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CRON(8)			  BSD System Manager's Manual		       CRON(8)

     cron -- clock daemon

     cron [-n] [-l load_avg]

     The cron daemon schedules commands	to be run at specified dates and
     times.  Commands that are to be run periodically are specified within
     crontab(5)	files.	Commands that are only to be run once are scheduled
     via the at(1) and batch(1)	commands.  Normally, the cron daemon is
     started from the /etc/rc command script.  Because it can execute commands
     on	a user's behalf, cron should be	run late in the	startup	sequence, as
     close to the time when logins are accepted	as possible.

     cron loads	crontab(5) and at(1) files when	it starts up and also when
     changes are made via the crontab(1) and at(1) commands.  Additionally,
     cron checks the modification time on the system crontab file
     (/etc/crontab), the crontab spool (/var/cron/tabs), and the at spool
     (/var/cron/atjobs)	once a minute.	If the modification time has changed,
     the affected files	are reloaded.

     Any output	produced by a command is sent to the user specified in the
     MAILTO environment	variable as set	in the crontab(5) file or, if no
     MAILTO variable is	set (or	if this	is an at(1) or batch(1)	job), to the
     job's owner.  If a	command	produces no output or if the MAILTO environ-
     ment variable is set to the empty string, no mail will be sent.  The ex-
     ception to	this is	at(1) or batch(1) jobs submitted with the -m flag.  In
     this case,	mail will be sent even if the job produces no output.

   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 time zone, and the new time is used immediately.

     The options are as	follows:

     -l	load_avg
	     If	the current load average is greater than load_avg, batch(1)
	     jobs will not be run.  The	default	value is 1.5.  To allow
	     batch(1) jobs to run regardless of	the load, a value of 0.0 may
	     be	used.

     -n	     By	default, cron will detach from the current tty and become a
	     daemon.  The -n option disables this behavior and causes it to
	     run in the	foreground.

     /etc/crontab	 system	crontab	file
     /var/cron/atjobs	 directory containing at(1) jobs
     /var/cron/log	 cron's	log file
     /var/cron/tabs	 directory containing individual crontab files
     /var/run/cron.sock	 used by crontab(1) to tell cron to check for crontab
			 changes immediately

     at(1), crontab(1),	syslog(3), crontab(5)

     Paul Vixie	<>

     crontab(5)	files will be ignored if they do not have the proper file
     mode.  For	user crontab files created by crontab(1), the mode must	be
     0600.  If the system crontab file is used,	/etc/crontab must not be
     writable by any user other	than root and must not have the	execute, set-
     user-ID, set-group-ID or sticky bits set.

BSD			       January 25, 2019				   BSD


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