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