Ubuntu Manpage: anacron - runs commands periodically

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 command.

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 timestamp 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 background 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 completely 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 priority 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 executed 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  accomplished  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.

DEBIAN-SPECIFIC CONFIGURATION

       On  Debian-based systems, anacron will be activated hourly every day from 07:30 local time to 23:30 local
       time through cron job (on non-systemd systems where cron is installed and enabled) or systemd  timer  (on
       systemd-based  systems).  On activation, anacron will check if it missed some jobs. If yes, it will start
       those jobs after a short period of time.

       By default, The hourly activation of anacron will not take place when the system is using battery and  no
       AC  power  is  connected  to the computer. It is meant to reduce power usage and extend battery life, but
       such design might lead to unwanted  results.   Users  may  disable  this  feature  and  let  anacron  run
       regardless      of     power     supply.     Please     read     Debian-specific     documentation     in
       /usr/share/doc/anacron/README.Debian file for detailed instruction in now to change such behaviour.

FILES

       /etc/anacrontab
              Contains specifications of jobs.  See anacrontab(5) for a complete description.

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

       /lib/systemd/system/anacron.service
              This file provides systemd service for anacron.

       /lib/systemd/system/anacron.timer
              This file provides systemd timer for anacron. Currently the service is  triggered  hourly  through
              systemd timer.

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 <shaleh@(debian.org|valinux.com)>.

AUTHOR

       Anacron  was  originally  conceived  and  implemented by Christian Schwarz <schwarz@monet.m.isar.de>. The
       current implementation is a complete rewrite by Itai Tzur <itzur@actcom.co.il>.

       The code base was maintained by Sean 'Shaleh' Perry <shaleh@(debian.org|valinux.com)>.  During 2004-2006,
       it  was  maintained  by  Pascal  Hakim  <pasc@(debian.org|redellipse.net)>.   During  2009-2014,  it  was
       maintained by Peter Eisentraut <petere@debian.org>.

       Nowadays anacron in Debian is co-maintained by various developers from Debian Project.