cron

PURPOSE

     Runs commands automatically.

SYNOPSIS
     cron

DESCRIPTION

     The cron  command runs shell commands  at specified dates
     and times.  Regularly scheduled commands can be specified
     according  to instructions  contained  in crontab  files.
     You can submit your crontab  file via the crontab command
     (see page  211).  Use  the at command  (see page  74)  to
     submit commands  that are to  be run only  once.  Because
     cron never  exits, it should  be run only once.   This is
     best done by running cron from the initialization process
     through the /etc/rc command file (see page 744).

     The cron  command examines  crontab files and  at command
     files only during process  initialization and when a file
     changes.  This  reduces the overhead of  checking for new
     or changed files at regularly scheduled intervals.

     The cron command also executes a sync system call approx-
     imately once a  minute to assure that  all information in
     memory  that  should  be  on disk  (buffered  output)  is
     written out.  These periodic  updates minimize the possi-
     bility of file system damage in the event of a crash.  In
     addition, cron  keeps a number of  frequently used system
     directories open  to keep their i-nodes  in kernel memory
     for faster access.

     The  cron command  creates  a log  of  its activities  in
     /usr/lib/cron/log.

     For  a  discussion  of  how  to  schedule  commands,  see
     "crontab."

FILES

     /usr/lib/cron        Main cron directory.
     /usr/lib/cron/log    Accounting information.
     /usr/spool/cron      Spool area.
     /bin                 Directory kept open.
     /lib                 Directory kept open.
     /usr                 Directory kept open.
     /usr/bin             Directory kept open.
     /usr/lib             Directory kept open.
     /etc                 Directory kept open.
     /tmp                 Directory kept open.

RELATED INFORMATION

     The  following commands:   "at,  batch,"  "crontab,"  and
     "rc."

     The sync  system call and  the crontab file in  AIX Oper-
     ating System Technical Reference.