher} (type: maybe-string)
Cipher name used by the target volume.

@item @code{file-system-key-hash} (type: maybe-string)
SSL hash name used by the target volume.

@item @code{file-system-key-file-name} (type: maybe-string)
File name of the file system key for the target volume.

@end table
@end deftp


@node Guix Services
@subsection Guix Services

@subsubheading Build Farm Front-End (BFFE)
The @uref{https://git.cbaines.net/guix/bffe/,Build Farm Front-End}
assists with building Guix packages in bulk.  It's responsible for
submitting builds and displaying the status of the build farm.

@defvar bffe-service-type
Service type for the Build Farm Front-End.  Its value must be a
@code{bffe-configuration} object.
@end defvar

@deftp {Data Type} bffe-configuration
Data type representing the configuration of the Build Farm Front-End.

@table @asis
@item @code{package} (default: @code{bffe})
The Build Farm Front-End package to use.

@item @code{user} (default: @code{"bffe"})
The system user to run the service as.

@item @code{group} (default: @code{"bffe"})
The system group to run the service as.

@item @code{arguments}
A list of arguments to the Build Farm Front-End.  These are passed to
the @code{run-bffe-service} procedure when starting the service.

For example, the following value directs the Build Farm Front-End to
submit builds for derivations available from @code{data.guix.gnu.org} to
the Build Coordinator instance assumed to be running on the same
machine.

@example
(list
 #:build
 (list
  (build-from-guix-data-service
   (data-service-url "https://data.guix.gnu.org")
   (build-coordinator-url "http://127.0.0.1:8746")
   (branches '("master"))
   (systems '("x86_64-linux" "i686-linux"))
   (systems-and-targets
    (map (lambda (target)
           (cons "x86_64-linux" target))
         '("aarch64-linux-gnu"
           "i586-pc-gnu")))
   (build-priority (const 0))))
 #:web-server-args
 '(#:event-source "https://example.com"
   #:controller-args
   (#:title "example.com build farm")))
@end example

@item @code{extra-environment-variables} (default: @var{'()})
Extra environment variables to set via the shepherd service.

@end table
@end deftp

@subsubheading Guix Build Coordinator
The @uref{https://git.cbaines.net/guix/build-coordinator/,Guix Build
Coordinator} aids in distributing derivation builds among machines
running an @dfn{agent}.  The build daemon is still used to build the
derivations, but the Guix Build Coordinator manages allocating builds
and working with the results.

The Guix Build Coordinator consists of one @dfn{coordinator}, and one or
more connected @dfn{agent} processes.  The coordinator process handles
clients submitting builds, and allocating builds to agents.  The agent
processes talk to a build daemon to actually perform the builds, then
send the results back to the coordinator.

There is a script to run the coordinator component of the Guix Build
Coordinator, but the Guix service uses a custom Guile script instead, to
provide better integration with G-expressions used in the configuration.

@defvar guix-build-coordinator-service-type
Service type for the Guix Build Coordinator.  Its value must be a
@code{guix-build-coordinator-configuration} object.
@end defvar

@deftp {Data Type} guix-build-coordinator-configuration
Data type representing the configuration of the Guix Build Coordinator.

@table @asis
@item @code{package} (default: @code{guix-build-coordinator})
The Guix Build Coordinator package to use.

@item @code{user} (default: @code{"guix-build-coordinator"})
The system user to run the service as.

@item @code{group} (default: @code{"guix-build-coordinator"})
The system group to run the service as.

@item @code{database-uri-string} (default: @code{"sqlite:///var/lib/guix-build-coordinator/guix_build_coordinator.db"})
The URI to use for the database.

@item @code{agent-communication-uri} (default: @code{"http://0.0.0.0:8745"})
The URI describing how to listen to requests from agent processes.

@item @code{client-communication-uri} (default: @code{"http://127.0.0.1:8746"})
The URI describing how to listen to requests from clients.  The client
API allows submitting builds and currently isn't authenticated, so take
care when configuring this value.

@item @code{allocation-strategy} (default: @code{#~basic-build-allocation-strategy})
A G-expression for the allocation strategy to be used.  This is a
procedure that takes the datastore as an argument and populates the
allocation plan in the database.

@item @code{hooks} (default: @var{'()})
An association list of hooks.  These provide a way to execute arbitrary
code upon certain events, like a build result being processed.

@item @code{parallel-hooks} (default: @var{'()})
Hooks can be configured to run in parallel.  This parameter is an
association list of hooks to do in parallel, where the key is the symbol
for the hook and the value is the number of threads to run.

@item @code{guile} (default: @code{guile-3.0-latest})
The Guile package with which to run the Guix Build Coordinator.

@item @code{extra-environment-variables} (default: @var{'()})
Extra environment variables to set via the shepherd service.

@end table
@end deftp

@defvar guix-build-coordinator-agent-service-type
Service type for a Guix Build Coordinator agent.  Its value must be a
@code{guix-build-coordinator-agent-configuration} object.
@end defvar

@deftp {Data Type} guix-build-coordinator-agent-configuration
Data type representing the configuration a Guix Build Coordinator agent.

@table @asis
@item @code{package} (default: @code{guix-build-coordinator/agent-only})
The Guix Build Coordinator package to use.

@item @code{user} (default: @code{"guix-build-coordinator-agent"})
The system user to run the service as.

@item @code{coordinator} (default: @code{"http://localhost:8745"})
The URI to use when connecting to the coordinator.

@item @code{authentication}
Record describing how this agent should authenticate with the
coordinator.  Possible record types are described below.

@item @code{systems} (default: @code{#f})
The systems for which this agent should fetch builds.  The agent process
will use the current system it's running on as the default.

@item @code{max-parallel-builds} (default: @code{1})
The number of builds to perform in parallel.

@item @code{max-parallel-uploads} (default: @code{1})
The number of uploads to perform in parallel.

@item @code{max-allocated-builds} (default: @code{#f})
The maximum number of builds this agent can be allocated.

@item @code{max-1min-load-average} (default: @code{#f})
Load average value to look at when considering starting new builds, if
the 1 minute load average exceeds this value, the agent will wait before
starting new builds.

This will be unspecified if the value is @code{#f}, and the agent will
use the number of cores reported by the system as the max 1 minute load
average.

@item @code{derivation-substitute-urls} (default: @code{#f})
URLs from which to attempt to fetch substitutes for derivations, if the
derivations aren't already available.

@item @code{non-derivation-substitute-urls} (default: @code{#f})
URLs from which to attempt to fetch substitutes for build inputs, if the
input store items aren't already available.

@end table
@end deftp

@deftp {Data Type} guix-build-coordinator-agent-password-auth
Data type representing an agent authenticating with a coordinator via a
UUID and password.

@table @asis
@item @code{uuid}
The UUID of the agent.  This should be generated by the coordinator
process, stored in the coordinator database, and used by the intended
agent.

@item @code{password}
The password to use when connecting to the coordinator.

@end table
@end deftp

@deftp {Data Type} guix-build-coordinator-agent-password-file-auth
Data type representing an agent authenticating with a coordinator via a
UUID and password read from a file.

@table @asis
@item @code{uuid}
The UUID of the agent.  This should be generated by the coordinator
process, stored in the coordinator database, and used by the intended
agent.

@item @code{password-file}
A file containing the password to use when connecting to the
coordinator.

@end table
@end deftp

@deftp {Data Type} guix-build-coordinator-agent-dynamic-auth
Data type representing an agent authenticating with a coordinator via a
dynamic auth token and agent name.

@table @asis
@item @code{agent-name}
Name of an agent, this is used to match up to an existing entry in the
database if there is one.  When no existing entry is found, a new entry
is automatically added.

@item @code{token}
Dynamic auth token, this is created and stored in the coordinator
database, and is used by the agent to authenticate.

@end table
@end deftp

@deftp {Data Type} guix-build-coordinator-agent-dynamic-auth-with-file
Data type representing an agent authenticating with a coordinator via a
dynamic auth token read from a file and agent name.

@table @asis
@item @code{agent-name}
Name of an agent, this is used to match up to an existing entry in the
database if there is one.  When no existing entry is found, a new entry
is automatically added.

@item @code{token-file}
File containing the dynamic auth token, this is created and stored in
the coordinator database, and is used by the agent to authenticate.

@end table
@end deftp

@subsubheading Guix Data Service
The @uref{http://data.guix.gnu.org,Guix Data Service} processes, stores
and provides data about GNU Guix.  This includes information about
packages, derivations and lint warnings.

The data is stored in a PostgreSQL database, and available through a web
interface.

@defvar guix-data-service-type
Service type for the Guix Data Service.  Its value must be a
@code{guix-data-service-configuration} object.  The service optionally
extends the getmail service, as the guix-commits mailing list is used to
find out about changes in the Guix git repository.
@end defvar

@deftp {Data Type} guix-data-service-configuration
Data type representing the configuration of the Guix Data Service.

@table @asis
@item @code{package} (default: @code{guix-data-service})
The Guix Data Service package to use.

@item @code{user} (default: @code{"guix-data-service"})
The system user to run the service as.

@item @code{group} (default: @code{"guix-data-service"})
The system group to run the service as.

@item @code{port} (default: @code{8765})
The port to bind the web service to.

@item @code{host} (default: @code{"127.0.0.1"})
The host to bind the web service to.

@item @code{getmail-idle-mailboxes} (default: @code{#f})
If set, this is the list of mailboxes that the getmail service will be
configured to listen to.

@item @code{commits-getmail-retriever-configuration} (default: @code{#f})
If set, this is the @code{getmail-retriever-configuration} object with
which to configure getmail to fetch mail from the guix-commits mailing
list.

@item @code{extra-options} (default: @var{'()})
Extra command line options for @code{guix-data-service}.

@item @code{extra-process-jobs-options} (default: @var{'()})
Extra command line options for @code{guix-data-service-process-jobs}.

@end table
@end deftp

@anchor{guix-home-service-type}
@subsubheading Guix Home Service

The Guix Home service is a way to let Guix System deploy the home
environment of one or more users (@pxref{Home Configuration}, for more
on Guix Home).  That way, the system configuration embeds declarations
of the home environment of those users and can be used to deploy
everything consistently at once, saving users the need to run
@command{guix home reconfigure} independently.

@defvar guix-home-service-type
Service type for the Guix Home service.  Its value must be a list of
lists containing user and home environment pairs.  The key of each pair
is a string representing the user to deploy the configuration under and
the value is a home-environment configuration.

@lisp
(use-modules (gnu home))

(define my-home
  (home-environment
    @dots{}))

(operating-system
  (services (append (list (service guix-home-service-type
                                   `(("alice" ,my-home))))
                    %base-services)))
@end lisp

This service can be extended by other services to add additional home
environments, as in this example:

@lisp
(simple-service 'my-extra-home guix-home-service-type
                `(("bob" ,my-extra-home))))
@end lisp
@end defvar

@subsubheading Nar Herder
The @uref{https://git.cbaines.net/guix/nar-herder/about/,Nar Herder} is
a utility for managing a collection of nars.

@defvar nar-herder-type
Service type for the Guix Data Service.  Its value must be a
@code{nar-herder-configuration} object.  The service optionally
extends the getmail service, as the guix-commits mailing list is used to
find out about changes in the Guix git repository.
@end defvar

@deftp {Data Type} nar-herder-configuration
Data type representing the configuration of the Guix Data Service.

@table @asis
@item @code{package} (default: @code{nar-herder})
The Nar Herder package to use.

@item @code{user} (default: @code{"nar-herder"})
The system user to run the service as.

@item @code{group} (default: @code{"nar-herder"})
The system group to run the service as.

@item @code{port} (default: @code{8734})
The port to bind the server to.

@item @code{host} (default: @code{"127.0.0.1"})
The host to bind the server to.

@item @code{mirror} (default: @code{#f})
Optional URL of the other Nar Herder instance which should be mirrored.
This means that this Nar Herder instance will download it's database,
and keep it up to date.

@item @code{database} (default: @code{"/var/lib/nar-herder/nar_herder.db"})
Location for the database.  If this Nar Herder instance is mirroring
another, the database will be downloaded if it doesn't exist.  If this
Nar Herder instance isn't mirroring another, an empty database will be
created.

@item @code{database-dump} (default: @code{"/var/lib/nar-herder/nar_herder_dump.db"})
Location of the database dump.  This is created and regularly updated by
taking a copy of the database.  This is the version of the database that
is available to download.

@item @code{storage} (default: @code{#f})
Optional location in which to store nars.

@item @code{storage-limit} (default: @code{"none"})
Limit in bytes for the nars stored in the storage location.  This can
also be set to ``none'' so that there is no limit.

When the storage location exceeds this size, nars are removed according
to the nar removal criteria.

@item @code{storage-nar-removal-criteria} (default: @code{'()})
Criteria used to remove nars from the storage location.  These are used
in conjunction with the storage limit.

When the storage location exceeds the storage limit size, nars will be
checked against the nar removal criteria and if any of the criteria
match, they will be removed.  This will continue until the storage
location is below the storage limit size.

Each criteria is specified by a string, then an equals sign, then
another string. Currently, only one criteria is supported, checking if a
nar is stored on another Nar Herder instance.

@item @code{ttl} (default: @code{#f})
Produce @code{Cache-Control} HTTP headers that advertise a time-to-live
(TTL) of @var{ttl}.  @var{ttl} must denote a duration: @code{5d} means 5
days, @code{1m} means 1 month, and so on.

This allows the user's Guix to keep substitute information in cache for
@var{ttl}.

@item @code{new-ttl} (default: @code{#f})
If specified, this will override the @code{ttl} setting when used for
the @code{Cache-Control} headers, but this value will be used when
scheduling the removal of nars.

Use this setting when the TTL is being reduced to avoid removing nars
while clients still have cached narinfos.

@item @code{negative-ttl} (default: @code{#f})
Similarly produce @code{Cache-Control} HTTP headers to advertise the
time-to-live (TTL) of @emph{negative} lookups---missing store items, for
which the HTTP 404 code is returned.  By default, no negative TTL is
advertised.

@item @code{log-level} (default: @code{'DEBUG})
Log level to use, specify a log level like @code{'INFO} to stop logging
individual requests.

@item @code{cached-compressions} (default: @code{'()})
Activate generating cached nars with different compression details from
the stored nars.  This is a list of
nar-herder-cached-compression-configuration records.

@item @code{min-uses} (default: @code{3})
When cached-compressions are enabled, generate cached nars when at least
this number of requests are made for a nar.

@item @code{workers} (default: @code{2})
Number of cached nars to generate at a time.

@item @code{nar-source} (default: @code{#f})
Location to fetch nars from when computing cached compressions.  By
default, the storage location will be used.

@item @code{extra-environment-variables} (default: @code{'()})
Extra environment variables to set via the shepherd service.

@end table
@end deftp

@deftp {Data Type} nar-herder-cached-compression-configuration
Data type representing the cached compression configuration.

@table @asis
@item @code{type}
Type of compression to use, e.g. @code{'zstd}.

@item @code{workers} (default: @code{#f})
Level of the compression to use.

@item @code{directory} (default: @code{#f})
Location to store the cached nars.  If unspecified, they will be stored
in /var/cache/nar-herder/nar/TYPE.

@item @code{directory-max-size} (default: @code{#f})
Maximum size in bytes of the directory.

@item @code{unused-removal-duration} (default: @code{#f})
If a cached nar isn't used for @code{unused-removal-duration}, it will
be scheduled for removal.

@var{unused-removal-duration} must denote a duration: @code{5d} means 5
days, @code{1m} means 1 month, and so on.

@item @code{ttl} (default: @code{#f})
If specified this overrides the @code{ttl} used for narinfos when this
cached compression is available.

@item @code{new-ttl} (default: @code{#f})
As with the @code{new-ttl} option for @code{nar-herder-configuration},
this value will override the @code{ttl} when used for narinfo requests.

@end table
@end deftp

@node Linux Services
@subsection Linux Services

@cindex oom
@cindex out of memory killer
@cindex earlyoom
@cindex early out of memory daemon
@subsubheading Early OOM Service

@uref{https://github.com/rfjakob/earlyoom,Early OOM}, also known as
Earlyoom, is a minimalist out of memory (OOM) daemon that runs in user
space and provides a more responsive and configurable alternative to the
in-kernel OOM killer.  It is useful to prevent the system from becoming
unresponsive when it runs out of memory.

@defvar earlyoom-service-type
The service type for running @command{earlyoom}, the Early OOM daemon.
Its value must be a @code{earlyoom-configuration} object, described
below.  The service can be instantiated in its default configuration
with:

@lisp
(service earlyoom-service-type)
@end lisp
@end defvar

@deftp {Data Type} earlyoom-configuration
This is the configuration record for the @code{earlyoom-service-type}.

@table @asis
@item @code{earlyoom} (default: @var{earlyoom})
The Earlyoom package to use.

@item @code{minimum-available-memory} (default: @code{10})
The threshold for the minimum @emph{available} memory, in percentages.

@item @code{minimum-free-swap} (default: @code{10})
The threshold for the minimum free swap memory, in percentages.

@item @code{prefer-regexp} (default: @code{#f})
A regular expression (as a string) to match the names of the processes
that should be preferably killed.

@item @code{avoid-regexp} (default: @code{#f})
A regular expression (as a string) to match the names of the processes
that should @emph{not} be killed.

@item @code{memory-report-interval} (default: @code{0})
The interval in seconds at which a memory report is printed.  It is
disabled by default.

@item @code{ignore-positive-oom-score-adj?} (default: @code{#f})
A boolean indicating whether the positive adjustments set in
@file{/proc/*/oom_score_adj} should be ignored.

@item @code{show-debug-messages?} (default: @code{#f})
A boolean indicating whether debug messages should be printed.  The logs
are saved at @file{/var/log/earlyoom.log}.

@item @code{send-notification-command} (default: @code{#f})
This can be used to provide a custom command used for sending
notifications.
@end table
@end deftp

@subsubheading fstrim Service
@cindex fstrim service
@cindex solid state drives, periodic trim
@cindex solid state drives, trim

The command @command{fstrim} can be used to discard (or @dfn{trim})
unused blocks on a mounted file system.

@c This was copied from the fstrim manpage, with some Texinfo touch-ups.
@quotation Warning
Running @command{fstrim} frequently, or even using
@command{mount -o discard}, might negatively affect the lifetime of
poor-quality SSD devices.  For most desktop and server systems a
sufficient trimming frequency is once a week.  Note that not all devices
support a queued trim, so each trim command incurs a performance penalty
on whatever else might be trying to use the disk at the time.
@end quotation

@defvar fstrim-service-type
Type for a service that periodically runs @command{fstrim}, whose value must
be an @code{<fstrim-configuration>} object.  The service can be instantiated
in its default configuration with:

@lisp
(service fstrim-service-type)
@end lisp
@end defvar

@c %start of fragment
@deftp {Data Type} fstrim-configuration
Available @code{fstrim-configuration} fields are:

@table @asis
@item @code{package} (default: @code{util-linux}) (type: file-like)
The package providing the @command{fstrim} command.

@item @code{schedule} (default: @code{"0 0 * * 0"}) (type: mcron-time)
Schedule for launching @command{fstrim}.  This can be a procedure, a
list or a string.  For additional information, see @ref{Guile
Syntax,,Job specification,mcron,the mcron manual}.  By default this is
set to run weekly on Sunday at 00:00.

@item @code{listed-in} (default: @code{'("/etc/fstab" "/proc/self/mountinfo")}) (type: maybe-list-of-strings)
List of files in fstab or kernel mountinfo format.  All missing or empty
files are silently ignored.  The evaluation of the list @emph{stops}
after the first non-empty file.  File systems with
@code{X-fstrim.notrim} mount option in fstab are skipped.

@item @code{verbose?} (default: @code{#t}) (type: boolean)
Verbose execution.

@item @code{quiet-unsupported?} (default: @code{#t}) (type: boolean)
Suppress error messages if trim operation (ioctl) is unsupported.

@item @code{extra-arguments} (type: maybe-list-of-strings)
Extra options to append to @command{fstrim} (run @samp{man fstrim} for
more information).

@end table
@end deftp
@c %end of fragment

@cindex modprobe
@cindex kernel module loader
@subsubheading Kernel Module Loader Service

The kernel module loader service allows one to load loadable kernel
modules at boot.  This is especially useful for modules that don't
autoload and need to be manually loaded, as is the case with
@code{ddcci}.

@defvar kernel-module-loader-service-type
The service type for loading loadable kernel modules at boot with
@command{modprobe}.  Its value must be a list of strings representing
module names.  For example loading the drivers provided by
@code{ddcci-driver-linux}, in debugging mode by passing some module
parameters, can be done as follow:

@lisp
(use-modules (gnu) (gnu services))
(use-package-modules linux)
(use-service-modules linux)

(define ddcci-config
  (plain-file "ddcci.conf"
              "options ddcci dyndbg delay=120"))

(operating-system
  ...
  (services (cons* (service kernel-module-loader-service-type
                            '("ddcci" "ddcci_backlight"))
                   (simple-service 'ddcci-config etc-service-type
                                   (list `("modprobe.d/ddcci.conf"
                                           ,ddcci-config)))
                   %base-services))
  (kernel-loadable-modules (list ddcci-driver-linux)))
@end lisp
@end defvar

@subsubheading Cachefilesd Service

@cindex cachefilesd
@cindex fscache, file system caching (Linux)
The Cachefilesd service starts a daemon that caches network file system
data locally.  It is especially useful for NFS and AFS shares, where it
reduces latencies for repeated access when reading files.

The daemon can be configured as follows:

@lisp
(service cachefilesd-service-type
         (cachefilesd-configuration
           (cache-directory "/var/cache/fscache")))
@end lisp

@defvar cachefilesd-service-type
The service type for starting @command{cachefilesd}.  The value for this
service type is a @code{cachefilesd-configuration}, whose only required
field is @var{cache-directory}.

@end defvar

@c %start of fragment
@deftp {Data Type} cachefilesd-configuration
Available @code{cachefilesd-configuration} fields are:

@table @asis
@item @code{cachefilesd} (default: @code{cachefilesd}) (type: file-like)
The cachefilesd package to use.

@item @code{debug-output?} (default: @code{#f}) (type: boolean)
Print debugging output to stderr.

@item @code{use-syslog?} (default: @code{#t}) (type: boolean)
Log to syslog facility instead of stdout.

@item @code{scan?} (default: @code{#t}) (type: boolean)
Scan for cachable objects.

@item @code{cache-directory} (type: maybe-string)
Location of the cache directory.

@item @code{cache-name} (default: @code{"CacheFiles"}) (type: maybe-string)
Name of cache (keep unique).

@item @code{security-context} (type: maybe-string)
SELinux security context.

@item @code{pause-culling-for-block-percentage} (default: @code{7}) (type: maybe-non-negative-integer)
Pause culling when available blocks exceed this percentage.

@item @code{pause-culling-for-file-percentage} (default: @code{7}) (type: maybe-non-negative-integer)
Pause culling when available files exceed this percentage.

@item @code{resume-culling-for-block-percentage} (default: @code{5}) (type: maybe-non-negative-integer)
Start culling when available blocks drop below this percentage.

@item @code{resume-culling-for-file-percentage} (default: @code{5}) (type: maybe-non-negative-integer)
Start culling when available files drop below this percentage.

@item @code{pause-caching-for-block-percentage} (default: @code{1}) (type: maybe-non-negative-integer)
Pause further allocations when available blocks drop below this
percentage.

@item @code{pause-caching-for-file-percentage} (default: @code{1}) (type: maybe-non-negative-integer)
Pause further allocations when available files drop below this
percentage.

@item @code{log2-table-size} (default: @code{12}) (type: maybe-non-negative-integer)
Size of tables holding cullable objects in logarithm of base 2.

@item @code{cull?} (default: @code{#t}) (type: boolean)
Create free space by culling (consumes system load).

@item @code{trace-function-entry-in-kernel-module?} (default: @code{#f}) (type: boolean)
Trace function entry in the kernel module (for debugging).

@item @code{trace-function-exit-in-kernel-module?} (default: @code{#f}) (type: boolean)
Trace function exit in the kernel module (for debugging).

@item @code{trace-internal-checkpoints-in-kernel-module?} (default: @code{#f}) (type: boolean)
Trace internal checkpoints in the kernel module (for debugging).

@end table
@end deftp
@c %end of fragment

@cindex rasdaemon
@cindex Platform Reliability, Availability and Serviceability daemon
@subsubheading Rasdaemon Service

The Rasdaemon service provides a daemon which monitors platform
@acronym{RAS, Reliability@comma{} Availability@comma{} and Serviceability} reports from
Linux kernel trace events, logging them to syslogd.

Reliability, Availability and Serviceability is a concept used on servers meant
to measure their robustness.

@strong{Relability} is the probability that a system will produce correct
outputs:

@itemize @bullet
@item Generally measured as Mean Time Between Failures (MTBF), and
@item Enhanced by features that help to avoid, detect and repair hardware
faults
@end itemize

@strong{Availability} is the probability that a system is operational at a
given time:

@itemize @bullet
@item Generally measured as a percentage of downtime per a period of time, and
@item Often uses mechanisms to detect and correct hardware faults in runtime.
@end itemize

@strong{Serviceability} is the simplicity and speed with which a system can be
repaired or maintained:

@itemize @bullet
@item Generally measured on Mean Time Between Repair (MTBR).
@end itemize


Among the monitoring measures, the most usual ones include:

@itemize @bullet
@item CPU – detect errors at instruction execution and at L1/L2/L3 caches;
@item Memory – add error correction logic (ECC) to detect and correct errors;
@item I/O – add CRC checksums for transferred data;
@item Storage – RAID, journal file systems, checksums, Self-Monitoring,
Analysis and Reporting Technology (SMART).
@end itemize

By monitoring the number of occurrences of error detections, it is possible to
identify if the probability of hardware errors is increasing, and, on such
case, do a preventive maintenance to replace a degraded component while those
errors are correctable.

For detailed information about the types of error events gathered and how to
make sense of them, see the kernel administrator's guide at
@url{https://www.kernel.org/doc/html/latest/admin-guide/ras.html}.

@defvar rasdaemon-service-type
Service type for the @command{rasdaemon} service.  It accepts a
@code{rasdaemon-configuration} object.  Instantiating like

@lisp
(service rasdaemon-service-type)
@end lisp

will load with a default configuration, which monitors all events and logs to
syslogd.
@end defvar

@deftp {Data Type} rasdaemon-configuration
The data type representing the configuration of @command{rasdaemon}.

@table @asis
@item @code{record?} (default: @code{#f})

A boolean indicating whether to record the events in an SQLite database.  This
provides a more structured access to the information contained in the log file.
The database location is hard-coded to @file{/var/lib/rasdaemon/ras-mc_event.db}.

@end table
@end deftp

@cindex zram
@cindex compressed swap
@cindex Compressed RAM-based block devices
@subsubheading Zram Device Service

The Zram device service provides a compressed swap device in system
memory.  The Linux Kernel documentation has more information about
@uref{https://www.kernel.org/doc/html/latest/admin-guide/blockdev/zram.html,zram}
devices.

@defvar zram-device-service-type
This service creates the zram block device, formats it as swap and
enables it as a swap device.  The service's value is a
@code{zram-device-configuration} record.

@deftp {Data Type} zram-device-configuration
This is the data type representing the configuration for the zram-device
service.

@table @asis
@item @code{size} (default @code{"1G"})
This is the amount of space you wish to provide for the zram device.  It
accepts a string and can be a number of bytes or use a suffix, eg.:
@code{"512M"} or @code{1024000}.
@item @code{compression-algorithm} (default @code{'lzo})
This is the compression algorithm you wish to use.  It is difficult to
list all the possible compression options, but common ones supported by
Guix's Linux Libre Kernel include @code{'lzo}, @code{'lz4} and @code{'zstd}.
@item @code{memory-limit} (default @code{0})
This is the maximum amount of memory which the zram device can use.
Setting it to '0' disables the limit.  While it is generally expected
that compression will be 2:1, it is possible that uncompressable data
can be written to swap and this is a method to limit how much memory can
be used.  It accepts a string and can be a number of bytes or use a
suffix, eg.: @code{"2G"}.
@item @code{priority} (default @code{#f})
This is the priority of the swap device created from the zram device.
@xref{Swap Space} for a description of swap priorities.  You might want
to set a specific priority for the zram device, otherwise it could end
up not being used much for the reasons described there.
@end table

@end deftp
@end defvar

@node Hurd Services
@subsection Hurd Services

@defvar hurd-console-service-type
This service starts the fancy @code{VGA} console client on the Hurd.

The service's value is a @code{hurd-console-configuration} record.
@end defvar

@deftp {Data Type} hurd-console-configuration
This is the data type representing the configuration for the
hurd-console-service.

@table @asis
@item @code{hurd} (default: @var{hurd})
The Hurd package to use.
@end table
@end deftp

@defvar hurd-getty-service-type
This service starts a tty using the Hurd @code{getty} program.

The service's value is a @code{hurd-getty-configuration} record.
@end defvar

@deftp {Data Type} hurd-getty-configuration
This is the data type representing the configuration for the
hurd-getty-service.

@table @asis
@item @code{hurd} (default: @var{hurd})
The Hurd package to use.

@item @code{tty}
The name of the console this Getty runs on---e.g., @code{"tty1"}.

@item @code{baud-rate} (default: @code{38400})
An integer specifying the baud rate of the tty.

@end table
@end deftp

@node Miscellaneous Services
@subsection Miscellaneous Services

@cindex fingerprint
@subsubheading Fingerprint Service

The @code{(gnu services authentication)} module provides a DBus service to
read and identify fingerprints via a fingerprint sensor.

@defvar fprintd-service-type
The service type for @command{fprintd}, which provides the fingerprint
reading capability.

@lisp
(service fprintd-service-type)
@end lisp
@end defvar

@cindex sysctl
@subsubheading System Control Service

The @code{(gnu services sysctl)} provides a service to configure kernel
parameters at boot.

@defvar sysctl-service-type
The service type for @command{sysctl}, which modifies kernel parameters
under @file{/proc/sys/}.  To enable IPv4 forwarding, it can be
instantiated as:

@lisp
(service sysctl-service-type
         (sysctl-configuration
           (settings '(("net.ipv4.ip_forward" . "1")))))
@end lisp

Since @code{sysctl-service-type} is used in the default lists of
services, @code{%base-services} and @code{%desktop-services}, you can
use @code{modify-services} to change its configuration and add the
kernel parameters that you want (@pxref{Service Reference,
@code{modify-services}}).

@lisp
(modify-services %base-services
  (sysctl-service-type config =>
                       (sysctl-configuration
                         (settings (append '(("net.ipv4.ip_forward" . "1"))
                                           %default-sysctl-settings)))))
@end lisp

@end defvar

@deftp {Data Type} sysctl-configuration
The data type representing the configuration of @command{sysctl}.

@table @asis
@item @code{sysctl} (default: @code{(file-append procps "/sbin/sysctl"})
The @command{sysctl} executable to use.

@item @code{settings} (default: @code{%default-sysctl-settings})
An association list specifies kernel parameters and their values.
@end table
@end deftp

@defvar %default-sysctl-settings
An association list specifying the default @command{sysctl} parameters
on Guix System.
@end defvar

@cindex pcscd
@subsubheading PC/SC Smart Card Daemon Service

The @code{(gnu services security-token)} module provides the following service
to run @command{pcscd}, the PC/SC Smart Card Daemon.  @command{pcscd} is the
daemon program for pcsc-lite and the MuscleCard framework.  It is a resource
manager that coordinates communications with smart card readers, smart cards
and cryptographic tokens that are connected to the system.

@defvar pcscd-service-type
Service type for the @command{pcscd} service.  Its value must be a
@code{pcscd-configuration} object.  To run pcscd in the default
configuration, instantiate it as:

@lisp
(service pcscd-service-type)
@end lisp
@end defvar

@deftp {Data Type} pcscd-configuration
The data type representing the configuration of @command{pcscd}.

@table @asis
@item @code{pcsc-lite} (default: @code{pcsc-lite})
The pcsc-lite package that provides pcscd.
@item @code{usb-drivers} (default: @code{(list ccid)})
List of packages that provide USB drivers to pcscd.  Drivers are expected to be
under @file{pcsc/drivers} in the store directory of the package.
@end table
@end deftp

@cindex LIRC
@subsubheading LIRC Service

The @code{(gnu services lirc)} module provides the following service.

@defvar lirc-service-type
Type for a service that runs @url{http://www.lirc.org, LIRC}, a daemon
that decodes infrared signals from remote controls.

The value for this service is a @code{<lirc-configuration>} object.
@end defvar

@deftp {Data Type} lirc-configuration
Data type representing the configuration of @command{lircd}.

@table @asis
@item @code{lirc} (default: @code{lirc}) (type: file-like)
Package object for @command{lirc}.

@item @code{device} (default: @code{#f}) (type: string)
@itemx @code{driver} (default: @code{#f}) (type: string)
@itemx @code{config-file} (default: @code{#f}) (type: string-or-file-like)
TODO.  See @command{lircd} manual for details.

@item @code{extra-options} (default: @code{'()}) (type: list-of-string)
Additional command-line options to pass to @command{lircd}.

@end table
@end deftp

@c TODO: Document <lirc-configuration>, preferably by refactoring this to use
@c       define-configuration and generating documentation from it.

@cindex SPICE
@subsubheading SPICE Service

The @code{(gnu services spice)} module provides the following service.

@defvar spice-vdagent-service-type
Type of the service that runs @url{https://www.spice-space.org, VDAGENT},
a daemon that enables sharing the clipboard with a vm and setting the
guest display resolution when the graphical console window resizes.
@end defvar

@deftp {Data Type} spice-vdagent-configuration
Data type representing the configuration of
@code{spice-vdagent-service-type}.

@table @asis
@item @code{spice-vdagent} (default: @code{spice-vdagent}) (type: file-like)
Package object for VDAGENT.

@end table
@end deftp

@cindex inputattach
@subsubheading inputattach Service

@cindex tablet input, for Xorg
@cindex touchscreen input, for Xorg
The @uref{https://linuxwacom.github.io/, inputattach} service allows you to
use input devices such as Wacom tablets, touchscreens, or joysticks with the
Xorg display server.

@defvar inputattach-service-type
Type of a service that runs @command{inputattach} on a device and
dispatches events from it.
@end defvar

@deftp {Data Type} inputattach-configuration
@table @asis
@item @code{device-type} (default: @code{"wacom"})
The type of device to connect to.  Run @command{inputattach --help}, from the
@code{inputattach} package, to see the list of supported device types.

@item @code{device} (default: @code{"/dev/ttyS0"})
The device file to connect to the device.

@item @code{baud-rate} (default: @code{#f})
Baud rate to use for the serial connection.
Should be a number or @code{#f}.

@item @code{log-file} (default: @code{#f})
If true, this must be the name of a file to log messages to.
@end table
@end deftp

@subsubheading Dictionary Service
@cindex dictionary

The @code{(gnu services dict)} module provides the following service:

@defvar dicod-service-type
This is the type of the service that runs the @command{dicod} daemon, an
implementation of DICT server (@pxref{Dicod,,, dico, GNU Dico Manual}).

You can add @command{open localhost} to your @file{~/.dico} file to make
@code{localhost} the default server for @command{dico} client
(@pxref{Initialization File,,, dico, GNU Dico Manual}).

@quotation Note
This service is also available for Guix Home, where it runs directly
with your user privileges (@pxref{Miscellaneous Home Services,
@code{home-dicod-service-type}}).
@end quotation
@end defvar

@deftp {Data Type} dicod-configuration
Data type representing the configuration of dicod.

@table @asis
@item @code{dico} (default: @var{dico})
Package object of the GNU Dico dictionary server.

@item @code{interfaces} (default: @var{'("localhost")})
This is the list of IP addresses and ports and possibly socket file
names to listen to (@pxref{Server Settings, @code{listen} directive,,
dico, GNU Dico Manual}).

@item @code{handlers} (default: @var{'()})
List of @code{<dicod-handler>} objects denoting handlers (module instances).

@item @code{databases} (default: @var{(list %dicod-database:gcide)})
List of @code{<dicod-database>} objects denoting dictionaries to be served.
@end table
@end deftp

@deftp {Data Type} dicod-handler
Data type representing a dictionary handler (module instance).

@table @asis
@item @code{name}
Name of the handler (module instance).

@item @code{module} (default: @var{#f})
Name of the dicod module of the handler (instance).  If it is @code{#f},
the module has the same name as the handler.
(@pxref{Modules,,, dico, GNU Dico Manual}).

@item @code{options}
List of strings or gexps representing the arguments for the module handler
@end table
@end deftp

@deftp {Data Type} dicod-database
Data type representing a dictionary database.

@table @asis
@item @code{name}
Name of the database, will be used in DICT commands.

@item @code{handler}
Name of the dicod handler (module instance) used by this database
(@pxref{Handlers,,, dico, GNU Dico Manual}).

@item @code{complex?} (default: @var{#f})
Whether the database configuration complex.  The complex configuration
will need a corresponding @code{<dicod-handler>} object, otherwise not.

@item @code{options}
List of strings or gexps representing the arguments for the database
(@pxref{Databases,,, dico, GNU Dico Manual}).
@end table
@end deftp

@defvar %dicod-database:gcide
A @code{<dicod-database>} object serving the GNU Collaborative International
Dictionary of English using the @code{gcide} package.
@end defvar

The following is an example @code{dicod-service-type} configuration.

@lisp
(service dicod-service-type
         (dicod-configuration
          (handlers (list
                     (dicod-handler
                      (name "wordnet")
                      (module "wordnet")
                      (options
                       (list #~(string-append "wnhome=" #$wordnet))))))
          (databases (list
                      (dicod-database
                       (name "wordnet")
                       (complex? #t)
                       (handler "wordnet"))
                      %dicod-database:gcide))))
@end lisp

@cindex Docker
@subsubheading Docker Service

The @code{(gnu services docker)} module provides the following services.

@cindex containerd, container runtime
@defvar containerd-service-type

This service type operates containerd
@url{https://containerd.io,containerd}, a daemon responsible for
overseeing the entire container lifecycle on its host system. This
includes image handling, storage management, container execution,
supervision, low-level storage operations, network connections, and
more.

@end defvar

@deftp {Data Type} containerd-configuration
This is the data type representing the configuration of containerd.

@table @asis

@item @code{containerd} (default: @code{containerd})
The containerd daemon package to use.

@item @code{debug?} (default @code{#f})
Enable or disable debug output.

@item @code{environment-variables} (default: @code{'()})
List of environment variables to set for @command{containerd}.

This must be a list of strings where each string has the form
@samp{@var{key}=@var{value}} as in this example:

@lisp
(list "HTTP_PROXY=socks5://127.0.0.1:9150"
      "HTTPS_PROXY=socks5://127.0.0.1:9150")
@end lisp

@end table
@end deftp

@defvar docker-service-type

This is the type of the service that runs @url{https://www.docker.com,Docker},
a daemon that can execute application bundles (sometimes referred to as
``containers'') in isolated environments.

The @code{containerd-service-type} service need to be added to a system
configuration, otherwise a message about not any service provides
@code{containerd} will be displayed during @code{guix system
reconfigure}.

@end defvar

@deftp {Data Type} docker-configuration
This is the data type representing the configuration of Docker and Containerd.

@table @asis

@item @code{docker} (default: @code{docker})
The Docker daemon package to use.

@item @code{docker-cli} (default: @code{docker-cli})
The Docker client package to use.

@item @code{containerd} (default: @var{containerd})
This field is deprecated in favor of @code{containerd-service-type} service.

@item @code{proxy} (default @var{docker-libnetwork-cmd-proxy})
The Docker user-land networking proxy package to use.

@item @code{enable-proxy?} (default @code{#t})
Enable or disable the use of the Docker user-land networking proxy.

@item @code{debug?} (default @code{#f})
Enable or disable debug output.

@item @code{enable-iptables?} (default @code{#t})
Enable or disable the addition of iptables rules.

@item @code{environment-variables} (default: @code{'()})
List of environment variables to set for @command{dockerd}.

This must be a list of strings where each string has the form
@samp{@var{key}=@var{value}} as in this example:

@lisp
(list "LANGUAGE=eo:ca:eu"
      "TMPDIR=/tmp/dockerd")
@end lisp

@item @code{config-file} (type: maybe-file-like)
JSON configuration file pass to @command{dockerd}.

@end table
@end deftp

@cindex Singularity, container service
@defvar singularity-service-type
This is the type of the service that allows you to run
@url{https://www.sylabs.io/singularity/, Singularity}, a Docker-style tool to
create and run application bundles (aka. ``containers'').  The value for this
service is the Singularity package to use.

The service does not install a daemon; instead, it installs helper programs as
setuid-root (@pxref{Privileged Programs}) such that unprivileged users can
invoke @command{singularity run} and similar commands.
@end defvar

@cindex OCI-backed, Shepherd services
@subsubheading OCI backed services

Should you wish to manage your Docker containers with the same consistent
interface you use for your other Shepherd services,
@var{oci-container-service-type} is the tool to use: given an
@acronym{Open Container Initiative, OCI} container image, it will run it in a
Shepherd service.  One example where this is useful: it lets you run services
that are available as Docker/OCI images but not yet packaged for Guix.

@defvar oci-container-service-type

This is a thin wrapper around Docker's CLI that executes OCI images backed
processes as Shepherd Services.

@lisp
(service oci-container-service-type
         (list
          (oci-container-configuration
           (network "host")
           (image
            (oci-image
             (repository "guile")
             (tag "3")
             (value (specifications->manifest '("guile")))
             (pack-options '(#:symlinks (("/bin/guile" -> "bin/guile"))
                             #:max-layers 2))))
           (entrypoint "/bin/guile")
           (command
            '("-c" "(display \"hello!\n\")")))
          (oci-container-configuration
           (image "prom/prometheus")
           (ports
             '(("9000" . "9000")
               ("9090" . "9090"))))
          (oci-container-configuration
           (image "grafana/grafana:10.0.1")
           (network "host")
           (volumes
             '("/var/lib/grafana:/var/lib/grafana")))))
@end lisp

In this example three different Shepherd services are going be added to the
system.  Each @code{oci-container-configuration} record translates to a
@code{docker run} invocation and its fields directly map to options.  You can
refer to the
@url{https://docs.docker.com/engine/reference/commandline/run,upstream},
documentation for the semantics of each value.  If the images are not found they
will be
@url{https://docs.docker.com/engine/reference/commandline/pull/,pulled}.  The
services with @code{(network "host")} are going to be attached to the host network
and are supposed to behave like native processes with regard to networking.

@end defvar

@c %start of fragment

@deftp {Data Type} oci-container-configuration
Available @code{oci-container-configuration} fields are:

@table @asis
@item @code{user} (default: @code{"oci-container"}) (type: string)
The user under whose authority docker commands will be run.

@item @code{group} (default: @code{"docker"}) (type: string)
The group under whose authority docker commands will be run.

@item @code{command} (default: @code{'()}) (type: list-of-strings)
Overwrite the default command (@code{CMD}) of the image.

@item @code{entrypoint} (default: @code{""}) (type: string)
Overwrite the default entrypoint (@code{ENTRYPOINT}) of the image.

@item @code{host-environment} (default: @code{'()}) (type: list)
Set environment variables in the host environment where @command{docker
run} is invoked.  This is especially useful to pass secrets from the
host to the container without having them on the @command{docker run}'s
command line: by setting the @code{MYSQL_PASSWORD} on the host and by passing
@code{--env MYSQL_PASSWORD} through the @code{extra-arguments} field, it is
possible to securely set values in the container environment.  This field's
value can be a list of pairs or strings, even mixed:

@lisp
(list '("LANGUAGE\" . "eo:ca:eu")
      "JAVA_HOME=/opt/java")
@end lisp

Pair members can be strings, gexps or file-like objects. Strings are passed
directly to @code{make-forkexec-constructor}.

@item @code{environment} (default: @code{'()}) (type: list)
Set environment variables. This can be a list of pairs or strings, even mixed:

@lisp
(list '("LANGUAGE" . "eo:ca:eu")
      "JAVA_HOME=/opt/java")
@end lisp

Pair members can be strings, gexps or file-like objects.
Strings are passed directly to the Docker CLI.  You can refer to the
@uref{https://docs.docker.com/engine/reference/commandline/run/#env,upstream}
documentation for semantics.

@item @code{image} (type: string-or-oci-image)
The image used to build the container.  It can be a string or an
@code{oci-image} record.  Strings are resolved by the Docker Engine, and
follow the usual format
@code{myregistry.local:5000/testing/test-image:tag}.

@item @code{provision} (default: @code{""}) (type: string)
Set the name of the provisioned Shepherd service.

@item @code{requirement} (default: @code{'()}) (type: list-of-symbols)
Set additional Shepherd services dependencies to the provisioned
Shepherd service.

@item @code{log-file} (type: maybe-string)
When @code{log-file} is set, it names the file to which the service's
standard output and standard error are redirected.  @code{log-file} is created
if it does not exist, otherwise it is appended to.

@item @code{auto-start?} (default: @code{#t}) (type: boolean)
Whether this service should be started automatically by the Shepherd.  If it
is @code{#f} the service has to be started manually with @command{herd start}.

@item @code{respawn?} (default: @code{#f}) (type: boolean)
Whether to have Shepherd restart the service when it stops, for instance when
the underlying process dies.

@item @code{shepherd-actions} (default: @code{'()}) (type: list-of-symbols)
This is a list of @code{shepherd-action} records defining actions supported
by the service.

@item @code{network} (default: @code{""}) (type: string)
Set a Docker network for the spawned container.

@item @code{ports} (default: @code{'()}) (type: list)
Set the port or port ranges to expose from the spawned container.  This can be a
list of pairs or strings, even mixed:

@lisp
(list '("8080" . "80")
      "10443:443")
@end lisp

Pair members can be strings, gexps or file-like objects.
Strings are passed directly to the Docker CLI.  You can refer to the
@uref{https://docs.docker.com/engine/reference/commandline/run/#publish,upstream}
documentation for semantics.

@item @code{volumes} (default: @code{'()}) (type: list)
Set volume mappings for the spawned container.  This can be a
list of pairs or strings, even mixed:

@lisp
(list '("/root/data/grafana" . "/var/lib/grafana")
      "/gnu/store:/gnu/store")
@end lisp

Pair members can be strings, gexps or file-like objects.
Strings are passed directly to the Docker CLI.  You can refer to the
@uref{https://docs.docker.com/engine/reference/commandline/run/#volume,upstream}
documentation for semantics.

@item @code{container-user} (default: @code{""}) (type: string)
Set the current user inside the spawned container.  You can refer to the
@url{https://docs.docker.com/engine/reference/run/#user,upstream}
documentation for semantics.

@item @code{workdir} (default: @code{""}) (type: string)
Set the current working for the spawned Shepherd service.
You can refer to the
@url{https://docs.docker.com/engine/reference/run/#workdir,upstream}
documentation for semantics.

@item @code{extra-arguments} (default: @code{'()}) (type: list)
A list of strings, gexps or file-like objects that will be directly
passed to the @command{docker run} invokation.

@end table

@end deftp


@c %end of fragment

@c %start of fragment

@deftp {Data Type} oci-image
Available @code{oci-image} fields are:

@table @asis
@item @code{repository} (type: string)
A string like @code{myregistry.local:5000/testing/test-image} that names
the OCI image.

@item @code{tag} (default: @code{"latest"}) (type: string)
A string representing the OCI image tag.  Defaults to @code{latest}.

@item @code{value} (type: oci-lowerable-image)
A @code{manifest} or @code{operating-system} record that will be lowered
into an OCI compatible tarball.  Otherwise this field's value can be a
gexp or a file-like object that evaluates to an OCI compatible tarball.

@item @code{pack-options} (default: @code{'()}) (type: list)
An optional set of keyword arguments that will be passed to the
@code{docker-image} procedure from @code{guix scripts pack}.  They can
be used to replicate @command{guix pack} behavior:

@lisp
(oci-image
  (repository "guile")
  (tag "3")
  (value
    (specifications->manifest '("guile")))
  (pack-options '(#:symlinks (("/bin/guile" -> "bin/guile"))
                  #:max-layers 2)))
@end lisp

If the @code{value} field is an @code{operating-system} record, this field's
value will be ignored.

@item @code{system} (default: @code{""}) (type: string)
Attempt to build for a given system, e.g. "i686-linux"

@item @code{target} (default: @code{""}) (type: string)
Attempt to cross-build for a given triple, e.g. "aarch64-linux-gnu"

@item @code{grafts?} (default: @code{#f}) (type: boolean)
Whether to allow grafting or not in the pack build.

@end table

@end deftp


@c %end of fragment

@cindex Audit
@subsubheading Auditd Service

The @code{(gnu services auditd)} module provides the following service.

@defvar auditd-service-type

This is the type of the service that runs
@url{https://people.redhat.com/sgrubb/audit/,auditd},
a daemon that tracks security-relevant information on your system.

Examples of things that can be tracked:

@enumerate
@item
File accesses
@item
System calls
@item
Invoked commands
@item
Failed login attempts
@item
Firewall filtering
@item
Network access
@end enumerate

@command{auditctl} from the @code{audit} package can be used in order
to add or remove events to be tracked (until the next reboot).
In order to permanently track events, put the command line arguments
of auditctl into a file called @code{audit.rules} in the configuration
directory (see below).
@command{aureport} from the @code{audit} package can be used in order
to view a report of all recorded events.
The audit daemon by default logs into the file
@file{/var/log/audit.log}.

@end defvar

@deftp {Data Type} auditd-configuration
This is the data type representing the configuration of auditd.

@table @asis

@item @code{audit} (default: @code{audit})
The audit package to use.

@item @code{configuration-directory} (default: @code{%default-auditd-configuration-directory})
The directory containing the configuration file for the audit package, which
must be named @code{auditd.conf}, and optionally some audit rules to
instantiate on startup.

@end table
@end deftp

@cindex rshiny
@subsubheading R-Shiny service

The @code{(gnu services science)} module provides the following service.

@defvar rshiny-service-type

This is a type of service which is used to run a webapp created with
@code{r-shiny}.  This service sets the @env{R_LIBS_USER} environment
variable and runs the provided script to call @code{runApp}.

@deftp {Data Type} rshiny-configuration
This is the data type representing the configuration of rshiny.

@table @asis

@item @code{package} (default: @code{r-shiny})
The package to use.

@item @code{binary} (default @code{"rshiny"})
The name of the binary or shell script located at @code{package/bin/} to
run when the service is run.

The common way to create this file is as follows:

@lisp
@dots{}
(let* ((out       (assoc-ref %outputs "out"))
       (targetdir (string-append out "/share/" ,name))
       (app       (string-append out "/bin/" ,name))
       (Rbin      (search-input-file %build-inputs "/bin/Rscript")))
  ;; @dots{}
  (mkdir-p (string-append out "/bin"))
  (call-with-output-file app
    (lambda (port)
      (format port
"#!~a
library(shiny)
setwd(\"~a\")
runApp(launch.browser=0, port=4202)~%\n"
      Rbin targetdir))))
@end lisp

@end table
@end deftp
@end defvar

@cindex Nix
@subsubheading Nix service

The @code{(gnu services nix)} module provides the following service.

@defvar nix-service-type

This is the type of the service that runs build daemon of the
@url{https://nixos.org/nix/, Nix} package manager.  Here is an example showing
how to use it:

@lisp
(use-modules (gnu))
(use-service-modules nix)
(use-package-modules package-management)

(operating-system
  ;; @dots{}
  (packages (append (list nix)
                    %base-packages))

  (services (append (list (service nix-service-type))
                    %base-services)))
@end lisp

After @command{guix system reconfigure} configure Nix for your user:

@itemize
@item Add a Nix channel and update it.  See
@url{https://wiki.nixos.org/wiki/Nix_channels, Nix channels} for more
information about the available channels.  If you would like to use the
unstable Nix channel you can do this by running:

@example
$ nix-channel --add https://nixos.org/channels/nixpkgs-unstable
$ nix-channel --update
@end example

@item Create your Nix profile directory:

@example
$ sudo mkdir -p /nix/var/nix/profiles/per-user/$USER
$ sudo chown $USER:root /nix/var/nix/profiles/per-user/$USER
@end example

@item Create a symlink to your profile and activate Nix profile:

@example
$ ln -s "/nix/var/nix/profiles/per-user/$USER/profile" ~/.nix-profile
$ source /run/current-system/profile/etc/profile.d/nix.sh
@end example

@end itemize

@end defvar

@deftp {Data Type} nix-configuration
This data type represents the configuration of the Nix daemon.

@table @asis
@item @code{nix} (default: @code{nix})
The Nix package to use.

@item @code{sandbox} (default: @code{#t})
Specifies whether builds are sandboxed by default.

@item @code{build-directory} (default: @code{"/tmp"})
The directory where build directory are stored during builds.
This is useful to change if, for example, the default location does not
have enough space to hold build trees for big packages.

This is similar to setting the @env{TMPDIR} environment variable for
@command{guix-daemon}.  @ref{Build Environment Setup, @env{TMPDIR}},
for more info.

@item @code{build-sandbox-items} (default: @code{'()})
This is a list of strings or objects appended to the
@code{build-sandbox-items} field of the configuration file.

@item @code{extra-config} (default: @code{'()})
This is a list of strings or objects appended to the configuration file.
It is used to pass extra text to be added verbatim to the configuration
file.

@item @code{extra-options} (default: @code{'()})
Extra command line options for @code{nix-service-type}.
@end table
@end deftp

@cindex Fail2Ban
@subsubheading Fail2Ban service

@uref{http://www.fail2ban.org/, @code{fail2ban}} scans log files
(e.g. @code{/var/log/apache/error_log}) and bans IP addresses that show
malicious signs -- repeated password failures, attempts to make use of
exploits, etc.

@code{fail2ban-service-type} service type is provided by the @code{(gnu
services security)} module.

This service type runs the @code{fail2ban} daemon.  It can be configured
in various ways, which are:

@table @asis
@item Basic configuration
The basic parameters of the Fail2Ban service can be configured via its
@code{fail2ban} configuration, which is documented below.

@item User-specified jail extensions
The @code{fail2ban-jail-service} function can be used to add new
Fail2Ban jails.

@item Shepherd extension mechanism
Service developers can extend the @code{fail2ban-service-type} service
type itself via the usual service extension mechanism.
@end table

@defvar fail2ban-service-type

This is the type of the service that runs @code{fail2ban} daemon.  Below
is an example of a basic, explicit configuration:

@lisp
(append
 (list
  (service fail2ban-service-type
           (fail2ban-configuration
            (extra-jails
             (list
              (fail2ban-jail-configuration
               (name "sshd")
               (enabled? #t))))))
  ;; There is no implicit dependency on an actual SSH
  ;; service, so you need to provide one.
  (service openssh-service-type))
 %base-services)
@end lisp
@end defvar

@deffn {Procedure} fail2ban-jail-service svc-type jail
Extend @var{svc-type}, a @code{<service-type>} object with @var{jail}, a
@code{fail2ban-jail-configuration} object.

For example:

@lisp
(append
 (list
  (service
   ;; The 'fail2ban-jail-service' procedure can extend any service type
   ;; with a fail2ban jail.  This removes the requirement to explicitly
   ;; extend services with fail2ban-service-type.
   (fail2ban-jail-service
    openssh-service-type
    (fail2ban-jail-configuration
     (name "sshd")
     (enabled? #t)))
   (openssh-configuration ...))))
@end lisp
@end deffn

Below is the reference for the different @code{jail-service-type}
configuration records.

@c The documentation is to be auto-generated via
@c 'generate-documentation'.  See at the bottom of (gnu services
@c security).

@deftp {Data Type} fail2ban-configuration
Available @code{fail2ban-configuration} fields are:

@table @asis
@item @code{fail2ban} (default: @code{fail2ban}) (type: package)
The @code{fail2ban} package to use.  It is used for both binaries and as
base default configuration that is to be extended with
@code{<fail2ban-jail-configuration>} objects.

@item @code{run-directory} (default: @code{"/var/run/fail2ban"}) (type: string)
The state directory for the @code{fail2ban} daemon.

@item @code{jails} (default: @code{'()}) (type: list-of-fail2ban-jail-configurations)
Instances of @code{<fail2ban-jail-configuration>} collected from
extensions.

@item @code{extra-jails} (default: @code{'()}) (type: list-of-fail2ban-jail-configurations)
Instances of @code{<fail2ban-jail-configuration>} explicitly provided.

@item @code{extra-content} (default: @code{'()}) (type: text-config)
Extra raw content to add to the end of the @file{jail.local} file,
provided as a list of file-like objects.

@end table

@end deftp

@deftp {Data Type} fail2ban-ignore-cache-configuration
Available @code{fail2ban-ignore-cache-configuration} fields are:

@table @asis
@item @code{key} (type: string)
Cache key.

@item @code{max-count} (type: integer)
Cache size.

@item @code{max-time} (type: integer)
Cache time.

@end table

@end deftp

@deftp {Data Type} fail2ban-jail-action-configuration
Available @code{fail2ban-jail-action-configuration} fields are:

@table @asis
@item @code{name} (type: string)
Action name.

@item @code{arguments} (default: @code{'()}) (type: list-of-arguments)
Action arguments.

@end table

@end deftp

@deftp {Data Type} fail2ban-jail-configuration
Available @code{fail2ban-jail-configuration} fields are:

@table @asis
@item @code{name} (type: string)
Required name of this jail configuration.

@item @code{enabled?} (default: @code{#t}) (type: boolean)
Whether this jail is enabled.

@item @code{backend} (type: maybe-symbol)
Backend to use to detect changes in the @code{log-path}.  The default is
'auto.  To consult the defaults of the jail configuration, refer to the
@file{/etc/fail2ban/jail.conf} file of the @code{fail2ban} package.

@item @code{max-retry} (type: maybe-integer)
The number of failures before a host gets banned (e.g.  @code{(max-retry
5)}).

@item @code{max-matches} (type: maybe-integer)
The number of matches stored in ticket (resolvable via tag
@code{<matches>}) in action.

@item @code{find-time} (type: maybe-string)
The time window during which the maximum retry count must be reached for
an IP address to be banned.  A host is banned if it has generated
@code{max-retry} during the last @code{find-time} seconds (e.g.
@code{(find-time "10m")}).  It can be provided in seconds or using
Fail2Ban's "time abbreviation format", as described in @command{man 5
jail.conf}.

@item @code{ban-time} (type: maybe-string)
The duration, in seconds or time abbreviated format, that a ban should
last.  (e.g.  @code{(ban-time "10m")}).

@item @code{ban-time-increment?} (type: maybe-boolean)
Whether to consider past bans to compute increases to the default ban
time of a specific IP address.

@item @code{ban-time-factor} (type: maybe-string)
The coefficient to use to compute an exponentially growing ban time.

@item @code{ban-time-formula} (type: maybe-string)
This is the formula used to calculate the next value of a ban time.

@item @code{ban-time-multipliers} (type: maybe-string)
Used to calculate next value of ban time instead of formula.

@item @code{ban-time-max-time} (type: maybe-string)
The maximum number of seconds a ban should last.

@item @code{ban-time-rnd-time} (type: maybe-string)
The maximum number of seconds a randomized ban time should last.  This
can be useful to stop ``clever'' botnets calculating the exact time an
IP address can be unbanned again.

@item @code{ban-time-overall-jails?} (type: maybe-boolean)
When true, it specifies the search of an IP address in the database
should be made across all jails.  Otherwise, only the current jail of
the ban IP address is considered.

@item @code{ignore-self?} (type: maybe-boolean)
Never ban the local machine's own IP address.

@item @code{ignore-ip} (default: @code{'()}) (type: list-of-strings)
A list of IP addresses, CIDR masks or DNS hosts to ignore.
@code{fail2ban} will not ban a host which matches an address in this
list.

@item @code{ignore-cache} (type: maybe-fail2ban-ignore-cache-configuration)
Provide cache parameters for the ignore failure check.

@item @code{filter} (type: maybe-fail2ban-jail-filter-configuration)
The filter to use by the jail, specified via a
@code{<fail2ban-jail-filter-configuration>} object.  By default, jails
have names matching their filter name.

@item @code{log-time-zone} (type: maybe-string)
The default time zone for log lines that do not have one.

@item @code{log-encoding} (type: maybe-symbol)
The encoding of the log files handled by the jail.  Possible values are:
@code{'ascii}, @code{'utf-8} and @code{'auto}.

@item @code{log-path} (default: @code{'()}) (type: list-of-strings)
The file names of the log files to be monitored.

@item @code{action} (default: @code{'()}) (type: list-of-fail2ban-jail-actions)
A list of @code{<fail2ban-jail-action-configuration>}.

@item @code{extra-content} (default: @code{'()}) (type: text-config)
Extra content for the jail configuration, provided as a list of file-like
objects.

@end table

@end deftp

@deftp {Data Type} fail2ban-jail-filter-configuration
Available @code{fail2ban-jail-filter-configuration} fields are:

@table @asis
@item @code{name} (type: string)
Filter to use.

@item @code{mode} (type: maybe-string)
Mode for filter.

@end table

@end deftp

@c End of auto-generated fail2ban documentation.

@cindex Backup
@subsubheading Backup Services

The @code{(gnu services backup)} module offers services for backing up
file system trees.  For now, it provides the @code{restic-backup-service-type}.

With @code{restic-backup-service-type}, you can periodically back up
directories and files with @uref{https://restic.net/, Restic}, which
supports end-to-end encryption and deduplication.  Consider the
following configuration:

@lisp
(use-service-modules backup @dots{}) ;for 'restic-backup-service-type'
(use-package-modules sync @dots{})   ;for 'rclone'

(operating-system
  ;; @dots{}
  (packages (append (list rclone)    ;for use by restic
                    %base-packages))
  (services
    (list
      (service restic-backup-service-type
               (restic-backup-configuration
                 (jobs
                   (list (restic-backup-job
                           (name "remote-ftp")
                           (repository "rclone:remote-ftp:backup/restic")
                           (password-file "/root/.restic")
                           ;; Every day at 23.
                           (schedule "0 23 * * *")
                           (files '("/root/.restic"
                                    "/root/.config/rclone"
                                    "/etc/ssh/ssh_host_rsa_key"
                                    "/etc/ssh/ssh_host_rsa_key.pub"
                                    "/etc/guix/signing-key.pub"
                                    "/etc/guix/signing-key.sec"))))))))))
@end lisp

Each @code{restic-backup-job} translates to an mcron job which sets the
@env{RESTIC_PASSWORD} environment variable by reading the first line of
@code{password-file} and runs @command{restic backup}, creating backups
using rclone of all the files listed in the @code{files} field.

The @code{restic-backup-service-type} installs as well @code{restic-guix}
to the system profile, a @code{restic} utility wrapper that allows for easier
interaction with the Guix configured backup jobs.  For example the following
could be used to instantaneusly trigger a backup for the above shown
configuration, without waiting for the scheduled job:

@example
restic-guix backup remote-ftp
@end example

@c %start of fragment

@deftp {Data Type} restic-backup-configuration
Available @code{restic-backup-configuration} fields are:

@table @asis
@item @code{jobs} (default: @code{'()}) (type: list-of-restic-backup-jobs)
The list of backup jobs for the current system.

@end table

@end deftp


@c %end of fragment

@c %start of fragment

@deftp {Data Type} restic-backup-job
Available @code{restic-backup-job} fields are:

@table @asis
@item @code{restic} (default: @code{restic}) (type: package)
The restic package to be used for the current job.

@item @code{user} (default: @code{"root"}) (type: string)
The user used for running the current job.

@item @code{repository} (type: string)
The restic repository target of this job.

@item @code{name} (type: string)
A string denoting a name for this job.

@item @code{password-file} (type: string)
Name of the password file, readable by the configured @code{user},
that will be used to set the @env{RESTIC_PASSWORD} environment variable
for the current job.

@item @code{schedule} (type: gexp-or-string)
A string or a gexp that will be passed as time specification in the
mcron job specification (@pxref{Syntax, mcron job specifications,,
mcron,GNU@tie{}mcron}).

@item @code{files} (default: @code{'()}) (type: list-of-lowerables)
The list of files or directories to be backed up.  It must be a list of
values that can be lowered to strings.

@item @code{verbose?} (default: @code{#f}) (type: boolean)
Whether to enable verbose output for the current backup job.

@item @code{extra-flags} (default: @code{'()}) (type: list-of-lowerables)
A list of values that are lowered to strings.  These will be passed as
command-line arguments to the current job @command{restic backup}
invokation.

@end table

@end deftp


@c %end of fragment

@node Privileged Programs
@section Privileged Programs

@cindex privileged programs
@cindex setuid programs
@cindex setgid programs
@cindex capabilities, POSIX
@cindex setcap
Some programs need to run with elevated privileges, even when they are
launched by unprivileged users.  A notorious example is the
@command{passwd} program, which users can run to change their
password, and which needs to access the @file{/etc/passwd} and
@file{/etc/shadow} files---something normally restricted to root, for
obvious security reasons.  To address that, @command{passwd} should be
@dfn{setuid-root}, meaning that it always runs with root privileges
(@pxref{How Change Persona,,, libc, The GNU C Library Reference Manual},
for more info about the setuid mechanism).

The store itself @emph{cannot} contain privileged programs: that would be
a security issue since any user on the system can write derivations that
populate the store (@pxref{The Store}).  Thus, a different mechanism is
used: instead of directly granting permissions to files that are in
the store, we let the system administrator @emph{declare} which
programs should be entrusted with these additional privileges.

The @code{privileged-programs} field of an @code{operating-system}
declaration contains a list of @code{<privileged-program>} denoting the
names of programs to have a setuid or setgid bit set (@pxref{Using the
Configuration System}).  For instance, the @command{mount.nfs} program,
which is part of the nfs-utils package, with a setuid root can be
designated like this:

@lisp
(privileged-program
  (program (file-append nfs-utils "/sbin/mount.nfs"))
  (setuid? #t))
@end lisp

And then, to make @command{mount.nfs} setuid on your system, add the
previous example to your operating system declaration by appending it to
@code{%default-privileged-programs} like this:

@lisp
(operating-system
  ;; Some fields omitted...
  (privileged-programs
    (append (list (privileged-program
                    (program (file-append nfs-utils "/sbin/mount.nfs"))
                    (setuid? #t))
            %default-privileged-programs)))
@end lisp

@deftp {Data Type} privileged-program
This data type represents a program with special privileges, such as setuid

@table @asis
@item @code{program}
A file-like object to which all given privileges should apply.

@item @code{setuid?} (default: @code{#f})
Whether to set user setuid bit.

@item @code{setgid?} (default: @code{#f})
Whether to set group setgid bit.

@item @code{user} (default: @code{0})
UID (integer) or user name (string) for the user owner of the program,
defaults to root.

@item @code{group} (default: @code{0})
GID (integer) group name (string) for the group owner of the program,
defaults to root.

@item @code{capabilities} (default: @code{#f})
A string representing the program's POSIX capabilities, as described by
the @code{cap_to_text(3)} man page from the libcap package, or @code{#f}
to make no changes.

@end table
@end deftp

A default set of privileged programs is defined by the
@code{%default-privileged-programs} variable of the @code{(gnu system)} module.

@defvar {Scheme Variable} %default-privileged-programs
A list of @code{<privileged-program>} denoting common programs with
elevated privileges.

The list includes commands such as @command{passwd}, @command{ping},
@command{su}, and @command{sudo}.
@end defvar

Under the hood, the actual privileged programs are created in the
@file{/run/privileged/bin} directory at system activation time.  The
files in this directory refer to the ``real'' binaries, which are in the
store.

@node X.509 Certificates
@section X.509 Certificates

@cindex HTTPS, certificates
@cindex X.509 certificates
@cindex TLS
Web servers available over HTTPS (that is, HTTP over the transport-layer
security mechanism, TLS) send client programs an @dfn{X.509 certificate}
that the client can then use to @emph{authenticate} the server.  To do
that, clients verify that the server's certificate is signed by a
so-called @dfn{certificate authority} (CA).  But to verify the CA's
signature, clients must have first acquired the CA's certificate.

Web browsers such as GNU@tie{}IceCat include their own set of CA
certificates, such that they are able to verify CA signatures
out-of-the-box.

However, most other programs that can talk HTTPS---@command{wget},
@command{git}, @command{w3m}, etc.---need to be told where CA
certificates can be found.

@cindex @code{nss-certs}
For users of Guix System, this is done by adding a package that
provides certificates to the @code{packages} field of the
@code{operating-system} declaration (@pxref{operating-system
Reference}).  Guix includes one such package, @code{nss-certs}, which
is a set of CA certificates provided as part of Mozilla's Network
Security Services.

This package is part of @code{%base-packages}, so there is no need to
explicitly add it.  The @file{/etc/ssl/certs} directory, which is where
most applications and libraries look for certificates by default, points
to the certificates installed globally.

Unprivileged users, including users of Guix on a foreign distro,
can also install their own certificate package in
their profile.  A number of environment variables need to be defined so
that applications and libraries know where to find them.  Namely, the
OpenSSL library honors the @env{SSL_CERT_DIR} and @env{SSL_CERT_FILE}
variables.  Some applications add their own environment variables; for
instance, the Git version control system honors the certificate bundle
pointed to by the @env{GIT_SSL_CAINFO} environment variable.  Thus, you
would typically run something like:

@example
guix install nss-certs
export SSL_CERT_DIR="$HOME/.guix-profile/etc/ssl/certs"
export SSL_CERT_FILE="$HOME/.guix-profile/etc/ssl/certs/ca-certificates.crt"
export GIT_SSL_CAINFO="$SSL_CERT_FILE"
@end example

As another example, R requires the @env{CURL_CA_BUNDLE} environment
variable to point to a certificate bundle, so you would have to run
something like this:

@example
guix install nss-certs
export CURL_CA_BUNDLE="$HOME/.guix-profile/etc/ssl/certs/ca-certificates.crt"
@end example

For other applications you may want to look up the required environment
variable in the relevant documentation.


@node Name Service Switch
@section Name Service Switch

@cindex name service switch
@cindex NSS
The @code{(gnu system nss)} module provides bindings to the
configuration file of the libc @dfn{name service switch} or @dfn{NSS}
(@pxref{NSS Configuration File,,, libc, The GNU C Library Reference
Manual}).  In a nutshell, the NSS is a mechanism that allows libc to be
extended with new ``name'' lookup methods for system databases, which
includes host names, service names, user accounts, and more (@pxref{Name
Service Switch, System Databases and Name Service Switch,, libc, The GNU
C Library Reference Manual}).

The NSS configuration specifies, for each system database, which lookup
method is to be used, and how the various methods are chained
together---for instance, under which circumstances NSS should try the
next method in the list.  The NSS configuration is given in the
@code{name-service-switch} field of @code{operating-system} declarations
(@pxref{operating-system Reference, @code{name-service-switch}}).

@cindex nss-mdns
@cindex .local, host name lookup
As an example, the declaration below configures the NSS to use the
@uref{https://0pointer.de/lennart/projects/nss-mdns/, @code{nss-mdns}
back-end}, which supports host name lookups over multicast DNS (mDNS)
for host names ending in @code{.local}:

@lisp
(name-service-switch
   (hosts (list %files    ;first, check /etc/hosts

                ;; If the above did not succeed, try
                ;; with 'mdns_minimal'.
                (name-service
                  (name "mdns_minimal")

                  ;; 'mdns_minimal' is authoritative for
                  ;; '.local'.  When it returns "not found",
                  ;; no need to try the next methods.
                  (reaction (lookup-specification
                             (not-found => return))))

                ;; Then fall back to DNS.
                (name-service
                  (name "dns"))

                ;; Finally, try with the "full" 'mdns'.
                (name-service
                  (name "mdns")))))
@end lisp

Do not worry: the @code{%mdns-host-lookup-nss} variable (see below)
contains this configuration, so you will not have to type it if all you
want is to have @code{.local} host lookup working.

Note that, in this case, in addition to setting the
@code{name-service-switch} of the @code{operating-system} declaration,
you also need to use @code{avahi-service-type} (@pxref{Networking Services,
@code{avahi-service-type}}), or @code{%desktop-services}, which includes it
(@pxref{Desktop Services}).  Doing this makes @code{nss-mdns} accessible
to the name service cache daemon (@pxref{Base Services,
@code{nscd-service}}).

For convenience, the following variables provide typical NSS
configurations.

@defvar %default-nss
This is the default name service switch configuration, a
@code{name-service-switch} object.
@end defvar

@defvar %mdns-host-lookup-nss
This is the name service switch configuration with support for host name
lookup over multicast DNS (mDNS) for host names ending in @code{.local}.
@end defvar

The reference for name service switch configuration is given below.  It
is a direct mapping of the configuration file format of the C library , so
please refer to the C library manual for more information (@pxref{NSS
Configuration File,,, libc, The GNU C Library Reference Manual}).
Compared to the configuration file format of libc NSS, it has the advantage
not only of adding this warm parenthetic feel that we like, but also
static checks: you will know about syntax errors and typos as soon as you
run @command{guix system}.

@deftp {Data Type} name-service-switch

This is the data type representation the configuration of libc's name
service switch (NSS).  Each field below represents one of the supported
system databases.

@table @code
@item aliases
@itemx ethers
@itemx group
@itemx gshadow
@itemx hosts
@itemx initgroups
@itemx netgroup
@itemx networks
@itemx password
@itemx public-key
@itemx rpc
@itemx services
@itemx shadow
The system databases handled by the NSS@.  Each of these fields must be a
list of @code{<name-service>} objects (see below).
@end table
@end deftp

@deftp {Data Type} name-service

This is the data type representing an actual name service and the
associated lookup action.

@table @code
@item name
A string denoting the name service (@pxref{Services in the NSS
configuration,,, libc, The GNU C Library Reference Manual}).

Note that name services listed here must be visible to nscd.  This is
achieved by passing the @code{#:name-services} argument to
@code{nscd-service} the list of packages providing the needed name
services (@pxref{Base Services, @code{nscd-service}}).

@item reaction
An action specified using the @code{lookup-specification} macro
(@pxref{Actions in the NSS configuration,,, libc, The GNU C Library
Reference Manual}).  For example:

@lisp
(lookup-specification (unavailable => continue)
                      (success => return))
@end lisp
@end table
@end deftp

@node Initial RAM Disk
@section Initial RAM Disk

@cindex initrd
@cindex initial RAM disk
For bootstrapping purposes, the Linux-Libre kernel is passed an
@dfn{initial RAM disk}, or @dfn{initrd}.  An initrd contains a temporary
root file system as well as an initialization script.  The latter is
responsible for mounting the real root file system, and for loading any
kernel modules that may be needed to achieve that.

The @code{initrd-modules} field of an @code{operating-system}
declaration allows you to specify Linux-libre kernel modules that must
be available in the initrd.  In particular, this is where you would list
modules needed to actually drive the hard disk where your root partition
is---although the default value of @code{initrd-modules} should cover
most use cases.  For example, assuming you need the @code{megaraid_sas}
module in addition to the default modules to be able to access your root
file system, you would write:

@lisp
(operating-system
  ;; @dots{}
  (initrd-modules (cons "megaraid_sas" %base-initrd-modules)))
@end lisp

@defvar %base-initrd-modules
This is the list of kernel modules included in the initrd by default.
@end defvar

Furthermore, if you need lower-level customization, the @code{initrd}
field of an @code{operating-system} declaration allows
you to specify which initrd you would like to use.  The @code{(gnu
system linux-initrd)} module provides three ways to build an initrd: the
high-level @code{base-initrd} procedure and the low-level
@code{raw-initrd} and @code{expression->initrd} procedures.

The @code{base-initrd} procedure is intended to cover most common uses.
For example, if you want to add a bunch of kernel modules to be loaded
at boot time, you can define the @code{initrd} field of the operating
system declaration like this:

@lisp
(initrd (lambda (file-systems . rest)
          ;; Create a standard initrd but set up networking
          ;; with the parameters QEMU expects by default.
          (apply base-initrd file-systems
                 #:qemu-networking? #t
                 rest)))
@end lisp

The @code{base-initrd} procedure also handles common use cases that
involves using the system as a QEMU guest, or as a ``live'' system with
volatile root file system.

The @code{base-initrd} procedure is built from @code{raw-initrd} procedure.
Unlike @code{base-initrd}, @code{raw-initrd} doesn't do anything high-level,
such as trying to guess which kernel modules and packages should be included
to the initrd.  An example use of @code{raw-initrd} is when a user has
a custom Linux kernel configuration and default kernel modules included by
@code{base-initrd} are not available.

The initial RAM disk produced by @code{base-initrd} or @code{raw-initrd}
honors several options passed on the Linux kernel command line
(that is, arguments passed @i{via} the @code{linux} command of GRUB, or the
@code{-append} option of QEMU), notably:

@table @code
@item gnu.load=@var{boot}
Tell the initial RAM disk to load @var{boot}, a file containing a Scheme
program, once it has mounted the root file system.

Guix uses this option to yield control to a boot program that runs the
service activation programs and then spawns the GNU@tie{}Shepherd, the
initialization system.

@item root=@var{root}
Mount @var{root} as the root file system.  @var{root} can be a device
name like @code{/dev/sda1}, a file system label, or a file system UUID.
When unspecified, the device name from the root file system of the
operating system declaration is used.

@item rootfstype=@var{type}
Set the type of the root file system.  It overrides the @code{type}
field of the root file system specified via the @code{operating-system}
declaration, if any.

@item rootflags=@var{options}
Set the mount @emph{options} of the root file system.  It overrides the
@code{options} field of the root file system specified via the
@code{operating-system} declaration, if any.

@item fsck.mode=@var{mode}
Whether to check the @var{root} file system for errors before mounting
it.  @var{mode} is one of @code{skip} (never check), @code{force} (always
check), or @code{auto} to respect the root @code{<file-system>} object's
@code{check?} setting (@pxref{File Systems}) and run a full scan only if
the file system was not cleanly shut down.

@code{auto} is the default if this option is not present or if @var{mode}
is not one of the above.

@item fsck.repair=@var{level}
The level of repairs to perform automatically if errors are found in the
@var{root} file system.  @var{level} is one of @code{no} (do not write to
@var{root} at all if possible), @code{yes} (repair as much as possible),
or @code{preen} to repair problems considered safe to repair automatically.

@code{preen} is the default if this option is not present or if @var{level}
is not one of the above.

@item gnu.system=@var{system}
Have @file{/run/booted-system} and @file{/run/current-system} point to
@var{system}.

@item modprobe.blacklist=@var{modules}@dots{}
@cindex module, black-listing
@cindex black list, of kernel modules
Instruct the initial RAM disk as well as the @command{modprobe} command
(from the kmod package) to refuse to load @var{modules}.  @var{modules}
must be a comma-separated list of module names---e.g.,
@code{usbkbd,9pnet}.

@item gnu.repl
Start a read-eval-print loop (REPL) from the initial RAM disk before it
tries to load kernel modules and to mount the root file system.  Our
marketing team calls it @dfn{boot-to-Guile}.  The Schemer in you will
love it.  @xref{Using Guile Interactively,,, guile, GNU Guile Reference
Manual}, for more information on Guile's REPL.

@end table

Now that you know all the features that initial RAM disks produced by
@code{base-initrd} and @code{raw-initrd} provide,
here is how to use it and customize it further.

@cindex initrd
@cindex initial RAM disk
@deffn {Procedure} raw-initrd file-systems @
       [#:linux-modules '()] [#:pre-mount #t] [#:mapped-devices '()] @
       [#:keyboard-layout #f] [#:helper-packages '()] @
       [#:qemu-networking? #f] [#:volatile-root? #f]
Return a derivation that builds a raw initrd.  @var{file-systems} is
a list of file systems to be mounted by the initrd, possibly in addition to
the root file system specified on the kernel command line via @option{root}.
@var{linux-modules} is a list of kernel modules to be loaded at boot time.
@var{mapped-devices} is a list of device mappings to realize before
@var{file-systems} are mounted (@pxref{Mapped Devices}).
@var{pre-mount} is a G-expression to evaluate before realizing
@var{mapped-devices}.
@var{helper-packages} is a list of packages to be copied in the initrd.
       It may
include @code{e2fsck/static} or other packages needed by the initrd to check
the root file system.

When true, @var{keyboard-layout} is a @code{<keyboard-layout>} record denoting
the desired console keyboard layout.  This is done before @var{mapped-devices}
are set up and before @var{file-systems} are mounted such that, should the
user need to enter a passphrase or use the REPL, this happens using the
intended keyboard layout.

When @var{qemu-networking?} is true, set up networking with the standard QEMU
parameters.  When @var{virtio?} is true, load additional modules so that the
initrd can be used as a QEMU guest with para-virtualized I/O drivers.

When @var{volatile-root?} is true, the root file system is writable but any changes
to it are lost.
@end deffn

@deffn {Procedure} base-initrd file-systems @
       [#:mapped-devices '()] [#:keyboard-layout #f] @
       [#:qemu-networking? #f] [#:volatile-root? #f] @
       [#:linux-modules '()]
Return as a file-like object a generic initrd, with kernel
modules taken from @var{linux}.  @var{file-systems} is a list of file-systems to be
mounted by the initrd, possibly in addition to the root file system specified
on the kernel command line via @option{root}.  @var{mapped-devices} is a list of device
mappings to realize before @var{file-systems} are mounted.

When true, @var{keyboard-layout} is a @code{<keyboard-layout>} record denoting
the desired console keyboard layout.  This is done before @var{mapped-devices}
are set up and before @var{file-systems} are mounted such that, should the
user need to enter a passphrase or use the REPL, this happens using the
intended keyboard layout.

@var{qemu-networking?} and @var{volatile-root?} behaves as in @code{raw-initrd}.

The initrd is automatically populated with all the kernel modules necessary
for @var{file-systems} and for the given options.  Additional kernel
modules can be listed in @var{linux-modules}.  They will be added to the initrd, and
loaded at boot time in the order in which they appear.
@end deffn

Needless to say, the initrds we produce and use embed a
statically-linked Guile, and the initialization program is a Guile
program.  That gives a lot of flexibility.  The
@code{expression->initrd} procedure builds such an initrd, given the
program to run in that initrd.

@deffn {Procedure} expression->initrd exp @
       [#:guile %guile-static-initrd] [#:name "guile-initrd"]
Return as a file-like object a Linux initrd (a gzipped cpio archive)
containing @var{guile} and that evaluates @var{exp}, a G-expression,
upon booting.  All the derivations referenced by @var{exp} are
automatically copied to the initrd.
@end deffn

@node Bootloader Configuration
@section Bootloader Configuration

@cindex bootloader
@cindex boot loader

The operating system supports multiple bootloaders.  The bootloader is
configured using @code{bootloader-configuration} declaration.  All the
fields of this structure are bootloader agnostic except for one field,
@code{bootloader} that indicates the bootloader to be configured and
installed.

Some of the bootloaders do not honor every field of
@code{bootloader-configuration}.  For instance, the extlinux
bootloader does not support themes and thus ignores the @code{theme}
field.

@deftp {Data Type} bootloader-configuration
The type of a bootloader configuration declaration.

@table @asis

@item @code{bootloader}
@cindex EFI, bootloader
@cindex UEFI, bootloader
@cindex BIOS, bootloader
The bootloader to use, as a @code{bootloader} object.  For now
@code{grub-bootloader}, @code{grub-efi-bootloader},
@code{grub-efi-removable-bootloader}, @code{grub-efi-netboot-bootloader},
@code{grub-efi-netboot-removable-bootloader}, @code{extlinux-bootloader}
and @code{u-boot-bootloader} are supported.

@cindex ARM, bootloaders
@cindex AArch64, bootloaders
Available bootloaders are described in @code{(gnu bootloader @dots{})}
modules.  In particular, @code{(gnu bootloader u-boot)} contains definitions
of bootloaders for a wide range of ARM and AArch64 systems, using the
@uref{https://www.denx.de/wiki/U-Boot/, U-Boot bootloader}.

@vindex grub-bootloader
@code{grub-bootloader} allows you to boot in particular Intel-based machines
in ``legacy'' BIOS mode.

@vindex grub-efi-bootloader
@code{grub-efi-bootloader} allows to boot on modern systems using the
@dfn{Unified Extensible Firmware Interface} (UEFI).  This is what you should
use if the installation image contains a @file{/sys/firmware/efi} directory
when you boot it on your system.

@vindex grub-efi-removable-bootloader
@code{grub-efi-removable-bootloader} allows you to boot your system from
removable media by writing the GRUB file to the UEFI-specification location of
@file{/EFI/BOOT/BOOTX64.efi} of the boot directory, usually @file{/boot/efi}.
This is also useful for some UEFI firmwares that ``forget'' their configuration
from their non-volatile storage. Like @code{grub-efi-bootloader}, this can only
be used if the @file{/sys/firmware/efi} directory is available.

@quotation Note
This @emph{will} overwrite the GRUB file from any other operating systems that
also place their GRUB file in the UEFI-specification location; making them
unbootable.
@end quotation

@vindex grub-efi-netboot-bootloader
@code{grub-efi-netboot-bootloader} allows you to boot your system over network
through TFTP@.  In combination with an NFS root file system this allows you to
build a diskless Guix system.

The installation of the @code{grub-efi-netboot-bootloader} generates the
content of the TFTP root directory at @code{targets} (@pxref{Bootloader
Configuration, @code{targets}}) below the sub-directory @file{efi/Guix}, to be
served by a TFTP server.  You may want to mount your TFTP server directories
onto the @code{targets} to move the required files to the TFTP server
automatically during installation.

If you plan to use an NFS root file system as well (actually if you mount the
store from an NFS share), then the TFTP server needs to serve the file
@file{/boot/grub/grub.cfg} and other files from the store (like GRUBs background
image, the kernel (@pxref{operating-system Reference, @code{kernel}}) and the
initrd (@pxref{operating-system Reference, @code{initrd}})), too.  All these
files from the store will be accessed by GRUB through TFTP with their normal
store path, for example as
@file{tftp://tftp-server/gnu/store/…-initrd/initrd.cpio.gz}.

Two symlinks are created to make this possible.  For each target in the
@code{targets} field, the first symlink is
@samp{target}@file{/efi/Guix/boot/grub/grub.cfg} pointing to
@file{../../../boot/grub/grub.cfg}, where @samp{target} may be
@file{/boot}.  In this case the link is not leaving the served TFTP root
directory, but otherwise it does.  The second link is
@samp{target}@file{/gnu/store} and points to @file{../gnu/store}.  This
link is leaving the served TFTP root directory.

The assumption behind all this is that you have an NFS server exporting
the root file system for your Guix system, and additionally a TFTP
server exporting your @code{targets} directories—usually a single
@file{/boot}—from that same root file system for your Guix system.  In
this constellation the symlinks will work.

For other constellations you will have to program your own bootloader
installer, which then takes care to make necessary files from the store
accessible through TFTP, for example by copying them into the TFTP root
directory for your @code{targets}.

It is important to note that symlinks pointing outside the TFTP root directory
may need to be allowed in the configuration of your TFTP server.  Further the
store link exposes the whole store through TFTP@.  Both points need to be
considered carefully for security aspects.  It is advised to disable any TFTP
write access!

Please note, that this bootloader will not modify the ‘UEFI Boot Manager’ of
the system.

Beside the @code{grub-efi-netboot-bootloader}, the already mentioned TFTP and
NFS servers, you also need a properly configured DHCP server to make the booting
over netboot possible.  For all this we can currently only recommend you to look
for instructions about @acronym{PXE, Preboot eXecution Environment}.

If a local EFI System Partition (ESP) or a similar partition with a FAT
file system is mounted in @code{targets}, then symlinks cannot be
created.  In this case everything will be prepared for booting from
local storage, matching the behavior of @code{grub-efi-bootloader}, with
the difference that all GRUB binaries are copied to @code{targets},
necessary for booting over the network.

@vindex grub-efi-netboot-removable-bootloader
@code{grub-efi-netboot-removable-bootloader} is identical to
@code{grub-efi-netboot-bootloader} with the exception that the
sub-directory @file{efi/boot} will be used instead of @file{efi/Guix} to
comply with the UEFI specification for removable media.

@quotation Note
This @emph{will} overwrite the GRUB file from any other operating systems that
also place their GRUB file in the UEFI-specification location; making them
unbootable.
@end quotation

@item @code{targets}
This is a list of strings denoting the targets onto which to install the
bootloader.

The interpretation of targets depends on the bootloader in question.
For @code{grub-bootloader}, for example, they should be device names
understood by the bootloader @command{installer} command, such as
@code{/dev/sda} or @code{(hd0)} (@pxref{Invoking grub-install,,, grub,
GNU GRUB Manual}).  For @code{grub-efi-bootloader} and
@code{grub-efi-removable-bootloader} they should be mount
points of the EFI file system, usually @file{/boot/efi}.  For
@code{grub-efi-netboot-bootloader}, @code{targets} should be the mount
points corresponding to TFTP root directories served by your TFTP
server.

@item @code{menu-entries} (default: @code{'()})
A possibly empty list of @code{menu-entry} objects (see below), denoting
entries to appear in the bootloader menu, in addition to the current
system entry and the entry pointing to previous system generations.

@item @code{default-entry} (default: @code{0})
The index of the default boot menu entry.  Index 0 is for the entry of the
current system.

@item @code{timeout} (default: @code{5})
The number of seconds to wait for keyboard input before booting.  Set to
0 to boot immediately, and to -1 to wait indefinitely.

@cindex keyboard layout, for the bootloader
@item @code{keyboard-layout} (default: @code{#f})
If this is @code{#f}, the bootloader's menu (if any) uses the default keyboard
layout, usually US@tie{}English (``qwerty'').

Otherwise, this must be a @code{keyboard-layout} object (@pxref{Keyboard
Layout}).

@quotation Note
This option is currently ignored by bootloaders other than @code{grub} and
@code{grub-efi}.
@end quotation

@item @code{theme} (default: @var{#f})
The bootloader theme object describing the theme to use.  If no theme
is provided, some bootloaders might use a default theme, that's true
for GRUB.

@item @code{terminal-outputs} (default: @code{'(gfxterm)})
The output terminals used for the bootloader boot menu, as a list of
symbols.  GRUB accepts the values: @code{console}, @code{serial},
@code{serial_@{0-3@}}, @code{gfxterm}, @code{vga_text},
@code{mda_text}, @code{morse}, and @code{pkmodem}.  This field
corresponds to the GRUB variable @code{GRUB_TERMINAL_OUTPUT} (@pxref{Simple
configuration,,, grub,GNU GRUB manual}).

@item @code{terminal-inputs} (default: @code{'()})
The input terminals used for the bootloader boot menu, as a list of
symbols.  For GRUB, the default is the native platform terminal as
determined at run-time.  GRUB accepts the values: @code{console},
@code{serial}, @code{serial_@{0-3@}}, @code{at_keyboard}, and
@code{usb_keyboard}.  This field corresponds to the GRUB variable
@code{GRUB_TERMINAL_INPUT} (@pxref{Simple configuration,,, grub,GNU GRUB
manual}).

@item @code{serial-unit} (default: @code{#f})
The serial unit used by the bootloader, as an integer from 0 to 3.
For GRUB, it is chosen at run-time; currently GRUB chooses 0, which
corresponds to COM1 (@pxref{Serial terminal,,, grub,GNU GRUB manual}).

@item @code{serial-speed} (default: @code{#f})
The speed of the serial interface, as an integer.  For GRUB, the
default value is chosen at run-time; currently GRUB chooses
9600@tie{}bps (@pxref{Serial terminal,,, grub,GNU GRUB manual}).

@item @code{device-tree-support?} (default: @code{#t})
Whether to support Linux @uref{https://en.wikipedia.org/wiki/Devicetree,
device tree} files loading.

This option in enabled by default.  In some cases involving the
@code{u-boot} bootloader, where the device tree has already been loaded
in RAM, it can be handy to disable the option by setting it to
@code{#f}.

@item @code{extra-initrd} (default: @code{#f})
File name of an additional initrd to load during the boot.  It may or
may not point to a file in the store, but the main use case is for
out-of-store files containing secrets.

In order to be able to provide decryption keys for the LUKS device, they
need to be available in the initial ram disk.  However they cannot be
stored inside the usual initrd, since it is stored in the store and
being a world-readable (as files in the store are) is not a desired
property for a initrd containing decryption keys.  You can therefore use
this field to instruct GRUB to also load a manually created initrd not
stored in the store.

For any use case not involving secrets, you should use regular initrd
(@pxref{operating-system Reference, @code{initrd}}) instead.

Suitable image can be created for example like this:

@example
echo /key-file.bin | cpio -oH newc >/key-file.cpio
chmod 0000 /key-file.cpio
@end example

After it is created, you can use it in this manner:

@lisp
;; Operating system with encrypted boot partition
(operating-system
  ...
  (bootloader (bootloader-configuration
               (bootloader grub-efi-bootloader)
               (targets '("/boot/efi"))
               ;; Load the initrd with a key file
               (extra-initrd "/key-file.cpio")))
  (mapped-devices
   (list (mapped-device
          (source (uuid "12345678-1234-1234-1234-123456789abc"))
          (target "my-root")
          (type (luks-device-mapping-with-options
                 ;; And use it to unlock the root device
                 #:key-file "/key-file.bin"))))))
@end lisp

Be careful when using this option, since pointing to a file that is not
readable by the grub while booting will cause the boot to fail and
require a manual edit of the initrd line in the grub menu.

Currently only supported by GRUB.
@end table

@end deftp

@cindex dual boot
@cindex boot menu
Should you want to list additional boot menu entries @i{via} the
@code{menu-entries} field above, you will need to create them with the
@code{menu-entry} form.  For example, imagine you want to be able to
boot another distro (hard to imagine!), you can define a menu entry
along these lines:

@lisp
(menu-entry
  (label "The Other Distro")
  (linux "/boot/old/vmlinux-2.6.32")
  (linux-arguments '("root=/dev/sda2"))
  (initrd "/boot/old/initrd"))
@end lisp

Details below.

@deftp {Data Type} menu-entry
The type of an entry in the bootloader menu.

@table @asis

@item @code{label}
The label to show in the menu---e.g., @code{"GNU"}.

@item @code{linux} (default: @code{#f})
The Linux kernel image to boot, for example:

@lisp
(file-append linux-libre "/bzImage")
@end lisp

For GRUB, it is also possible to specify a device explicitly in the
file path using GRUB's device naming convention (@pxref{Naming
convention,,, grub, GNU GRUB manual}), for example:

@example
"(hd0,msdos1)/boot/vmlinuz"
@end example

If the device is specified explicitly as above, then the @code{device}
field is ignored entirely.

@item @code{linux-arguments} (default: @code{'()})
The list of extra Linux kernel command-line arguments---e.g.,
@code{'("console=ttyS0")}.

@item @code{initrd} (default: @code{#f})
A G-Expression or string denoting the file name of the initial RAM disk
to use (@pxref{G-Expressions}).

@item @code{device} (default: @code{#f})
The device where the kernel and initrd are to be found---i.e., for GRUB,
@dfn{root} for this menu entry (@pxref{root,,, grub, GNU GRUB manual}).

This may be a file system label (a string), a file system UUID (a
bytevector, @pxref{File Systems}), or @code{#f}, in which case
the bootloader will search the device containing the file specified by
the @code{linux} field (@pxref{search,,, grub, GNU GRUB manual}).  It
must @emph{not} be an OS device name such as @file{/dev/sda1}.

@item @code{multiboot-kernel} (default: @code{#f})
The kernel to boot in Multiboot-mode (@pxref{multiboot,,, grub, GNU GRUB
manual}).  When this field is set, a Multiboot menu-entry is generated.
For example:

@lisp
(file-append mach "/boot/gnumach")
@end lisp

@item @code{multiboot-arguments} (default: @code{'()})
The list of extra command-line arguments for the multiboot-kernel.

For example, when running in QEMU it can be useful to use a text-based
console (use options @option{--nographic} @option{--serial mon:stdio}):

@lisp
'("console=com0")
@end lisp

To use the new and still experimental
@uref{https://darnassus.sceen.net/~hurd-web/rump_kernel/, rumpdisk
user-level disk driver} instead of GNU@tie{}Mach's in-kernel IDE driver,
set @code{kernel-arguments} to:

@lisp
'("noide")
@end lisp

Of course, these options can be combined:

@lisp
'("console=com0" "noide")
@end lisp

@item @code{multiboot-modules} (default: @code{'()})
The list of commands for loading Multiboot modules.  For example:

@lisp
(list (list (file-append hurd "/hurd/ext2fs.static") "ext2fs"
             @dots{})
      (list (file-append libc "/lib/ld.so.1") "exec"
             @dots{}))
@end lisp

@item @code{chain-loader} (default: @code{#f})
A string that can be accepted by @code{grub}'s @code{chainloader}
directive. This has no effect if either @code{linux} or
@code{multiboot-kernel} fields are specified. The following is an
example of chainloading a different GNU/Linux system.

@lisp
(bootloader
 (bootloader-configuration
  ;; @dots{}
  (menu-entries
   (list
    (menu-entry
     (label "GNU/Linux")
     (device (uuid "1C31-A17C" 'fat))
     (chain-loader "/EFI/GNULinux/grubx64.efi"))))))
@end lisp

@end table
@end deftp

@cindex HDPI
@cindex HiDPI
@cindex resolution
@c FIXME: Write documentation once it's stable.
For now only GRUB has theme support.  GRUB themes are created using
the @code{grub-theme} form, which is not fully documented yet.

@deftp {Data Type} grub-theme
Data type representing the configuration of the GRUB theme.

@table @asis
@item @code{gfxmode} (default: @code{'("auto")})
The GRUB @code{gfxmode} to set (a list of screen resolution strings,
@pxref{gfxmode,,, grub, GNU GRUB manual}).
@end table
@end deftp

@deffn {Procedure} grub-theme
Return the default GRUB theme used by the operating system if no
@code{theme} field is specified in @code{bootloader-configuration}
record.

It comes with a fancy background image displaying the GNU and Guix
logos.
@end deffn

For example, to override the default resolution, you may use something
like

@lisp
(bootloader
 (bootloader-configuration
 ;; @dots{}
 (theme (grub-theme
         (inherit (grub-theme))
         (gfxmode '("1024x786x32" "auto"))))))
@end lisp

@node Invoking guix system
@section Invoking @command{guix system}

@cindex @command{guix system}
Once you have written an operating system declaration as seen in the
previous section, it can be @dfn{instantiated} using the @command{guix
system} command.  The synopsis is:

@example
guix system @var{options}@dots{} @var{action} @var{file}
@end example

@var{file} must be the name of a file containing an
@code{operating-system} declaration.  @var{action} specifies how the
operating system is instantiated.  Currently the following values are
supported:

@table @code
@item search
Display available service type definitions that match the given regular
expressions, sorted by relevance:

@cindex HDPI
@cindex HiDPI
@cindex resolution
@example
$ guix system search console
name: console-fonts
location: gnu/services/base.scm:806:2
extends: shepherd-root
description: Install the given fonts on the specified ttys (fonts are per
+ virtual console on GNU/Linux).  The value of this service is a list of
+ tty/font pairs.  The font can be the name of a font provided by the `kbd'
+ package or any valid argument to `setfont', as in this example:
+
+      '(("tty1" . "LatGrkCyr-8x16")
+        ("tty2" . (file-append
+                      font-tamzen
+                      "/share/kbd/consolefonts/TamzenForPowerline10x20.psf"))
+        ("tty3" . (file-append
+                      font-terminus
+                      "/share/consolefonts/ter-132n"))) ; for HDPI
relevance: 9

name: mingetty
location: gnu/services/base.scm:1190:2
extends: shepherd-root
description: Provide console login using the `mingetty' program.
relevance: 2

name: login
location: gnu/services/base.scm:860:2
extends: pam
description: Provide a console log-in service as specified by its
+ configuration value, a `login-configuration' object.
relevance: 2

@dots{}
@end example

As for @command{guix package --search}, the result is written in
@code{recutils} format, which makes it easy to filter the output
(@pxref{Top, GNU recutils databases,, recutils, GNU recutils manual}).

@cindex service type definition, editing
@cindex editing, service type definition
@item edit
Edit or view the definition of the given service types.

For example, the command below opens your editor, as specified by the
@env{EDITOR} environment variable, on the definition of the
@code{openssh} service type:

@example
guix system edit openssh
@end example

@item reconfigure
Build the operating system described in @var{file}, activate it, and
switch to it@footnote{This action (and the related actions
@code{switch-generation} and @code{roll-back}) are usable only on
systems already running Guix System.}.

@quotation Note
@c The paragraph below refers to the problem discussed at
@c <https://lists.gnu.org/archive/html/guix-devel/2014-08/msg00057.html>.
It is highly recommended to run @command{guix pull} once before you run
@command{guix system reconfigure} for the first time (@pxref{Invoking
guix pull}).  Failing to do that you would see an older version of Guix
once @command{reconfigure} has completed.
@end quotation

This effects all the configuration specified in @var{file}: user
accounts, system services, global package list, privileged programs, etc.
The command starts system services specified in @var{file} that are not
currently running; if a service is currently running this command will
arrange for it to be upgraded the next time it is stopped (e.g.@: by
@code{herd stop X} or @code{herd restart X}).

This command creates a new generation whose number is one greater than
the current generation (as reported by @command{guix system
list-generations}).  If that generation already exists, it will be
overwritten.  This behavior mirrors that of @command{guix package}
(@pxref{Invoking guix package}).

It also adds a bootloader menu entry for the new OS configuration,
---unless @option{--no-bootloader} is passed.  For GRUB, it moves
entries for older configurations to a submenu, allowing you to choose
an older system generation at boot time should you need it.

@cindex provenance tracking, of the operating system
Upon completion, the new system is deployed under
@file{/run/current-system}.  This directory contains @dfn{provenance
meta-data}: the list of channels in use (@pxref{Channels}) and
@var{file} itself, when available.  You can view it by running:

@example
guix system describe
@end example

This information is useful should you later want to inspect how this
particular generation was built.  In fact, assuming @var{file} is
self-contained, you can later rebuild generation @var{n} of your
operating system with:

@example
guix time-machine \
  -C /var/guix/profiles/system-@var{n}-link/channels.scm -- \
  system reconfigure \
  /var/guix/profiles/system-@var{n}-link/configuration.scm
@end example

You can think of it as some sort of built-in version control!  Your
system is not just a binary artifact: @emph{it carries its own source}.
@xref{Service Reference, @code{provenance-service-type}}, for more
information on provenance tracking.

By default, @command{reconfigure} @emph{prevents you from downgrading
your system}, which could (re)introduce security vulnerabilities and
also cause problems with ``stateful'' services such as database
management systems.  You can override that behavior by passing
@option{--allow-downgrades}.

@item switch-generation
@cindex generations
Switch to an existing system generation.  This action atomically
switches the system profile to the specified system generation.  It
also rearranges the system's existing bootloader menu entries.  It
makes the menu entry for the specified system generation the default,
and it moves the entries for the other generations to a submenu, if
supported by the bootloader being used.  The next time the system
boots, it will use the specified system generation.

The bootloader itself is not being reinstalled when using this
command.  Thus, the installed bootloader is used with an updated
configuration file.

The target generation can be specified explicitly by its generation
number.  For example, the following invocation would switch to system
generation 7:

@example
guix system switch-generation 7
@end example

The target generation can also be specified relative to the current
generation with the form @code{+N} or @code{-N}, where @code{+3} means
``3 generations ahead of the current generation,'' and @code{-1} means
``1 generation prior to the current generation.''  When specifying a
negative value such as @code{-1}, you must precede it with @code{--} to
prevent it from being parsed as an option.  For example:

@example
guix system switch-generation -- -1
@end example

Currently, the effect of invoking this action is @emph{only} to switch
the system profile to an existing generation and rearrange the
bootloader menu entries.  To actually start using the target system
generation, you must reboot after running this action.  In the future,
it will be updated to do the same things as @command{reconfigure},
like activating and deactivating services.

This action will fail if the specified generation does not exist.

@item roll-back
@cindex rolling back
Switch to the preceding system generation.  The next time the system
boots, it will use the preceding system generation.  This is the inverse
of @command{reconfigure}, and it is exactly the same as invoking
@command{switch-generation} with an argument of @code{-1}.

Currently, as with @command{switch-generation}, you must reboot after
running this action to actually start using the preceding system
generation.

@item delete-generations
@cindex deleting system generations
@cindex saving space
Delete system generations, making them candidates for garbage collection
(@pxref{Invoking guix gc}, for information on how to run the ``garbage
collector'').

This works in the same way as @samp{guix package --delete-generations}
(@pxref{Invoking guix package, @option{--delete-generations}}).  With no
arguments, all system generations but the current one are deleted:

@example
guix system delete-generations
@end example

You can also select the generations you want to delete.  The example below
deletes all the system generations that are more than two months old:

@example
guix system delete-generations 2m
@end example

Running this command automatically reinstalls the bootloader with an updated
list of menu entries---e.g., the ``old generations'' sub-menu in GRUB no
longer lists the generations that have been deleted.

@item build
Build the derivation of the operating system, which includes all the
configuration files and programs needed to boot and run the system.
This action does not actually install anything.

@item init
Populate the given directory with all the files necessary to run the
operating system specified in @var{file}.  This is useful for first-time
installations of Guix System.  For instance:

@example
guix system init my-os-config.scm /mnt
@end example

copies to @file{/mnt} all the store items required by the configuration
specified in @file{my-os-config.scm}.  This includes configuration
files, packages, and so on.  It also creates other essential files
needed for the system to operate correctly---e.g., the @file{/etc},
@file{/var}, and @file{/run} directories, and the @file{/bin/sh} file.

This command also installs bootloader on the targets specified in
@file{my-os-config}, unless the @option{--no-bootloader} option was
passed.

@item vm
@cindex virtual machine
@cindex VM
@anchor{guix system vm}
Build a virtual machine (VM) that contains the operating system declared
in @var{file}, and return a script to run that VM.

@quotation Note
The @code{vm} action and others below
can use KVM support in the Linux-libre kernel.  Specifically, if the
machine has hardware virtualization support, the corresponding
KVM kernel module should be loaded, and the @file{/dev/kvm} device node
must exist and be readable and writable by the user and by the
build users of the daemon (@pxref{Build Environment Setup}).
@end quotation

Arguments given to the script are passed to QEMU as in the example
below, which enables networking and requests 1@tie{}GiB of RAM for the
emulated machine:

@example
$ /gnu/store/@dots{}-run-vm.sh -m 1024 -smp 2 -nic user,model=virtio-net-pci
@end example

It's possible to combine the two steps into one:

@example
$ $(guix system vm my-config.scm) -m 1024 -smp 2 -nic user,model=virtio-net-pci
@end example

The VM shares its store with the host system.

By default, the root file system of the VM is mounted volatile; the
@option{--persistent} option can be provided to make it persistent
instead.  In that case, the VM disk-image file will be copied from the
store to the @env{TMPDIR} directory to make it writable.

Additional file systems can be shared between the host and the VM using
the @option{--share} and @option{--expose} command-line options: the former
specifies a directory to be shared with write access, while the latter
provides read-only access to the shared directory.

The example below creates a VM in which the user's home directory is
accessible read-only, and where the @file{/exchange} directory is a
read-write mapping of @file{$HOME/tmp} on the host:

@example
guix system vm my-config.scm \
   --expose=$HOME --share=$HOME/tmp=/exchange
@end example

On GNU/Linux, the default is to boot directly to the kernel; this has
the advantage of requiring only a very tiny root disk image since the
store of the host can then be mounted.

The @option{--full-boot} option forces a complete boot sequence, starting
with the bootloader.  This requires more disk space since a root image
containing at least the kernel, initrd, and bootloader data files must
be created.

The @option{--image-size} option can be used to specify the size of the
image.

The @option{--no-graphic} option will instruct @command{guix system} to
spawn a headless VM that will use the invoking tty for IO.  Among other
things, this enables copy-pasting, and scrollback.  Use the @kbd{ctrl-a}
prefix to issue QEMU commands; e.g. @kbd{ctrl-a h} prints a help,
@kbd{ctrl-a x} quits the VM, and @kbd{ctrl-a c} switches between the
QEMU monitor and the VM.

@cindex System images, creation in various formats
@cindex Creating system images in various formats
@item image
@cindex image, creating disk images
The @code{image} command can produce various image types.  The image
type can be selected using the @option{--image-type} option.  It
defaults to @code{mbr-hybrid-raw}.  When its value is @code{iso9660},
the @option{--label} option can be used to specify a volume ID with
@code{image}.  By default, the root file system of a disk image is
mounted non-volatile; the @option{--volatile} option can be provided to
make it volatile instead.  When using @code{image}, the bootloader
installed on the generated image is taken from the provided
@code{operating-system} definition.  The following example demonstrates
how to generate an image that uses the @code{grub-efi-bootloader}
bootloader and boot it with QEMU:

@example
image=$(guix system image --image-type=qcow2 \
        gnu/system/examples/lightweight-desktop.tmpl)
cp $image /tmp/my-image.qcow2
chmod +w /tmp/my-image.qcow2
qemu-system-x86_64 -enable-kvm -hda /tmp/my-image.qcow2 -m 1000 \
                   -bios $(guix build ovmf-x86-64)/share/firmware/ovmf_x64.bin
@end example

When using the @code{mbr-hybrid-raw} image type, a raw disk image is
produced; it can be copied as is to a USB stick, for instance.  Assuming
@code{/dev/sdc} is the device corresponding to a USB stick, one can copy
the image to it using the following command:

@example
# dd if=$(guix system image my-os.scm) of=/dev/sdc status=progress
@end example

The @code{--list-image-types} command lists all the available image
types.

@cindex creating virtual machine images
When using the @code{qcow2} image type, the returned image is in qcow2
format, which the QEMU emulator can efficiently use. @xref{Running Guix
in a VM}, for more information on how to run the image in a virtual
machine.  The @code{grub-bootloader} bootloader is always used
independently of what is declared in the @code{operating-system} file
passed as argument.  This is to make it easier to work with QEMU, which
uses the SeaBIOS BIOS by default, expecting a bootloader to be installed
in the Master Boot Record (MBR).

@cindex docker-image, creating docker images
When using the @code{docker} image type, a Docker image is produced.
Guix builds the image from scratch, not from a pre-existing Docker base
image.  As a result, it contains @emph{exactly} what you define in the
operating system configuration file.  You can then load the image and
launch a Docker container using commands like the following:

@example
image_id="$(docker load < guix-system-docker-image.tar.gz)"
container_id="$(docker create $image_id)"
docker start $container_id
@end example

This command starts a new Docker container from the specified image.  It
will boot the Guix system in the usual manner, which means it will
start any services you have defined in the operating system
configuration.  You can get an interactive shell running in the container
using @command{docker exec}:

@example
docker exec -ti $container_id /run/current-system/profile/bin/bash --login
@end example

Depending on what you run in the Docker container, it
may be necessary to give the container additional permissions.  For
example, if you intend to build software using Guix inside of the Docker
container, you may need to pass the @option{--privileged} option to
@code{docker create}.

Last, the @option{--network} option applies to @command{guix system
docker-image}: it produces an image where network is supposedly shared
with the host, and thus without services like nscd or NetworkManager.

@item container
Return a script to run the operating system declared in @var{file}
within a container.  Containers are a set of lightweight isolation
mechanisms provided by the kernel Linux-libre.  Containers are
substantially less resource-demanding than full virtual machines since
the kernel, shared objects, and other resources can be shared with the
host system; this also means they provide thinner isolation.

Currently, the script must be run as root in order to support more than
a single user and group.  The container shares its store with the host
system.

As with the @code{vm} action (@pxref{guix system vm}), additional file
systems to be shared between the host and container can be specified
using the @option{--share} and @option{--expose} options:

@example
guix system container my-config.scm \
   --expose=$HOME --share=$HOME/tmp=/exchange
@end example

The @option{--share} and @option{--expose} options can also be passed to
the generated script to bind-mount additional directories into the
container.

@quotation Note
This option requires Linux-libre 3.19 or newer.
@end quotation

@end table

@var{options} can contain any of the common build options (@pxref{Common
Build Options}).  In addition, @var{options} can contain one of the
following:

@table @option
@item --expression=@var{expr}
@itemx -e @var{expr}
Consider the operating-system @var{expr} evaluates to.
This is an alternative to specifying a file which evaluates to an
operating system.
This is used to generate the Guix system installer @pxref{Building the
Installation Image}).

@item --system=@var{system}
@itemx -s @var{system}
Attempt to build for @var{system} instead of the host system type.
This works as per @command{guix build} (@pxref{Invoking guix build}).

@item --target=@var{triplet}
Cross-build for @var{triplet}, which must be a valid GNU triplet, such
as @code{"aarch64-linux-gnu"} (@pxref{Specifying target triplets, GNU
configuration triplets,, autoconf, Autoconf}).

@item --derivation
@itemx -d
Return the derivation file name of the given operating system without
building anything.

@cindex provenance tracking, of the operating system
@item --save-provenance
As discussed above, @command{guix system init} and @command{guix system
reconfigure} always save provenance information @i{via} a dedicated
service (@pxref{Service Reference, @code{provenance-service-type}}).
However, other commands don't do that by default.  If you wish to, say,
create a virtual machine image that contains provenance information, you
can run:

@example
guix system image -t qcow2 --save-provenance config.scm
@end example

That way, the resulting image will effectively ``embed its own source''
in the form of meta-data in @file{/run/current-system}.  With that
information, one can rebuild the image to make sure it really contains
what it pretends to contain; or they could use that to derive a variant
of the image.

@item --image-type=@var{type}
@itemx -t @var{type}
For the @code{image} action, create an image with given @var{type}.

When this option is omitted, @command{guix system} uses the
@code{mbr-hybrid-raw} image type.

@cindex ISO-9660 format
@cindex CD image format
@cindex DVD image format
@option{--image-type=iso9660} produces an ISO-9660 image, suitable
for burning on CDs and DVDs.

@item --image-size=@var{size}
For the @code{image} action, create an image of the given @var{size}.
@var{size} may be a number of bytes, or it may include a unit as a
suffix (@pxref{Block size, size specifications,, coreutils, GNU
Coreutils}).

When this option is omitted, @command{guix system} computes an estimate
of the image size as a function of the size of the system declared in
@var{file}.

@item --network
@itemx -N
For the @code{container} action, allow containers to access the host network,
that is, do not create a network namespace.

@item --root=@var{file}
@itemx -r @var{file}
Make @var{file} a symlink to the result, and register it as a garbage
collector root.

@item --skip-checks
Skip pre-installation safety checks.

By default, @command{guix system init} and @command{guix system
reconfigure} perform safety checks: they make sure the file systems that
appear in the @code{operating-system} declaration actually exist
(@pxref{File Systems}), and that any Linux kernel modules that may be
needed at boot time are listed in @code{initrd-modules} (@pxref{Initial
RAM Disk}).  Passing this option skips these tests altogether.

@item --allow-downgrades
Instruct @command{guix system reconfigure} to allow system downgrades.

By default, @command{reconfigure} prevents you from downgrading your
system.  It achieves that by comparing the provenance info of your
system (shown by @command{guix system describe}) with that of your
@command{guix} command (shown by @command{guix describe}).  If the
commits for @command{guix} are not descendants of those used for your
system, @command{guix system reconfigure} errors out.  Passing
@option{--allow-downgrades} allows you to bypass these checks.

@quotation Note
Make sure you understand its security implications before using
@option{--allow-downgrades}.
@end quotation

@cindex on-error
@cindex on-error strategy
@cindex error strategy
@item --on-error=@var{strategy}
Apply @var{strategy} when an error occurs when reading @var{file}.
@var{strategy} may be one of the following:

@table @code
@item nothing-special
Report the error concisely and exit.  This is the default strategy.

@item backtrace
Likewise, but also display a backtrace.

@item debug
Report the error and enter Guile's debugger.  From there, you can run
commands such as @code{,bt} to get a backtrace, @code{,locals} to
display local variable values, and more generally inspect the state of the
program.  @xref{Debug Commands,,, guile, GNU Guile Reference Manual}, for
a list of available debugging commands.
@end table
@end table

Once you have built, configured, re-configured, and re-re-configured
your Guix installation, you may find it useful to list the operating
system generations available on disk---and that you can choose from the
bootloader boot menu:

@table @code

@item describe
Describe the running system generation: its file name, the kernel and
bootloader used, etc., as well as provenance information when available.

The @code{--list-installed} flag is available, with the same
syntax that is used in @command{guix package --list-installed}
(@pxref{Invoking guix package}).  When the flag is used,
the description will include a list of packages that are currently
installed in the system profile, with optional filtering based on a
regular expression.

@quotation Note
The @emph{running} system generation---referred to by
@file{/run/current-system}---is not necessarily the @emph{current}
system generation---referred to by @file{/var/guix/profiles/system}: it
differs when, for instance, you chose from the bootloader menu to boot
an older generation.

It can also differ from the @emph{booted} system generation---referred
to by @file{/run/booted-system}---for instance because you reconfigured
the system in the meantime.
@end quotation

@item list-generations
List a summary of each generation of the operating system available on
disk, in a human-readable way.  This is similar to the
@option{--list-generations} option of @command{guix package}
(@pxref{Invoking guix package}).

Optionally, one can specify a pattern, with the same syntax that is used
in @command{guix package --list-generations}, to restrict the list of
generations displayed.  For instance, the following command displays
generations that are up to 10 days old:

@example
$ guix system list-generations 10d
@end example

The @code{--list-installed} flag may also be specified, with the same
syntax that is used in @command{guix package --list-installed}.  This
may be helpful if trying to determine when a package was added to the
system.

@end table

The @command{guix system} command has even more to offer!  The following
sub-commands allow you to visualize how your system services relate to
each other:

@anchor{system-extension-graph}
@table @code

@item extension-graph
Emit to standard output the @dfn{service
extension graph} of the operating system defined in @var{file}
(@pxref{Service Composition}, for more information on service
extensions).  By default the output is in Dot/Graphviz format, but you
can choose a different format with @option{--graph-backend}, as with
@command{guix graph} (@pxref{Invoking guix graph, @option{--backend}}):

The command:

@example
$ guix system extension-graph @var{file} | xdot -
@end example

shows the extension relations among services.

@quotation Note
The @command{dot} program is provided by the @code{graphviz} package.
@end quotation

@anchor{system-shepherd-graph}
@item shepherd-graph
Emit to standard output the @dfn{dependency
graph} of shepherd services of the operating system defined in
@var{file}.  @xref{Shepherd Services}, for more information and for an
example graph.

Again, the default output format is Dot/Graphviz, but you can pass
@option{--graph-backend} to select a different one.

@end table

@node Invoking guix deploy
@section Invoking @command{guix deploy}

@cindex @command{guix deploy}
We've already seen @code{operating-system} declarations used to manage a
machine's configuration locally.  Suppose you need to configure multiple
machines, though---perhaps you're managing a service on the web that's
comprised of several servers.  @command{guix deploy} enables you to use those
same @code{operating-system} declarations to manage multiple remote hosts at
once as a logical ``deployment''.

@quotation Note
The functionality described in this section is still under development
and is subject to change.  Get in touch with us on
@email{guix-devel@@gnu.org}!
@end quotation

@example
guix deploy @var{file}
@end example

Such an invocation will deploy the machines that the code within @var{file}
evaluates to.  As an example, @var{file} might contain a definition like this:

@lisp
;; This is a Guix deployment of a "bare bones" setup, with
;; no X11 display server, to a machine with an SSH daemon
;; listening on localhost:2222. A configuration such as this
;; may be appropriate for virtual machine with ports
;; forwarded to the host's loopback interface.

(use-service-modules networking ssh)
(use-package-modules bootloaders)

(define %system
  (operating-system
   (host-name "gnu-deployed")
   (timezone "Etc/UTC")
   (bootloader (bootloader-configuration
                (bootloader grub-bootloader)
                (targets '("/dev/vda"))
                (terminal-outputs '(console))))
   (file-systems (cons (file-system
                        (mount-point "/")
                        (device "/dev/vda1")
                        (type "ext4"))
                       %base-file-systems))
   (services
    (append (list (service dhcp-client-service-type)
                  (service openssh-service-type
                           (openssh-configuration
                            (permit-root-login #t)
                            (allow-empty-passwords? #t))))
            %base-services))))

(list (machine
       (operating-system %system)
       (environment managed-host-environment-type)
       (configuration (machine-ssh-configuration
                       (host-name "localhost")
                       (system "x86_64-linux")
                       (user "alice")
                       (identity "./id_rsa")
                       (port 2222)))))
@end lisp

The file should evaluate to a list of @var{machine} objects.  This example,
upon being deployed, will create a new generation on the remote system
realizing the @code{operating-system} declaration @code{%system}.
@code{environment} and @code{configuration} specify how the machine should be
provisioned---that is, how the computing resources should be created and
managed.  The above example does not create any resources, as a
@code{'managed-host} is a machine that is already running the Guix system and
available over the network.  This is a particularly simple case; a more
complex deployment may involve, for example, starting virtual machines through
a Virtual Private Server (VPS) provider.  In such a case, a different
@var{environment} type would be used.

Do note that you first need to generate a key pair on the coordinator machine
to allow the daemon to export signed archives of files from the store
(@pxref{Invoking guix archive}), though this step is automatic on Guix
System:

@example
# guix archive --generate-key
@end example

@noindent
Each target machine must authorize the key of the master machine so that it
accepts store items it receives from the coordinator:

@example
# guix archive --authorize < coordinator-public-key.txt
@end example

@code{user}, in this example, specifies the name of the user account to log in
as to perform the deployment.  Its default value is @code{root}, but root
login over SSH may be forbidden in some cases.  To work around this,
@command{guix deploy} can log in as an unprivileged user and employ
@code{sudo} to escalate privileges.  This will only work if @code{sudo} is
currently installed on the remote and can be invoked non-interactively as
@code{user}.  That is, the line in @code{sudoers} granting @code{user} the
ability to use @code{sudo} must contain the @code{NOPASSWD} tag.  This can
be accomplished with the following operating system configuration snippet:

@lisp
(use-modules ...
             (gnu system))               ;for %sudoers-specification

(define %user "username")

(operating-system
  ...
  (sudoers-file
     (plain-file "sudoers"
                 (string-append (plain-file-content %sudoers-specification)
                                (format #f "~a ALL = NOPASSWD: ALL~%"
                                        %user)))))

@end lisp

For more information regarding the format of the @file{sudoers} file,
consult @command{man sudoers}.

Once you've deployed a system on a set of machines, you may find it
useful to run a command on all of them.  The @option{--execute} or
@option{-x} option lets you do that; the example below runs
@command{uname -a} on all the machines listed in the deployment file:

@example
guix deploy @var{file} -x -- uname -a
@end example

One thing you may often need to do after deployment is restart specific
services on all the machines, which you can do like so:

@example
guix deploy @var{file} -x -- herd restart @var{service}
@end example

The @command{guix deploy -x} command returns zero if and only if the
command succeeded on all the machines.

@c FIXME/TODO: Separate the API doc from the CLI doc.

Below are the data types you need to know about when writing a
deployment file.

@deftp {Data Type} machine
This is the data type representing a single machine in a heterogeneous Guix
deployment.

@table @asis
@item @code{operating-system}
The object of the operating system configuration to deploy.

@item @code{environment}
An @code{environment-type} describing how the machine should be provisioned.

@item @code{configuration} (default: @code{#f})
An object describing the configuration for the machine's @code{environment}.
If the @code{environment} has a default configuration, @code{#f} may be used.
If @code{#f} is used for an environment with no default configuration,
however, an error will be thrown.
@end table
@end deftp

@deftp {Data Type} machine-ssh-configuration
This is the data type representing the SSH client parameters for a machine
with an @code{environment} of @code{managed-host-environment-type}.

@table @asis
@item @code{host-name}
@item @code{build-locally?} (default: @code{#t})
If false, system derivations will be built on the machine being deployed to.
@item @code{system}
The system type describing the architecture of the machine being deployed
to---e.g., @code{"x86_64-linux"}.
@item @code{authorize?} (default: @code{#t})
If true, the coordinator's signing key will be added to the remote's ACL
keyring.
@item @code{port} (default: @code{22})
@item @code{user} (default: @code{"root"})
@item @code{identity} (default: @code{#f})
If specified, the path to the SSH private key to use to authenticate with the
remote host.

@item @code{host-key} (default: @code{#f})
This should be the SSH host key of the machine, which looks like this:

@example
ssh-ed25519 AAAAC3Nz@dots{} root@@example.org
@end example

When @code{host-key} is @code{#f}, the server is authenticated against
the @file{~/.ssh/known_hosts} file, just like the OpenSSH @command{ssh}
client does.

@item @code{allow-downgrades?} (default: @code{#f})
Whether to allow potential downgrades.

Like @command{guix system reconfigure}, @command{guix deploy} compares
the channel commits currently deployed on the remote host (as returned
by @command{guix system describe}) to those currently in use (as
returned by @command{guix describe}) to determine whether commits
currently in use are descendants of those deployed.  When this is not
the case and @code{allow-downgrades?} is false, it raises an error.
This ensures you do not accidentally downgrade remote machines.

@item @code{safety-checks?} (default: @code{#t})
Whether to perform ``safety checks'' before deployment.  This includes
verifying that devices and file systems referred to in the operating
system configuration actually exist on the target machine, and making
sure that Linux modules required to access storage devices at boot time
are listed in the @code{initrd-modules} field of the operating system.

These safety checks ensure that you do not inadvertently deploy a system
that would fail to boot.  Be careful before turning them off!
@end table
@end deftp

@deftp {Data Type} digital-ocean-configuration
This is the data type describing the Droplet that should be created for a
machine with an @code{environment} of @code{digital-ocean-environment-type}.

@table @asis
@item @code{ssh-key}
The path to the SSH private key to use to authenticate with the remote
host.  In the future, this field may not exist.
@item @code{tags}
A list of string ``tags'' that uniquely identify the machine.  Must be given
such that no two machines in the deployment have the same set of tags.
@item @code{region}
A Digital Ocean region slug, such as @code{"nyc3"}.
@item @code{size}
A Digital Ocean size slug, such as @code{"s-1vcpu-1gb"}
@item @code{enable-ipv6?}
Whether or not the droplet should be created with IPv6 networking.
@end table
@end deftp

@node Running Guix in a VM
@section Running Guix in a Virtual Machine

@cindex virtual machine
To run Guix in a virtual machine (VM), one can use the pre-built Guix VM
image distributed at
@url{@value{BASE-URL}/guix-system-vm-image-@value{VERSION}.x86_64-linux.qcow2}.
This image is a compressed image in QCOW format.  You can pass it to an
emulator such as @uref{https://qemu.org/, QEMU} (see below for details).

This image boots the Xfce graphical environment and it contains some
commonly used tools.  You can install more software in the image by running
@command{guix package} in a terminal (@pxref{Invoking guix package}).  You can
also reconfigure the system based on its initial configuration file available
as @file{/run/current-system/configuration.scm} (@pxref{Using the
Configuration System}).

Instead of using this pre-built image, one can also build their own
image using @command{guix system image} (@pxref{Invoking guix system}).

@cindex QEMU
If you built your own image, you must copy it out of the store
(@pxref{The Store}) and give yourself permission to write to the copy
before you can use it.  When invoking QEMU, you must choose a system
emulator that is suitable for your hardware platform.  Here is a minimal
QEMU invocation that will boot the result of @command{guix system
image -t qcow2} on x86_64 hardware:

@example
$ qemu-system-x86_64 \
   -nic user,model=virtio-net-pci \
   -enable-kvm -m 2048 \
   -device virtio-blk,drive=myhd \
   -drive if=none,file=guix-system-vm-image-@value{VERSION}.x86_64-linux.qcow2,id=myhd
@end example

Here is what each of these options means:

@table @code
@item qemu-system-x86_64
This specifies the hardware platform to emulate.  This should match the
host.

@item -nic user,model=virtio-net-pci
Enable the unprivileged user-mode network stack.  The guest OS can
access the host but not vice versa.  This is the simplest way to get the
guest OS online.  @code{model} specifies which network device to emulate:
@code{virtio-net-pci} is a special device made for virtualized operating
systems and recommended for most uses.  Assuming your hardware platform is
x86_64, you can get a list of available NIC models by running
@command{qemu-system-x86_64 -nic model=help}.

@item -enable-kvm
If your system has hardware virtualization extensions, enabling the
virtual machine support (KVM) of the Linux kernel will make things run
faster.

@c To run Xfce + 'guix pull', we need at least 1G of RAM.
@item -m 2048
RAM available to the guest OS, in mebibytes.  Defaults to 128@tie{}MiB,
which may be insufficient for some operations.

@item -device virtio-blk,drive=myhd
Create a @code{virtio-blk} drive called ``myhd''.  @code{virtio-blk} is a
``paravirtualization'' mechanism for block devices that allows QEMU to achieve
better performance than if it were emulating a complete disk drive.  See the
QEMU and KVM documentation for more info.

@item -drive if=none,file=/tmp/qemu-image,id=myhd
Use our QCOW image, the
@file{guix-system-vm-image-@value{VERSION}.x86_64-linux.qcow2} file, as
the backing store of the ``myhd'' drive.
@end table

The default @command{run-vm.sh} script that is returned by an invocation of
@command{guix system vm} does not add a @command{-nic user} flag by default.
To get network access from within the vm add the @code{(dhcp-client-service)}
to your system definition and start the VM using
@command{$(guix system vm config.scm) -nic user}.  An important caveat of using
@command{-nic user} for networking is that @command{ping} will not work, because
it uses the ICMP protocol.  You'll have to use a different command to check for
network connectivity, for example @command{guix download}.

@subsection Connecting Through SSH

@cindex SSH
@cindex SSH server
To enable SSH inside a VM you need to add an SSH server like
@code{openssh-service-type} to your VM (@pxref{Networking Services,
@code{openssh-service-type}}).  In addition you need to forward the SSH port,
22 by default, to the host.  You can do this with

@example
$(guix system vm config.scm) -nic user,model=virtio-net-pci,hostfwd=tcp::10022-:22
@end example

To connect to the VM you can run

@example
ssh -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no -p 10022 localhost
@end example

The @command{-p} tells @command{ssh} the port you want to connect to.
@command{-o UserKnownHostsFile=/dev/null} prevents @command{ssh} from complaining
every time you modify your @command{config.scm} file and the
@command{-o StrictHostKeyChecking=no} prevents you from having to allow a
connection to an unknown host every time you connect.

@quotation Note
If you find the above @samp{hostfwd} example not to be working (e.g.,
your SSH client hangs attempting to connect to the mapped port of your
VM), make sure that your Guix System VM has networking support, such as
by using the @code{dhcp-client-service-type} service type.
@end quotation

@subsection Using @command{virt-viewer} with Spice

As an alternative to the default @command{qemu} graphical client you can
use the @command{remote-viewer} from the @command{virt-viewer} package.  To
connect pass the @command{-spice port=5930,disable-ticketing} flag to
@command{qemu}.  See previous section for further information on how to do this.

Spice also allows you to do some nice stuff like share your clipboard with your
VM@.  To enable that you'll also have to pass the following flags to @command{qemu}:

@example
-device virtio-serial-pci,id=virtio-serial0,max_ports=16,bus=pci.0,addr=0x5
-chardev spicevmc,name=vdagent,id=vdagent
-device virtserialport,nr=1,bus=virtio-serial0.0,chardev=vdagent,\
name=com.redhat.spice.0
@end example

You'll also need to add the @code{(spice-vdagent-service)} to your
system definition (@pxref{Miscellaneous Services, Spice service}).

@node Defining Services
@section Defining Services

The previous sections show the available services and how one can combine
them in an @code{operating-system} declaration.  But how do we define
them in the first place?  And what is a service anyway?

@menu
* Service Composition::         The model for composing services.
* Service Types and Services::  Types and services.
* Service Reference::           API reference.
* Shepherd Services::           A particular type of service.
* Complex Configurations::      Defining bindings for complex configurations.
@end menu

@node Service Composition
@subsection Service Composition

@cindex services
@cindex daemons
Here we define a @dfn{service} as, broadly, something that extends the
functionality of the operating system.  Often a service is a process---a
@dfn{daemon}---started when the system boots: a secure shell server, a
Web server, the Guix build daemon, etc.  Sometimes a service is a daemon
whose execution can be triggered by another daemon---e.g., an FTP server
started by @command{inetd} or a D-Bus service activated by
@command{dbus-daemon}.  Occasionally, a service does not map to a
daemon.  For instance, the ``account'' service collects user accounts
and makes sure they exist when the system runs; the ``udev'' service
collects device management rules and makes them available to the eudev
daemon; the @file{/etc} service populates the @file{/etc} directory
of the system.

@cindex service extensions
Guix system services are connected by @dfn{extensions}.  For instance, the
secure shell service @emph{extends} the Shepherd---the
initialization system, running as PID@tie{}1---by giving it the command
lines to start and stop the secure shell daemon (@pxref{Networking
Services, @code{openssh-service-type}}); the UPower service extends the D-Bus
service by passing it its @file{.service} specification, and extends the
udev service by passing it device management rules (@pxref{Desktop
Services, @code{upower-service}}); the Guix daemon service extends the
Shepherd by passing it the command lines to start and stop the daemon,
and extends the account service by passing it a list of required build
user accounts (@pxref{Base Services}).

All in all, services and their ``extends'' relations form a directed
acyclic graph (DAG).  If we represent services as boxes and extensions
as arrows, a typical system might provide something like this:

@image{images/service-graph,,5in,Typical service extension graph.}

@cindex system service
At the bottom, we see the @dfn{system service}, which produces the
directory containing everything to run and boot the system, as returned
by the @command{guix system build} command.  @xref{Service Reference},
to learn about the other service types shown here.
@xref{system-extension-graph, the @command{guix system extension-graph}
command}, for information on how to generate this representation for a
particular operating system definition.

@cindex service types
Technically, developers can define @dfn{service types} to express these
relations.  There can be any number of services of a given type on the
system---for instance, a system running two instances of the GNU secure
shell server (lsh) has two instances of @code{lsh-service-type}, with
different parameters.

The following section describes the programming interface for service
types and services.

@node Service Types and Services
@subsection Service Types and Services

A @dfn{service type} is a node in the DAG described above.  Let us start
with a simple example, the service type for the Guix build daemon
(@pxref{Invoking guix-daemon}):

@lisp
(define guix-service-type
  (service-type
   (name 'guix)
   (extensions
    (list (service-extension shepherd-root-service-type guix-shepherd-service)
          (service-extension account-service-type guix-accounts)
          (service-extension activation-service-type guix-activation)))
   (default-value (guix-configuration))))
@end lisp

@noindent
It defines three things:

@enumerate
@item
A name, whose sole purpose is to make inspection and debugging easier.

@item
A list of @dfn{service extensions}, where each extension designates the
target service type and a procedure that, given the parameters of the
service, returns a list of objects to extend the service of that type.

Every service type has at least one service extension.  The only
exception is the @dfn{boot service type}, which is the ultimate service.

@item
Optionally, a default value for instances of this type.
@end enumerate

In this example, @code{guix-service-type} extends three services:

@table @code
@item shepherd-root-service-type
The @code{guix-shepherd-service} procedure defines how the Shepherd
service is extended.  Namely, it returns a @code{<shepherd-service>}
object that defines how @command{guix-daemon} is started and stopped
(@pxref{Shepherd Services}).

@item account-service-type
This extension for this service is computed by @code{guix-accounts},
which returns a list of @code{user-group} and @code{user-account}
objects representing the build user accounts (@pxref{Invoking
guix-daemon}).

@item activation-service-type
Here @code{guix-activation} is a procedure that returns a gexp, which is
a code snippet to run at ``activation time''---e.g., when the service is
booted.
@end table

A service of this type is instantiated like this:

@lisp
(service guix-service-type
         (guix-configuration
           (build-accounts 5)
           (extra-options '("--gc-keep-derivations"))))
@end lisp

The second argument to the @code{service} form is a value representing
the parameters of this specific service instance.
@xref{guix-configuration-type, @code{guix-configuration}}, for
information about the @code{guix-configuration} data type.  When the
value is omitted, the default value specified by
@code{guix-service-type} is used:

@lisp
(service guix-service-type)
@end lisp

@code{guix-service-type} is quite simple because it extends other
services but is not extensible itself.

@c @subsubsubsection Extensible Service Types

The service type for an @emph{extensible} service looks like this:

@lisp
(define udev-service-type
  (service-type (name 'udev)
                (extensions
                 (list (service-extension shepherd-root-service-type
                                          udev-shepherd-service)))

                (compose concatenate)       ;concatenate the list of rules
                (extend (lambda (config rules)
                          (udev-configuration
                           (inherit config)
                           (rules (append (udev-configuration-rules config)
                                          rules)))))))
@end lisp

This is the service type for the
@uref{https://github.com/eudev-project/eudev, eudev device
management daemon}.  Compared to the previous example, in addition to an
extension of @code{shepherd-root-service-type}, we see two new fields:

@table @code
@item compose
This is the procedure to @dfn{compose} the list of extensions to
services of this type.

Services can extend the udev service by passing it lists of rules; we
compose those extensions simply by concatenating them.

@item extend
This procedure defines how the value of the service is @dfn{extended} with
the composition of the extensions.

Udev extensions are composed into a list of rules, but the udev service
value is itself a @code{<udev-configuration>} record.  So here, we
extend that record by appending the list of rules it contains to the
list of contributed rules.

@item description
This is a string giving an overview of the service type.  The string can
contain Texinfo markup (@pxref{Overview,,, texinfo, GNU Texinfo}).  The
@command{guix system search} command searches these strings and displays
them (@pxref{Invoking guix system}).
@end table

There can be only one instance of an extensible service type such as
@code{udev-service-type}.  If there were more, the
@code{service-extension} specifications would be ambiguous.

Still here?  The next section provides a reference of the programming
interface for services.

@node Service Reference
@subsection Service Reference

We have seen an overview of service types (@pxref{Service Types and
Services}).  This section provides a reference on how to manipulate
services and service types.  This interface is provided by the
@code{(gnu services)} module.

@deffn {Procedure} service type [value]
Return a new service of @var{type}, a @code{<service-type>} object (see
below).  @var{value} can be any object; it represents the parameters of
this particular service instance.

When @var{value} is omitted, the default value specified by @var{type}
is used; if @var{type} does not specify a default value, an error is
raised.

For instance, this:

@lisp
(service openssh-service-type)
@end lisp

@noindent
is equivalent to this:

@lisp
(service openssh-service-type
         (openssh-configuration))
@end lisp

In both cases the result is an instance of @code{openssh-service-type}
with the default configuration.
@end deffn

@deffn {Procedure} service? obj
Return true if @var{obj} is a service.
@end deffn

@deffn {Procedure} service-kind service
Return the type of @var{service}---i.e., a @code{<service-type>} object.
@end deffn

@deffn {Procedure} service-value service
Return the value associated with @var{service}.  It represents its
parameters.
@end deffn

Here is an example of how a service is created and manipulated:

@lisp
(define s
  (service nginx-service-type
           (nginx-configuration
            (nginx nginx)
            (log-directory log-directory)
            (run-directory run-directory)
            (file config-file))))

(service? s)
@result{} #t

(eq? (service-kind s) nginx-service-type)
@result{} #t
@end lisp

The @code{modify-services} form provides a handy way to change the
parameters of some of the services of a list such as
@code{%base-services} (@pxref{Base Services, @code{%base-services}}).  It
evaluates to a list of services.  Of course, you could always use
standard list combinators such as @code{map} and @code{fold} to do that
(@pxref{SRFI-1, List Library,, guile, GNU Guile Reference Manual});
@code{modify-services} simply provides a more concise form for this
common pattern.

@defspec modify-services services @
  (type variable => body) @dots{}

Modify the services listed in @var{services} according to the given
clauses.  Each clause has the form:

@example
(@var{type} @var{variable} => @var{body})
@end example

where @var{type} is a service type---e.g.,
@code{guix-service-type}---and @var{variable} is an identifier that is
bound within the @var{body} to the service parameters---e.g., a
@code{guix-configuration} instance---of the original service of that
@var{type}.

The @var{body} should evaluate to the new service parameters, which will
be used to configure the new service.  This new service will replace the
original in the resulting list.  Because a service's service parameters
are created using @code{define-record-type*}, you can write a succinct
@var{body} that evaluates to the new service parameters by using the
@code{inherit} feature that @code{define-record-type*} provides.

Clauses can also have the following form:

@lisp
(delete @var{type})
@end lisp

Such a clause removes all services of the given @var{type} from
@var{services}.

@xref{Using the Configuration System}, for example usage.

@end defspec

Next comes the programming interface for service types.  This is
something you want to know when writing new service definitions, but not
necessarily when simply looking for ways to customize your
@code{operating-system} declaration.

@deftp {Data Type} service-type
@cindex service type
This is the representation of a @dfn{service type} (@pxref{Service Types
and Services}).

@table @asis
@item @code{name}
This is a symbol, used only to simplify inspection and debugging.

@item @code{extensions}
A non-empty list of @code{<service-extension>} objects (see below).

@item @code{compose} (default: @code{#f})
If this is @code{#f}, then the service type denotes services that cannot
be extended---i.e., services that do not receive ``values'' from other
services.

Otherwise, it must be a one-argument procedure.  The procedure is called
by @code{fold-services} and is passed a list of values collected from
extensions.  It may return any single value.

@item @code{extend} (default: @code{#f})
If this is @code{#f}, services of this type cannot be extended.

Otherwise, it must be a two-argument procedure: @code{fold-services}
calls it, passing it the initial value of the service as the first
argument and the result of applying @code{compose} to the extension
values as the second argument.  It must return a value that is a valid
parameter value for the service instance.

@item @code{description}
This is a string, possibly using Texinfo markup, describing in a couple
of sentences what the service is about.  This string allows users to
find about the service through @command{guix system search}
(@pxref{Invoking guix system}).

@item @code{default-value} (default: @code{&no-default-value})
The default value associated for instances of this service type.  This
allows users to use the @code{service} form without its second argument:

@lisp
(service @var{type})
@end lisp

The returned service in this case has the default value specified by
@var{type}.
@end table

@xref{Service Types and Services}, for examples.
@end deftp

@deffn {Procedure} service-extension target-type compute
Return a new extension for services of type @var{target-type}.
@var{compute} must be a one-argument procedure: @code{fold-services}
calls it, passing it the value associated with the service that provides
the extension; it must return a valid value for the target service.
@end deffn

@deffn {Procedure} service-extension? obj
Return true if @var{obj} is a service extension.
@end deffn

Occasionally, you might want to simply extend an existing service.  This
involves creating a new service type and specifying the extension of
interest, which can be verbose; the @code{simple-service} procedure
provides a shorthand for this.

@deffn {Procedure} simple-service name target value
Return a service that extends @var{target} with @var{value}.  This works
by creating a singleton service type @var{name}, of which the returned
service is an instance.

For example, this extends mcron (@pxref{Scheduled Job Execution}) with
an additional job:

@lisp
(simple-service 'my-mcron-job mcron-service-type
                #~(job '(next-hour (3)) "guix gc -F 2G"))
@end lisp
@end deffn

At the core of the service abstraction lies the @code{fold-services}
procedure, which is responsible for ``compiling'' a list of services
down to a single directory that contains everything needed to boot and
run the system---the directory shown by the @command{guix system build}
command (@pxref{Invoking guix system}).  In essence, it propagates
service extensions down the service graph, updating each node parameters
on the way, until it reaches the root node.

@deffn {Procedure} fold-services services [#:target-type system-service-type]
Fold @var{services} by propagating their extensions down to the root of
type @var{target-type}; return the root service adjusted accordingly.
@end deffn

Lastly, the @code{(gnu services)} module also defines several essential
service types, some of which are listed below.

@defvar system-service-type
This is the root of the service graph.  It produces the system directory
as returned by the @command{guix system build} command.
@end defvar

@defvar boot-service-type
The type of the ``boot service'', which produces the @dfn{boot script}.
The boot script is what the initial RAM disk runs when booting.
@end defvar

@defvar etc-service-type
The type of the @file{/etc} service.  This service is used to create
files under @file{/etc} and can be extended by
passing it name/file tuples such as:

@lisp
(list `("issue" ,(plain-file "issue" "Welcome!\n")))
@end lisp

In this example, the effect would be to add an @file{/etc/issue} file
pointing to the given file.
@end defvar

@defvar privileged-program-service-type
Type for the ``privileged-program service''.  This service collects lists of
executable file names, passed as gexps, and adds them to the set of
privileged programs on the system (@pxref{Privileged Programs}).
@end defvar

@defvar profile-service-type
Type of the service that populates the @dfn{system profile}---i.e., the
programs under @file{/run/current-system/profile}.  Other services can
extend it by passing it lists of packages to add to the system profile.
@end defvar

@cindex provenance tracking, of the operating system
@anchor{provenance-service-type}
@defvar provenance-service-type
This is the type of the service that records @dfn{provenance meta-data}
in the system itself.  It creates several files under
@file{/run/current-system}:

@table @file
@item channels.scm
This is a ``channel file'' that can be passed to @command{guix pull -C}
or @command{guix time-machine -C}, and which describes the channels used
to build the system, if that information was available
(@pxref{Channels}).

@item configuration.scm
This is the file that was passed as the value for this
@code{provenance-service-type} service.  By default, @command{guix
system reconfigure} automatically passes the OS configuration file it
received on the command line.

@item provenance
This contains the same information as the two other files but in a
format that is more readily processable.
@end table

In general, these two pieces of information (channels and configuration
file) are enough to reproduce the operating system ``from source''.

@quotation Caveats
This information is necessary to rebuild your operating system, but it
is not always sufficient.  In particular, @file{configuration.scm}
itself is insufficient if it is not self-contained---if it refers to
external Guile modules or to extra files.  If you want
@file{configuration.scm} to be self-contained, we recommend that modules
or files it refers to be part of a channel.

Besides, provenance meta-data is ``silent'' in the sense that it does
not change the bits contained in your system, @emph{except for the
meta-data bits themselves}.  Two different OS configurations or sets of
channels can lead to the same system, bit-for-bit; when
@code{provenance-service-type} is used, these two systems will have
different meta-data and thus different store file names, which makes
comparison less trivial.
@end quotation

This service is automatically added to your operating system
configuration when you use @command{guix system reconfigure},
@command{guix system init}, or @command{guix deploy}.
@end defvar

@defvar linux-loadable-module-service-type
Type of the service that collects lists of packages containing
kernel-loadable modules, and adds them to the set of kernel-loadable
modules.

This service type is intended to be extended by other service types,
such as below:

@lisp
(simple-service 'installing-module
                linux-loadable-module-service-type
                (list module-to-install-1
                      module-to-install-2))
@end lisp

This does not actually load modules at bootup, only adds it to the
kernel profile so that it @emph{can} be loaded by other means.
@end defvar

@node Shepherd Services
@subsection Shepherd Services

@cindex shepherd services
@cindex PID 1
@cindex init system
The @code{(gnu services shepherd)} module provides a way to define
services managed by the GNU@tie{}Shepherd, which is the
initialization system---the first process that is started when the
system boots, also known as PID@tie{}1
(@pxref{Introduction,,, shepherd, The GNU Shepherd Manual}).

Services in the Shepherd can depend on each other.  For instance, the
SSH daemon may need to be started after the syslog daemon has been
started, which in turn can only happen once all the file systems have
been mounted.  The simple operating system defined earlier (@pxref{Using
the Configuration System}) results in a service graph like this:

@image{images/shepherd-graph,,5in,Typical shepherd service graph.}

You can actually generate such a graph for any operating system
definition using the @command{guix system shepherd-graph} command
(@pxref{system-shepherd-graph, @command{guix system shepherd-graph}}).

The @code{%shepherd-root-service} is a service object representing
PID@tie{}1, of type @code{shepherd-root-service-type}; it can be extended
by passing it lists of @code{<shepherd-service>} objects.

@deftp {Data Type} shepherd-service
The data type representing a service managed by the Shepherd.

@table @asis
@item @code{provision}
This is a list of symbols denoting what the service provides.

These are the names that may be passed to @command{herd start},
@command{herd status}, and similar commands (@pxref{Invoking herd,,,
shepherd, The GNU Shepherd Manual}).  @xref{Defining Services,,,
shepherd, The GNU Shepherd Manual}, for details.

@item @code{requirement} (default: @code{'()})
List of symbols denoting the Shepherd services this one depends on.

@cindex one-shot services, for the Shepherd
@item @code{one-shot?} (default: @code{#f})
Whether this service is @dfn{one-shot}.  One-shot services stop immediately
after their @code{start} action has completed.  @xref{Slots of services,,,
shepherd, The GNU Shepherd Manual}, for more info.

@item @code{respawn?} (default: @code{#t})
Whether to restart the service when it stops, for instance when the
underlying process dies.

@item @code{respawn-limit} (default: @code{#f})
Set a limit on how many times and how frequently a service may be
restarted by Shepherd before it is disabled.  @xref{Defining
Services,,, shepherd, The GNU Shepherd Manual}, for details.

@item @code{respawn-delay} (default: @code{#f})
When true, this is the delay in seconds before restarting a failed
service.

@item @code{start} (default: @code{#~(const #t)})
@itemx @code{stop} (default: @code{#~(const #f)})
The @code{start} and @code{stop} fields refer to the Shepherd's
facilities to start and stop processes (@pxref{Service De- and
Constructors,,, shepherd, The GNU Shepherd Manual}).  They are given as
G-expressions that get expanded in the Shepherd configuration file
(@pxref{G-Expressions}).

@item @code{actions} (default: @code{'()})
@cindex actions, of Shepherd services
This is a list of @code{shepherd-action} objects (see below) defining
@dfn{actions} supported by the service, in addition to the standard
@code{start} and @code{stop} actions.  Actions listed here become available as
@command{herd} sub-commands:

@example
herd @var{action} @var{service} [@var{arguments}@dots{}]
@end example

@item @code{free-form} (default: @code{#f})
When set, this field replaces the @code{start}, @code{stop}, and
@code{actions} fields.  It is meant to be used when the service
definition comes from some other source, typically the service
collection provided by the Shepherd proper (@pxref{Service Collection,,,
shepherd, The GNU Shepherd Manual}).

@cindex REPL service, for shepherd
For example, the snippet below defines a service for the Shepherd's
built-in @acronym{REPL, read-eval-print loop} service (@pxref{REPL
Service,,, shepherd, The GNU Shepherd Manual}):

@lisp
(shepherd-service
  (provision '(repl))
  (modules '((shepherd service repl)))
  (free-form #~(repl-service)))
@end lisp

In this case, the service object is returned by the @code{repl-service}
procedure of the Shepherd, so all the @code{free-form} G-expression does
is call that procedure.  Note that the @code{provision} field must be
consistent with the actual service provision.

@item @code{auto-start?} (default: @code{#t})
Whether this service should be started automatically by the Shepherd.  If it
is @code{#f} the service has to be started manually with @code{herd start}.

@item @code{documentation}
A documentation string, as shown when running:

@example
herd doc @var{service-name}
@end example

where @var{service-name} is one of the symbols in @code{provision}
(@pxref{Invoking herd,,, shepherd, The GNU Shepherd Manual}).

@item @code{modules} (default: @code{%default-modules})
This is the list of modules that must be in scope when @code{start} and
@code{stop} are evaluated.

@end table
@end deftp

The example below defines a Shepherd service that spawns
@command{syslogd}, the system logger from the GNU Networking Utilities
(@pxref{syslogd invocation, @command{syslogd},, inetutils, GNU
Inetutils}):

@example
(let ((config (plain-file "syslogd.conf" "@dots{}")))
  (shepherd-service
    (documentation "Run the syslog daemon (syslogd).")
    (provision '(syslogd))
    (requirement '(user-processes))
    (start #~(make-forkexec-constructor
               (list #$(file-append inetutils "/libexec/syslogd")
                     "--rcfile" #$config)
               #:pid-file "/var/run/syslog.pid"))
    (stop #~(make-kill-destructor))))
@end example

Key elements in this example are the @code{start} and @code{stop}
fields: they are @dfn{staged} code snippets that use the
@code{make-forkexec-constructor} procedure provided by the Shepherd and
its dual, @code{make-kill-destructor} (@pxref{Service De- and
Constructors,,, shepherd, The GNU Shepherd Manual}).  The @code{start}
field will have @command{shepherd} spawn @command{syslogd} with the
given option; note that we pass @code{config} after @option{--rcfile},
which is a configuration file declared above (contents of this file are
omitted).  Likewise, the @code{stop} field tells how this service is to
be stopped; in this case, it is stopped by making the @code{kill} system
call on its PID@.  Code staging is achieved using G-expressions:
@code{#~} stages code, while @code{#$} ``escapes'' back to host code
(@pxref{G-Expressions}).

@deftp {Data Type} shepherd-action
This is the data type that defines additional actions implemented by a
Shepherd service (see above).

@table @code
@item name
Symbol naming the action.

@item documentation
This is a documentation string for the action.  It can be viewed by running:

@example
herd doc @var{service} action @var{action}
@end example

@item procedure
This should be a gexp that evaluates to a procedure of at least one argument,
which is the ``running value'' of the service (@pxref{Slots of services,,,
shepherd, The GNU Shepherd Manual}).
@end table

The following example defines an action called @code{say-hello} that kindly
greets the user:

@lisp
(shepherd-action
  (name 'say-hello)
  (documentation "Say hi!")
  (procedure #~(lambda (running . args)
                 (format #t "Hello, friend! arguments: ~s\n"
                         args)
                 #t)))
@end lisp

Assuming this action is added to the @code{example} service, then you can do:

@example
# herd say-hello example
Hello, friend! arguments: ()
# herd say-hello example a b c
Hello, friend! arguments: ("a" "b" "c")
@end example

This, as you can see, is a fairly sophisticated way to say hello.
@xref{Defining Services,,, shepherd, The GNU Shepherd Manual}, for more
info on actions.
@end deftp

@cindex configuration file, of Shepherd services
@deffn {Procedure} shepherd-configuration-action
Return a @code{configuration} action to display @var{file}, which should
be the name of the service's configuration file.

It can be useful to equip services with that action.  For example, the
service for the Tor anonymous router (@pxref{Networking Services,
@code{tor-service-type}}) is defined roughly like this:

@lisp
(let ((torrc (plain-file "torrc" @dots{})))
  (shepherd-service
    (provision '(tor))
    (requirement '(user-processes loopback syslogd))

    (start #~(make-forkexec-constructor
              (list #$(file-append tor "/bin/tor") "-f" #$torrc)
              #:user "tor" #:group "tor"))
    (stop #~(make-kill-destructor))
    (actions (list (shepherd-configuration-action torrc)))
    (documentation "Run the Tor anonymous network overlay.")))
@end lisp

Thanks to this action, administrators can inspect the configuration file
passed to @command{tor} with this shell command:

@example
cat $(herd configuration tor)
@end example

This can come in as a handy debugging tool!
@end deffn

@defvar shepherd-root-service-type
The service type for the Shepherd ``root service''---i.e., PID@tie{}1.

This is the service type that extensions target when they want to create
shepherd services (@pxref{Service Types and Services}, for an example).
Each extension must pass a list of @code{<shepherd-service>}.  Its
value must be a @code{shepherd-configuration}, as described below.
@end defvar

@deftp {Data Type} shepherd-configuration
This data type represents the Shepherd's configuration.

@table @code
@item shepherd (default: @code{shepherd})
The Shepherd package to use.

@item services (default: @code{'()})
A list of @code{<shepherd-service>} to start.
You should probably use the service extension
mechanism instead (@pxref{Shepherd Services}).
@end table
@end deftp

The following example specifies the Shepherd package for the operating
system:

@lisp
(operating-system
  ;; ...
  (services (append (list openssh-service-type))
            ;; ...
            %desktop-services)
  ;; ...
  ;; Use own Shepherd package.
  (essential-services
   (modify-services (operating-system-default-essential-services
                     this-operating-system)
     (shepherd-root-service-type config => (shepherd-configuration
                                            (inherit config)
                                            (shepherd my-shepherd))))))
@end lisp

@defvar %shepherd-root-service
This service represents PID@tie{}1.
@end defvar

@node Complex Configurations
@subsection Complex Configurations
@cindex complex configurations
Some programs might have rather complex configuration files or formats,
and to make it easier to create Scheme bindings for these configuration
files, you can use the utilities defined in the @code{(gnu services
configuration)} module.

The main utility is the @code{define-configuration} macro, a helper
used to define a Scheme record type (@pxref{Record Overview,,,
guile, GNU Guile Reference Manual}).  The fields from this Scheme record
can be serialized using @dfn{serializers}, which are procedures that take
some kind of Scheme value and translates them into another Scheme value or
@ref{G-Expressions}.

@defmac define-configuration name clause1 clause2 @dots{}
Create a record type named @code{@var{name}} that contains the
fields found in the clauses.

A clause has the following form:

@example
(@var{field-name}
 @var{type-decl}
 @var{documentation}
 @var{option*}
 @dots{})
@end example

@var{field-name} is an identifier that denotes the name of the field in
the generated record.

@var{type-decl} is either @code{@var{type}} for fields that require a
value to be set or @code{(@var{type} @var{default-value})} otherwise.

@var{type} is the type of the value corresponding to @var{field-name};
since Guile is untyped, a predicate
procedure---@code{@var{type}?}---will be called on the value
corresponding to the field to ensure that the value is of the correct
type.  This means that if say, @var{type} is @code{package}, then a
procedure named @code{package?} will be applied on the value to make
sure that it is indeed a @code{<package>} object.

@var{default-value} is the default value corresponding to the field; if
none is specified, the user is forced to provide a value when creating
an object of the record type.

@c XXX: Should these be full sentences or are they allow to be very
@c short like package synopses?
@var{documentation} is a string formatted with Texinfo syntax which
should provide a description of what setting this field does.

@var{option*} is one of the following subclauses:

@table @asis
@item @code{empty-serializer}
Exclude this field from serialization.

@item @code{(serializer @var{serializer})}
@var{serializer} is the name of a procedure which takes two arguments,
the first is the name of the field, and the second is the value
corresponding to the field.  The procedure should return a string or
@ref{G-Expressions} that represents the content that will be serialized
to the configuration file.  If none is specified, a procedure of the
name @code{serialize-@var{type}} will be used.

An example of a simple serializer procedure:
@lisp
(define (serialize-boolean field-name value)
  (let ((value (if value "true" "false")))
    #~(string-append '#$field-name " = " #$value)))
@end lisp

@item @code{(sanitizer @var{sanitizer})}
@var{sanitizer} is a procedure which takes one argument,
a user-supplied value, and returns a ``sanitized'' value for the field.
If no sanitizer is specified, a default sanitizer is used, which raises
an error if the value is not of type @var{type}.

An example of a sanitizer for a field that accepts both strings and
symbols looks like this:
@lisp
(define (sanitize-foo value)
  (cond ((string? value) value)
        ((symbol? value) (symbol->string value))
        (else (error "bad value"))))
@end lisp
@end table

In some cases multiple different configuration records might be defined
in the same file, but their serializers for the same type might have to
be different, because they have different configuration formats.  For
example, the @code{serialize-boolean} procedure for the Getmail service
would have to be different from the one for the Transmission service.  To
make it easier to deal with this situation, one can specify a serializer
prefix by using the @code{prefix} literal in the
@code{define-configuration} form.  This means that one doesn't have to
manually specify a custom @var{serializer} for every field.

@lisp
(define (foo-serialize-string field-name value)
  @dots{})

(define (bar-serialize-string field-name value)
  @dots{})

(define-configuration foo-configuration
  (label
   string
   "The name of label.")
  (prefix foo-))

(define-configuration bar-configuration
  (ip-address
   string
   "The IPv4 address for this device.")
  (prefix bar-))
@end lisp

However, in some cases you might not want to serialize any of the values
of the record, to do this, you can use the @code{no-serialization}
literal.  There is also the @code{define-configuration/no-serialization}
macro which is a shorthand of this.

@lisp
;; Nothing will be serialized to disk.
(define-configuration foo-configuration
  (field
   (string "test")
   "Some documentation.")
  (no-serialization))

;; The same thing as above.
(define-configuration/no-serialization bar-configuration
  (field
   (string "test")
   "Some documentation."))
@end lisp
@end defmac

@defmac define-maybe type
Sometimes a field should not be serialized if the user doesn’t specify a
value.  To achieve this, you can use the @code{define-maybe} macro to
define a ``maybe type''; if the value of a maybe type is left unset, or
is set to the @code{%unset-value} value, then it will not be serialized.

When defining a ``maybe type'', the corresponding serializer for the
regular type will be used by default.  For example, a field of type
@code{maybe-string} will be serialized using the @code{serialize-string}
procedure by default, you can of course change this by specifying a
custom serializer procedure.  Likewise, the type of the value would have
to be a string, or left unspecified.

@lisp
(define-maybe string)

(define (serialize-string field-name value)
  @dots{})

(define-configuration baz-configuration
  (name
   ;; If set to a string, the `serialize-string' procedure will be used
   ;; to serialize the string.  Otherwise this field is not serialized.
   maybe-string
   "The name of this module."))
@end lisp

Like with @code{define-configuration}, one can set a prefix for the
serializer name by using the @code{prefix} literal.

@lisp
(define-maybe integer
  (prefix baz-))

(define (baz-serialize-integer field-name value)
  @dots{})
@end lisp

There is also the @code{no-serialization} literal, which when set means
that no serializer will be defined for the ``maybe type'', regardless of
whether its value is set or not.
@code{define-maybe/no-serialization} is a shorthand for specifying the
@code{no-serialization} literal.

@lisp
(define-maybe/no-serialization symbol)

(define-configuration/no-serialization test-configuration
  (mode
   maybe-symbol
   "Docstring."))
@end lisp
@end defmac

@deffn {Procedure} maybe-value-set? value
Predicate to check whether a user explicitly specified the value of a
maybe field.
@end deffn

@deffn {Procedure} serialize-configuration configuration fields
Return a G-expression that contains the values corresponding to the
@var{fields} of @var{configuration}, a record that has been generated by
@code{define-configuration}.  The G-expression can then be serialized to
disk by using something like @code{mixed-text-file}.
@end deffn

Once you have defined a configuration record, you will most likely also
want to document it so that other people know to use it.  To help with
that, there are two procedures, both of which are documented below.

@deffn {Procedure} generate-documentation documentation documentation-name
Generate a Texinfo fragment from the docstrings in @var{documentation},
a list of @code{(@var{label} @var{fields} @var{sub-documentation} ...)}.
@var{label} should be a symbol and should be the name of the
configuration record.  @var{fields} should be a list of all the fields
available for the configuration record.

@var{sub-documentation} is a @code{(@var{field-name}
@var{configuration-name})} tuple.  @var{field-name} is the name of the
field which takes another configuration record as its value, and
@var{configuration-name} is the name of that configuration record.

@var{sub-documentation} is only needed if there are nested configuration
records.  For example, the @code{getmail-configuration} record
(@pxref{Mail Services}) accepts a @code{getmail-configuration-file}
record in one of its @code{rcfile} field, therefore documentation for
@code{getmail-configuration-file} is nested in
@code{getmail-configuration}.

@lisp
(generate-documentation
  `((getmail-configuration ,getmail-configuration-fields
     (rcfile getmail-configuration-file))
    @dots{})
  'getmail-configuration)
@end lisp

@var{documentation-name} should be a symbol and should be the name of
the configuration record.

@end deffn

@deffn {Procedure} configuration->documentation configuration-symbol
Take @var{configuration-symbol}, the symbol corresponding to the name
used when defining a configuration record with
@code{define-configuration}, and print the Texinfo documentation of its
fields.  This is useful if there aren’t any nested configuration records
since it only prints the documentation for the top-level fields.
@end deffn

As of right now, there is no automated way to generate documentation for
configuration records and put them in the manual.  Instead, every
time you make a change to the docstrings of a configuration record, you
have to manually call @code{generate-documentation} or
@code{configuration->documentation}, and paste the output into the
@file{doc/guix.texi} file.

@c TODO: Actually test this
Below is an example of a record type created using
@code{define-configuration} and friends.

@lisp
(use-modules (gnu services)
             (guix gexp)
             (gnu services configuration)
             (srfi srfi-26)
             (srfi srfi-1))

;; Turn field names, which are Scheme symbols into strings
(define (uglify-field-name field-name)
  (let ((str (symbol->string field-name)))
    ;; field? -> is-field
    (if (string-suffix? "?" str)
        (string-append "is-" (string-drop-right str 1))
        str)))

(define (serialize-string field-name value)
  #~(string-append #$(uglify-field-name field-name) " = " #$value "\n"))

(define (serialize-integer field-name value)
  (serialize-string field-name (number->string value)))

(define (serialize-boolean field-name value)
  (serialize-string field-name (if value "true" "false")))

(define (serialize-contact-name field-name value)
  #~(string-append "\n[" #$value "]\n"))

(define (list-of-contact-configurations? lst)
  (every contact-configuration? lst))

(define (serialize-list-of-contact-configurations field-name value)
  #~(string-append #$@@(map (cut serialize-configuration <>
                                contact-configuration-fields)
                           value)))

(define (serialize-contacts-list-configuration configuration)
  (mixed-text-file
   "contactrc"
   #~(string-append "[Owner]\n"
                    #$(serialize-configuration
                       configuration contacts-list-configuration-fields))))

(define-maybe integer)
(define-maybe string)

(define-configuration contact-configuration
  (name
   string
   "The name of the contact."
   serialize-contact-name)
  (phone-number
   maybe-integer
   "The person's phone number.")
  (email
   maybe-string
   "The person's email address.")
  (married?
   boolean
   "Whether the person is married."))

(define-configuration contacts-list-configuration
  (name
   string
   "The name of the owner of this contact list.")
  (email
   string
   "The owner's email address.")
  (contacts
   (list-of-contact-configurations '())
   "A list of @@code@{contact-configuation@} records which contain
information about all your contacts."))
@end lisp

A contacts list configuration could then be created like this:

@lisp
(define my-contacts
  (contacts-list-configuration
   (name "Alice")
   (email "alice@@example.org")
   (contacts
    (list (contact-configuration
           (name "Bob")
           (phone-number 1234)
           (email "bob@@gnu.org")
           (married? #f))
          (contact-configuration
           (name "Charlie")
           (phone-number 0000)
           (married? #t))))))
@end lisp

After serializing the configuration to disk, the resulting file would
look like this:

@example
[owner]
name = Alice
email = alice@@example.org

[Bob]
phone-number = 1234
email = bob@@gnu.org
is-married = false

[Charlie]
phone-number = 0
is-married = true
@end example


@c *********************************************************************
@cindex troubleshooting, Guix System
@cindex guix system troubleshooting
@node System Troubleshooting Tips
@chapter System Troubleshooting Tips

Guix System allows rebooting into a previous generation should the last
one be malfunctioning, which makes it quite robust against being broken
irreversibly.  This feature depends on GRUB being correctly functioning
though, which means that if for whatever reasons your GRUB installation
becomes corrupted during a system reconfiguration, you may not be able
to easily boot into a previous generation.  A technique that can be used
in this case is to @i{chroot} into your broken system and reconfigure it
from there.  Such technique is explained below.

@cindex chroot, guix system
@cindex chrooting, guix system
@cindex repairing GRUB, via chroot
@menu
* Chrooting into an existing system::
@end menu

@node Chrooting into an existing system
@section Chrooting into an existing system

This section details how to @i{chroot} to an already installed Guix
System with the aim of reconfiguring it, for example to fix a broken
GRUB installation.  The process is similar to how it would be done on
other GNU/Linux systems, but there are some Guix System particularities
such as the daemon and profiles that make it worthy of explaining here.

@enumerate
@item
Obtain a bootable image of Guix System.  It is recommended the latest
development snapshot so the kernel and the tools used are at least as as
new as those of your installed system; it can be retrieved from the
@url{https://ci.guix.gnu.org/search/latest/ISO-9660?query=spec:images+status:success+system:x86_64-linux+image.iso,
https://ci.guix.gnu.org} URL.  Follow the @pxref{USB Stick and DVD
Installation} section for copying it to a bootable media.

@item
Boot the image, and proceed with the graphical text-based installer
until your network is configured.  Alternatively, you could configure
the network manually by following the
@ref{manual-installation-networking} section.  If you get the error
@samp{RTNETLINK answers: Operation not possible due to RF-kill}, try
@samp{rfkill list} followed by @samp{rfkill unblock 0}, where @samp{0}
is your device identifier (ID).

@item
Switch to a virtual console (tty) if you haven't already by pressing
simultaneously the @kbd{Control + Alt + F4} keys.  Mount your file
system at @file{/mnt}.  Assuming your root partition is
@file{/dev/sda2}, you would do:

@example sh
mount /dev/sda2 /mnt
@end example

@item
Mount special block devices and Linux-specific directories:

@example sh
mount --rbind /proc /mnt/proc
mount --rbind /sys /mnt/sys
mount --rbind /dev /mnt/dev
@end example

If your system is EFI-based, you must also mount the ESP partition.
Assuming it is @file{/dev/sda1}, you can do so with:

@example sh
mount /dev/sda1 /mnt/boot/efi
@end example

@item
Enter your system via chroot:

@example sh
chroot /mnt /bin/sh
@end example

@item
Source the system profile as well as your @var{user} profile to setup
the environment, where @var{user} is the user name used for the Guix
System you are attempting to repair:

@example sh
source /var/guix/profiles/system/profile/etc/profile
source /home/@var{user}/.guix-profile/etc/profile
@end example

To ensure you are working with the Guix revision you normally would as
your normal user, also source your current Guix profile:

@example sh
source /home/@var{user}/.config/guix/current/etc/profile
@end example

@item
Start a minimal @command{guix-daemon} in the background:

@example sh
guix-daemon --build-users-group=guixbuild --disable-chroot &
@end example

@item
Edit your Guix System configuration if needed, then reconfigure with:

@example sh
guix system reconfigure your-config.scm
@end example

@item
Finally, you should be good to reboot the system to test your fix.

@end enumerate

@node Home Configuration
@chapter Home Configuration
@cindex home configuration
Guix supports declarative configuration of @dfn{home environments} by
utilizing the configuration mechanism described in the previous chapter
(@pxref{Defining Services}), but for user's dotfiles and packages.  It
works both on Guix System and foreign distros and allows users to
declare all the packages and services that should be installed and
configured for the user.  Once a user has written a file containing a
@code{home-environment} record, such a configuration can be
@dfn{instantiated} by an unprivileged user with the @command{guix home}
command (@pxref{Invoking guix home}).
@c Maybe later, it will be possible to make home configuration a part of
@c system configuration to make everything managed by guix system.

The user's home environment usually consists of three basic parts:
software, configuration, and state.  Software in mainstream distros are
usually installed system-wide, but with GNU Guix most software packages
can be installed on a per-user basis without needing root privileges,
and are thus considered part of the user’s @dfn{home environment}.
Packages on their own are not very useful in many cases, because often they
require some additional configuration, usually config files that reside
in @env{XDG_CONFIG_HOME} (@file{~/.config} by default) or other
directories.  Everything else can be considered state, like media files,
application databases, and logs.

Using Guix for managing home environments provides a number of
advantages:

@itemize

@item All software can be configured in one language (Guile Scheme),
this gives users the ability to share values between configurations of
different programs.

@item A well-defined home environment is self-contained and can be
created in a declarative and reproducible way---there is no need to grab
external binaries or manually edit some configuration file.

@item After every @command{guix home reconfigure} invocation, a new home
environment generation will be created.  This means that users can
rollback to a previous home environment generation so they don’t have to
worry about breaking their configuration.

@item It is possible to manage stateful data with Guix Home, this
includes the ability to automatically clone Git repositories on the
initial setup of the machine, and periodically running commands like
@command{rsync} to sync data with another host.  This functionality is
still in an experimental stage, though.

@end itemize

@menu
* Declaring the Home Environment::  Customizing your Home.
* Configuring the Shell::       Enabling home environment.
* Home Services::               Specifying home services.
* Invoking guix home::          Instantiating a home configuration.
@end menu

@node Declaring the Home Environment
@section Declaring the Home Environment
The home environment is configured by providing a
@code{home-environment} declaration in a file that can be passed to the
@command{guix home} command (@pxref{Invoking guix home}).  The easiest
way to get started is by generating an initial configuration with
@command{guix home import}:

@example
guix home import ~/src/guix-config
@end example

The @command{guix home import} command reads some of the ``dot files''
such as @file{~/.bashrc} found in your home directory and copies them to
the given directory, @file{~/src/guix-config} in this case; it also
reads the contents of your profile, @file{~/.guix-profile}, and, based
on that, it populates @file{~/src/guix-config/home-configuration.scm}
with a Home configuration that resembles your current configuration.

A simple setup can include Bash and a custom text configuration, like in
the example below.  Don't be afraid to declare home environment parts,
which overlaps with your current dot files: before installing any
configuration files, Guix Home will back up existing config files to a
separate place in the home directory.

@quotation Note
It is highly recommended that you manage your shell or shells with Guix
Home, because it will make sure that all the necessary scripts are
sourced by the shell configuration file.  Otherwise you will need to do
it manually. (@pxref{Configuring the Shell}).
@end quotation

@findex home-environment
@lisp
@include he-config-bare-bones.scm
@end lisp

The @code{packages} field should be self-explanatory, it will install
the list of packages into the user's profile.  The most important field
is @code{services}, it contains a list of @dfn{home services}, which are
the basic building blocks of a home environment.

There is no daemon (at least not necessarily) related to a home service,
a home service is just an element that is used to declare part of home
environment and extend other parts of it.  The extension mechanism
discussed in the previous chapter (@pxref{Defining Services}) should not
be confused with Shepherd services (@pxref{Shepherd Services}).  Using this extension
mechanism and some Scheme code that glues things together gives the user
the freedom to declare their own, very custom, home environments.

@cindex container, for @command{guix home}
Once the configuration looks good, you can first test it in a throw-away
``container'':

@example
guix home container config.scm
@end example

The command above spawns a shell where your home environment is running.
The shell runs in a container, meaning it's isolated from the rest of
the system, so it's a good way to try out your configuration---you can
see if configuration bits are missing or misbehaving, if daemons get
started, and so on.  Once you exit that shell, you're back to the prompt
of your original shell ``in the real world''.

Once you have a configuration file that suits your needs, you can
reconfigure your home by running:

@example
guix home reconfigure config.scm
@end example

This ``builds'' your home environment and creates @file{~/.guix-home}
pointing to it.  Voilà!

@quotation Note
Make sure the operating system has elogind, systemd, or a similar
mechanism to create the XDG run-time directory and has the
@env{XDG_RUNTIME_DIR} variable set.  Failing that, the
@file{on-first-login} script will not execute anything, and processes
like user Shepherd and its descendants will not start.
@end quotation

If you're using Guix System, you can embed your home configuration in
your system configuration such that @command{guix system reconfigure}
will deploy both the system @emph{and} your home at once!
@xref{guix-home-service-type, @code{guix-home-service-type}}, for how to
do that.

@node Configuring the Shell
@section Configuring the Shell
This section is safe to skip if your shell or shells are managed by
Guix Home.  Otherwise, read it carefully.

There are a few scripts that must be evaluated by a login shell to
activate the home environment.  The shell startup files only read by
login shells often have @code{profile} suffix.  For more information
about login shells see @ref{Invoking Bash,,, bash, The GNU Bash
Reference Manual} and see @ref{Bash Startup Files,,, bash, The GNU Bash
Reference Manual}.

The first script that needs to be sourced is @file{setup-environment},
which sets all the necessary environment variables (including variables
declared by the user) and the second one is @file{on-first-login}, which
starts Shepherd for the current user and performs actions declared by
other home services that extends
@code{home-run-on-first-login-service-type}.

Guix Home will always create @file{~/.profile}, which contains the
following lines:

@example
HOME_ENVIRONMENT=$HOME/.guix-home
. $HOME_ENVIRONMENT/setup-environment
$HOME_ENVIRONMENT/on-first-login
@end example

This makes POSIX compliant login shells activate the home environment.
However, in most cases this file won't be read by most modern shells,
because they are run in non POSIX mode by default and have their own
@file{*profile} startup files.  For example Bash will prefer
@file{~/.bash_profile} in case it exists and only if it doesn't will it
fallback to @file{~/.profile}.  Zsh (if no additional options are
specified) will ignore @file{~/.profile}, even if @file{~/.zprofile}
doesn't exist.

To make your shell respect @file{~/.profile}, add @code{. ~/.profile} or
@code{source ~/.profile} to the startup file for the login shell.  In
case of Bash, it is @file{~/.bash_profile}, and in case of Zsh, it is
@file{~/.zprofile}.

@quotation Note
This step is only required if your shell is @emph{not} managed by Guix Home.
Otherwise, everything will be done automatically.
@end quotation

@node Home Services
@section Home Services
@cindex home services

A @dfn{home service} is not necessarily something that has a daemon and
is managed by Shepherd (@pxref{Jump Start,,, shepherd, The GNU Shepherd
Manual}), in most cases it doesn't.  It's a simple building block of the
home environment, often declaring a set of packages to be installed in
the home environment profile, a set of config files to be symlinked into
@env{XDG_CONFIG_HOME} (@file{~/.config} by default), and environment
variables to be set by a login shell.

There is a service extension mechanism (@pxref{Service Composition})
which allows home services to extend other home services and utilize
capabilities they provide; for example: declare mcron jobs
(@pxref{Top,,, mcron, GNU@tie{}Mcron}) by extending @ref{Mcron Home
Service}; declare daemons by extending @ref{Shepherd Home Service}; add
commands, which will be invoked on by the Bash by extending
@ref{Shells Home Services, @code{home-bash-service-type}}.

A good way to discover available home services is using the
@command{guix home search} command (@pxref{Invoking guix home}).  After
the required home services are found, include its module with the
@code{use-modules} form (@pxref{use-modules,, Using Guile Modules,
guile, The GNU Guile Reference Manual}), or the @code{#:use-modules}
directive (@pxref{define-module,, Creating Guile Modules, guile, The GNU
Guile Reference Manual}) and declare a home service using the
@code{service} function, or extend a service type by declaring a new
service with the @code{simple-service} procedure from @code{(gnu
services)}.

@menu
* Essential Home Services::     Environment variables, packages, on-* scripts.
* Shells: Shells Home Services.  POSIX shells, Bash, Zsh.
* Mcron: Mcron Home Service.    Scheduled User's Job Execution.
* Power Management: Power Management Home Services.  Services for battery power.
* Shepherd: Shepherd Home Service.  Managing User's Daemons.
* SSH: Secure Shell.            Setting up the secure shell client.
* GPG: GNU Privacy Guard.       Setting up GPG and related tools.
* Desktop: Desktop Home Services.  Services for graphical environments.
* Guix: Guix Home Services.     Services for Guix.
* Fonts: Fonts Home Services.   Services for managing User's fonts.
* Sound: Sound Home Services.   Dealing with audio.
* Mail: Mail Home Services.     Services for managing mail.
* Messaging: Messaging Home Services.  Services for managing messaging.
* Media: Media Home Services.   Services for managing media.
* Networking: Networking Home Services.  Networking services.
* Miscellaneous: Miscellaneous Home Services.  More services.
@end menu
@c In addition to that Home Services can provide

@node Essential Home Services
@subsection Essential Home Services
There are a few essential home services defined in
@code{(gnu home services)}, they are mostly for internal use and are
required to build a home environment, but some of them will be useful
for the end user.

@cindex environment variables

@defvar home-environment-variables-service-type
The service of this type will be instantiated by every home environment
automatically by default, there is no need to define it, but someone may
want to extend it with a list of pairs to set some environment
variables.

@lisp
(list ("ENV_VAR1" . "value1")
      ("ENV_VAR2" . "value2"))
@end lisp

The easiest way to extend a service type, without defining a new service
type is to use the @code{simple-service} helper from @code{(gnu
services)}.

@findex literal-string
@lisp
(simple-service 'some-useful-env-vars-service
		home-environment-variables-service-type
		`(("LESSHISTFILE" . "$XDG_CACHE_HOME/.lesshst")
                  ("SHELL" . ,(file-append zsh "/bin/zsh"))
                  ("USELESS_VAR" . #f)
                  ("_JAVA_AWT_WM_NONREPARENTING" . #t)
                  ("LITERAL_VALUE" . ,(literal-string "$@{abc@}"))))
@end lisp

If you include such a service in you home environment definition, it
will add the following content to the @file{setup-environment} script
(which is expected to be sourced by the login shell):

@example
export LESSHISTFILE="$XDG_CACHE_HOME/.lesshst"
export SHELL="/gnu/store/2hsg15n644f0glrcbkb1kqknmmqdar03-zsh-5.8/bin/zsh"
export _JAVA_AWT_WM_NONREPARENTING
export LITERAL_VALUE='$@{abc@}'
@end example

Notice that @code{literal-string} above lets us declare that a value is
to be interpreted as a @dfn{literal string}, meaning that ``special
characters'' such as the dollar sign will not be interpreted by the
shell.

@quotation Note
Make sure that module @code{(gnu packages shells)} is imported with
@code{use-modules} or any other way, this namespace contains the
definition of the @code{zsh} package, which is used in the example
above.
@end quotation

The association list (@pxref{Association Lists, alists, Association
Lists, guile, The GNU Guile Reference manual}) is a data structure
containing key-value pairs, for
@code{home-environment-variables-service-type} the key is always a
string, the value can be a string, string-valued gexp
(@pxref{G-Expressions}), file-like object (@pxref{G-Expressions,
file-like object}) or boolean.  For gexps, the variable will be set to
the value of the gexp; for file-like objects, it will be set to the path
of the file in the store (@pxref{The Store}); for @code{#t}, it will
export the variable without any value; and for @code{#f}, it will omit
variable.

@end defvar

@defvar home-profile-service-type
The service of this type will be instantiated by every home environment
automatically, there is no need to define it, but you may want to extend
it with a list of packages if you want to install additional packages
into your profile.  Other services, which need to make some programs
available to the user will also extend this service type.

The extension value is just a list of packages:

@lisp
(list htop vim emacs)
@end lisp

The same approach as @code{simple-service} (@pxref{Service Reference,
simple-service}) for @code{home-environment-variables-service-type} can
be used here, too.  Make sure that modules containing the specified
packages are imported with @code{use-modules}.  To find a package or
information about its module use @command{guix search} (@pxref{Invoking
guix package}).  Alternatively, @code{specification->package} can be
used to get the package record from a string without importing its
related module.
@end defvar

There are few more essential services, but users are not expected to
extend them.

@defvar home-service-type
The root of home services DAG, it generates a folder, which later will be
symlinked to @file{~/.guix-home}, it contains configurations,
profile with binaries and libraries, and some necessary scripts to glue
things together.
@end defvar

@defvar home-run-on-first-login-service-type
The service of this type generates a Guile script, which is expected to
be executed by the login shell.  It is only executed if the special flag
file inside @env{XDG_RUNTIME_DIR} hasn't been created, this prevents
redundant executions of the script if multiple login shells are spawned.

It can be extended with a gexp.  However, to autostart an application,
users @emph{should not} use this service, in most cases it's better to extend
@code{home-shepherd-service-type} with a Shepherd service
(@pxref{Shepherd Services}), or extend the shell's startup file with
the required command using the appropriate service type.
@end defvar

@defvar home-files-service-type
The service of this type allows to specify a list of files, which will
go to @file{~/.guix-home/files}, usually this directory contains
configuration files (to be more precise it contains symlinks to files in
@file{/gnu/store}), which should be placed in @file{$XDG_CONFIG_DIR} or
in rare cases in @file{$HOME}.  It accepts extension values in the
following format:

@lisp
`((".sway/config" ,sway-file-like-object)
  (".tmux.conf" ,(local-file "./tmux.conf")))
@end lisp

Each nested list contains two values: a subdirectory and file-like
object.  After building a home environment @file{~/.guix-home/files}
will be populated with appropriate content and all nested directories will
be created accordingly, however, those files won't go any further until
some other service will do it.  By default a
@code{home-symlink-manager-service-type}, which creates necessary
symlinks in home folder to files from @file{~/.guix-home/files} and
backs up already existing, but clashing configs and other things, is a
part of essential home services (enabled by default), but it's possible
to use alternative services to implement more advanced use cases like
read-only home.  Feel free to experiment and share your results.
@end defvar

@cindex dot files in Guix Home
It is often the case that Guix Home users already have a setup for versioning
their user configuration files (also known as @emph{dot files}) in a single
directory, and some way of automatically deploy changes to their user home.

@cindex Stow-like dot file management
The @code{home-dotfiles-service-type} from @code{(gnu home services dotfiles)}
is designed to ease the way into using Guix Home for this kind of users,
allowing them to point the service to their dotfiles directory without
migrating them to Guix native configurations.

Please keep in mind that it is advisable to keep your dotfiles directories under
version control, for example in the same repository where you'd track your
Guix Home configuration.

There are two supported dotfiles directory layouts, for now. The
@code{'plain} layout, which is structured as follows:

@example
~$ tree -a ./dotfiles/
dotfiles/
├── .gitconfig
├── .gnupg
│   ├── gpg-agent.conf
│   └── gpg.conf
├── .guile
├── .config
│   ├── guix
│   │   └── channels.scm
│   └── nixpkgs
│       └── config.nix
├── .nix-channels
├── .tmux.conf
└── .vimrc
@end example

This tree structure is installed as is to the
home directory upon @command{guix home reconfigure}.

The @code{'stow} layout, which must
follow the layout suggested by
@uref{https://www.gnu.org/software/stow/, GNU Stow} presents an additional
application specific directory layer, just like:

@example
~$ tree -a ./dotfiles/
dotfiles/
├── git
│   └── .gitconfig
├── gpg
│   └── .gnupg
│       ├── gpg-agent.conf
│       └── gpg.conf
├── guile
│   └── .guile
├── guix
│   └── .config
│       └── guix
│           └── channels.scm
├── nix
│   ├── .config
│   │   └── nixpkgs
│   │       └── config.nix
│   └── .nix-channels
├── tmux
│   └── .tmux.conf
└── vim
    └── .vimrc

13 directories, 10 files
@end example

For an informal specification please refer to the Stow manual
(@pxref{Top,,, stow, Introduction}). This tree structure is installed following
GNU Stow's logic to the home directory upon @command{guix home reconfigure}.

A suitable configuration with a @code{'plain} layout could be:

@lisp
(home-environment
  ;; @dots{}
  (services
    (service home-dotfiles-service-type
             (home-dotfiles-configuration
               (directories '("./dotfiles"))))))
@end lisp

The expected home directory state would then be:

@example
.
├── .config
│   ├── guix
│   │   └── channels.scm
│   └── nixpkgs
│       └── config.nix
├── .gitconfig
├── .gnupg
│   ├── gpg-agent.conf
│   └── gpg.conf
├── .guile
├── .nix-channels
├── .tmux.conf
└── .vimrc
@end example

@defvar home-dotfiles-service-type
Return a service which is very similiar to @code{home-files-service-type}
(and actually extends it), but designed to ease the way into using Guix
Home for users that already track their dotfiles under some kind of version
control.  This service allows users to point Guix Home to their dotfiles
directory and have their files automatically provisioned to their home
directory, without migrating all of their dotfiles to Guix native
configurations.
@end defvar

@c %start of fragment

@deftp {Data Type} home-dotfiles-configuration
Available @code{home-dotfiles-configuration} fields are:

@table @asis
@item @code{source-directory} (default: @code{(current-source-directory)}) (type: string)
The path where dotfile directories are resolved.  By default dotfile
directories are resolved relative the source location where
@code{home-dotfiles-configuration} appears.

@item @code{layout} (default: @code{'plain}) (type: symbol)
The intended layout of the specified @code{directory}.  It can be either
@code{'stow} or @code{'plain}.

@item @code{directories} (default: @code{'()}) (type: list-of-strings)
The list of dotfiles directories where @code{home-dotfiles-service-type}
will look for application dotfiles.

@item @code{packages} (type: maybe-list-of-strings)
The names of a subset of the GNU Stow package layer directories.  When provided
the @code{home-dotfiles-service-type} will only provision dotfiles from this
subset of applications.  This field will be ignored if @code{layout} is set
to @code{'plain}.

@item @code{excluded} (default: @code{'(".*~" ".*\\.swp" "\\.git" "\\.gitignore")}) (type: list-of-strings)
The list of file patterns @code{home-dotfiles-service-type} will exclude
while visiting each one of the @code{directories}.

@end table

@end deftp


@c %end of fragment

@defvar home-xdg-configuration-files-service-type
The service is very similar to @code{home-files-service-type} (and
actually extends it), but used for defining files, which will go to
@file{~/.guix-home/files/.config}, which will be symlinked to
@file{$XDG_CONFIG_DIR} by @code{home-symlink-manager-service-type} (for
example) during activation.  It accepts extension values in the
following format:

@lisp
`(("sway/config" ,sway-file-like-object)
  ;; -> ~/.guix-home/files/.config/sway/config
  ;; -> $XDG_CONFIG_DIR/sway/config (by symlink-manager)
  ("tmux/tmux.conf" ,(local-file "./tmux.conf")))
@end lisp
@end defvar

@defvar home-activation-service-type
The service of this type generates a guile script, which runs on every
@command{guix home reconfigure} invocation or any other action, which
leads to the activation of the home environment.
@end defvar

@defvar home-symlink-manager-service-type
The service of this type generates a guile script, which will be
executed during activation of home environment, and do a few following
steps:

@enumerate
@item
Reads the content of @file{files/} directory of current and pending home
environments.

@item
Cleans up all symlinks created by symlink-manager on previous
activation.  Also, sub-directories, which become empty also will be
cleaned up.

@item
Creates new symlinks the following way: It looks @file{files/} directory
(usually defined with @code{home-files-service-type},
@code{home-xdg-configuration-files-service-type} and maybe some others),
takes the files from @file{files/.config/} subdirectory and put
respective links in @env{XDG_CONFIG_DIR}.  For example symlink for
@file{files/.config/sway/config} will end up in
@file{$XDG_CONFIG_DIR/sway/config}.  The rest files in @file{files/}
outside of @file{files/.config/} subdirectory will be treated slightly
different: symlink will just go to @file{$HOME}.
@file{files/.some-program/config} will end up in
@file{$HOME/.some-program/config}.

@item
If some sub-directories are missing, they will be created.

@item
If there is a clashing files on the way, they will be backed up.

@end enumerate

symlink-manager is a part of essential home services and is enabled and
used by default.
@end defvar


@node Shells Home Services
@subsection Shells

@cindex shell
@cindex login shell
@cindex interactive shell
@cindex bash
@cindex zsh

Shells play a quite important role in the environment initialization
process, you can configure them manually as described in section
@ref{Configuring the Shell}, but the recommended way is to use home services
listed below.  It's both easier and more reliable.

Each home environment instantiates
@code{home-shell-profile-service-type}, which creates a
@file{~/.profile} startup file for all POSIX-compatible shells.  This
file contains all the necessary steps to properly initialize the
environment, but many modern shells like Bash or Zsh prefer their own
startup files, that's why the respective home services
(@code{home-bash-service-type} and @code{home-zsh-service-type}) ensure
that @file{~/.profile} is sourced by @file{~/.bash_profile} and
@file{~/.zprofile}, respectively.

@subsubheading Shell Profile Service

@deftp {Data Type} home-shell-profile-configuration
Available @code{home-shell-profile-configuration} fields are:

@table @asis
@item @code{profile} (default: @code{'()}) (type: text-config)
@code{home-shell-profile} is instantiated automatically by
@code{home-environment}, DO NOT create this service manually, it can
only be extended.  @code{profile} is a list of file-like objects, which
will go to @file{~/.profile}.  By default @file{~/.profile} contains the
initialization code which must be evaluated by the login shell to make
home-environment's profile available to the user, but other commands can
be added to the file if it is really necessary.  In most cases shell's
configuration files are preferred places for user's customizations.
Extend home-shell-profile service only if you really know what you do.

@end table

@end deftp

@subsubheading Bash Home Service

@anchor{home-bash-configuration}
@deftp {Data Type} home-bash-configuration
Available @code{home-bash-configuration} fields are:

@table @asis
@item @code{package} (default: @code{bash}) (type: package)
The Bash package to use.

@item @code{guix-defaults?} (default: @code{#t}) (type: boolean)
Add sane defaults like reading @file{/etc/bashrc} and coloring the output of
@command{ls} to the top of the @file{.bashrc} file.

@item @code{environment-variables} (default: @code{'()}) (type: alist)
Association list of environment variables to set for the Bash session.  The
rules for the @code{home-environment-variables-service-type} apply
here (@pxref{Essential Home Services}).  The contents of this field will be
added after the contents of the @code{bash-profile} field.

@item @code{aliases} (default: @code{'()}) (type: alist)
Association list of aliases to set for the Bash session.  The aliases
will be defined after the contents of the @code{bashrc} field has been
put in the @file{.bashrc} file.  The alias will automatically be quoted,
so something like this:

@lisp
'(("ls" . "ls -alF"))
@end lisp

turns into

@example
alias ls="ls -alF"
@end example

@item @code{bash-profile} (default: @code{'()}) (type: text-config)
List of file-like objects, which will be added to @file{.bash_profile}.
Used for executing user's commands at start of login shell (In most
cases the shell started on tty just after login).  @file{.bash_login}
won't be ever read, because @file{.bash_profile} always present.

@item @code{bashrc} (default: @code{'()}) (type: text-config)
List of file-like objects, which will be added to @file{.bashrc}.  Used
for executing user's commands at start of interactive shell (The shell
for interactive usage started by typing @code{bash} or by terminal app
or any other program).

@item @code{bash-logout} (default: @code{'()}) (type: text-config)
List of file-like objects, which will be added to @file{.bash_logout}.
Used for executing user's commands at the exit of login shell.  It won't
be read in some cases (if the shell terminates by exec'ing another
process for example).

@end table
@end deftp

You can extend the Bash service by using the @code{home-bash-extension}
configuration record, whose fields must mirror that of
@code{home-bash-configuration} (@pxref{home-bash-configuration}).  The
contents of the extensions will be added to the end of the corresponding
Bash configuration files (@pxref{Bash Startup Files,,, bash, The GNU
Bash Reference Manual}.

For example, here is how you would define a service that extends the
Bash service such that @file{~/.bash_profile} defines an additional
environment variable, @env{PS1}:

@lisp
(define bash-fancy-prompt-service
  (simple-service 'bash-fancy-prompt
                  home-bash-service-type
                  (home-bash-extension
                   (environment-variables
                    '(("PS1" . "\\u \\wλ "))))))
@end lisp

You would then add @code{bash-fancy-prompt-service} to the list in the
@code{services} field of your @code{home-environment}.  The reference of
@code{home-bash-extension} follows.

@deftp {Data Type} home-bash-extension
Available @code{home-bash-extension} fields are:

@table @asis
@item @code{environment-variables} (default: @code{'()}) (type: alist)
Additional environment variables to set.  These will be combined with the
environment variables from other extensions and the base service to form one
coherent block of environment variables.

@item @code{aliases} (default: @code{'()}) (type: alist)
Additional aliases to set.  These will be combined with the aliases from
other extensions and the base service.

@item @code{bash-profile} (default: @code{'()}) (type: text-config)
Additional text blocks to add to @file{.bash_profile}, which will be combined
with text blocks from other extensions and the base service.

@item @code{bashrc} (default: @code{'()}) (type: text-config)
Additional text blocks to add to @file{.bashrc}, which will be combined
with text blocks from other extensions and the base service.

@item @code{bash-logout} (default: @code{'()}) (type: text-config)
Additional text blocks to add to @file{.bash_logout}, which will be combined
with text blocks from other extensions and the base service.

@end table
@end deftp

@subsubheading Zsh Home Service

@deftp {Data Type} home-zsh-configuration
Available @code{home-zsh-configuration} fields are:

@table @asis
@item @code{package} (default: @code{zsh}) (type: package)
The Zsh package to use.

@item @code{xdg-flavor?} (default: @code{#t}) (type: boolean)
Place all the configs to @file{$XDG_CONFIG_HOME/zsh}.  Makes
@file{~/.zshenv} to set @env{ZDOTDIR} to @file{$XDG_CONFIG_HOME/zsh}.
Shell startup process will continue with
@file{$XDG_CONFIG_HOME/zsh/.zshenv}.

@item @code{environment-variables} (default: @code{'()}) (type: alist)
Association list of environment variables to set for the Zsh session.

@item @code{zshenv} (default: @code{'()}) (type: text-config)
List of file-like objects, which will be added to @file{.zshenv}.  Used
for setting user's shell environment variables.  Must not contain
commands assuming the presence of tty or producing output.  Will be read
always.  Will be read before any other file in @env{ZDOTDIR}.

@item @code{zprofile} (default: @code{'()}) (type: text-config)
List of file-like objects, which will be added to @file{.zprofile}.  Used
for executing user's commands at start of login shell (In most cases the
shell started on tty just after login).  Will be read before
@file{.zlogin}.

@item @code{zshrc} (default: @code{'()}) (type: text-config)
List of file-like objects, which will be added to @file{.zshrc}.  Used
for executing user's commands at start of interactive shell (The shell
for interactive usage started by typing @code{zsh} or by terminal app or
any other program).

@item @code{zlogin} (default: @code{'()}) (type: text-config)
List of file-like objects, which will be added to @file{.zlogin}.  Used
for executing user's commands at the end of starting process of login
shell.

@item @code{zlogout} (default: @code{'()}) (type: text-config)
List of file-like objects, which will be added to @file{.zlogout}.  Used
for executing user's commands at the exit of login shell.  It won't be
read in some cases (if the shell terminates by exec'ing another process
for example).

@end table

@end deftp

@subsubheading Inputrc Profile Service
@cindex inputrc
@cindex readline

The @uref{https://tiswww.cwru.edu/php/chet/readline/rltop.html, GNU
Readline package} includes Emacs and vi editing modes, with the ability
to customize the configuration with settings in the @file{~/.inputrc}
file.  With the @code{gnu home services shells} module, you can setup
your readline configuration in a predictable manner, as shown below.
For more information about configuring an @file{~/.inputrc} file,
@pxref{Readline Init File,,, readline, GNU Readline}.

@defvar home-inputrc-service-type

This is the service to setup various @file{.inputrc} configurations. The
settings in @file{.inputrc} are read by all programs which are linked
with GNU Readline.

Here is an example of a service and its configuration that you could add
to the @code{services} field of your @code{home-environment}:

@lisp
(service home-inputrc-service-type
         (home-inputrc-configuration
           (key-bindings
            `(("Control-l" . "clear-screen")))
           (variables
            `(("bell-style" . "visible")
              ("colored-completion-prefix" . #t)
              ("editing-mode" . "vi")
              ("show-mode-in-prompt" . #t)))
           (conditional-constructs
            `(("$if mode=vi" .
               ,(home-inputrc-configuration
                  (variables
                   `(("colored-stats" . #t)
                     ("enable-bracketed-paste" . #t)))))
              ("$else" .
               ,(home-inputrc-configuration
                  (variables
                   `(("show-all-if-ambiguous" . #t)))))
              ("endif" . #t)
              ("$include" . "/etc/inputrc")
              ("$include" . ,(file-append
                               (specification->package "readline")
                               "/etc/inputrc"))))))
@end lisp

The example above starts with a combination of @code{key-bindings} and
@code{variables}.  The @code{conditional-constructs} show how it is
possible to add conditionals and includes.  In the example above
@code{colored-stats} is only enabled if the editing mode is @code{vi}
style, and it also reads any additional configuration located in
@file{/etc/inputrc} or in @file{/gnu/store/@dots{}-readline/etc/inputrc}.

The value associated with a @code{home-inputrc-service-type} instance
must be a @code{home-inputrc-configuration} record, as described below.

@end defvar

@anchor{home-inputrc-configuration}
@deftp {Data Type} home-inputrc-configuration
Available @code{home-inputrc-configuration} fields are:

@table @asis
@item @code{key-bindings} (default: @code{'()}) (type: alist)
Association list of readline key bindings to be added to the
@file{~/.inputrc} file.

@lisp
'((\"Control-l\" . \"clear-screen\"))
@end lisp

turns into

@example
Control-l: clear-screen
@end example

@item @code{variables} (default: @code{'()}) (type: alist)
Association list of readline variables to set.

@lisp
'((\"bell-style\" . \"visible\")
  (\"colored-completion-prefix\" . #t))
@end lisp

turns into

@example
set bell-style visible
set colored-completion-prefix on
@end example

@item @code{conditional-constructs} (default: @code{'()}) (type: alist)
Association list of conditionals to add to the initialization file.  This
includes @command{$if}, @command{else}, @command{endif} and @command{include}
and they receive a value of another @command{home-inputrc-configuration}.

@lisp
(conditional-constructs
 `((\"$if mode=vi\" .
     ,(home-inputrc-configuration
        (variables
         `((\"show-mode-in-prompt\" . #t)))))
   (\"$else\" .
     ,(home-inputrc-configuration
        (key-bindings
         `((\"Control-l\" . \"clear-screen\")))))
   (\"$endif\" . #t)))
@end lisp

turns into

@example
$if mode=vi
set show-mode-in-prompt on
$else
Control-l: clear-screen
$endif
@end example

@item @code{extra-content} (default: @code{""}) (type: text-config)
Extra content appended as-is to the configuration file.  Run @command{man
readline} for more information about all the configuration options.

@end table
@end deftp

@node Mcron Home Service
@subsection Scheduled User's Job Execution

@cindex cron
@cindex mcron
@cindex scheduling jobs

The @code{(gnu home services mcron)} module provides an interface to
GNU@tie{}mcron, a daemon to run jobs at scheduled times (@pxref{Top,,,
mcron, GNU@tie{}mcron}).  The information about system's mcron is
applicable here (@pxref{Scheduled Job Execution}), the only difference
for home services is that they have to be declared in a
@code{home-environment} record instead of an @code{operating-system}
record.

@defvar home-mcron-service-type
This is the type of the @code{mcron} home service, whose value is a
@code{home-mcron-configuration} object.  It allows to manage scheduled
tasks.

This service type can be the target of a service extension that provides
additional job specifications (@pxref{Service Composition}).  In other
words, it is possible to define services that provide additional mcron
jobs to run.
@end defvar

@deftp {Data Type} home-mcron-configuration
Available @code{home-mcron-configuration} fields are:

@c Auto-generated with (gnu home services mcron)'s
@c generate-documentation procedure.
@c %start of fragment
@table @asis
@item @code{mcron} (default: @code{mcron}) (type: file-like)
The mcron package to use.

@item @code{jobs} (default: @code{'()}) (type: list-of-gexps)
This is a list of gexps (@pxref{G-Expressions}), where each gexp
corresponds to an mcron job specification (@pxref{Syntax, mcron job
specifications,, mcron,GNU@tie{}mcron}).

@item @code{log?} (default: @code{#t}) (type: boolean)
Log messages to standard output.

@item @code{log-format} (default: @code{"~1@@*~a ~a: ~a~%"}) (type: string)
@code{(ice-9 format)} format string for log messages.  The default value
produces messages like "@samp{@var{pid} @var{name}: @var{message}"}
(@pxref{Invoking mcron, Invoking,, mcron,GNU@tie{}mcron}).  Each message
is also prefixed by a timestamp by GNU Shepherd.

@end table
@end deftp
@c %end of fragment

@node Power Management Home Services
@subsection Power Management Home Services

@cindex power management
The @code{(gnu home services pm)} module provides home services
pertaining to battery power.

@defvar home-batsignal-service-type
Service for @code{batsignal}, a program that monitors battery levels
and warns the user through desktop notifications when their battery
is getting low.  You can also configure a command to be run when the
battery level passes a point deemed ``dangerous''.  This service is
configured with the @code{home-batsignal-configuration} record.
@end defvar

@deftp {Data Type} home-batsignal-configuration
Data type representing the configuration for batsignal.

@table @asis
@item @code{warning-level} (default: @code{15})
The battery level to send a warning message at.

@item @code{warning-message} (default: @code{#f})
The message to send as a notification when the battery level reaches
the @code{warning-level}.  Setting to @code{#f} uses the default
message.

@item @code{critical-level} (default: @code{5})
The battery level to send a critical message at.

@item @code{critical-message} (default: @code{#f})
The message to send as a notification when the battery level reaches
the @code{critical-level}.  Setting to @code{#f} uses the default
message.

@item @code{danger-level} (default: @code{2})
The battery level to run the @code{danger-command} at.

@item @code{danger-command} (default: @code{#f})
The command to run when the battery level reaches the @code{danger-level}.
Setting to @code{#f} disables running the command entirely.

@item @code{full-level} (default: @code{#f})
The battery level to send a full message at.  Setting to @code{#f}
disables sending the full message entirely.

@item @code{full-message} (default: @code{#f})
The message to send as a notification when the battery level reaches
the @code{full-level}.  Setting to @code{#f} uses the default message.

@item @code{batteries} (default: @code{'()})
The batteries to monitor.  Setting to @code{'()} tries to find batteries
automatically.

@item @code{poll-delay} (default: @code{60})
The time in seconds to wait before checking the batteries again.

@item @code{icon} (default: @code{#f})
A file-like object to use as the icon for battery notifications.  Setting
to @code{#f} disables notification icons entirely.

@item @code{notifications?} (default: @code{#t})
Whether to send any notifications.

@item @code{notifications-expire?} (default: @code{#f})
Whether notifications sent expire after a time.

@item @code{notification-command} (default: @code{#f})
Command to use to send messages.  Setting to @code{#f} sends a notification
through @code{libnotify}.

@item @code{ignore-missing?} (default: @code{#f})
Whether to ignore missing battery errors.
@end table
@end deftp

@node Shepherd Home Service
@subsection Managing User Daemons

@cindex shepherd services, for users
The @code{(gnu home services shepherd)} module supports the definitions
of per-user Shepherd services (@pxref{Introduction,,, shepherd, The GNU
Shepherd Manual}).  You extend @code{home-shepherd-service-type} with
new services; Guix Home then takes care of starting the @code{shepherd}
daemon for you when you log in, which in turns starts the services you
asked for.

@defvar home-shepherd-service-type
The service type for the userland Shepherd, which allows one to manage
long-running processes or one-shot tasks.  User's Shepherd is not an
init process (PID 1), but almost all other information described in
(@pxref{Shepherd Services}) is applicable here too.

This is the service type that extensions target when they want to create
shepherd services (@pxref{Service Types and Services}, for an example).
Each extension must pass a list of @code{<shepherd-service>}.  Its
value must be a @code{home-shepherd-configuration}, as described below.
@end defvar

@deftp {Data Type} home-shepherd-configuration
This data type represents the Shepherd's configuration.

@table @code
@item shepherd (default: @code{shepherd})
The Shepherd package to use.

@item auto-start? (default: @code{#t})
Whether or not to start Shepherd on first login.

@item services (default: @code{'()})
A list of @code{<shepherd-service>} to start.
You should probably use the service extension
mechanism instead (@pxref{Shepherd Services}).
@end table
@end deftp

@node Secure Shell
@subsection Secure Shell

@cindex secure shell client, configuration
@cindex SSH client, configuration
The @uref{https://www.openssh.com, OpenSSH package} includes a client,
the @command{ssh} command, that allows you to connect to remote machines
using the @acronym{SSH, secure shell} protocol.  With the @code{(gnu
home services ssh)} module, you can set up OpenSSH so that it works in a
predictable fashion, almost independently of state on the local machine.
To do that, you instantiate @code{home-openssh-service-type} in your
Home configuration, as explained below.

@defvar home-openssh-service-type
This is the type of the service to set up the OpenSSH client.  It takes
care of several things:

@itemize
@item
providing a @file{~/.ssh/config} file based on your configuration so
that @command{ssh} knows about hosts you regularly connect to and their
associated parameters;

@item
providing a @file{~/.ssh/authorized_keys}, which lists public keys that
the local SSH server, @command{sshd}, may accept to connect to this user
account;

@item
optionally providing a @file{~/.ssh/known_hosts} file so that @file{ssh}
can authenticate hosts you connect to.
@end itemize

Here is an example of a service and its configuration that you could add
to the @code{services} field of your @code{home-environment}:

@lisp
(service home-openssh-service-type
         (home-openssh-configuration
          (hosts
           (list (openssh-host (name "ci.guix.gnu.org")
                               (user "charlie"))
                 (openssh-host (name "chbouib")
                               (host-name "chbouib.example.org")
                               (user "supercharlie")
                               (port 10022))))
          (authorized-keys (list (local-file "alice.pub")))))
@end lisp

The example above lists two hosts and their parameters.  For instance,
running @command{ssh chbouib} will automatically connect to
@code{chbouib.example.org} on port 10022, logging in as user
@samp{supercharlie}.  Further, it marks the public key in
@file{alice.pub} as authorized for incoming connections.

The value associated with a @code{home-openssh-service-type} instance
must be a @code{home-openssh-configuration} record, as describe below.
@end defvar

@deftp {Data Type} home-openssh-configuration
This is the datatype representing the OpenSSH client and server
configuration in one's home environment.  It contains the following
fields:

@table @asis
@item @code{hosts} (default: @code{'()})
A list of @code{openssh-host} records specifying host names and
associated connection parameters (see below).  This host list goes into
@file{~/.ssh/config}, which @command{ssh} reads at startup.

@item @code{known-hosts} (default: @code{*unspecified*})
This must be either:

@itemize
@item
@code{*unspecified*}, in which case @code{home-openssh-service-type}
leaves it up to @command{ssh} and to the user to maintain the list of
known hosts at @file{~/.ssh/known_hosts}, or

@item
a list of file-like objects, in which case those are concatenated and
emitted as @file{~/.ssh/known_hosts}.
@end itemize

The @file{~/.ssh/known_hosts} contains a list of host name/host key
pairs that allow @command{ssh} to authenticate hosts you connect to and
to detect possible impersonation attacks.  By default, @command{ssh}
updates it in a @dfn{TOFU, trust-on-first-use} fashion, meaning that it
records the host's key in that file the first time you connect to it.
This behavior is preserved when @code{known-hosts} is set to
@code{*unspecified*}.

If you instead provide a list of host keys upfront in the
@code{known-hosts} field, your configuration becomes self-contained and
stateless: it can be replicated elsewhere or at another point in time.
Preparing this list can be relatively tedious though, which is why
@code{*unspecified*} is kept as a default.

@item @code{authorized-keys} (default: @code{#false})
The default @code{#false} value means: Leave any
@file{~/.ssh/authorized_keys} file alone.  Otherwise, this must be a
list of file-like objects, each of which containing an SSH public key
that should be authorized to connect to this machine.

Concretely, these files are concatenated and made available as
@file{~/.ssh/authorized_keys}.  If an OpenSSH server, @command{sshd}, is
running on this machine, then it @emph{may} take this file into account:
this is what @command{sshd} does by default, but be aware that it can
also be configured to ignore it.

@item @code{add-keys-to-agent} (default: @code{no})
This string specifies whether keys should be automatically added to a
running ssh-agent.  If this option is set to @code{yes} and a key is
loaded from a file, the key and its passphrase are added to the agent
with the default lifetime, as if by @code{ssh-add}.  If this option is
set to @code{ask}, @code{ssh} will require confirmation.  If this
option is set to @code{confirm}, each use of the key must be
confirmed.  If this option is set to @code{no}, no keys are added to
the agent.  Alternately, this option may be specified as a time interval
to specify the key's lifetime in @code{ssh-agent}, after which it will
automatically be removed.  The argument must be @code{no},
@code{yes}, @code{confirm} (optionally followed by a time
interval), @code{ask} or a time interval.
@end table
@end deftp

@c %start of fragment

@deftp {Data Type} openssh-host
Available @code{openssh-host} fields are:

@table @asis
@item @code{name} (type: string)
Name of this host declaration.  A @code{openssh-host} must define only
@code{name} or @code{match-criteria}.  Use host-name @code{\"*\"} for
top-level options.

@item @code{host-name} (type: maybe-string)
Host name---e.g., @code{"foo.example.org"} or @code{"192.168.1.2"}.

@item @code{match-criteria} (type: maybe-match-criteria)
When specified, this string denotes the set of hosts to which the entry
applies, superseding the @code{host-name} field.  Its first element must be
all or one of @code{ssh-match-keywords}.  The rest of the elements are
arguments for the keyword, or other criteria.  A @code{openssh-host} must
define only @code{name} or @code{match-criteria}.  Other host configuration
options will apply to all hosts matching @code{match-criteria}.

@item @code{address-family} (type: maybe-address-family)
Address family to use when connecting to this host: one of
@code{AF_INET} (for IPv4 only), @code{AF_INET6} (for IPv6 only).
Additionally, the field can be left unset to allow any address family.

@item @code{identity-file} (type: maybe-string)
The identity file to use---e.g., @code{"/home/charlie/.ssh/id_ed25519"}.

@item @code{port} (type: maybe-natural-number)
TCP port number to connect to.

@item @code{user} (type: maybe-string)
User name on the remote host.

@item @code{forward-x11?} (type: maybe-boolean)
Whether to forward remote client connections to the local X11 graphical
display.

@item @code{forward-x11-trusted?} (type: maybe-boolean)
Whether remote X11 clients have full access to the original X11
graphical display.

@item @code{forward-agent?} (type: maybe-boolean)
Whether the authentication agent (if any) is forwarded to the remote
machine.

@item @code{compression?} (type: maybe-boolean)
Whether to compress data in transit.

@item @code{proxy} (type: maybe-proxy-command-or-jump-list)
The command to use to connect to the server or a list of SSH hosts to
jump through before connecting to the server.  The field may be set to either a
@code{proxy-command} or a list of @code{proxy-jump} records.

As an example, a @code{proxy-command} to connect via an HTTP proxy at 192.0.2.0
would be constructed with: @code{(proxy-command "nc -X connect -x
192.0.2.0:8080 %h %p")}.

@deftp {Data Type} proxy-jump
Available @code{proxy-jump} fields are:

@table @asis
@item @code{user} (type: maybe-string)
User name on the remote host.

@item @code{host-name} (type: string)
Host name---e.g., @code{foo.example.org} or @code{192.168.1.2}.

@item @code{port} (type: maybe-natural-number)
TCP port number to connect to.

@end table

@end deftp

@item @code{host-key-algorithms} (type: maybe-string-list)
The list of accepted host key algorithms---e.g.,
@code{'("ssh-ed25519")}.

@item @code{accepted-key-types} (type: maybe-string-list)
The list of accepted user public key types.

@item @code{extra-content} (default: @code{""}) (type: raw-configuration-string)
Extra content appended as-is to this @code{Host} block in
@file{~/.ssh/config}.

@end table

@end deftp

@cindex Parcimonie, Home service
The @code{parcimonie} service runs a daemon that slowly refreshes a GnuPG
public key from a keyserver.  It refreshes one key at a time; between every
key update parcimonie sleeps a random amount of time, long enough for the
previously used Tor circuit to expire.  This process is meant to make it hard
for an attacker to correlate the multiple key update.

As an example, here is how you would configure @code{parcimonie} to refresh the
keys in your GnuPG keyring, as well as those keyrings created by Guix, such as
when running @code{guix import}:

@lisp
(service home-parcimonie-service-type
         (home-parcimonie-configuration
           (refresh-guix-keyrings? #t)))
@end lisp

This assumes that the Tor anonymous routing daemon is already running on your
system.  On Guix System, this can be achieved by setting up
@code{tor-service-type} (@pxref{Networking Services, @code{tor-service-type}}).

The service reference is given below.

@defvar parcimonie-service-type
This is the service type for @command{parcimonie}
(@uref{https://salsa.debian.org/intrigeri/parcimonie, Parcimonie's web site}).
Its value must be a @code{home-parcimonie-configuration}, as shown below.
@end defvar

@c %start of fragment

@deftp {Data Table} home-parcimonie-configuration
Available @code{home-parcimonie-configuration} fields are:

@table @asis
@item @code{parcimonie} (default: @code{parcimonie}) (type: file-like)
The parcimonie package to use.

@item @code{verbose?} (default: @code{#f}) (type: boolean)
Whether to have more verbose logging from the service.

@item @code{gnupg-already-torified?} (default: @code{#f}) (type: boolean)
Whether GnuPG is already configured to pass all traffic through
@uref{https://torproject.org, Tor}.

@item @code{refresh-guix-keyrings?} (default: @code{#f}) (type: boolean)
Guix creates a few keyrings in the @var{$XDG_CONFIG_DIR}, such as when running
@code{guix import} (@pxref{Invoking guix import}).  Setting this to @code{#t}
will also refresh any keyrings which Guix has created.

@item @code{extra-content} (default: @code{#f}) (type: raw-configuration-string)
Raw content to add to the parcimonie command.

@end table

@end deftp

@c %end of fragment

@cindex ssh-agent
The @uref{https://www.openssh.com, OpenSSH package} includes a daemon,
the @command{ssh-agent} command, that manages keys to connect to remote
machines using the @acronym{SSH, secure shell} protocol.  With the
@code{(gnu home services ssh)} service, you can configure the
OpenSSH ssh-agent to run upon login.  @xref{GNU Privacy Guard,
@code{home-gpg-agent-service-type}}, for an alternative to OpenSSH's
@command{ssh-agent}.


Here is an example of a service and its configuration that you could add
to the @code{services} field of your @code{home-environment}:

@lisp
(service home-ssh-agent-service-type
         (home-ssh-agent-configuration
          (extra-options '("-t" "1h30m"))))
@end lisp

@defvar home-ssh-agent-service-type
This is the type of the @code{ssh-agent} home service, whose value is a
@code{home-ssh-agent-configuration} object.
@end defvar

@deftp {Data Type} home-ssh-agent-configuration
Available @code{home-ssh-agent-configuration} fields are:

@table @asis
@item @code{openssh} (default: @code{openssh}) (type: file-like)
The OpenSSH package to use.

@item @code{socket-directory} (default: @code{@env{XDG_RUNTIME_DIR}/ssh-agent"}) (type: gexp)
The directory to write the ssh-agent's @file{socket} file.

@item @code{extra-options} (default: @code{'()})
Extra options will be passed to @command{ssh-agent}, please run
@command{man ssh-agent} for more information.

@end table
@end deftp

@node GNU Privacy Guard
@subsection GNU Privacy Guard

@cindex GNU Privacy Guard, Home service
@cindex GPG, Home service
The @code{(gnu home services gnupg)} module provides services that help
you set up the GNU Privacy Guard, also known as GnuPG or GPG, in your
home environment.

@cindex gpg-agent, Home service
@cindex SSH agent, with gpg-agent
The @code{gpg-agent} service configures and sets up GPG's agent, the
program that is responsible for managing OpenPGP private keys and,
optionally, OpenSSH (secure shell) private keys (@pxref{Invoking
GPG-AGENT,,, gnupg, Using the GNU Privacy Guard}).

As an example, here is how you would configure @code{gpg-agent} with SSH
support such that it uses the Emacs-based Pinentry interface when
prompting for a passphrase:

@lisp
(service home-gpg-agent-service-type
         (home-gpg-agent-configuration
          (pinentry-program
           (file-append pinentry-emacs "/bin/pinentry-emacs"))
          (ssh-support? #t)))
@end lisp

The service reference is given below.

@defvar home-gpg-agent-service-type
This is the service type for @command{gpg-agent} (@pxref{Invoking
GPG-AGENT,,, gnupg, Using the GNU Privacy Guard}).  Its value must be a
@code{home-gpg-agent-configuration}, as shown below.
@end defvar

@c %start of fragment

@deftp {Data Type} home-gpg-agent-configuration
Available @code{home-gpg-agent-configuration} fields are:

@table @asis
@item @code{gnupg} (default: @code{gnupg}) (type: file-like)
The GnuPG package to use.

@item @code{pinentry-program} (type: file-like)
Pinentry program to use.  Pinentry is a small user interface that
@command{gpg-agent} delegates to anytime it needs user input for a
passphrase or @acronym{PIN,personal identification number}
(@pxref{Top,,, pinentry,Using the PIN-Entry}).

@item @code{ssh-support?} (default: @code{#f}) (type: boolean)
Whether to enable @acronym{SSH,secure shell} support.  When true,
@command{gpg-agent} acts as a drop-in replacement for OpenSSH's
@command{ssh-agent} program, taking care of OpenSSH secret keys and
directing passphrase requests to the chosen Pinentry program.

@item @code{default-cache-ttl} (default: @code{600}) (type: integer)
Time a cache entry is valid, in seconds.

@item @code{max-cache-ttl} (default: @code{7200}) (type: integer)
Maximum time a cache entry is valid, in seconds.  After this time a
cache entry will be expired even if it has been accessed recently.

@item @code{default-cache-ttl-ssh} (default: @code{1800}) (type: integer)
Time a cache entry for SSH keys is valid, in seconds.

@item @code{max-cache-ttl-ssh} (default: @code{7200}) (type: integer)
Maximum time a cache entry for SSH keys is valid, in seconds.

@item @code{extra-content} (default: @code{""}) (type: raw-configuration-string)
Raw content to add to the end of @file{~/.gnupg/gpg-agent.conf}.

@end table

@end deftp


@c %end of fragment


@node Desktop Home Services
@subsection Desktop Home Services

The @code{(gnu home services desktop)} module provides services that you
may find useful on ``desktop'' systems running a graphical user
environment such as Xorg.

@cindex X Window, for Guix Home services
@cindex X11, in Guix Home
@defvar home-x11-service-type
This is the service type representing the X Window graphical display
server (also referred to as ``X11'').

X Window is necessarily started by a system service; on Guix System,
starting it is the responsibility of @code{gdm-service-type} and similar
services (@pxref{X Window}).  At the level of Guix Home, as an
unprivileged user, we cannot start X Window; all we can do is check
whether it is running.  This is what this service does.

As a user, you probably don't need to worry or explicitly instantiate
@code{home-x11-service-type}.  Services that require an X Window
graphical display, such as @code{home-redshift-service-type} below,
instantiate it and depend on its corresponding @code{x11-display}
Shepherd service (@pxref{Shepherd Home Service}).

When X Window is running, the @code{x11-display} Shepherd service starts
and sets the @env{DISPLAY} environment variable of the
@command{shepherd} process, using its original value if it was already
set; otherwise, it fails to start.

The service can also be forced to use a given value for @env{DISPLAY},
like so:

@example
herd start x11-display :3
@end example

In the example above, @code{x11-display} is instructed to set
@env{DISPLAY} to @code{:3}.
@end defvar

@defvar home-redshift-service-type
This is the service type for @uref{https://github.com/jonls/redshift,
Redshift}, a program that adjusts the display color temperature
according to the time of day.  Its associated value must be a
@code{home-redshift-configuration} record, as shown below.

A typical configuration, where we manually specify the latitude and
longitude, might look like this:

@lisp
(service home-redshift-service-type
         (home-redshift-configuration
          (location-provider 'manual)
          (latitude 35.81)    ;northern hemisphere
          (longitude -0.80))) ;west of Greenwich
@end lisp
@end defvar

@deftp {Data Type} home-redshift-configuration
Available @code{home-redshift-configuration} fields are:

@table @asis
@item @code{redshift} (default: @code{redshift}) (type: file-like)
Redshift package to use.

@item @code{location-provider} (default: @code{geoclue2}) (type: symbol)
Geolocation provider---@code{'manual} or @code{'geoclue2}.  In the
former case, you must also specify the @code{latitude} and
@code{longitude} fields so Redshift can determine daytime at your place.
In the latter case, the Geoclue system service must be running; it will
be queried for location information.

@item @code{adjustment-method} (default: @code{randr}) (type: symbol)
Color adjustment method.

@item @code{daytime-temperature} (default: @code{6500}) (type: integer)
Daytime color temperature (kelvins).

@item @code{nighttime-temperature} (default: @code{4500}) (type: integer)
Nighttime color temperature (kelvins).

@item @code{daytime-brightness} (type: maybe-inexact-number)
Daytime screen brightness, between 0.1 and 1.0, or left unspecified.

@item @code{nighttime-brightness} (type: maybe-inexact-number)
Nighttime screen brightness, between 0.1 and 1.0, or left unspecified.

@item @code{latitude} (type: maybe-inexact-number)
Latitude, when @code{location-provider} is @code{'manual}.

@item @code{longitude} (type: maybe-inexact-number)
Longitude, when @code{location-provider} is @code{'manual}.

@item @code{dawn-time} (type: maybe-string)
Custom time for the transition from night to day in the
morning---@code{"HH:MM"} format.  When specified, solar elevation is not
used to determine the daytime/nighttime period.

@item @code{dusk-time} (type: maybe-string)
Likewise, custom time for the transition from day to night in the
evening.

@item @code{extra-content} (default: @code{""}) (type: raw-configuration-string)
Extra content appended as-is to the Redshift configuration file.  Run
@command{man redshift} for more information about the configuration file
format.

@end table

@end deftp

@defvar home-dbus-service-type
This is the service type for running a session-specific D-Bus, for
unprivileged applications that require D-Bus to be running.
@end defvar

@deftp {Data Type} home-dbus-configuration
The configuration record for @code{home-dbus-service-type}.

@table @asis
@item @code{dbus} (default: @code{dbus})
The package providing the @code{/bin/dbus-daemon} command.
@end table
@end deftp

@defvar home-unclutter-service-type
This is the service type for Unclutter, a program that runs on the
background of an X11 session and detects when the X pointer hasn't moved
for a specified idle timeout, after which it hides the cursor so that
you can focus on the text underneath.  Its associated value must be a
@code{home-unclutter-configuration} record, as shown below.

A typical configuration, where we manually specify the idle timeout (in
seconds), might look like this:

@lisp
(service home-unclutter-service-type
         (home-unclutter-configuration
          (idle-timeout 2)))
@end lisp
@end defvar

@deftp {Data Type} home-unclutter-configuration
The configuration record for @code{home-unclutter-service-type}.

@table @asis
@item @code{unclutter} (default: @code{unclutter}) (type: file-like)
Unclutter package to use.

@item @code{idle-timeout} (default: @code{5}) (type: integer)
A timeout in seconds after which to hide cursor.
@end table

@end deftp

@defvar home-xmodmap-service-type
This is the service type for the
@uref{https://gitlab.freedesktop.org/xorg/app/xmodmap,xmodmap} utility
to modify keymaps and pointer button mappings under the Xorg display
server.  Its associated value must be a
@code{home-xmodmap-configuration} record, as shown below.

The @code{key-map} field takes a list of objects, each of which is
either a @dfn{statement} (a string) or an @dfn{assignment} (a pair of
strings).  As an example, the snippet below swaps around the
@kbd{Caps_Lock} and the @kbd{Control_L} keys, by first removing the
keysyms (on the right-hand side) from the corresponding modifier maps
(on the left-hand side), re-assigning them by swapping each other out,
and finally adding back the keysyms to the modifier maps.

@lisp
(service home-xmodmap-service-type
         (home-xmodmap-configuration
          (key-map '(("remove Lock" . "Caps_Lock")
                     ("remove Control" . "Control_L")
                     ("keysym Control_L" . "Caps_Lock")
                     ("keysym Caps_Lock" . "Control_L")
                     ("add Lock" . "Caps_Lock")
                     ("add Control" . "Control_L")))))
@end lisp
@end defvar

@deftp {Data Type} home-xmodmap-configuration
The configuration record for @code{home-xmodmap-service-type}.  Its
available fields are:

@table @asis
@item @code{xmodmap} (default: @code{xmodmap}) (type: file-like)
The @code{xmodmap} package to use.

@item @code{key-map} (default: @code{'()}) (type: list)
The list of expressions to be read by @code{xmodmap} on service startup.

@end table
@end deftp

@defvar home-startx-command-service-type
Add @command{startx} to the home profile putting it onto @env{PATH}.

The value for this service is a @code{<xorg-configuration>} object which
is passed to the @code{xorg-start-command-xinit} procedure producing the
@command{startx} used.  Default value is @code{(xorg-configuration)}.
@end defvar


@node Guix Home Services
@subsection Guix Home Services

The @code{(gnu home services guix)} module provides services for
user-specific Guix configuration.

@defvar home-channels-service-type
This is the service type for managing
@file{$XDG_CONFIG_HOME/guix/channels.scm}, the file that controls the
channels received on @command{guix pull} (@pxref{Channels}).  Its
associated value is a list of @code{channel} records, defined in the
@code{(guix channels)} module.

Generally, it is better to extend this service than to directly
configure it, as its default value is the default guix channel(s)
defined by @code{%default-channels}.  If you configure this service
directly, be sure to include a guix channel.  @xref{Specifying
Additional Channels} and @ref{Using a Custom Guix Channel} for more
details.

A typical extension for adding a channel might look like this:

@lisp
(simple-service 'variant-packages-service
                home-channels-service-type
                (list
                 (channel
                  (name 'variant-packages)
                  (url "https://example.org/variant-packages.git"))))
@end lisp
@end defvar

@node Fonts Home Services
@subsection Fonts Home Services

The @code{(gnu home services fontutils)} module provides services for
user-specific Fontconfig setup.  The
@uref{https://www.freedesktop.org/wiki/Software/fontconfig,Fontconfig}
library is used by many applications to access fonts on the system.

@defvar home-fontconfig-service-type
This is the service type for generating configurations for Fontconfig.
Its associated value is a list of either strings (or gexps) pointing to
fonts locations, or SXML (@pxref{SXML,,, guile, GNU Guile Reference
Manual}) fragments to be converted into XML and put inside the main
@code{fontconfig} node.

Generally, it is better to extend this service than to directly
configure it, as its default value is the default Guix Home's profile
font installation path (@file{~/.guix-home/profile/share/fonts}).  If
you configure this service directly, be sure to include the above
directory.

Here's how you'd extend it to include fonts installed with the Nix
package manager, and to prefer your favourite monospace font:

@lisp
(simple-service 'additional-fonts-service
                home-fontconfig-service-type
                (list "~/.nix-profile/share/fonts"
                      '(alias
                        (family "monospace")
                        (prefer
                         (family "Liberation Mono")))))
@end lisp
@end defvar

@node Sound Home Services
@subsection Sound Home Services

The @code{(gnu home services sound)} module provides services related to
sound support.

@cindex PulseAudio, home service
@cindex RTP, for PulseAudio
@subsubheading PulseAudio RTP Streaming Services

The following services dynamically reconfigure the
@uref{https://pulseaudio.org,PulseAudio sound server}: they let you
toggle broadcast of audio output over the network using the
@acronym{RTP, real-time transport protocol} and, correspondingly,
playback of sound received over RTP.  Once
@code{home-pulseaudio-rtp-sink-service-type} is among your home
services, you can start broadcasting audio output by running this
command:

@example
herd start pulseaudio-rtp-sink
@end example

You can then run a PulseAudio-capable mixer, such as @code{pavucontrol}
or @code{pulsemixer} (both from the same-named package) to control which
audio stream(s) should be sent to the RTP ``sink''.

By default, audio is broadcasted to a multicast address: any device on
the @acronym{LAN, local area network} receives it and may play it.
Using multicast in this way puts a lot of pressure on the network and
degrades its performance, so you may instead prefer sending to
specifically one device.  The first way to do that is by specifying the
IP address of the target device when starting the service:

@example
herd start pulseaudio-rtp-sink 192.168.1.42
@end example

The other option is to specify this IP address as the one to use by
default in your home environment configuration:

@lisp
(service home-pulseaudio-rtp-sink-service-type
         "192.168.1.42")
@end lisp

On the device where you intend to receive and play the RTP stream, you
can use @code{home-pulseaudio-rtp-source-service-type}, like so:

@lisp
(service home-pulseaudio-rtp-source-service-type)
@end lisp

This will then let you start the receiving module for PulseAudio:

@example
herd start pulseaudio-rtp-source
@end example

Again, by default it will listen on the multicast address.  If, instead,
you'd like it to listen for direct incoming connections, you can do that
by running:

@lisp
(service home-pulseaudio-rtp-source-service-type
         "0.0.0.0")
@end lisp

The reference of these services is given below.

@defvar home-pulseaudio-rtp-sink-service-type
@defvarx home-pulseaudio-rtp-source-service-type
This is the type of the service to send, respectively receive, audio
streams over @acronym{RTP, real-time transport protocol}.

The value associated with this service is the IP address (a string)
where to send, respectively receive, the audio stream.  By default,
audio is sent/received on multicast address
@code{%pulseaudio-rtp-multicast-address}.

This service defines one Shepherd service: @code{pulseaudio-rtp-sink},
respectively @code{pulseaudio-rtp-source}.  The service is not started
by default, so you have to explicitly start it when you want to turn it
on, as in this example:

@example
herd start pulseaudio-rtp-sink
@end example

Stopping the Shepherd service turns off broadcasting.
@end defvar

@defvar %pulseaudio-rtp-multicast-address
This is the multicast address used by default by the two services above.
@end defvar

@cindex PipeWire, home service
@subsubheading PipeWire Home Service

@uref{https://pipewire.org, PipeWire} provides a low-latency,
graph-based audio and video processing service.  In addition to its
native protocol, it can also be used as a replacement for both JACK and
PulseAudio.

While PipeWire provides the media processing and API, it does not,
directly, know about devices such as sound cards, nor how you might want
to connect applications, hardware, and media processing filters.
Instead, PipeWire relies on a @dfn{session manager} to specify all these
relationships.  While you may use any session manager you wish, for most
people the @url{https://pipewire.pages.freedesktop.org/wireplumber/,
WirePlumber} session manager, a reference implementation provided by the
PipeWire project itself, suffices, and that is the one
@code{home-pipewire-service-type} uses.

PipeWire can be used as a replacement for PulseAudio by setting
@code{enable-pulseaudio?} to @code{#t} in
@code{home-pipewire-configuration}, so that existing PulseAudio clients
may use it without any further configuration.

In addition, JACK clients may connect to PipeWire by using the
@command{pw-jack} program, which comes with PipeWire.  Simply prefix the
command with @command{pw-jack} when you run it, and audio data should go
through PipeWire:

@example
pw-jack mpv -ao=jack sound-file.wav
@end example

For more information on PulseAudio emulation, see
@uref{https://gitlab.freedesktop.org/pipewire/pipewire/-/wikis/Config-PulseAudio},
for JACK, see
@uref{https://gitlab.freedesktop.org/pipewire/pipewire/-/wikis/Config-JACK}.

As PipeWire does not use @code{dbus} to start its services on demand
(as PulseAudio does), @code{home-pipewire-service-type} uses Shepherd
to start services when logged in, provisioning the @code{pipewire},
@code{wireplumber}, and, if configured, @code{pipewire-pulseaudio}
services.  @xref{Shepherd Home Service}.

@defvar home-pipewire-service-type
This provides the service definition for @command{pipewire}, which will
run on login.  Its value is a @code{home-pipewire-configuration} object.

To start the service, add it to the @code{service} field of your
@code{home-environment}, such as:

@lisp
(service home-pipewire-service-type)
@end lisp
@end defvar

@deftp {Data Type} home-pipewire-configuration
Available @code{home-pipewire-configuration} fields are:

@table @asis
@item @code{pipewire} (default: @code{pipewire}) (type: file-like)
The PipeWire package to use.

@item @code{wireplumber} (default: @code{wireplumber}) (type: file-like)
The WirePlumber package to use.

@item @code{enable-pulseaudio?} (default: @code{#t}) (type: boolean)
When true, enable PipeWire's PulseAudio emulation support, allowing
PulseAudio clients to use PipeWire transparently.
@end table
@end deftp

@node Mail Home Services
@subsection Mail Home Services

The @code{(gnu home services mail)} module provides services that help
you set up the tools to work with emails in your home environment.

@cindex msmtp
@uref{https://marlam.de/msmtp, MSMTP} is a @acronym{SMTP, Simple Mail
Transfer Protocol} client.  It sends mail to a predefined SMTP server
that takes care of proper delivery.

The service reference is given below.

@defvar home-msmtp-service-type
This is the service type for @command{msmtp}.  Its value must be a
@code{home-msmtp-configuration}, as shown below.  It provides the
@file{~/.config/msmtp/config} file.

As an example, here is how you would configure @code{msmtp} for a single
account:

@lisp
(service home-msmtp-service-type
         (home-msmtp-configuration
          (accounts
           (list
            (msmtp-account
             (name "alice")
             (configuration
              (msmtp-configuration
               (host "mail.example.org")
               (port 587)
               (user "alice")
               (password-eval "pass Mail/alice"))))))))
@end lisp
@end defvar

@c %start of fragment

@deftp {Data Type} home-msmtp-configuration
Available @code{home-msmtp-configuration} fields are:

@table @asis
@item @code{defaults} (type: msmtp-configuration)
The configuration that will be set as default for all accounts.

@item @code{accounts} (default: @code{'()}) (type: list-of-msmtp-accounts)
A list of @code{msmtp-account} records which contain information about
all your accounts.

@item @code{default-account} (type: maybe-string)
Set the default account.

@item @code{extra-content} (default: @code{""}) (type: string)
Extra content appended as-is to the configuration file.  Run
@command{man msmtp} for more information about the configuration file
format.

@end table

@end deftp

@c %end of fragment

@c %start of fragment

@deftp {Data Type} msmtp-account
Available @code{msmtp-account} fields are:

@table @asis
@item @code{name} (type: string)
The unique name of the account.

@item @code{configuration} (type: msmtp-configuration)
The configuration for this given account.

@end table

@end deftp

@c %end of fragment

@c %start of fragment

@deftp {Data Type} msmtp-configuration
Available @code{msmtp-configuration} fields are:

@table @asis
@item @code{auth?} (type: maybe-boolean)
Enable or disable authentication.

@item @code{tls?} (type: maybe-boolean)
Enable or disable TLS (also known as SSL) for secured connections.

@item @code{tls-starttls?} (type: maybe-boolean)
Choose the TLS variant: start TLS from within the session (‘on’,
default), or tunnel the session through TLS (‘off’).

@item @code{tls-trust-file} (type: maybe-string)
Activate server certificate verification using a list of trusted
Certification Authorities (CAs).

@item @code{log-file} (type: maybe-string)
Enable logging to the specified file.  An empty argument disables
logging.  The file name ‘-’ directs the log information to standard
output.

@item @code{host} (type: maybe-string)
The SMTP server to send the mail to.

@item @code{port} (type: maybe-integer)
The port that the SMTP server listens on.  The default is 25 ("smtp"),
unless TLS without STARTTLS is used, in which case it is 465 ("smtps").

@item @code{user} (type: maybe-string)
Set the user name for authentication.

@item @code{from} (type: maybe-string)
Set the envelope-from address.

@item @code{password-eval} (type: maybe-string)
Set the password for authentication to the output (stdout) of the
command cmd.

@item @code{extra-content} (default: @code{""}) (type: string)
Extra content appended as-is to the configuration block.  Run
@command{man msmtp} for more information about the configuration file
format.

@end table

@end deftp

@c %end of fragment

@node Messaging Home Services
@subsection Messaging Home Services

@cindex znc
The @uref{https://znc.in, ZNC bouncer} can be run as a daemon to manage
your IRC presence.  With the @code{(gnu home services messaging)} service, you
can configure ZNC to run upon login.

You will have to provide a @file{~/.znc/configs/znc.conf} separately.

Here is an example of a service and its configuration that you could add
to the @code{services} field of your @code{home-environment}:

@lisp
(service home-znc-service-type)
@end lisp

@defvar home-znc-service-type
This is the type of the ZNC home service, whose value is a
@code{home-znc-configuration} object.
@end defvar

@deftp {Data Type} home-znc-configuration
Available @code{home-znc-configuration} fields are:

@table @asis
@item @code{znc} (default: @code{znc}) (type: file-like)
The ZNC package to use.

@item @code{extra-options} (default: @code{'()})
Extra options will be passed to @command{znc}, please run @command{man
znc} for more information.

@end table
@end deftp

@node Media Home Services
@subsection Media Home Services

@cindex kodi
The @uref{https://kodi.tv, Kodi media center} can be run as a daemon on
a media server.  With the @code{(gnu home services kodi)} service, you
can configure Kodi to run upon login.

Here is an example of a service and its configuration that you could add
to the @code{services} field of your @code{home-environment}:

@lisp
(service home-kodi-service-type
  (home-kodi-configuration
   (extra-options '("--settings="<settings-file>"))))
@end lisp

@defvar home-kodi-service-type
This is the type of the Kodi home service, whose value is a
@code{home-kodi-configuration} object.
@end defvar

@deftp {Data Type} home-kodi-configuration
Available @code{home-kodi-configuration} fields are:

@table @asis
@item @code{kodi} (default: @code{kodi}) (type: file-like)
The Kodi package to use.

@item @code{extra-options} (default: @code{'()})
Extra options will be passed to @command{kodi}, please run @command{man
kodi} for more information.

@end table
@end deftp

@node Networking Home Services
@subsection Networking Home Services

This section lists services somewhat networking-related that you may use
with Guix Home.

@cindex Syncthing, file synchronization service
@cindex backup service, Syncthing
The @code{(gnu home services syncthing)} module provides a service to
set up the @uref{Syncthing, https://syncthing.net} continuous file
backup service.

@defvar home-syncthing-service-type
This is the service type for the @command{syncthing} daemon; it is the
Home counterpart of the @code{syncthing-service-type} system service
(@pxref{Networking Services, @code{syncthing-service-type}}).  The value
for this service type is a @command{syncthing-configuration}.

Here is how you would set it up with the default configuration:

@lisp
(service home-syncthing-service-type)
@end lisp

For a custom configuration, wrap you @code{syncthing-configuration} in
@code{for-home}, as in this example:

@lisp
(service home-syncthing-service-type
         (for-home
          (syncthing-configuration (logflags 5))))
@end lisp

For details about @code{syncthing-configuration}, check out the
documentation of the system service (@pxref{Networking Services,
@code{syncthing-service-type}}).
@end defvar


@node Miscellaneous Home Services
@subsection Miscellaneous Home Services

This section lists Home services that lack a better place.

@subsubheading Beets Service

@cindex Beets service, for Home
The @code{(gnu home services music)} module provides the following
service:

@defvar home-beets-service-type
@uref{https://beets.io, Beets} is a music file and metadata manager
that can be used via its command-line interface, @command{beet}. Beets
requires a YAML configuration file and this Guix Home service is to
create such file.
@end defvar

The service can be used as follows:

@lisp
(service home-beets-service-type
         (home-beets-configuration (directory "/home/alice/music")))
@end lisp

Additional options can be specified via the service wild-card field
@code{extra-options}:

@lisp
(service home-beets-service-type
         (home-beets-configuration
          (directory "/home/alice/music")
          (extra-options '("
import:
  move: yes"))))
@end lisp

@subsubheading Dictionary Service

@cindex dictionary service, for Home
The @code{(gnu home services dict)} module provides the following service:

@defvar home-dicod-service-type
This is the type of the service that runs the @command{dicod} daemon, an
implementation of DICT server (@pxref{Dicod,,, dico, GNU Dico Manual}).

You can add @command{open localhost} to your @file{~/.dico} file to make
@code{localhost} the default server for @command{dico} client
(@pxref{Initialization File,,, dico, GNU Dico Manual}).
@end defvar

This service is a direct mapping of the @code{dicod-service-type} system
service (@pxref{Miscellaneous Services, Dictionary Service}).  You can
use it like this:

@lisp
(service home-dicod-service-type)
@end lisp

You may specify a custom configuration by providing a
@code{dicod-configuration} record, exactly like for
@code{dicod-service-type}, but wrapping it in @code{for-home}:

@lisp
(service home-dicod-service-type
         (for-home
          (dicod-configuration @dots{})))
@end lisp

@node Invoking guix home
@section Invoking @command{guix home}

@cindex @command{guix home}

Once you have written a home environment declaration (@pxref{Declaring
the Home Environment,,,,}, it can be @dfn{instantiated} using the
@command{guix home} command.  The synopsis is:

@example
guix home @var{options}@dots{} @var{action} @var{file}
@end example

@var{file} must be the name of a file containing a
@code{home-environment} declaration.  @var{action} specifies how the
home environment is instantiated, but there are few auxiliary actions
which don't instantiate it.  Currently the following values are
supported:

@table @code
@item search
Display available home service type definitions that match the given
regular expressions, sorted by relevance:

@cindex shell
@cindex shell-profile
@cindex bash
@cindex zsh
@example
$ guix home search shell
name: home-shell-profile
location: gnu/home/services/shells.scm:100:2
extends: home-files
description: Create `~/.profile', which is used for environment initialization of POSIX compliant login shells.
+ This service type can be extended with a list of file-like objects.
relevance: 6

name: home-fish
location: gnu/home/services/shells.scm:640:2
extends: home-files home-profile
description: Install and configure Fish, the friendly interactive shell.
relevance: 3

name: home-zsh
location: gnu/home/services/shells.scm:290:2
extends: home-files home-profile
description: Install and configure Zsh.
relevance: 1

name: home-bash
location: gnu/home/services/shells.scm:508:2
extends: home-files home-profile
description: Install and configure GNU Bash.
relevance: 1

@dots{}
@end example

As for @command{guix search}, the result is written in
@code{recutils} format, which makes it easy to filter the output
(@pxref{Top, GNU recutils databases,, recutils, GNU recutils manual}).

@cindex container, for @command{guix home}
@item container
Spawn a shell in an isolated environment---a
@dfn{container}---containing your home as specified by @var{file}.

For example, this is how you would start an interactive shell in a
container with your home:

@example
guix home container config.scm
@end example

This is a throw-away container where you can lightheartedly fiddle with
files; any changes made within the container, any process started---all
this disappears as soon as you exit that shell.

As with @command{guix shell}, several options control that container:

@table @option
@item --network
@itemx -N
Enable networking within the container (it is disabled by default).

@item --expose=@var{source}[=@var{target}]
@itemx --share=@var{source}[=@var{target}]
As with @command{guix shell}, make directory @var{source} of the host
system available as @var{target} inside the container---read-only if you
pass @option{--expose}, and writable if you pass @option{--share}
(@pxref{Invoking guix shell, @option{--expose} and @option{--share}}).
@end table

Additionally, you can run a command in that container, instead of
spawning an interactive shell.  For instance, here is how you would
check which Shepherd services are started in a throw-away home
container:

@example
guix home container config.scm -- herd status
@end example

The command to run in the container must come after @code{--} (double
hyphen).

@cindex service type definition, editing
@cindex editing, service type definition
@item edit
Edit or view the definition of the given Home service types.

For example, the command below opens your editor, as specified by the
@env{EDITOR} environment variable, on the definition of the
@code{home-mcron} service type:

@example
guix home edit home-mcron
@end example

@item reconfigure
Build the home environment described in @var{file}, and switch to it.
Switching means that the activation script will be evaluated and (in
basic scenario) symlinks to configuration files generated from
@code{home-environment} declaration will be created in @file{~}.  If the
file with the same path already exists in home folder it will be moved
to @file{~/@var{timestamp}-guix-home-legacy-configs-backup}, where @var{timestamp}
is a current UNIX epoch time.

@quotation Note
It is highly recommended to run @command{guix pull} once before you run
@command{guix home reconfigure} for the first time (@pxref{Invoking guix
pull}).
@end quotation

This effects all the configuration specified in @var{file}.  The command
starts Shepherd services specified in @var{file} that are not currently
running; if a service is currently running, this command will arrange
for it to be upgraded the next time it is stopped (e.g.@: by @code{herd
stop @var{service}} or @code{herd restart @var{service}}).

This command creates a new generation whose number is one greater than
the current generation (as reported by @command{guix home
list-generations}).  If that generation already exists, it will be
overwritten.  This behavior mirrors that of @command{guix package}
(@pxref{Invoking guix package}).

@cindex provenance tracking, of the home environment
Upon completion, the new home is deployed under @file{~/.guix-home}.
This directory contains @dfn{provenance meta-data}: the list of channels
in use (@pxref{Channels}) and @var{file} itself, when available.  You
can view the provenance information by running:

@example
guix home describe
@end example

This information is useful should you later want to inspect how this
particular generation was built.  In fact, assuming @var{file} is
self-contained, you can later rebuild generation @var{n} of your
home environment with:

@example
guix time-machine \
  -C /var/guix/profiles/per-user/@var{USER}/guix-home-@var{n}-link/channels.scm -- \
  home reconfigure \
  /var/guix/profiles/per-user/@var{USER}/guix-home-@var{n}-link/configuration.scm

@end example

You can think of it as some sort of built-in version control!  Your
home is not just a binary artifact: @emph{it carries its own source}.

@quotation Note
If you're using Guix System, @ref{guix-home-service-type,
@code{guix-home-service-type}}, on how to embed your home configuration
in your system configuration such that @command{guix system reconfigure}
deploys both your system and your home.
@end quotation

@item switch-generation
@cindex home generations
Switch to an existing home generation.  This action atomically switches
the home profile to the specified home generation.

The target generation can be specified explicitly by its generation
number.  For example, the following invocation would switch to home
generation 7:

@example
guix home switch-generation 7
@end example

The target generation can also be specified relative to the current
generation with the form @code{+N} or @code{-N}, where @code{+3} means
``3 generations ahead of the current generation,'' and @code{-1} means
``1 generation prior to the current generation.''  When specifying a
negative value such as @code{-1}, you must precede it with @code{--} to
prevent it from being parsed as an option.  For example:

@example
guix home switch-generation -- -1
@end example

This action will fail if the specified generation does not exist.

@item roll-back
@cindex rolling back
Switch to the preceding home generation.  This is the inverse
of @command{reconfigure}, and it is exactly the same as invoking
@command{switch-generation} with an argument of @code{-1}.

@item delete-generations
@cindex deleting home generations
@cindex saving space
Delete home generations, making them candidates for garbage collection
(@pxref{Invoking guix gc}, for information on how to run the ``garbage
collector'').

This works in the same way as @samp{guix package --delete-generations}
(@pxref{Invoking guix package, @option{--delete-generations}}).  With no
arguments, all home generations but the current one are deleted:

@example
guix home delete-generations
@end example

You can also select the generations you want to delete.  The example below
deletes all the home generations that are more than two months old:

@example
guix home delete-generations 2m
@end example

@item build
Build the derivation of the home environment, which includes all the
configuration files and programs needed.  This action does not actually
install anything.

@item describe
Describe the current home generation: its file name, as well as
provenance information when available.

To show installed packages in the current home generation's profile, the
@code{--list-installed} flag is provided, with the same syntax that is
used in @command{guix package --list-installed} (@pxref{Invoking guix
package}).  For instance, the following command shows a table of all the
packages with ``emacs'' in their name that are installed in the current
home generation's profile:

@example
guix home describe --list-installed=emacs
@end example

@item list-generations
List a summary of each generation of the home environment available on
disk, in a human-readable way.  This is similar to the
@option{--list-generations} option of @command{guix package}
(@pxref{Invoking guix package}).

Optionally, one can specify a pattern, with the same syntax that is used
in @command{guix package --list-generations}, to restrict the list of
generations displayed.  For instance, the following command displays
generations that are up to 10 days old:

@example
guix home list-generations 10d
@end example

The @code{--list-installed} flag may also be specified, with the same
syntax that is used in @command{guix home describe}.  This may be
helpful if trying to determine when a package was added to the home
profile.

@item import
Generate a @dfn{home environment} from the packages in the default
profile and configuration files found in the user's home directory.  The
configuration files will be copied to the specified directory, and a
@file{home-configuration.scm} will be populated with the home
environment.  Note that not every home service that exists is supported
(@pxref{Home Services}).

@example
$ guix home import ~/guix-config
guix home: '/home/alice/guix-config' populated with all the Home configuration files
@end example
@end table

And there's more!  @command{guix home} also provides the following
sub-commands to visualize how the services of your home environment
relate to one another:

@table @code
@cindex service extension graph, of a home environment
@item extension-graph
Emit to standard output the @dfn{service extension graph} of the home
environment defined in @var{file} (@pxref{Service Composition}, for more
information on service extensions).  By default the output is in
Dot/Graphviz format, but you can choose a different format with
@option{--graph-backend}, as with @command{guix graph} (@pxref{Invoking
guix graph, @option{--backend}}):

The command:

@example
guix home extension-graph @var{file} | xdot -
@end example

shows the extension relations among services.

@cindex Shepherd dependency graph, for a home environment
@item shepherd-graph
Emit to standard output the @dfn{dependency graph} of shepherd services
of the home environment defined in @var{file}.  @xref{Shepherd
Services}, for more information and for an example graph.

Again, the default output format is Dot/Graphviz, but you can pass
@option{--graph-backend} to select a different one.
@end table

@var{options} can contain any of the common build options (@pxref{Common
Build Options}).  In addition, @var{options} can contain one of the
following:

@table @option

@item --expression=@var{expr}
@itemx -e @var{expr}
Consider the home-environment @var{expr} evaluates to.
This is an alternative to specifying a file which evaluates to a home
environment.

@item --allow-downgrades
Instruct @command{guix home reconfigure} to allow system downgrades.

Just like @command{guix system}, @command{guix home reconfigure}, by
default, prevents you from downgrading your home to older or unrelated
revisions compared to the channel revisions that were used to deploy
it---those shown by @command{guix home describe}.  Using
@option{--allow-downgrades} allows you to bypass that check, at the risk
of downgrading your home---be careful!

@end table

@node Documentation
@chapter Documentation

@cindex documentation, searching for
@cindex searching for documentation
@cindex Info, documentation format
@cindex man pages
@cindex manual pages
In most cases packages installed with Guix come with documentation.
There are two main documentation formats: ``Info'', a browsable
hypertext format used for GNU software, and ``manual pages'' (or ``man
pages''), the linear documentation format traditionally found on Unix.
Info manuals are accessed with the @command{info} command or with Emacs,
and man pages are accessed using @command{man}.

You can look for documentation of software installed on your system by
keyword.  For example, the following command searches for information
about ``TLS'' in Info manuals:

@example
$ info -k TLS
"(emacs)Network Security" -- STARTTLS
"(emacs)Network Security" -- TLS
"(gnutls)Core TLS API" -- gnutls_certificate_set_verify_flags
"(gnutls)Core TLS API" -- gnutls_certificate_set_verify_function
@dots{}
@end example

@noindent
The command below searches for the same keyword in man
pages@footnote{The database searched by @command{man -k} is only created
in profiles that contain the @code{man-db} package.}:

@example
$ man -k TLS
SSL (7)              - OpenSSL SSL/TLS library
certtool (1)         - GnuTLS certificate tool
@dots {}
@end example

These searches are purely local to your computer so you have the
guarantee that documentation you find corresponds to what you have
actually installed, you can access it off-line, and your privacy is
respected.

Once you have these results, you can view the relevant documentation by
running, say:

@example
$ info "(gnutls)Core TLS API"
@end example

@noindent
or:

@example
$ man certtool
@end example

Info manuals contain sections and indices as well as hyperlinks like
those found in Web pages.  The @command{info} reader (@pxref{Top, Info
reader,, info-stnd, Stand-alone GNU Info}) and its Emacs counterpart
(@pxref{Misc Help,,, emacs, The GNU Emacs Manual}) provide intuitive key
bindings to navigate manuals.  @xref{Getting Started,,, info, Info: An
Introduction}, for an introduction to Info navigation.

@node Platforms
@chapter Platforms

The packages and systems built by Guix are intended, like most computer
programs, to run on a CPU with a specific instruction set, and under a
specific operating system.  Those programs are often also targeting a
specific kernel and system library.  Those constraints are captured by
Guix in @code{platform} records.

@menu
* platform Reference::          Detail of platform declarations.
* Supported Platforms::         Description of the supported platforms.
@end menu

@node platform Reference
@section @code{platform} Reference

The @code{platform} data type describes a @dfn{platform}: an
@acronym{ISA, instruction set architecture}, combined with an operating
system and possibly additional system-wide settings such as the
@acronym{ABI, application binary interface}.

@deftp {Data Type} platform
This is the data type representing a platform.

@table @asis
@item @code{target}
This field specifies the platform's GNU triplet as a string
(@pxref{Specifying Target Triplets, GNU configuration triplets,,
autoconf, Autoconf}).

@item @code{system}
This string is the system type as it is known to Guix and passed,
for instance, to the @option{--system} option of most commands.

It usually has the form @code{"@var{cpu}-@var{kernel}"}, where
@var{cpu} is the target CPU and @var{kernel} the target operating
system kernel.

It can be for instance @code{"aarch64-linux"} or @code{"armhf-linux"}.
You will encounter system types when you perform native builds
(@pxref{Native Builds}).

@item @code{linux-architecture} (default: @code{#false})
This optional string field is only relevant if the kernel is Linux.  In
that case, it corresponds to the ARCH variable used when building Linux,
@code{"mips"} for instance.

@item @code{rust-target} (default: @code{#false})
This optional string field is used to determine which rust target is best
supported by this platform.  For example, the base level system targeted by
@code{armhf-linux} system is closest to @code{armv7-unknown-linux-gnueabihf}.

@item @code{glibc-dynamic-linker}
This field is the name of the GNU C Library dynamic linker for the
corresponding system, as a string.  It can be
@code{"/lib/ld-linux-armhf.so.3"}.

@end table
@end deftp

@node Supported Platforms
@section Supported Platforms

The @code{(guix platforms @dots{})} modules export the following
variables, each of which is bound to a @code{platform} record.

@defvar armv7-linux
Platform targeting ARM v7 CPU running GNU/Linux.
@end defvar

@defvar aarch64-linux
Platform targeting ARM v8 CPU running GNU/Linux.
@end defvar

@defvar mips64-linux
Platform targeting MIPS little-endian 64-bit CPU running GNU/Linux.
@end defvar

@defvar powerpc-linux
Platform targeting PowerPC big-endian 32-bit CPU running GNU/Linux.
@end defvar

@defvar powerpc64le-linux
Platform targeting PowerPC little-endian 64-bit CPU running GNU/Linux.
@end defvar

@defvar riscv64-linux
Platform targeting RISC-V 64-bit CPU running GNU/Linux.
@end defvar

@defvar i686-linux
Platform targeting x86 CPU running GNU/Linux.
@end defvar

@defvar x86_64-linux
Platform targeting x86 64-bit CPU running GNU/Linux.
@end defvar

@defvar x86_64-linux-x32
Platform targeting x86 64-bit CPU running GNU/Linux with the run-time using
the X32 ABI.
@end defvar

@defvar i686-mingw
Platform targeting x86 CPU running Windows, with run-time support from
MinGW.
@end defvar

@defvar x86_64-mingw
Platform targeting x86 64-bit CPU running Windows, with run-time support
from MinGW.
@end defvar

@defvar i586-gnu
Platform targeting x86 CPU running GNU/Hurd (also referred to as
``GNU'').
@end defvar

@defvar avr
Platform targeting AVR CPUs without an operating system, with run-time support
from AVR Libc.
@end defvar

@defvar or1k-elf
Platform targeting OpenRISC 1000 CPU without an operating system and without a
C standard library.
@end defvar

@defvar xtensa-ath9k-elf
Platform targeting Xtensa CPU used in the Qualcomm Atheros AR7010 and AR9271
USB 802.11n @acronym{NICs, Network Interface Controllers}.
@end defvar

@node System Images
@chapter Creating System Images

@cindex system images
When it comes to installing Guix System for the first time on a new
machine, you can basically proceed in three different ways.  The first
one is to use an existing operating system on the machine to run the
@command{guix system init} command (@pxref{Invoking guix system}).  The
second one, is to produce an installation image (@pxref{Building the
Installation Image}). This is a bootable system which role is to
eventually run @command{guix system init}.  Finally, the third option
would be to produce an image that is a direct instantiation of the
system you wish to run.  That image can then be copied on a bootable
device such as an USB drive or a memory card.  The target machine would
then directly boot from it, without any kind of installation procedure.

The @command{guix system image} command is able to turn an operating
system definition into a bootable image.  This command supports
different image types, such as @code{mbr-hybrid-raw}, @code{iso9660} and
@code{docker}.  Any modern @code{x86_64} machine will probably be able
to boot from an @code{iso9660} image.  However, there are a few machines
out there that require specific image types.  Those machines, in general
using @code{ARM} processors, may expect specific partitions at specific
offsets.

This chapter explains how to define customized system images and how to
turn them into actual bootable images.

@menu
* image Reference::             Detail of image declarations.
* Instantiate an Image::        How to instantiate an image record.
* image-type Reference::        Detail of image types declaration.
* Image Modules::               Definition of image modules.
@end menu

@node image Reference
@section @code{image} Reference

The @code{image} record, described right after, allows you to define a
customized bootable system image.

@deftp {Data Type} image
This is the data type representing a system image.

@table @asis
@item @code{name} (default: @code{#false})
The image name as a symbol, @code{'my-iso9660} for instance.  The name
is optional and it defaults to @code{#false}.

@item @code{format}
The image format as a symbol.  The following formats are supported:

@itemize
@item @code{disk-image}, a raw disk image composed of one or multiple
partitions.

@item @code{compressed-qcow2}, a compressed qcow2 image composed of
one or multiple partitions.

@item @code{docker}, a Docker image.

@item @code{iso9660}, an ISO-9660 image.

@item @code{tarball}, a tar.gz image archive.

@item @code{wsl2}, a WSL2 image.

@end itemize

@item @code{platform} (default: @code{#false})
The @code{platform} record the image is targeting (@pxref{Platforms}),
@code{aarch64-linux} for instance.  By default, this field is set to
@code{#false} and the image will target the host platform.

@item @code{size} (default: @code{'guess})
The image size in bytes or @code{'guess}.  The @code{'guess} symbol,
which is the default, means that the image size will be inferred based
on the image content.

@item @code{operating-system}
The image's @code{operating-system} record that is instantiated.

@item @code{partition-table-type} (default: @code{'mbr})
The image partition table type as a symbol.  Possible values are
@code{'mbr} and @code{'gpt}.  It default to @code{'mbr}.

@item @code{partitions} (default: @code{'()})
The image partitions as a list of @code{partition} records
(@pxref{partition Reference}).

@item @code{compression?} (default: @code{#true})
Whether the image content should be compressed, as a boolean.  It
defaults to @code{#true} and only applies to @code{'iso9660} image
formats.

@item @code{volatile-root?} (default: @code{#true})
Whether the image root partition should be made volatile, as a boolean.

This is achieved by using a RAM backed file system (overlayfs) that is
mounted on top of the root partition by the initrd.  It defaults to
@code{#true}.  When set to @code{#false}, the image root partition is
mounted as read-write partition by the initrd.

@item @code{shared-store?} (default: @code{#false})
Whether the image's store should be shared with the host system, as a
boolean.  This can be useful when creating images dedicated to virtual
machines.  When set to @code{#false}, which is the default, the image's
@code{operating-system} closure is copied to the image.  Otherwise, when
set to @code{#true}, it is assumed that the host store will be made
available at boot, using a @code{9p} mount for instance.

@item @code{shared-network?} (default: @code{#false})
Whether to use the host network interfaces within the image, as a
boolean.  This is only used for the @code{'docker} image format.  It
defaults to @code{#false}.

@item @code{substitutable?} (default: @code{#true})
Whether the image derivation should be substitutable, as a boolean.  It
defaults to @code{true}.

@end table
@end deftp

@menu
* partition Reference::
@end menu

@node partition Reference
@subsection @code{partition} Reference

In @code{image} record may contain some partitions.

@deftp {Data Type} partition
This is the data type representing an image partition.

@table @asis
@item @code{size} (default: @code{'guess})
The partition size in bytes or @code{'guess}.  The @code{'guess} symbol,
which is the default, means that the partition size will be inferred
based on the partition content.

@item @code{offset} (default: @code{0})
The partition's start offset in bytes, relative to the image start or
the previous partition end.  It defaults to @code{0} which means that
there is no offset applied.

@item @code{file-system} (default: @code{"ext4"})
The partition file system as a string, defaulting to @code{"ext4"}.  The
supported values are @code{"vfat"}, @code{"fat16"}, @code{"fat32"} and
@code{"ext4"}.  @code{"vfat"}, @code{"fat16"} and @code{"fat32"}
partitions without the @code{'esp} flag are by default LBA compatible.

@item @code{file-system-options} (default: @code{'()})
The partition file system creation options that should be passed to the
partition creation tool, as a list of strings.  This is only supported
when creating @code{"ext4"} partitions.

See the @code{"extended-options"} man page section of the
@code{"mke2fs"} tool for a more complete reference.

@item @code{label}
The partition label as a mandatory string, @code{"my-root"} for
instance.

@item @code{uuid} (default: @code{#false})
The partition UUID as an @code{uuid} record (@pxref{File Systems}).  By
default it is @code{#false}, which means that the partition creation
tool will attribute a random UUID to the partition.

@item @code{flags} (default: @code{'()})
The partition flags as a list of symbols.  Possible values are
@code{'boot} and @code{'esp}.  The @code{'boot} flags should be set if
you want to boot from this partition.  Exactly one partition should have
this flag set, usually the root one. The @code{'esp} flag identifies a
UEFI System Partition.

@item @code{initializer} (default: @code{#false})
The partition initializer procedure as a gexp.  This procedure is called
to populate a partition.  If no initializer is passed, the
@code{initialize-root-partition} procedure from the @code{(gnu build
image)} module is used.

@end table
@end deftp

@node Instantiate an Image
@section Instantiate an Image

Let's say you would like to create an MBR image with three distinct
partitions:

@itemize
@item The @acronym{ESP, EFI System Partition}, a partition of
40@tie{}MiB at offset 1024@tie{}KiB with a vfat file system.

@item an ext4 partition of 50@tie{}MiB data file, and labeled ``data''.

@item an ext4 bootable partition containing the @code{%simple-os}
operating-system.
@end itemize

You would then write the following image definition in a
@code{my-image.scm} file for instance.

@lisp
(use-modules (gnu)
             (gnu image)
             (gnu tests)
             (gnu system image)
             (guix gexp))

(define MiB (expt 2 20))

(image
 (format 'disk-image)
 (operating-system %simple-os)
 (partitions
  (list
   (partition
    (size (* 40 MiB))
    (offset (* 1024 1024))
    (label "GNU-ESP")
    (file-system "vfat")
    (flags '(esp))
    (initializer (gexp initialize-efi-partition)))
   (partition
    (size (* 50 MiB))
    (label "DATA")
    (file-system "ext4")
    (initializer #~(lambda* (root . rest)
                     (mkdir root)
                     (call-with-output-file
                         (string-append root "/data")
                       (lambda (port)
                         (format port "my-data"))))))
   (partition
    (size 'guess)
    (label root-label)
    (file-system "ext4")
    (flags '(boot))
    (initializer (gexp initialize-root-partition))))))
@end lisp

Note that the first and third partitions use generic initializers
procedures, initialize-efi-partition and initialize-root-partition
respectively.  The initialize-efi-partition installs a GRUB EFI loader
that is loading the GRUB bootloader located in the root partition.  The
initialize-root-partition instantiates a complete system as defined by
the @code{%simple-os} operating-system.

You can now run:

@example
guix system image my-image.scm
@end example

to instantiate the @code{image} definition.  That produces a disk image
which has the expected structure:

@example
$ parted $(guix system image my-image.scm) print
@dots{}
Model:  (file)
Disk /gnu/store/yhylv1bp5b2ypb97pd3bbhz6jk5nbhxw-disk-image: 1714MB
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Disk Flags:

Number  Start   End     Size    Type     File system  Flags
 1      1049kB  43.0MB  41.9MB  primary  fat16        esp
 2      43.0MB  95.4MB  52.4MB  primary  ext4
 3      95.4MB  1714MB  1619MB  primary  ext4         boot
@end example

The size of the @code{boot} partition has been inferred to @code{1619MB}
so that it is large enough to host the @code{%simple-os}
operating-system.

You can also use existing @code{image} record definitions and inherit
from them to simplify the @code{image} definition.  The @code{(gnu
system image)} module provides the following @code{image} definition
variables.

@defvar mbr-disk-image
An MBR disk-image composed of a single ROOT partition.  The ROOT
partition starts at a 1@tie{}MiB offset so that the bootloader can
install itself in the post-MBR gap.
@end defvar

@defvar mbr-hybrid-disk-image
An MBR disk-image composed of two partitions: a 64 bits ESP partition
and a ROOT boot partition.  The ESP partition starts at a 1@tie{}MiB
offset so that a BIOS compatible bootloader can install itself in the
post-MBR gap.  The image can be used by @code{x86_64} and @code{i686}
machines supporting only legacy BIOS booting.  The ESP partition ensures
that it can also be used by newer machines relying on UEFI booting,
hence the @emph{hybrid} denomination.
@end defvar

@defvar efi-disk-image
A GPT disk-image composed of two partitions: a 64 bits ESP partition and
a ROOT boot partition.  This image can be used on most @code{x86_64} and
@code{i686} machines, supporting BIOS or UEFI booting.
@end defvar

@defvar efi32-disk-image
Same as @code{efi-disk-image} but with a 32 bits EFI partition.
@end defvar

@defvar iso9660-image
An ISO-9660 image composed of a single bootable partition.  This image
can also be used on most @code{x86_64} and @code{i686} machines.
@end defvar

@defvar docker-image
A Docker image that can be used to spawn a Docker container.
@end defvar

Using the @code{efi-disk-image} we can simplify our previous
@code{image} declaration this way:

@lisp
(use-modules (gnu)
             (gnu image)
             (gnu tests)
             (gnu system image)
             (guix gexp)
             (ice-9 match))

(define MiB (expt 2 20))

(define data
  (partition
   (size (* 50 MiB))
   (label "DATA")
   (file-system "ext4")
   (initializer #~(lambda* (root . rest)
                    (mkdir root)
                    (call-with-output-file
                        (string-append root "/data")
                      (lambda (port)
                        (format port "my-data")))))))

(image
 (inherit efi-disk-image)
 (operating-system %simple-os)
 (partitions
  (match (image-partitions efi-disk-image)
    ((esp root)
     (list esp data root)))))
@end lisp

This will give the exact same @code{image} instantiation but the
@code{image} declaration is simpler.

@node image-type Reference
@section image-type Reference

The @command{guix system image} command can, as we saw above, take a
file containing an @code{image} declaration as argument and produce an
actual disk image from it.  The same command can also handle a file
containing an @code{operating-system} declaration as argument.  In that
case, how is the @code{operating-system} turned into an image?

That's where the @code{image-type} record intervenes.  This record
defines how to transform an @code{operating-system} record into an
@code{image} record.

@deftp {Data Type} image-type
This is the data type representing an image-type.

@table @asis
@item @code{name}
The image-type name as a mandatory symbol, @code{'efi32-raw} for
instance.

@item @code{constructor}
The image-type constructor, as a mandatory procedure that takes an
@code{operating-system} record as argument and returns an @code{image}
record.

@end table
@end deftp

There are several @code{image-type} records provided by the @code{(gnu
system image)} and the @code{(gnu system images @dots{})} modules.

@defvar mbr-raw-image-type
Build an image based on the @code{mbr-disk-image} image.
@end defvar

@defvar mbr-hybrid-raw-image-type
Build an image based on the @code{mbr-hybrid-disk-image} image.
@end defvar

@defvar efi-raw-image-type
Build an image based on the @code{efi-disk-image} image.
@end defvar

@defvar efi32-raw-image-type
Build an image based on the @code{efi32-disk-image} image.
@end defvar

@defvar qcow2-image-type
Build an image based on the @code{mbr-disk-image} image but with the
@code{compressed-qcow2} image format.
@end defvar

@defvar iso-image-type
Build a compressed image based on the @code{iso9660-image} image.
@end defvar

@defvar uncompressed-iso-image-type
Build an image based on the @code{iso9660-image} image but with the
@code{compression?} field set to @code{#false}.
@end defvar

@defvar docker-image-type
Build an image based on the @code{docker-image} image.
@end defvar

@defvar raw-with-offset-image-type
Build an MBR image with a single partition starting at a @code{1024KiB}
offset.  This is useful to leave some room to install a bootloader in
the post-MBR gap.
@end defvar

@defvar pinebook-pro-image-type
Build an image that is targeting the Pinebook Pro machine.  The MBR
image contains a single partition starting at a @code{9MiB} offset.  The
@code{u-boot-pinebook-pro-rk3399-bootloader} bootloader will be
installed in this gap.
@end defvar

@defvar rock64-image-type
Build an image that is targeting the Rock64 machine.  The MBR image
contains a single partition starting at a @code{16MiB} offset.  The
@code{u-boot-rock64-rk3328-bootloader} bootloader will be installed in
this gap.
@end defvar

@defvar novena-image-type
Build an image that is targeting the Novena machine.  It has the same
characteristics as @code{raw-with-offset-image-type}.
@end defvar

@defvar pine64-image-type
Build an image that is targeting the Pine64 machine.  It has the same
characteristics as @code{raw-with-offset-image-type}.
@end defvar

@defvar hurd-image-type
Build an image that is targeting a @code{i386} machine running the Hurd
kernel.  The MBR image contains a single ext2 partitions with specific
@code{file-system-options} flags.
@end defvar

@defvar hurd-qcow2-image-type
Build an image similar to the one built by the @code{hurd-image-type}
but with the @code{format} set to @code{'compressed-qcow2}.
@end defvar

@defvar wsl2-image-type
Build an image for the @acronym{WSL2, Windows Subsystem for Linux 2}.
It can be imported by running:

@example
wsl --import Guix ./guix ./wsl2-image.tar.gz
wsl -d Guix
@end example

@end defvar

So, if we get back to the @code{guix system image} command taking an
@code{operating-system} declaration as argument.  By default, the
@code{mbr-raw-image-type} is used to turn the provided
@code{operating-system} into an actual bootable image.

To use a different @code{image-type}, the @code{--image-type} option can
be used.  The @code{--list-image-types} option will list all the
supported image types.  It turns out to be a textual listing of all the
@code{image-types} variables described just above (@pxref{Invoking guix
system}).

@node Image Modules
@section Image Modules

Let's take the example of the Pine64, an ARM based machine.  To be able
to produce an image targeting this board, we need the following
elements:

@itemize
@item An @code{operating-system} record containing at least
an appropriate kernel (@code{linux-libre-arm64-generic}) and bootloader
@code{u-boot-pine64-lts-bootloader}) for the Pine64.

@item Possibly, an @code{image-type} record providing a way to
turn an @code{operating-system} record to an @code{image} record
suitable for the Pine64.

@item An actual @code{image} that can be instantiated with the
@command{guix system image} command.

@end itemize

The @code{(gnu system images pine64)} module provides all those
elements: @code{pine64-barebones-os}, @code{pine64-image-type} and
@code{pine64-barebones-raw-image} respectively.

The module returns the @code{pine64-barebones-raw-image} in order for
users to be able to run:

@example
guix system image gnu/system/images/pine64.scm
@end example

Now, thanks to the @code{pine64-image-type} record declaring the
@code{'pine64-raw} @code{image-type}, one could also prepare a
@code{my-pine.scm} file with the following content:

@lisp
(use-modules (gnu system images pine64))
(operating-system
  (inherit pine64-barebones-os)
  (timezone "Europe/Athens"))
@end lisp

to customize the @code{pine64-barebones-os}, and run:

@example
$ guix system image --image-type=pine64-raw my-pine.scm
@end example

Note that there are other modules in the @code{gnu/system/images}
directory targeting @code{Novena}, @code{Pine64}, @code{PinebookPro} and
@code{Rock64} machines.

@node Installing Debugging Files
@chapter Installing Debugging Files

@cindex debugging files
Program binaries, as produced by the GCC compilers for instance, are
typically written in the ELF format, with a section containing
@dfn{debugging information}.  Debugging information is what allows the
debugger, GDB, to map binary code to source code; it is required to
debug a compiled program in good conditions.

This chapter explains how to use separate debug info when packages
provide it, and how to rebuild packages with debug info when it's
missing.

@menu
* Separate Debug Info::         Installing 'debug' outputs.
* Rebuilding Debug Info::       Building missing debug info.
@end menu

@node Separate Debug Info
@section Separate Debug Info

The problem with debugging information is that it takes up a fair amount
of disk space.  For example, debugging information for the GNU C Library
weighs in at more than 60 MiB@.  Thus, as a user, keeping all the
debugging info of all the installed programs is usually not an option.
Yet, space savings should not come at the cost of an impediment to
debugging---especially in the GNU system, which should make it easier
for users to exert their computing freedom (@pxref{GNU Distribution}).

Thankfully, the GNU Binary Utilities (Binutils) and GDB provide a
mechanism that allows users to get the best of both worlds: debugging
information can be stripped from the binaries and stored in separate
files.  GDB is then able to load debugging information from those files,
when they are available (@pxref{Separate Debug Files,,, gdb, Debugging
with GDB}).

The GNU distribution takes advantage of this by storing debugging
information in the @code{lib/debug} sub-directory of a separate package
output unimaginatively called @code{debug} (@pxref{Packages with
Multiple Outputs}).  Users can choose to install the @code{debug} output
of a package when they need it.  For instance, the following command
installs the debugging information for the GNU C Library and for GNU
Guile:

@example
guix install glibc:debug guile:debug
@end example

GDB must then be told to look for debug files in the user's profile, by
setting the @code{debug-file-directory} variable (consider setting it
from the @file{~/.gdbinit} file, @pxref{Startup,,, gdb, Debugging with
GDB}):

@example
(gdb) set debug-file-directory ~/.guix-profile/lib/debug
@end example

From there on, GDB will pick up debugging information from the
@file{.debug} files under @file{~/.guix-profile/lib/debug}.

Below is an alternative GDB script which is useful when working with
other profiles.  It takes advantage of the optional Guile integration in
GDB.  This snippet is included by default on Guix System in the
@file{~/.gdbinit} file.

@example
guile
(use-modules (gdb))
(execute (string-append "set debug-file-directory "
                        (or (getenv "GDB_DEBUG_FILE_DIRECTORY")
                            "~/.guix-profile/lib/debug")))
end
@end example

In addition, you will most likely want GDB to be able to show the source
code being debugged.  To do that, you will have to unpack the source
code of the package of interest (obtained with @code{guix build
--source}, @pxref{Invoking guix build}), and to point GDB to that source
directory using the @code{directory} command (@pxref{Source Path,
@code{directory},, gdb, Debugging with GDB}).

@c XXX: keep me up-to-date
The @code{debug} output mechanism in Guix is implemented by the
@code{gnu-build-system} (@pxref{Build Systems}).  Currently, it is
opt-in---debugging information is available only for the packages with
definitions explicitly declaring a @code{debug} output.  To check
whether a package has a @code{debug} output, use @command{guix package
--list-available} (@pxref{Invoking guix package}).

Read on for how to deal with packages lacking a @code{debug} output.

@node Rebuilding Debug Info
@section Rebuilding Debug Info

@cindex debugging info, rebuilding
As we saw above, some packages, but not all, provide debugging info in a
@code{debug} output.  What can you do when debugging info is missing?
The @option{--with-debug-info} option provides a solution to that: it
allows you to rebuild the package(s) for which debugging info is
missing---and only those---and to graft those onto the application
you're debugging.  Thus, while it's not as fast as installing a
@code{debug} output, it is relatively inexpensive.

Let's illustrate that.  Suppose you're experiencing a bug in Inkscape
and would like to see what's going on in GLib, a library that's deep
down in its dependency graph.  As it turns out, GLib does not have a
@code{debug} output and the backtrace GDB shows is all sadness:

@example
(gdb) bt
#0  0x00007ffff5f92190 in g_getenv ()
   from /gnu/store/@dots{}-glib-2.62.6/lib/libglib-2.0.so.0
#1  0x00007ffff608a7d6 in gobject_init_ctor ()
   from /gnu/store/@dots{}-glib-2.62.6/lib/libgobject-2.0.so.0
#2  0x00007ffff7fe275a in call_init (l=<optimized out>, argc=argc@@entry=1, argv=argv@@entry=0x7fffffffcfd8,
    env=env@@entry=0x7fffffffcfe8) at dl-init.c:72
#3  0x00007ffff7fe2866 in call_init (env=0x7fffffffcfe8, argv=0x7fffffffcfd8, argc=1, l=<optimized out>)
    at dl-init.c:118
@end example

To address that, you install Inkscape linked against a variant GLib that
contains debug info:

@example
guix install inkscape --with-debug-info=glib
@end example

This time, debugging will be a whole lot nicer:

@example
$ gdb --args sh -c 'exec inkscape'
@dots{}
(gdb) b g_getenv
Function "g_getenv" not defined.
Make breakpoint pending on future shared library load? (y or [n]) y
Breakpoint 1 (g_getenv) pending.
(gdb) r
Starting program: /gnu/store/@dots{}-profile/bin/sh -c exec\ inkscape
@dots{}
(gdb) bt
#0  g_getenv (variable=variable@@entry=0x7ffff60c7a2e "GOBJECT_DEBUG") at ../glib-2.62.6/glib/genviron.c:252
#1  0x00007ffff608a7d6 in gobject_init () at ../glib-2.62.6/gobject/gtype.c:4380
#2  gobject_init_ctor () at ../glib-2.62.6/gobject/gtype.c:4493
#3  0x00007ffff7fe275a in call_init (l=<optimized out>, argc=argc@@entry=3, argv=argv@@entry=0x7fffffffd088,
    env=env@@entry=0x7fffffffd0a8) at dl-init.c:72
@dots{}
@end example

Much better!

Note that there can be packages for which @option{--with-debug-info}
will not have the desired effect.  @xref{Package Transformation Options,
@option{--with-debug-info}}, for more information.

@node Using TeX and LaTeX
@chapter Using @TeX{} and @LaTeX{}

@cindex @TeX{} packages
@cindex @LaTeX{} packages
Guix provides packages for the @TeX{}, @LaTeX{}, ConTeXt, LuaTeX, and
related typesetting systems, taken from the
@uref{https://www.tug.org/texlive/, @TeX{} Live distribution}.  However,
because @TeX{} Live is so huge and because finding one's way in this
maze is tricky, so this section provides some guidance on how to deploy
the relevant packages to compile @TeX{} and @LaTeX{} documents.

@TeX{} Live currently comes in two mutually exclusive flavors in Guix:

@itemize
@item
The ``monolithic'' @code{texlive} package: it comes with @emph{every
single @TeX{} Live package} (roughly 4,200), but it is huge---more than
4@tie{}GiB for a single package!

@item
A ``modular'' @TeX{} Live distribution, in which you only install the
packages, always prefixed with @samp{texlive-}, you need.
@end itemize

So to insist, these two flavors cannot be combined@footnote{No rule
without exception! As the monolithic @TeX{} Live does not contain the
@command{biber} executable, it is okay to combine it with
@code{texlive-biber}, which does.}.  If in the modular setting your
document does not compile, the solution is not to add the monolithic
@code{texlive} package, but to add the set of missing packages from the
modular distribution.

Building a coherent system that provides all the essential tools and, at
the same time, satisfies all of its internal dependencies can be
a difficult task.  It is therefore recommended to start with sets of
packages, called @dfn{collections}, and @dfn{schemes}, the name for
collections of collections.  The following command lists available
schemes and collections (@pxref{guix-search,, Invoking guix package}):

@example
guix search texlive-\(scheme\|collection\) | recsel -p name,description
@end example

If needed, you may then complete your system with individual packages,
particularly when they belong to a large collection you're not otherwise
interested in.

For instance, the following manifest is a reasonable, yet frugal
starting point for a French @LaTeX{} user:

@lisp
(specifications->manifest
 '("rubber"

   "texlive-scheme-basic"
   "texlive-collection-latexrecommended"
   "texlive-collection-fontsrecommended"
   "texlive-babel-french"

   ;; From "latexextra" collection.
   "texlive-tabularray"
   ;; From "binextra" collection.
   "texlive-texdoc"))
@end lisp

If you come across a document that does not compile in such a basic
setting, the main difficulty is finding the missing packages.  In this
case, @command{pdflatex} and similar commands tend to fail with obscure
error messages along the lines of:

@example
doc.tex: File `tikz.sty' not found.
doc.tex:7: Emergency stop.
@end example

@noindent
or, for a missing font:

@example
kpathsea: Running mktexmf phvr7t
! I can't find file `phvr7t'.
@end example

How do you determine what the missing package is?  In the first case,
you will find the answer by running:

@example
$ guix search texlive tikz
name: texlive-pgf
version: 59745
@dots{}
@end example

In the second case, @command{guix search} turns up nothing.  Instead,
you can search the @TeX{} Live package database using the
@command{tlmgr} command:

@example
$ tlmgr info phvr7t
tlmgr: cannot find package phvr7t, searching for other matches:

Packages containing `phvr7t' in their title/description:

Packages containing files matching `phvr7t':
helvetic:
        texmf-dist/fonts/tfm/adobe/helvetic/phvr7t.tfm
        texmf-dist/fonts/tfm/adobe/helvetic/phvr7tn.tfm
        texmf-dist/fonts/vf/adobe/helvetic/phvr7t.vf
        texmf-dist/fonts/vf/adobe/helvetic/phvr7tn.vf
tex4ht:
        texmf-dist/tex4ht/ht-fonts/alias/adobe/helvetic/phvr7t.htf
@end example

@noindent
The file is available in the @TeX{} Live @code{helvetic} package, which
is known in Guix as @code{texlive-helvetic}.  Quite a ride, but you
found it!

@node Security Updates
@chapter Security Updates

@cindex security updates
@cindex security vulnerabilities
Occasionally, important security vulnerabilities are discovered in software
packages and must be patched.  Guix developers try hard to keep track of
known vulnerabilities and to apply fixes as soon as possible in the
@code{master} branch of Guix (we do not yet provide a ``stable'' branch
containing only security updates).  The @command{guix lint} tool helps
developers find out about vulnerable versions of software packages in the
distribution:

@smallexample
$ guix lint -c cve
gnu/packages/base.scm:652:2: glibc@@2.21: probably vulnerable to CVE-2015-1781, CVE-2015-7547
gnu/packages/gcc.scm:334:2: gcc@@4.9.3: probably vulnerable to CVE-2015-5276
gnu/packages/image.scm:312:2: openjpeg@@2.1.0: probably vulnerable to CVE-2016-1923, CVE-2016-1924
@dots{}
@end smallexample

@xref{Invoking guix lint}, for more information.

Guix follows a functional
package management discipline (@pxref{Introduction}), which implies
that, when a package is changed, @emph{every package that depends on it}
must be rebuilt.  This can significantly slow down the deployment of
fixes in core packages such as libc or Bash, since basically the whole
distribution would need to be rebuilt.  Using pre-built binaries helps
(@pxref{Substitutes}), but deployment may still take more time than
desired.

@cindex grafts
To address this, Guix implements @dfn{grafts}, a mechanism that allows
for fast deployment of critical updates without the costs associated
with a whole-distribution rebuild.  The idea is to rebuild only the
package that needs to be patched, and then to ``graft'' it onto packages
explicitly installed by the user and that were previously referring to
the original package.  The cost of grafting is typically very low, and
order of magnitudes lower than a full rebuild of the dependency chain.

@cindex replacements of packages, for grafts
For instance, suppose a security update needs to be applied to Bash.
Guix developers will provide a package definition for the ``fixed''
Bash, say @code{bash-fixed}, in the usual way (@pxref{Defining
Packages}).  Then, the original package definition is augmented with a
@code{replacement} field pointing to the package containing the bug fix:

@lisp
(define bash
  (package
    (name "bash")
    ;; @dots{}
    (replacement bash-fixed)))
@end lisp

From there on, any package depending directly or indirectly on Bash---as
reported by @command{guix gc --requisites} (@pxref{Invoking guix
gc})---that is installed is automatically ``rewritten'' to refer to
@code{bash-fixed} instead of @code{bash}.  This grafting process takes
time proportional to the size of the package, usually less than a
minute for an ``average'' package on a recent machine.  Grafting is
recursive: when an indirect dependency requires grafting, then grafting
``propagates'' up to the package that the user is installing.

Currently, the length of the name and version of the graft and that of
the package it replaces (@code{bash-fixed} and @code{bash} in the example
above) must be equal.  This restriction mostly comes from the fact that
grafting works by patching files, including binary files, directly.
Other restrictions may apply: for instance, when adding a graft to a
package providing a shared library, the original shared library and its
replacement must have the same @code{SONAME} and be binary-compatible.

The @option{--no-grafts} command-line option allows you to forcefully
avoid grafting (@pxref{Common Build Options, @option{--no-grafts}}).
Thus, the command:

@example
guix build bash --no-grafts
@end example

@noindent
returns the store file name of the original Bash, whereas:

@example
guix build bash
@end example

@noindent
returns the store file name of the ``fixed'', replacement Bash.  This
allows you to distinguish between the two variants of Bash.

To verify which Bash your whole profile refers to, you can run
(@pxref{Invoking guix gc}):

@example
guix gc -R $(readlink -f ~/.guix-profile) | grep bash
@end example

@noindent
@dots{} and compare the store file names that you get with those above.
Likewise for a complete Guix system generation:

@example
guix gc -R $(guix system build my-config.scm) | grep bash
@end example

Lastly, to check which Bash running processes are using, you can use the
@command{lsof} command:

@example
lsof | grep /gnu/store/.*bash
@end example


@node Bootstrapping
@chapter Bootstrapping

@c Adapted from the ELS 2013 paper.

@cindex bootstrapping

Bootstrapping in our context refers to how the distribution gets built
``from nothing''.  Remember that the build environment of a derivation
contains nothing but its declared inputs (@pxref{Introduction}).  So
there's an obvious chicken-and-egg problem: how does the first package
get built?  How does the first compiler get compiled?

It is tempting to think of this question as one that only die-hard
hackers may care about.  However, while the answer to that question is
technical in nature, its implications are wide-ranging.  How the
distribution is bootstrapped defines the extent to which we, as
individuals and as a collective of users and hackers, can trust the
software we run.  It is a central concern from the standpoint of
@emph{security} and from a @emph{user freedom} viewpoint.

@cindex bootstrap binaries
The GNU system is primarily made of C code, with libc at its core.  The
GNU build system itself assumes the availability of a Bourne shell and
command-line tools provided by GNU Coreutils, Awk, Findutils, `sed', and
`grep'.  Furthermore, build programs---programs that run
@code{./configure}, @code{make}, etc.---are written in Guile Scheme
(@pxref{Derivations}).  Consequently, to be able to build anything at
all, from scratch, Guix relies on pre-built binaries of Guile, GCC,
Binutils, libc, and the other packages mentioned above---the
@dfn{bootstrap binaries}.

These bootstrap binaries are ``taken for granted'', though we can also
re-create them if needed (@pxref{Preparing to Use the Bootstrap
Binaries}).

@menu
* Full-Source Bootstrap::       A Bootstrap worthy of GNU.
* Preparing to Use the Bootstrap Binaries::  Building that what matters most.
@end menu

@node Full-Source Bootstrap
@section The Full-Source Bootstrap

Guix---like other GNU/Linux distributions---is traditionally bootstrapped from
a set of bootstrap binaries: Bourne shell, command-line tools provided by GNU
Coreutils, Awk, Findutils, `sed', and `grep' and Guile, GCC, Binutils, and the
GNU C Library (@pxref{Bootstrapping}).  Usually, these bootstrap binaries are
``taken for granted.''

Taking the bootstrap binaries for granted means that we consider them to
be a correct and trustworthy ``seed'' for building the complete system.
Therein lies a problem: the combined size of these bootstrap binaries is
about 250MB (@pxref{Bootstrappable Builds,,, mes, GNU Mes}).  Auditing
or even inspecting these is next to impossible.

For @code{i686-linux} and @code{x86_64-linux}, Guix now features a
@dfn{full-source bootstrap}.  This bootstrap is rooted in
@file{hex0-seed} from the @url{https://savannah.gnu.org/projects/stage0,
Stage0} package.  The hex0 program is minimalist assembler: it reads
space-separated hexadecimal digits (nibbles) from a file, possibly
including comments, and emits on standard output the bytes corresponding
to those hexadecimal numbers.  The source code of this initial hex0
program is a file called
@c XXX TODO: update to savannah url, once accepted there
@url{https://github.com/oriansj/bootstrap-seeds/blob/master/POSIX/x86/hex0_x86.hex0,@file{hex0_x86.hex0}}
and is written in the @code{hex0} language.

Hex0 is self-hosting, which means that it can build itself:

@example
./hex0-seed hex0_x86.hex0 hex0
@end example

Hex0 it is the ASCII-equivalent of the binary program and can be
produced by doing something much like:

@example
sed 's/[;#].*$//g' hex0_x86.hex0 | xxd -r -p > hex0
chmod +x hex0
@end example

It is because of this ASCII-binary equivalence that we can bless this
initial 357-byte binary as source, and hence `full-source bootstrap''.

The bootstrap then continues: @code{hex0} builds @code{hex1} and then on
to @code{M0}, @code{hex2}, @code{M1}, @code{mescc-tools} and finally
@code{M2-Planet}.  Then, using @code{mescc-tools}, @code{M2-Planet} we
build Mes (@pxref{Top, GNU Mes Reference Manual,, mes, GNU Mes}, a
Scheme interpreter and C compiler in Scheme).  From here on starts
the more traditional @code{C}-based bootstrap of the GNU System.

Another step that Guix has taken is to replace the shell and all its
utilities with implementations in Guile Scheme, the @emph{Scheme-only
bootstrap}.  Gash (@pxref{Gash,,, gash, The Gash manual}) is a
POSIX-compatible shell that replaces Bash, and it comes with Gash Utils
which has minimalist replacements for Awk, the GNU Core Utilities, Grep,
Gzip, Sed, and Tar.

Building the GNU System from source is currently only possible by adding
some historical GNU packages as intermediate steps@footnote{Packages
such as @code{gcc-2.95.3}, @code{binutils-2.14}, @code{glibc-2.2.5},
@code{gzip-1.2.4}, @code{tar-1.22}, and some others.  For details, see
@file{gnu/packages/commencement.scm}.}.  As Gash and Gash Utils mature,
and GNU packages become more bootstrappable again (e.g., new releases of
GNU Sed will also ship as gzipped tarballs again, as alternative to the
hard to bootstrap @code{xz}-compression), this set of added packages can
hopefully be reduced again.

The graph below shows the resulting dependency graph for
@code{gcc-core-mesboot0}, the bootstrap compiler used for the
traditional bootstrap of the rest of the Guix System.

@c ./pre-inst-env guix graph \
@c   -e '(@@ (gnu packages commencement) gcc-core-mesboot0)' \
@c   | sed -r \
@c     -e 's,((bootstrap-seeds|guile-bootstrap).*shape =) box,\1 ellipse,' \
@c     -e 's,fontname = sans,fontname = "dejavu sans",' \
@c   > doc/images/gcc-core-mesboot0-graph.dot
@image{images/gcc-core-mesboot0-graph,6in,,Dependency graph of gcc-core-mesboot0}

Work is ongoing to bring these bootstraps to the @code{arm-linux} and
@code{aarch64-linux} architectures and to the Hurd.

If you are interested, join us on @samp{#bootstrappable} on the Libera.Chat
IRC network or discuss on @email{bug-mes@@gnu.org} or
@email{gash-devel@@nongnu.org}.

@node Preparing to Use the Bootstrap Binaries
@section Preparing to Use the Bootstrap Binaries

@c As of Emacs 24.3, Info-mode displays the image, but since it's a
@c large image, it's hard to scroll.  Oh well.
@image{images/bootstrap-graph,6in,,Dependency graph of the early bootstrap derivations}

The figure above shows the very beginning of the dependency graph of the
distribution, corresponding to the package definitions of the @code{(gnu
packages bootstrap)} module.  A similar figure can be generated with
@command{guix graph} (@pxref{Invoking guix graph}), along the lines of:

@example
guix graph -t derivation \
  -e '(@@@@ (gnu packages bootstrap) %bootstrap-gcc)' \
  | dot -Tps > gcc.ps
@end example

or, for the further Reduced Binary Seed bootstrap

@example
guix graph -t derivation \
  -e '(@@@@ (gnu packages bootstrap) %bootstrap-mes)' \
  | dot -Tps > mes.ps
@end example

At this level of detail, things are
slightly complex.  First, Guile itself consists of an ELF executable,
along with many source and compiled Scheme files that are dynamically
loaded when it runs.  This gets stored in the @file{guile-2.0.7.tar.xz}
tarball shown in this graph.  This tarball is part of Guix's ``source''
distribution, and gets inserted into the store with @code{add-to-store}
(@pxref{The Store}).

But how do we write a derivation that unpacks this tarball and adds it
to the store?  To solve this problem, the @code{guile-bootstrap-2.0.drv}
derivation---the first one that gets built---uses @code{bash} as its
builder, which runs @code{build-bootstrap-guile.sh}, which in turn calls
@code{tar} to unpack the tarball.  Thus, @file{bash}, @file{tar},
@file{xz}, and @file{mkdir} are statically-linked binaries, also part of
the Guix source distribution, whose sole purpose is to allow the Guile
tarball to be unpacked.

Once @code{guile-bootstrap-2.0.drv} is built, we have a functioning
Guile that can be used to run subsequent build programs.  Its first task
is to download tarballs containing the other pre-built binaries---this
is what the @file{.tar.xz.drv} derivations do.  Guix modules such as
@code{ftp-client.scm} are used for this purpose.  The
@code{module-import.drv} derivations import those modules in a directory
in the store, using the original layout.  The
@code{module-import-compiled.drv} derivations compile those modules, and
write them in an output directory with the right layout.  This
corresponds to the @code{#:modules} argument of
@code{build-expression->derivation} (@pxref{Derivations}).

Finally, the various tarballs are unpacked by the derivations
@code{gcc-bootstrap-0.drv}, @code{glibc-bootstrap-0.drv}, or
@code{bootstrap-mes-0.drv} and @code{bootstrap-mescc-tools-0.drv}, at which
point we have a working C tool chain.

@unnumberedsec Building the Build Tools

Bootstrapping is complete when we have a full tool chain that does not
depend on the pre-built bootstrap tools discussed above.  This
no-dependency requirement is verified by checking whether the files of
the final tool chain contain references to the @file{/gnu/store}
directories of the bootstrap inputs.  The process that leads to this
``final'' tool chain is described by the package definitions found in
the @code{(gnu packages commencement)} module.

The @command{guix graph} command allows us to ``zoom out'' compared to
the graph above, by looking at the level of package objects instead of
individual derivations---remember that a package may translate to
several derivations, typically one derivation to download its source,
one to build the Guile modules it needs, and one to actually build the
package from source.  The command:

@example
guix graph -t bag \
  -e '(@@@@ (gnu packages commencement)
          glibc-final-with-bootstrap-bash)' | xdot -
@end example

@noindent
displays the dependency graph leading to the ``final'' C
library@footnote{You may notice the @code{glibc-intermediate} label,
suggesting that it is not @emph{quite} final, but as a good
approximation, we will consider it final.}, depicted below.

@image{images/bootstrap-packages,6in,,Dependency graph of the early packages}

@c See <https://lists.gnu.org/archive/html/gnu-system-discuss/2012-10/msg00000.html>.
The first tool that gets built with the bootstrap binaries is
GNU@tie{}Make---noted @code{make-boot0} above---which is a prerequisite
for all the following packages.  From there Findutils and Diffutils get
built.

Then come the first-stage Binutils and GCC, built as pseudo cross
tools---i.e., with @option{--target} equal to @option{--host}.  They are
used to build libc.  Thanks to this cross-build trick, this libc is
guaranteed not to hold any reference to the initial tool chain.

From there the final Binutils and GCC (not shown above) are built.  GCC
uses @command{ld} from the final Binutils, and links programs against
the just-built libc.  This tool chain is used to build the other
packages used by Guix and by the GNU Build System: Guile, Bash,
Coreutils, etc.

And voilà!  At this point we have the complete set of build tools that
the GNU Build System expects.  These are in the @code{%final-inputs}
variable of the @code{(gnu packages commencement)} module, and are
implicitly used by any package that uses @code{gnu-build-system}
(@pxref{Build Systems, @code{gnu-build-system}}).


@unnumberedsec Building the Bootstrap Binaries

@cindex bootstrap binaries
Because the final tool chain does not depend on the bootstrap binaries,
those rarely need to be updated.  Nevertheless, it is useful to have an
automated way to produce them, should an update occur, and this is what
the @code{(gnu packages make-bootstrap)} module provides.

The following command builds the tarballs containing the bootstrap binaries
(Binutils, GCC, glibc, for the traditional bootstrap and linux-libre-headers,
bootstrap-mescc-tools, bootstrap-mes for the Reduced Binary Seed bootstrap,
and Guile, and a tarball containing a mixture of Coreutils and other basic
command-line tools):

@example
guix build bootstrap-tarballs
@end example

The generated tarballs are those that should be referred to in the
@code{(gnu packages bootstrap)} module mentioned at the beginning of
this section.

Still here?  Then perhaps by now you've started to wonder: when do we
reach a fixed point?  That is an interesting question!  The answer is
unknown, but if you would like to investigate further (and have
significant computational and storage resources to do so), then let us
know.

@unnumberedsec Reducing the Set of Bootstrap Binaries

Our traditional bootstrap includes GCC, GNU Libc, Guile, etc.  That's a lot of
binary code!  Why is that a problem?  It's a problem because these big chunks
of binary code are practically non-auditable, which makes it hard to establish
what source code produced them.  Every unauditable binary also leaves us
vulnerable to compiler backdoors as described by Ken Thompson in the 1984
paper @emph{Reflections on Trusting Trust}.

This is mitigated by the fact that our bootstrap binaries were generated
from an earlier Guix revision.  Nevertheless it lacks the level of
transparency that we get in the rest of the package dependency graph,
where Guix always gives us a source-to-binary mapping.  Thus, our goal
is to reduce the set of bootstrap binaries to the bare minimum.

The @uref{https://bootstrappable.org, Bootstrappable.org web site} lists
on-going projects to do that.  One of these is about replacing the
bootstrap GCC with a sequence of assemblers, interpreters, and compilers
of increasing complexity, which could be built from source starting from
a simple and auditable assembler.

Our first major achievement is the replacement of GCC, the GNU C Library
and Binutils by MesCC-Tools (a simple hex linker and macro assembler) and Mes
(@pxref{Top, GNU Mes Reference Manual,, mes, GNU Mes}, a Scheme interpreter
and C compiler in Scheme).  Neither MesCC-Tools nor Mes can be fully
bootstrapped yet and thus we inject them as binary seeds.  We call this the
Reduced Binary Seed bootstrap, as it has halved the size of our bootstrap
binaries!  Also, it has eliminated the C compiler binary; i686-linux and
x86_64-linux Guix packages are now bootstrapped without any binary C compiler.

Work is ongoing to make MesCC-Tools and Mes fully bootstrappable and we are
also looking at any other bootstrap binaries.  Your help is welcome!

@node Porting
@chapter Porting to a New Platform

As discussed above, the GNU distribution is self-contained, and
self-containment is achieved by relying on pre-built ``bootstrap
binaries'' (@pxref{Bootstrapping}).  These binaries are specific to an
operating system kernel, CPU architecture, and application binary
interface (ABI).  Thus, to port the distribution to a platform that is
not yet supported, one must build those bootstrap binaries, and update
the @code{(gnu packages bootstrap)} module to use them on that platform.

Fortunately, Guix can @emph{cross compile} those bootstrap binaries.
When everything goes well, and assuming the GNU tool chain supports the
target platform, this can be as simple as running a command like this
one:

@example
guix build --target=armv5tel-linux-gnueabi bootstrap-tarballs
@end example

For this to work, it is first required to register a new platform as
defined in the @code{(guix platform)} module.  A platform is making the
connection between a GNU triplet (@pxref{Specifying Target Triplets, GNU
configuration triplets,, autoconf, Autoconf}), the equivalent
@var{system} in Nix notation, the name of the
@var{glibc-dynamic-linker}, and the corresponding Linux architecture
name if applicable (@pxref{Platforms}).

Once the bootstrap tarball are built, the @code{(gnu packages
bootstrap)} module needs to be updated to refer to these binaries on the
target platform.  That is, the hashes and URLs of the bootstrap tarballs
for the new platform must be added alongside those of the currently
supported platforms.  The bootstrap Guile tarball is treated specially:
it is expected to be available locally, and @file{gnu/local.mk} has
rules to download it for the supported architectures; a rule for the new
platform must be added as well.

In practice, there may be some complications.  First, it may be that the
extended GNU triplet that specifies an ABI (like the @code{eabi} suffix
above) is not recognized by all the GNU tools.  Typically, glibc
recognizes some of these, whereas GCC uses an extra @option{--with-abi}
configure flag (see @code{gcc.scm} for examples of how to handle this).
Second, some of the required packages could fail to build for that
platform.  Lastly, the generated binaries could be broken for some
reason.

@c *********************************************************************
@include contributing.texi

@c *********************************************************************
@node Acknowledgments
@chapter Acknowledgments

Guix is based on the @uref{https://nixos.org/nix/, Nix package manager},
which was designed and
implemented by Eelco Dolstra, with contributions from other people (see
the @file{nix/AUTHORS} file in Guix).  Nix pioneered functional package
management, and promoted unprecedented features, such as transactional
package upgrades and rollbacks, per-user profiles, and referentially
transparent build processes.  Without this work, Guix would not exist.

The Nix-based software distributions, Nixpkgs and NixOS, have also been
an inspiration for Guix.

GNU@tie{}Guix itself is a collective work with contributions from a
number of people.  See the @file{AUTHORS} file in Guix for more
information on these fine people.  The @file{THANKS} file lists people
who have helped by reporting bugs, taking care of the infrastructure,
providing artwork and themes, making suggestions, and more---thank you!


@c *********************************************************************
@node GNU Free Documentation License
@appendix GNU Free Documentation License
@cindex license, GNU Free Documentation License
@include fdl-1.3.texi

@c *********************************************************************
@node Concept Index
@unnumbered Concept Index
@printindex cp

@node Programming Index
@unnumbered Programming Index
@syncodeindex tp fn
@syncodeindex vr fn
@printindex fn

@bye

@c Local Variables:
@c ispell-local-dictionary: "american";
@c End:
