Skip site navigation (1)Skip section navigation (2)

FreeBSD Man Pages

Man Page or Keyword Search:
Man Architecture
Apropos Keyword Search (all sections) Output format
home | help
CRON(8)                 FreeBSD System Manager's Manual                CRON(8)

       cron - daemon to execute scheduled commands (ISC Cron V4.1)

       cron [-l load_avg] [-n]

       Cron should be started from /etc/rc or /etc/rc.local.  It will return
       immediately, so you don't need to start it with '&'.  The -n option
       changes this default behavior causing it to run in the foreground.
       This can be useful when starting it out of init.

       Cron searches /var/spool/cron for crontab files which are named after
       accounts in /etc/passwd; crontabs found are loaded into memory.  Cron
       also searches for /etc/crontab and the files in the /etc/cron.d
       directory, which are in a different format (see crontab(5)).  Cron then
       wakes up every minute, examining all stored crontabs, checking each
       command to see if it should be run in the current minute.  When
       executing commands, any output is mailed to the owner of the crontab
       (or to the user named in the MAILTO environment variable in the
       crontab, if such exists).

       Additionally, cron checks each minute to see if its spool directory's
       modtime (or the modtime on /etc/crontab) has changed, and if it has,
       cron will then examine the modtime on all crontabs and reload those
       which have changed.  Thus cron need not be restarted whenever a crontab
       file is modified.  Note that the Crontab(1) command updates the modtime
       of the spool directory whenever it changes a crontab.

   Daylight Saving Time and other time changes
       Local time changes of less than three hours, such as those caused by
       the start or end of Daylight Saving Time, are handled specially.  This
       only applies to jobs that run at a specific time and jobs that are run
       with a granularity greater than one hour.  Jobs that run more
       frequently are scheduled normally.

       If time has moved forward, those jobs that would have run in the
       interval that has been skipped will be run immediately.  Conversely, if
       time has moved backward, care is taken to avoid running jobs twice.

       Time changes of more than 3 hours are considered to be corrections to
       the clock or timezone, and the new time is used immediately.

   PAM Access Control
       On SUSE LINUX systems, crond now supports access control with PAM - see
       pam(8).  A PAM configuration file for crond is installed in
       /etc/pam.d/crond .  crond loads the PAM environment from the pam_env
       module, but these can be overriden by settings in the crontab file.

       On receipt of a SIGHUP, the cron daemon will close and reopen its log
       file.  This is useful in scripts which rotate and age log files.
       Naturally this is not relevant if cron was built to use syslog(3).

       In this version of cron, /etc/crontab must not be writable by any user
       other than root.  No crontab files may be links, or linked to by any
       other file.  No crontab files may be executable, or be writable by any
       user other than their owner.

       crontab(1), crontab(5), pam(8)

       Paul Vixie <>

4th Berkeley Distribution      10 January 1996"                        CRON(8)


Want to link to this manual page? Use this URL:

home | help