cron - clock daemon
cron [ -j jobs ] [ nofork ]
cron executes commands at specified dates and times. Regularly scheduled
commands can be specified according to instructions found in crontab
files in the directory /var/spool/cron/crontabs. Users can submit their
own crontab file via the crontab(1) command. Commands that are to be
executed only once can be submitted using the at(1) command.
The following options are supported:
-j jobs Specify the maximum number of jobs (MAXRUN) that cron can
simultaneously run. The default value is 25. The maximum
allowed value is 250.
nofork If this option is supplied, cron runs in the foreground.
cron examines crontab files and at command files only during process
initialization and when a file changes via crontab or at. This reduces
the overhead of checking for new or changed files at regularly scheduled
Since cron never exits, it should be executed only once. This is done
routinely through /etc/rc2.d/S75cron at system boot time.
/etc/cron.d/FIFO is used as a lock file to prevent the execution of more
than one cron and is also used by the crontab command for notification of
changes to the crontab files.
If MAXRUN jobs are running and another is scheduled, cron does not run
the new job. A message is logged via syslog(3C).
cron attempts to handle changes to the system date correctly, either
forward or backward. There may be some delay for jobs scheduled during
the interval on large forward-time changes.
For each job launched, cron reads in configuration information from
/etc/default/cron. Currently the only option supported is the
SVR4_SIGNALS option, which may be set to `YES' or `NO' (it defaults to
NO). Setting SVR4_SIGNALS to `YES' will result in processes forked with
the SIGXFSZ and SIGXCPU signals ignored. For CPU and filesize resource
limiting to work correctly, SVR4_SIGNALS should be set to `NO', so that
these signal retain their default behaviour, which is to terminate the
/etc/cron.d main cron directory
/etc/cron.d/FIFO used as a lock file against multiple copies
running and also for notification of new or
changed crontab files
/var/cron/log accounting information
/var/spool/cron spool area
/etc/config/cron.options site-dependent options /etc/default/cron
default behaviour configuration file
A SIGHUP signal can be sent to cron to cause it to reexamine all the
crontab and configuration files. A message is logged for this event.
The SIGTERM signal should be used to shut cron down cleanly.
at(1), crontab(1), sh(1).
A history of all actions taken by cron is recorded in /var/cron/log.
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