@@ 20858,14 20858,123 @@ instance of @code{greetd-user-session}.
@subsection Scheduled Job Execution
@cindex cron
-@cindex mcron
@cindex scheduling jobs
-The @code{(gnu services mcron)} module provides an interface to
+It is often useful to have system tasks run periodically. This can be
+achieved by defining Shepherd @dfn{timers} or by using the historical
+and somewhat less flexible mcron service.
+
+@subsubsection Shepherd Timers
+
+@cindex timers, Shepherd
+@cindex Shepherd timers
+The Shepherd supports running jobs periodically by defining
+@dfn{timers}, a special kind of service. A Shepherd timer can be
+defined like another Shepherd service, but with specific @code{start}
+and @code{stop} methods (@pxref{Shepherd Services}):
+
+@lisp
+;; Defining a timer, verbosely.
+(shepherd-service
+ (provision '(updatedb))
+ (requirement '(user-processes))
+ (modules '((shepherd service timer)))
+ (start #~(make-timer-constructor
+ ;; Everyday at 3AM (using Vixie cron syntax).
+ (cron-string->calendar-event "0 3 * * *")
+ (command '(#$(file-append findutils "/bin/updatedb")))
+ #:wait-for-termination? #t))
+ (stop #~(make-timer-destructor))
+ (documentation "Periodically run 'updatedb'.")
+ (actions (list shepherd-trigger-action)))
+@end lisp
+
+This is quite some boilerplate so you can instead use this equivalent
+shorthand notation:
+
+@lisp
+;; Equivalent timer definition, but shorter.
+(shepherd-timer '(updatedb) "0 3 * * *"
+ #~(#$(file-append findutils "/bin/updatedb"))
+ #:requirement '(user-processes))
+@end lisp
+
+This procedure is defined as follows.
+
+@anchor{shepherd-timer-procedure}
+@deffn {Procedure} shepherd-timer @var{provision} @var{schedule} @
+ @var{command} [#:requirement '()] @
+ [#:documentation %default-timer-documentation]
+Return a Shepherd service with the given @var{provision} periodically
+running @var{command}, a list-valued gexp, according to @var{schedule},
+a string in Vixie cron syntax or a gexp providing a Shepherd calendar
+event. @var{documentation} is the string that appears when running
+@code{herd doc @var{service}}.
+@end deffn
+
+The example below shows how to define a timer and to add it to your
+operating system configuration.
+
+@lisp
+(use-modules (gnu))
+(use-service-modules shepherd)
+(use-package-modules base)
+
+(define updatedb-timer
+ ;; Run 'updatedb' at 3AM everyday.
+ (shepherd-timer '(updatedb)
+ "0 3 * * *" ;Vixie cron syntax
+ #~(#$(file-append findutils "/bin/updatedb")
+ "--prunepaths=/tmp /var/tmp /gnu/store")
+ #:requirement '(user-processes)))
+
+(define garbage-collection-timer
+ ;; Run 'guix gc' everyday at 5AM.
+ (shepherd-timer '(garbage-collection)
+ #~(calendar-event #:hours '(5) #:minutes '(0))
+ #~("/run/current-system/profile/bin/guix"
+ "gc" "-F" "10G")
+ #:requirement '(guix-daemon)))
+
+(operating-system
+ ;; @dots{}
+
+ ;; Extend the Shepherd service with additional timers
+ ;; using 'simple-service'.
+ (services (cons (simple-service 'my-timers
+ shepherd-root-service-type
+ (list garbage-collection-timer
+ updatedb-timer))
+ %base-services)))
+@end lisp
+
+The resulting system contains these two services, which can be inspected
+with @command{herd status}. They can also be triggered manually:
+
+@example
+herd trigger garbage-collection
+@end example
+
+@xref{Timers,,, shepherd, The GNU Shepherd Manual} for more information
+on Shepherd timers.
+
+@anchor{mcron-service}
+@subsubsection Mcron
+
+@cindex mcron
+Alternatively,
+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.
+implemented in Guile Scheme. It is overall less convenient than
+Shepherd timers: individual jobs cannot depend on specific Shepherd
+services, logging is coarse-grain (one file for all the jobs), jobs may
+not be inspected, updated, or triggered manually.
+
+@quotation Note
+For the reasons given above, we recommend using Shepherd timers rather
+than mcron for your periodic tasks.
+@end quotation
The example below defines an operating system that runs the
@command{updatedb} (@pxref{Invoking updatedb,,, find, Finding Files})
@@ 48619,18 48728,23 @@ readline} for more information about all the configuration options.
@node Mcron Home Service
@subsection Scheduled User's Job Execution
-@cindex cron
-@cindex mcron
-@cindex scheduling jobs
-
+@cindex cron, per-user
+@cindex mcron, per-user
+@cindex scheduling jobs per-user
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
+applicable here (@pxref{mcron-service, mcron reference}), 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.
+@quotation Note
+We recommend defining periodic tasks as Shepherd timers, which provide
+more flexibility than mcron. @xref{Shepherd Home Service}, for more
+info.
+@end quotation
+
@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
@@ 48793,6 48907,45 @@ mechanism instead (@pxref{Shepherd Services}).
@end table
@end deftp
+@cindex timers, per-user
+The Shepherd allows you to define @dfn{timers}, a special type of
+service that performs a given task periodically. Just like you can
+define timers at the system level (@pxref{Scheduled Job Execution}), you
+can do so in your home environment.
+
+The example below defines a home environment where a Shepherd timer runs
+the @command{mkid} command twice per day (@pxref{mkid invocation,,,
+idutils, ID Database Utilities}). It does so by extending
+@code{home-shepherd-service-type} with @code{simple-service}; the
+Shepherd timer itself is produced by the @code{shepherd-timer} procedure
+(@pxref{shepherd-timer-procedure, @code{shepherd-timer}}), which is
+given the service name, a gexp specifying its schedule, and a gexp
+specifying the command to run.
+
+@lisp
+(use-modules (gnu) (guix)
+ (gnu home services shepherd)
+ (gnu packages idutils))
+
+(define idutils-service
+ ;; Index my 'doc' directory everyday at 12:15PM and 7:15PM.
+ (simple-service
+ 'update-idutils-database home-shepherd-service-type
+ (list (shepherd-timer '(update-idutils-database)
+ #~(calendar-event #:hours '(12 19)
+ #:minutes '(15))
+ #~(#$(file-append idutils "/bin/mkid")
+ "doc")))))
+
+(home-environment
+ ;; @dots{}
+ (services (append (list idutils-service)
+ %base-home-services)))
+@end lisp
+
+@xref{Timers,,, shepherd, The GNU Shepherd Manual} for more information
+on Shepherd timers.
+
@cindex log rotation, for user services
The Shepherd also comes with a @dfn{log rotation service}, which
compresses and then deletes old log files produced by services and