FreeBSD Manual Pages
cron(1M) System Administration Commands cron(1M) 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 accord- ing to instructions found in crontab files in the directory /var/spool/cron/crontabs. Users can submit their own crontab file using the crontab(1) command. Commands which are to be executed only once may be submitted using the at(1) command. cron only examines crontab or at command files during its own process initialization phase and when the crontab or at command is run. 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. The file /etc/cron.d/FIFO is used (among other things) as a lock file to prevent the execution of more than one instance of cron. cron captures the output of the job's stdout and stderr streams, and, if it is non-empty, mails the output to the user. If the job does not produce output, no mail is sent to the user (unless the job is an at(1) job and the -m option was specified when the job was submitted). cron and at jobs will be not be executed if the user's account is locked. Only accounts which are not locked as defined in shadow(4) will have their job or process executed. Setting cron Defaults 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 spec- ified, no logging is done. Keeping the log is a user configurable op- tion since cron usually creates huge log files. The PATH for user cron jobs can be set using PATH= in /etc/de- fault/cron. The PATH for root cron jobs can be set using SUPATH= in /etc/default/cron. The security implications of setting PATH and SUPATH should be carefully considered. Example /etc/default/cron file: CRONLOG=YES PATH=/usr/bin:/usr/ucb: This example enables logging and sets the default PATH used by non-root jobs to /usr/bin:/usr/ucb:. Root jobs will continue to use /usr/sbin:/usr/bin. /etc/cron.d/logchecker is a script that checks to see if the log file has exceeded the system ulimit. If so, the log file is moved to /var/cron/olog. FILES /etc/cron.d main cron directory /etc/cron.d/FIFO used as a lock file /etc/default/cron contains cron default settings /var/cron/log cron history information /var/spool/cron spool area /etc/cron.d/logchecker moves log file to /var/cron/olog if log file exceeds system ulimit. /etc/cron.d/queuedefs queue description file for at, batch, and cron. ATTRIBUTES See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Availability |SUNWcsu | +-----------------------------+-----------------------------+ SEE ALSO at(1), crontab(1), sh(1), queuedefs(4), shadow(4), attributes(5) DIAGNOSTICS A history of all actions taken by cron is stored in /var/cron/log and (possibly) /var/cron/olog. SunOS 5.9 11 Jan 2002 cron(1M)
NAME | SYNOPSIS | DESCRIPTION | FILES | ATTRIBUTES | SEE ALSO | DIAGNOSTICS
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