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

FreeBSD Manual Pages


home | help
cron(1M)		System Administration Commands		      cron(1M)

       cron - clock daemon


       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:


       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

       /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

	     main cron directory

	     used as a lock file

	     contains cron default settings

	     cron history information

	     spool area

	     moves  log	 file  to  /var/cron/olog  if  log file	exceeds	system

	     queue description file for	at, batch, and cron.

       See attributes(5) for descriptions of the following attributes:

       |      ATTRIBUTE	TYPE	     |	    ATTRIBUTE VALUE	   |
       |Availability		     |SUNWcsu			   |

       at(1), crontab(1), sh(1), queuedefs(4), shadow(4), attributes(5)

       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)


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

home | help