cron - clock daemon




     cron starts a process that executes  commands  at  specified
     dates and times.

     You can specify regularly scheduled commands to cron accord-
     ing  to instructions found in crontab files in the directory
     /var/spool/cron/crontabs. Users can submit their own crontab
     file  using the crontab(1) command. Commands which are to be
     executed only once can be submitted using the at(1) command.

     cron only examines crontab or at command  files  during  its
     own  process initialization phase and when the crontab or at
     command is run. This reduces the overhead  of  checking  for
     new or changed files at regularly scheduled intervals.

     As cron never exits, it should be executed only  once.  This
     is  done  routinely by way of the /etc/rc2.d/S75cron file at
     system boot time. The file /etc/cron.d/FIFO file is used  as
     a  lock  file  to  prevent  the  execution  of more than one
     instance of cron.

     cron captures the output of  the  job's  stdout  and  stderr
     streams,  and,  if  it is not empty, mails the output to the
     user. If the job does not produce output, no mail is sent to
     the user. An exception is if the job is an at(1) job and the
     -m option was specified when the job was submitted.

     cron and at jobs are not executed if your account is locked.
     Jobs  and  processses  execute.  The  shadow(4) file defines
     which accounts are not locked and will have their  jobs  and
     processes executed.

  Setting cron Jobs Across Timezones
     The  timezone  of  the  cron  daemon  sets  the  system-wide
     timezone  for  cron  entries.   This,  in turn, is by set by
     default system-wide using /etc/default/init.

     If some form of daylight savings or summer/winter time is in
     effect,  then  jobs  scheduled  during the switchover period
     could be executed once, twice, or not at all.

  Setting cron Defaults
     To keep a log of all actions taken by cron, you must specify
     CRONLOG=YES  in  the  /etc/default/cron file. If you specify
     CRONLOG=NO, no logging is done. Keeping the log  is  a  user
     configurable  option  since  cron  usually  creates huge log

     You can specify the PATH for user cron jobs by  using  PATH=
     in  /etc/default/cron.  You  can  set the PATH for root cron
     jobs using SUPATH=  in /etc/default/cron. Carefully consider
     the security implications of setting PATH and SUPATH.

     Example /etc/default/cron file:


     This example enables logging and sets the default PATH  used
     by  non-root  jobs to /usr/bin:/usr/ucb:. Root jobs continue
     to use /usr/sbin:/usr/bin.

     The cron log file is periodically rotated by logadm(1M).


           Main cron directory

           Lock file

           cron default settings file

           cron history information

           Spool area

           Queue description file for at, batch, and cron

           Configuration file for logadm


     See attributes(5) for descriptions of the  following  attri-

    |       ATTRIBUTE TYPE        |       ATTRIBUTE VALUE       |
    | Availability                | SUNWcsu                     |


     at(1), crontab(1),  sh(1),  logadm(1M),  queuedefs(4),  sha-
     dow(4), attributes(5)


     A history  of  all  actions  taken  by  cron  is  stored  in
     /var/cron/log and possibly in /var/cron/olog.

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