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

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

     cron [-j jitter] [-J rootjitter] [-s] [-o] [-x debugflag[,...]]

     The cron utility should be started from /etc/rc or /etc/rc.local.  It
     will return immediately, so you do not need to start it with '&'.

     The cron utility searches /var/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:

     -j jitter
             Enable time jitter.  Prior to executing commands, cron will sleep
             a random number of seconds in the range from 0 to jitter.  This
             will not affect superuser jobs (see -J).  A value for jitter must
             be between 0 and 60 inclusive.  Default is 0, which effectively
             disables time jitter.

             This option can help to smooth down system load spikes during
             moments when a lot of jobs are likely to start at once, e.g., at
             the beginning of the first minute of each hour.

     -J rootjitter
             Enable time jitter for superuser jobs.  The same as -j except
             that it will affect jobs run by the superuser only.

     -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

     crontab(1), crontab(5)

     Paul Vixie <>

FreeBSD 6.2                    December 20, 1993                   FreeBSD 6.2


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