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       Cron  should be started from /sbin/init.d/cron, /etc/rc or
       /etc/rc.local.  It will return immediately, so  you  don't
       need to start it with '&'.

       Cron searches /var/spool/cron/tabs for crontab files which
       are named after accounts in  /etc/passwd;  crontabs  found
       are   loaded   into   memory.    Cron  also  searches  for
       /etc/crontab  which  is  in  a   different   format   (see
       crontab(5)).    Additionally,  cron  reads  the  files  in
       /etc/cron.d; it treats the files in /etc/cron.d as  exten­
       sions  to  the  /etc/crontab file (they follow the special
       format of that file, i.e. they include  the  user  field).
       The  intended purpose of this feature is to allow packages
       that require finer control of their  scheduling  than  the
       /etc/cron.{daily,weekly,monthly}  directories allow to add
       a crontab file to /etc/cron.d. Such files should be  named
       after  the  package that supplies them. Files must conform
       to the same naming convention  as  used  by  run-parts(8):
       they must consist solely of upper- and lower-case letters,
       digits, underscores, and hyphens. Like  /etc/crontab,  the
       files  in  the  /etc/cron.d  directory  are  monitored for
       changes.  Cron 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 modtime (or the modtime on  /etc/crontab)  has
       changed, and if it has, cron will then examine the modtime
       on all crontabs and reload those which have changed.  Thus
       cron need not be restarted whenever a crontab file is mod­
       ified.  Note that the crontab(1) command updates the  mod­
       time of the spool directory whenever it changes a crontab.


       crontab(1), crontab(5)


       Paul Vixie <paul@vix.com>

                         20 December 1993                 CRON(8)



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