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

NAME
     cron — daemon to execute scheduled commands (Vixie Cron)

SYNOPSIS
     cron [-s] [-o] [-x debugflag[,...]]

DESCRIPTION
     The cron utility is launched by launchd(8) when it sees the existence of
     /etc/crontab or files in /usr/lib/cron/tabs.  There should be no need to
     start it manually.	 See /System/Library/LaunchDaemons/com.vix.cron.plist
     for details.

     The cron utility searches /usr/lib/cron/tabs for crontab files which are
     named after accounts in /etc/passwd; crontabs found are loaded into mem‐
     ory.  The cron utility also searches for /etc/crontab which is in a dif‐
     ferent format (see crontab(5)).

     The cron utility 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
     modification time (or the modification time on /etc/crontab) has changed,
     and if it has, cron will then examine the modification time 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 modification time of the spool directory whenever it
     changes a crontab.

     Available options:

     -s	     Enable special handling of situations when the GMT offset of the
	     local timezone changes, such as the switches between the standard
	     time and daylight saving time.

	     The jobs run during the GMT offset changes time as intuitively
	     expected.	If a job falls into a time interval that disappears
	     (for example, during the switch from standard time) to daylight
	     saving time or is duplicated (for example, during the reverse
	     switch), then it is handled in one of two ways:

	     The first case is for the jobs that run every at hour of a time
	     interval overlapping with the disappearing or duplicated inter‐
	     val.  In other words, if the job had run within one hour before
	     the GMT offset change (and cron was not restarted nor the
	     crontab(5) changed after that) or would run after the change at
	     the next hour.  They work as always, skip the skipped time or run
	     in the added time as usual.

	     The second case is for the jobs that run less frequently.	They
	     are executed exactly once, they are not skipped nor executed
	     twice (unless cron is restarted or the user's crontab(5) is
	     changed during such a time interval).  If an interval disappears
	     due to the GMT offset change, such jobs are executed at the same
	     absolute point of time as they would be in the old time zone.
	     For example, if exactly one hour disappears, this point would be
	     during the next hour at the first minute that is specified for
	     them in crontab(5).

     -o	     Disable the special handling of situations when the GMT offset of
	     the local timezone changes, to be compatible with the old
	     (default) behavior.  If both options -o and -s are specified, the
	     option specified last wins.

     -x debugflag[,...]
	     Enable writing of debugging information to standard output.  One
	     or more of the following comma separated debugflag identifiers
	     must be specified:

	     bit   currently not used
	     ext   make the other debug flags more verbose
	     load  be verbose when loading crontab files
	     misc  be verbose about miscellaneous one-off events
	     pars  be verbose about parsing individual crontab lines
	     proc  be verbose about the state of the process, including all of
		   its offspring
	     sch   be verbose when iterating through the scheduling algorithms
	     test  trace through the execution, but do not perform any actions

FILES
     /usr/lib/cron/tabs	 Directory for personal crontab files

SEE ALSO
     crontab(1), launchctl(1), crontab(5), launchd.plist(5), launchd(8)

AUTHORS
     Paul Vixie ⟨paul@vix.com⟩

BSD				 June 17, 2007				   BSD
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