doc: Recommend avoiding execl, execle or execlp in mcron job specifications.

* doc/guix.texi (Scheduled Job Execution): Adjust the 'updatedb' example and
add a new tip.
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Maxim Cournoyer 2022-11-28 22:47:16 -05:00
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@ -18940,8 +18940,7 @@ gexps to introduce job definitions that are passed to mcron
;; job's action as a Scheme procedure.
#~(job '(next-hour '(3))
(lambda ()
(execl (string-append #$findutils "/bin/updatedb")
"updatedb"
(system* (string-append #$findutils "/bin/updatedb")
"--prunepaths=/tmp /var/tmp /gnu/store"))
"updatedb"))
@ -18980,6 +18979,12 @@ 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