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doc: Augment mcron example. 

Suggested by Danny Milosavljevic.

* doc/guix.texi (Scheduled Job Execution): Add unprivileged job example,
and show the use of thunks as job actions and gexps.
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Ludovic Courtès 2016-06-26 15:27:34 +02:00
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@ -7507,27 +7507,45 @@ Unix @command{cron} daemon; the main difference is that it is
implemented in Guile Scheme, which provides a lot of flexibility when implemented in Guile Scheme, which provides a lot of flexibility when
specifying the scheduling of jobs and their actions. specifying the scheduling of jobs and their actions.
For example, to define an operating system that runs the The example below defines an operating system that runs the
@command{updatedb} (@pxref{Invoking updatedb,,, find, Finding Files}) @command{updatedb} (@pxref{Invoking updatedb,,, find, Finding Files})
and the @command{guix gc} commands (@pxref{Invoking guix gc}) daily: 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 @lisp
(use-modules (guix) (gnu) (gnu services mcron)) (use-modules (guix) (gnu) (gnu services mcron))
(use-package-modules base idutils)
(define updatedb-job (define updatedb-job
;; Run 'updatedb' at 3 AM every day. ;; Run 'updatedb' at 3AM every day. Here we write the
;; job's action as a Scheme procedure.
#~(job '(next-hour '(3)) #~(job '(next-hour '(3))
"updatedb --prunepaths='/tmp /var/tmp /gnu/store'")) (lambda ()
(execl (string-append #$findutils "/bin/updatedb")
"updatedb"
"--prunepaths=/tmp /var/tmp /gnu/store"))))
(define garbage-collector-job (define garbage-collector-job
;; Collect garbage 5 minutes after midnight every day. ;; Collect garbage 5 minutes after midnight every day.
;; The job's action is a shell command.
#~(job "5 0 * * *" ;Vixie cron syntax #~(job "5 0 * * *" ;Vixie cron syntax
"guix gc -F 1G")) "guix gc -F 1G"))
(define idutils-jobs
;; Update the index database as user "charlie" at 12:15PM
;; and 19:15PM. This runs from the user's home directory.
#~(job '(next-minute-from (next-hour '(12 19)) '(15))
(string-append #$idutils "/bin/mkid src")
#:user "charlie"))
(operating-system (operating-system
;; @dots{} ;; @dots{}
(services (cons (mcron-service (list garbage-collector-job (services (cons (mcron-service (list garbage-collector-job
updatedb-job)) updatedb-job
idutils-job))
%base-services))) %base-services)))
@end lisp @end lisp