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

     cron -- daemon to execute scheduled commands (Vixie Cron)

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

     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 memory.  The cron utility also searches for /etc/crontab
     which is in a different 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

     Additionally, cron checks each minute to see if its spool directory's modification time (or the modifi-cation modification
     cation 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 interval.  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

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

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

     Paul Vixie <>

BSD                              June 17, 2007                             BSD

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