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anacron, ou en anglais : anachronistic command scheduler (en français : planificateur de commande anachronique), est un programme informatique qui permet l’exécution de tâches quotidiennes, hebdomadaires ou mensuelles sur un système Unix. À la différence de cron, il ne suppose pas que la machine tourne en permanence. En conséquence, il peut être utilisé sur des machines qui ne tournent pas 24 heures sur 24, pour contrôler quotidiennement, hebdomadairement ou mensuellement des tâches qui sont ordinairement contrôlées par cron.
De plus, anacron n’est pas un daemon qui tourne en permanence sur une machine : il vérifie s’il y a des tâches à exécuter, les exécute éventuellement, puis se termine. Autrement dit, il doit y avoir un autre système qui s’assure qu’anacron est lancé périodiquement : il nécessite donc d’être lancé par des scripts de démarrage, par des tâches cron (on utilise bien souvent une tâche cron.hourly), ou encore d’être lancé manuellement.

ANACRON(8) Anacron Users’ Manual ANACRON(8)

NAME

anacron – runs commands periodically

SYNOPSIS

anacron [-s] [-f] [-n] [-d] [-q] [-t anacrontab] [-S spooldir] [job] …
anacron [-S spooldir] -u [-t anacrontab] [job] …
anacron [-V|-h] anacron -T [-t anacrontab]

DESCRIPTION

Anacron can be used to execute commands periodically, with a frequency
specified in days. Unlike cron(8), it does not assume that the machine
is running continuously. Hence, it can be used on machines that aren’t
running 24 hours a day, to control daily, weekly, and monthly jobs that
are usually controlled by cron.

When executed, Anacron reads a list of jobs from a configuration file,
normally /etc/anacrontab (see anacrontab(5)). This file contains the
list of jobs that Anacron controls. Each job entry specifies a period
in days, a delay in minutes, a unique job identifier, and a shell com‐
mand.

For each job, Anacron checks whether this job has been executed in the
last n days, where n is the period specified for that job. If not,
Anacron runs the job’s shell command, after waiting for the number of
minutes specified as the delay parameter.

After the command exits, Anacron records the date in a special time‐
stamp file for that job, so it can know when to execute it again. Only
the date is used for the time calculations. The hour is not used.

When there are no more jobs to be run, Anacron exits.

Anacron only considers jobs whose identifier, as specified in the
anacrontab matches any of the job command-line arguments. The job
arguments can be shell wildcard patterns (be sure to protect them from
your shell with adequate quoting). Specifying no job arguments, is
equivalent to specifying “*” (That is, all jobs will be considered).

Unless the -d option is given (see below), Anacron forks to the back‐
ground when it starts, and the parent process exits immediately.

Unless the -s or -n options are given, Anacron starts jobs immediately
when their delay is over. The execution of different jobs is com‐
pletely independent.

If a job generates any output on its standard output or standard error,
the output is mailed to the user running Anacron (usually root), or to
the address contained by the MAILTO environment variable in the
crontab, if such exists.

Informative messages about what Anacron is doing are sent to syslogd(8)
under facility cron, priority notice. Error messages are sent at pri‐
ority error.

“Active” jobs (i.e. jobs that Anacron already decided to run and now
wait for their delay to pass, and jobs that are currently being exe‐
cuted by Anacron), are “locked”, so that other copies of Anacron won’t
run them at the same time.

OPTIONS

-f Force execution of the jobs, ignoring the timestamps.

-u Only update the timestamps of the jobs, to the current date, but
don’t run anything.

-s Serialize execution of jobs. Anacron will not start a new job
before the previous one finished.

-n Run jobs now. Ignore the delay specifications in the
/etc/anacrontab file. This options implies -s.

-d Don’t fork to the background. In this mode, Anacron will output
informational messages to standard error, as well as to syslog.
The output of jobs is mailed as usual.

-q Suppress messages to standard error. Only applicable with -d.

-t anacrontab
Use specified anacrontab, rather than the default

-T Anacrontab testing. The configuration file will be tested for
validity. If there is an error in the file, an error will be
shown and anacron will return 1. Valid anacrontabs will return
0.

-S spooldir
Use the specified spooldir to store timestamps in. This option
is required for users who wish to run anacron themselves.

-V Print version information, and exit.

-h Print short usage message, and exit.

SIGNALS
After receiving a SIGUSR1 signal, Anacron waits for running jobs, if
any, to finish and then exits. This can be used to stop Anacron
cleanly.

NOTES
Make sure that the time-zone is set correctly before Anacron is
started. (The time-zone affects the date). This is usually accom‐
plished by setting the TZ environment variable, or by installing a
/usr/lib/zoneinfo/localtime file. See tzset(3) for more information.

Timestamp files are created in the spool directory for each job in
anacrontab. These are never removed automatically by anacron, and
should be removed by hand if a job is no longer being scheduled.

FILES
/etc/anacrontab
Contains specifications of jobs. See anacrontab(5) for a com‐
plete description.

/var/spool/anacron
This directory is used by Anacron for storing timestamp files.

SEE ALSO

anacrontab(5), cron(8), tzset(3)

The Anacron README file.

BUGS

Anacron never removes timestamp files. Remove unused files manually.

Anacron uses up to two file descriptors for each active job. It may
run out of descriptors if there are more than about 125 active jobs (on
normal kernels).

Mail comments, suggestions and bug reports to Sean ‘Shaleh’ Perry
.

AUTHOR

Anacron was originally conceived and implemented by Christian Schwarz
.

The current implementation is a complete rewrite by Itai Tzur
.

The code base was maintained by Sean ‘Shaleh’ Perry
.

Since 2004, it is maintained by Pascal Hakim .

Pascal Hakim 2004-07-11 ANACRON(8)

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