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RocketLink!--> Man page versions: OpenBSD FreeBSD NetBSD Others

CRON(8)                                                   CRON(8)

       cron - daemon to execute scheduled commands (Vixie Cron)


       Cron  should be started from /etc/rc or /etc/rc.local.  It
       will return immediately, so you don't  need  to  start  it
       with '&'.

       Cron  searches  /var/cron/tabs for crontab files which are
       named after accounts in /etc/passwd;  crontabs  found  are
       loaded  into  memory.  Cron also searches for /etc/crontab
       which is 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

       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 mod-
       ified.   Note that the Crontab(1) command updates the mod-
       time of the spool directory whenever it changes a crontab.

       Special  considerations exist when the clock is changed by
       less than 3 hours, for example at the beginning and end of
       daylight  savings  time.  If  the time has moved forwards,
       those jobs which would have  run  in  the  time  that  was
       skipped will be run soon after the change.  Conversely, if
       the time has moved backwards by less than 3  hours,  those
       jobs that fall into the repeated time will not be run.

       Only  jobs that run at a particular time (not specified as
       @hourly, nor with '*' in the hour or minute specifier) are
       affected.  Jobs which are specified with wildcards are run
       based on the new time immediately.

       Clock changes of more than 3 hours are  considered  to  be
       corrections to the clock, and the new time is used immedi-

       crontab(1), crontab(5)

       Paul Vixie <paul@vix.com>

                         20 December 1993                       1

Source: OpenBSD 2.6 man pages. Copyright: Portions are copyrighted by BERKELEY
SOFTWARE DESIGN, INC., The Regents of the University of California, Massachusetts
Institute of Technology, Free Software Foundation, FreeBSD Inc., and others.

(Corrections, notes, and links courtesy of RocketAware.com)

[Detailed Topics]
FreeBSD Sources for cron(8)
OpenBSD sources for cron(8)

[Overview Topics]

Up to: Process Creation and Control - child process control (like sending signals), renice, fork, et al

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