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           cron [-n | -p | -s | -m<mailcommand>]
           cron -x [ext,sch,proc,pars,load,misc,test,bit]


           Cron should be started from /etc/rc.d/init.d or /etc/init.d
           Cron  searches  /var/spool/cron for crontab files which are named after
           accounts in /etc/passwd; The founded crontabs are loaded  into  memory.
           Cron also searches for /etc/anacrontab and the files in the /etc/cron.d
           directory, which are in a different format  (see  crontab(5)  ).   Cron
           examines 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).  Job  output  can
           also be sent to syslog by using the -s option.
           There  are  two  ways,  how  the changes are checked in crontables. The
           first is checking the modtime of file and the other  is  using  inotify
           support.   You  can  find out which of them are you using, if you check
           /var/log/cron where is (or isn't) inotify mentioned after start of dae-
           mon.  The inotify support is watching for changes in all crontables and
           touch the disk only in case that something was changed.
           In other case cron checks each minute to see if its crontables  modtime
           have  changes  and reload those which have changes. There is no need to
           restart cron after some of  the  crontable  is  modified.  The  modtime
           option is used also when inotify couldn't be initialized.
           Cron  is  checking  those  files or directories: /etc/anacrontab system
           crontab  is  usually  for  running  daily,  weekly,  monthly  jobs.
           /etc/cron.d/  where  are  system cronjobs stored for different users.
           /var/spool/cron that's mean spool directory for user crontables.
           Note that the crontab(1) command  updates  the  modtime  of  the  spool
           directory whenever it changes a crontab.
       Daylight Saving Time and other time changes
           Local  time  changes  of less than three hours, such as those caused by
           the start or end of Daylight Saving Time, are handled specially.   This
           only  applies to jobs that run at a specific time and jobs that are run
           with a granularity greater than one hour.   Jobs  that  run  more  fre-
           quently are scheduled normally.
           If time has moved forward, those jobs that would have run in the inter-
           val that has been skipped will be run immediately.  Conversely, if time
           has moved backward, care is taken to avoid running jobs twice.
           Time  changes  of more than 3 hours are considered to be corrections to
           the clock or timezone, and the new time is used immediately.
                  log using syslog(3).  This is useful if your system has no send-
                  mail(8), or if mail is disabled using -m off.
           -m     This  option allows you to specify a shell command string to use
                  for sending cron mail output instead of sendmail(8).  This  com-
                  mand  must  accept a fully formatted mail message (with headers)
                  on stdin and send it as a mail message to the recipients  speci-
                  fied in the mail headers.
           -n     This  option changes default behavior causing it to run crond in
                  the foreground.  This can be useful  when  starting  it  out  of
           -p     Cron permit any crontab, which user set.
           -x     With this option is possible to set debug flags.
           -P     Don't set PATH.  PATH is instead inherited from the environment.


           On receipt of a SIGHUP, the cron daemon will close and reopen  its  log
           file.  This is useful in scripts which rotate and age log files.  Natu-
           rally this is not relevant if cron was built to use syslog(3).


           The crontab files have to be  regular  files  or  symlinks  to  regular
           files,  they must not be executable or writable by anyone else than the
           owner.  This requirement can be overridden by using the  -p  option  on
           the  crond  command line.  If inotify support is in use, changes in the
           symlinked crontabs are not automatically noticed by  the  cron  daemon.
           The  cron daemon must receive a SIGHUP to reload the crontabs.  This is
           a limitation of inotify API.


           crontab(1), crontab(5), inotify(7), pam(8)


           Paul Vixie <>
           Marcela Maslanova <>

    Marcela Maslanova December 2009 CRON(8)


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