gnu: Add mpd service.

* doc/guix.texi: Add documentation.
* gnu/services/audio.scm (<mpd-configuration>): New record type.
  (mpd-service-type): New service type.
* gnu/tests/audio.scm: New file.
* gnu/local.mk: Add new files.

Signed-off-by: Christopher Baines <mail@cbaines.net>

services: admin: Simplify the handling of the Tailon debug? option.

* gnu/services/admin.scm (tailon-configuration-file-compiler): Simplify the
  handling of debug?.

services: Update the Tailon service for Tailon 1.3.0.

Tailon 1.3.0 (upgraded from 1.1.1) adds support for HTTP authentication.

* gnu/services/admin.scm (<tailon-configuration-file>): Add http-auth and
  users configuration values.
  (tailon-configuration-file-http-auth, tailon-configuration-file-users): New
  procedures.
  (tailon-configuration-file-compiler): Add support for the http-auth and
  users configuration options.
* doc/guix.texi (Monitoring Services): Document authentication for Tailon.

services: Add missing wrap-lines option to tailon.

* gnu/services/admin.scm (<tailon-configuration-file>): Add wrap-lines.
  (tailon-configuration-wrap-lines): New procedure.
  (tailon-configuration-file-compiler): Add support for wrap-lines.
* doc/guix.texi (Monitoring Services): Document the wrap-lines Tailon
  configuration option.

services: herd: Add a stop-service procedure.

* gnu/services/herd.scm (stop-service): New procedure.

services: herd: Fix matching ok responses from shepherd service.

Previously the match expression case for a successful response
(where error is #f) required that the result component contained a list with a
single element.

As far as I see when looking at the responses from the shepherd, this is not
normally the case. Therefore, to avoid treating successful responses as
errors, make the match requirement more permissive, accepting any value.

* gnu/services/herd.scm (invoke-action): Change match condition for ok responses.

services: ntp: Use the NTP pool via the 'guix' zone.

* gnu/services/networking.scm (%ntp-servers): Use *.guix.pool.ntp.org.

services: openssh: Extensions provide extra authorized keys.

* gnu/services/ssh.scm (extend-openssh-authorized-keys): New procedure.
(openssh-service-type)[compose, extend]: New fields.
* doc/guix.texi (Networking Services): Document the extension.

services: openssh: Add 'authorized-keys' field.

* gnu/services/ssh.scm (<openssh-configuration>)[authorized-keys]: New
field.
(authorized-key-directory): New procedure.
(openssh-config-file): Honor 'authorized-keys'.
(openssh-activation): Use 'with-imported-modules'.  Make /etc/ssh
755.  Create /etc/ssh/authorized_keys.d.
* doc/guix.texi (Networking Services): Document it.

services: cuirass: Set 'GIT_SSL_CAINFO' and 'GIT_EXEC_PATH'.

Reported by Ricardo Wurmus.

* gnu/services/cuirass.scm (cuirass-shepherd-service): Pass
 #:environment-variables.

services: Add memcached.

* gnu/services/databases.scm (memcached-service-type, %memcached-accounts):
  New variables.
  (<memcached-configuration>): New record type.
  (memcached-service-type): New procedures.
* gnu/tests/databases.scm: New file.
* doc/guix.texi (Database Services): Document the new memcached service.
* gnu/local.mk (GNU_SYSTEM_MODULES): Add entry for tests/databases.scm.

gnu: services: admin: Add tailon.

* gnu/services/admin.scm
  (<tailon-configuration>, <tailon-configuration-file>): New record types.
  (tailon-configuration-files-string, tailon-shepherd-service): New
  procedures.
  (%tailon-accounts, tailon-service-type: New variables.
* doc/guix.texi (Monitoring Services: Document the Tailon service.
* gnu/local.mk (GNU_SYSTEM_MODULES): Add gnu/tests/admin.scm.
* gnu/tests/admin.scm: New file.

services: guix-publish: Run in a UTF-8 locale.

Works around <https://bugs.gnu.org/26948>.

* gnu/services/base.scm (guix-publish-shepherd-service): Pass
  #:environment-variables to 'make-forkexec-constructor'.

gnu: Add fcgiwrap service.

* doc/guix.texi (Web Services): Add documentation.
* gnu/services/web.scm (<fcgiwrap-configuration>): New record type.
(fcgiwrap-accounts, fcgiwrap-shepherd-service): New service extensions.
(fcgiwrap-service-type): New service type.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>

services: cuirass: Add fallback parameter.

* gnu/services/cuirass.scm (<cuirass-configuration>)[fallback?]: New field.
(cuirass-shepherd-service): Take it into account.
* doc/guix.texi (Continuous Integration): Document it.

services: sysctl: Fix typo.

* gnu/services/sysctl.scm: Fix typo of 'make-sysctl-configuration'.

services: elogind: Start from the Shepherd.

Fixes <http://bugs.gnu.org/27580>.
Reported by William <w@vieta.uk>.

* gnu/services/desktop.scm (elogind-shepherd-service): New procedure.
(elogind-service-type): Extend SHEPHERD-ROOT-SERVICE-TYPE.

services: dbus, polkit: Add default value.

* gnu/services/dbus.scm (dbus-root-service-type)[default-value]: New
field.
(polkit-service-type)[default-value]: New field.

services: Add 'sysctl-service-type'.

* gnu/services/sysctl.scm: New file.
* doc/guix.texi (Miscellaneous Services): Document it.
* gnu/local.mk (GNU_SYSTEM_MODULES): Add it.

gnu: services: use seconds instead of duration strings.

* gnu/services/dns.scm (zone-file, knot-policy-configuration): Use numbers
instead of duration strings.
(verify-knot-policy-configuration): Fix typo.
* doc/guix.texi (DNS Services): Update documentation.