NAME

cron − clock daemon

SYNOPSIS

/usr/sbin/cron

DESCRIPTION

The cron command starts a process that 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 command.  Commands which are to be executed only once may be submitted via the at command. 

cron only examines crontab files and at command files during process initialization and when a file changes via the crontab or at commands.  This reduces the overhead of checking for new or changed files at regularly scheduled intervals. 

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. 

To keep a log of all actions taken by cron, CRONLOG=YES (by default) must be specified in the /etc/default/cron file.  If CRONLOG=NO is specified, no logging is done.  Keeping the log is a user configurable option since cron usually creates huge log files. 

FILES

/etc/cron.d main cron directory

/etc/default/cron used to maintain a log

/etc/cron.d/FIFO used as a lock file

/var/cron/log accounting information

/var/spool/cron spool area

SEE ALSO

at(1), crontab(1), sh(1). 

DIAGNOSTICS

A history of all actions taken by cron are recorded in /var/cron/log. 

  —  Essential Utilities