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

FreeBSD Manual Pages


home | help
CRON(8)								       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	direc-
       tory,  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 execut-
       ing 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  fre-
       quently are scheduled normally.

       If time has moved forward, those	jobs that would	have run in the	inter-
       val 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.	 Natu-
       rally 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