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 is 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 are not running 24 hours a day to control regular jobs as daily, weekly, and monthly jobs.
Anacron reads a list of jobs from the /etc/anacrontab configuration file (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 time period specified for that job. If a job has not been executed in n days or more, 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 (excludes the hour) in a special timestamp file for that job, so it knows when to execute that job again.
When there are no more jobs to be run, Anacron exits.
Anacron only considers jobs whose identifier, as specified in anacrontab(5), matches any of the job command-line arguments. The job command-line arguments can be represented by shell wildcard patterns (be sure to protect them from your shell with adequate quoting). Specifying no job command-line arguments is equivalent to specifying "*" (that is, all jobs are considered by Anacron).
Unless Anacron is run with the -d option (specified below), it forks to the background when it starts, and any parent processes exit immediately.
Unless Anacron is run with the -s or -n options, it starts jobs immediately when their delay is over. The execution of different jobs is completely independent.
If an executed job generates any output to standard output or to standard error, the output is mailed to the user under whom Anacron is running (usually root), or to the address specified in the MAILTO environment variable in the /etc/anacrontab file, if such exists. If the LOGNAME environment variable is set, it is used in the From: field of the mail.
Any informative messages generated by Anacron are sent to syslogd(8) or rsyslogd(8) under with facility set to cron and priority set to notice. Any error messages are sent with the priority error.
"Active" jobs (i.e., jobs that Anacron already decided to run and are now waiting for their delay to pass, and jobs that are currently being executed by Anacron), are "locked", so that other copies of Anacron cannot run them at the same time.
Options
- -f
Forces execution of all jobs, ignoring any timestamps.
- -u
Updates the timestamps of all jobs to the current date, but does not run any.
- -s
Serializes execution of jobs. Anacron does not start a new job before the previous one finished.
- -n
Runs jobs immediately and ignores the specified delays in the /etc/anacrontab file. This options implies -s.
- -d
Does not fork Anacron to the background. In this mode, Anacron will output informational messages to standard error, as well as to syslog. The output of any job is mailed by Anacron.
- -q
Suppresses any messages to standard error. Only applicable with -d.
- -t some_anacrontab
Uses the specified anacrontab, rather than the /etc/anacrontab default one.
- -T
Anacrontab testing. Tests the /etc/anacrontab configuration file for validity. If there is an error in the file, it is shown on the standard output and Anacron returns the value of 1. Valid anacrontabs return the value of 0.
- -S spooldir
Uses the specified spooldir to store timestamps in. This option is required for users who wish to run anacron themselves.
- -V
Prints version information, and exits.
- -h
Prints short usage message, and exits.
Signals
After receiving a SIGUSR1 signal, Anacron waits for any running jobs to finish and then exits. This can be used to stop Anacron cleanly.
Notes
Make sure your time-zone is set correctly before Anacron is started since 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 specified in an anacrontab. These files 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 complete 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 lots of active jobs. See echo $(($(ulimit -n) / 2)) for information how many concurent jobs anacron may run.
Mail comments, suggestions and bug reports to Sean 'Shaleh' Perry.
Referenced By
anacrontab(5), cronnext(1), crontabs(4).