CRONTAB(5)                                                          CRONTAB(5)



NAME
       crontab - tables for driving cron

DESCRIPTION
       A  crontab file contains instructions to the cron(8) daemon of the gen-
       eral form: ``run this command at this time on this date''.   Each  user
       has  their  own crontab, and commands in any given crontab will be exe-
       cuted as the user who owns the crontab.  Uucp  and  News  will  usually
       have  their  own  crontabs, eliminating the need for explicitly running
       su(1) as part of a cron command.

       Blank lines and leading spaces and tabs are ignored.  Lines whose first
       non-space  character is a pound-sign (#) are comments, and are ignored.
       Note that comments are not allowed on the same line as  cron  commands,
       since  they  will  be taken to be part of the command.  Similarly, com-
       ments are not allowed on the same line  as  environment  variable  set-
       tings.

       An  active line in a crontab will be either an environment setting or a
       cron command.  An environment setting is of the form,

           name = value

       where the spaces around the equal-sign (=) are optional, and any subse-
       quent non-leading spaces in value will be part of the value assigned to
       name.  The value string may be placed in quotes (single or double,  but
       matching)  to preserve leading or trailing blanks.  The name string may
       also be placed in quotes (single or double, but matching)  to  preserve
       leading, trailing or inner blanks.

       Several  environment  variables are set up automatically by the cron(8)
       daemon.  SHELL is set to /bin/sh, and LOGNAME and HOME are set from the
       /etc/passwd  line  of the crontab's owner.  HOME and SHELL may be over-
       ridden by settings in the crontab; LOGNAME may not.

       (Another note: the LOGNAME variable is sometimes  called  USER  on  BSD
       systems...  on these systems, USER will be set also.)

       In addition to LOGNAME, HOME, and SHELL, cron(8) will look at MAILTO if
       it has any reason to send mail as  a  result  of  running  commands  in
       ``this''  crontab.   If MAILTO is defined (and non-empty), mail is sent
       to the user so named.  If MAILTO is defined but empty  (MAILTO=""),  no
       mail will be sent.  Otherwise mail is sent to the owner of the crontab.
       This  option  is  useful  if  you  decide  on  /bin/mail   instead   of
       /usr/lib/sendmail  as  your  mailer  when you install cron -- /bin/mail
       doesn't do aliasing, and UUCP usually doesn't read its mail.

       In order to provide finer control over when  jobs  execute,  users  can
       also  set  the  environment  variables  CRON_TZ  and  CRON_WITHIN.  The
       CRON_TZ variable can be set to an  alternate  time  zone  in  order  to
       affect when the job is run.  Note that this only affects the scheduling
       of the job, not the time zone that the job perceives when  it  is  run.
       If  CRON_TZ  is defined but empty (CRON_TZ=""), jobs are scheduled with
       respect to the local time zone.

       The CRON_WITHIN variable should indicate the number of seconds within a
       job's  scheduled time that it should still be run.  On a heavily loaded
       system, or on a system that has just been "woken up", jobs  will  some-
       times  start later than originally intended, and by skipping non-criti-
       cal  jobs  because  of  delays,  system  load  can  be  lightened.   If
       CRON_WITHIN  is  defined but empty (CRON_WITHIN="") or set to some non-
       positive value (0, a negative number, or a non-numeric string),  it  is
       treated as if it was unset.

       The  format of a cron command is very much the V7 standard, with a num-
       ber of upward-compatible extensions.  Each line has five time and  date
       fields,  followed  by  a  user name if this is the system crontab file,
       followed by a command.  Commands  are  executed  by  cron(8)  when  the
       minute, hour, and month of year fields match the current time, and when
       at least one of the two day fields (day of month, or day of week) match
       the  current  time (see ``Note'' below).  cron(8) examines cron entries
       once every minute.  The time and date fields are:

              field          allowed values
              -----          --------------
              minute         0-59
              hour           0-23
              day of month   1-31
              month          1-12 (or names, see below)
              day of week    0-7 (0 or 7 is Sun, or use names)

       A field may be an asterisk (*), which always stands for ``first-last''.

       Ranges of numbers are allowed.  Ranges are two numbers separated with a
       hyphen.  The specified range is inclusive.  For example,  8-11  for  an
       ``hours'' entry specifies execution at hours 8, 9, 10 and 11.

       Lists are allowed.  A list is a set of numbers (or ranges) separated by
       commas.  Examples: ``1,2,5,9'', ``0-4,8-12''.

       Step values can be used in conjunction with ranges.  Following a  range
       with  ``/<number>''  specifies  skips of the number's value through the
       range.  For example, ``0-23/2'' can be used in the hours field to spec-
       ify command execution every other hour (the alternative in the V7 stan-
       dard is ``0,2,4,6,8,10,12,14,16,18,20,22'').  Steps are also  permitted
       after  an asterisk, so if you want to say ``every two hours'', just use
       ``*/2''.

       Names can also be used for the ``month'' and ``day  of  week''  fields.
       Use  the  first  three  letters  of  the  particular day or month (case
       doesn't matter).  Ranges or lists of names are not allowed.

       The ``sixth'' field (the rest of the line) specifies the command to  be
       run.   The  entire  command  portion  of the line, up to a newline or %
       character, will be executed by /bin/sh or by the shell specified in the
       SHELL  variable  of  the  cronfile.   Percent-signs (%) in the command,
       unless escaped with backslash (\), will be changed into newline charac-
       ters,  and  all  data  after the first % will be sent to the command as
       standard input.

       Note: The day of a command's execution can be specified by  two  fields
       --  day  of month, and day of week.  If both fields are restricted (ie,
       aren't *), the command will be run when either field matches  the  cur-
       rent time.  For example,
       ``30 4 1,15 * 5'' would cause a command to be run at 4:30 am on the 1st
       and 15th of each month, plus every Friday.

       Instead of the first five fields, one  of  eight  special  strings  may
       appear:

              string         meaning
              ------         -------
              @reboot        Run once, at startup.
              @yearly        Run once a year, "0 0 1 1 *".
              @annually      (same as @yearly)
              @monthly       Run once a month, "0 0 1 * *".
              @weekly        Run once a week, "0 0 * * 0".
              @daily         Run once a day, "0 0 * * *".
              @midnight      (same as @daily)
              @hourly        Run once an hour, "0 * * * *".

EXAMPLE CRON FILE
       # use /bin/sh to run commands, no matter what /etc/passwd says
       SHELL=/bin/sh
       # mail any output to `paul', no matter whose crontab this is
       MAILTO=paul
       #
       # run five minutes after midnight, every day
       5 0 * * *       $HOME/bin/daily.job >> $HOME/tmp/out 2>&1
       # run at 2:15pm on the first of every month -- output mailed to paul
       15 14 1 * *     $HOME/bin/monthly
       # run at 10 pm on weekdays, annoy Joe
       0 22 * * 1-5    mail -s "It's 10pm" joe%Joe,%%Where are your kids?%
       23 0-23/2 * * * echo "run 23 minutes after midn, 2am, 4am ..., everyday"
       5 4 * * sun     echo "run at 5 after 4 every sunday"

SEE ALSO
       cron(8), crontab(1)

EXTENSIONS
       When  specifying  day  of week, both day 0 and day 7 will be considered
       Sunday.  BSD and ATT seem to disagree about this.

       Lists and ranges are allowed to co-exist in the same field.   "1-3,7-9"
       would  be  rejected  by  ATT  or  BSD cron -- they want to see "1-3" or
       "7,8,9" ONLY.

       Ranges can include "steps", so "1-9/2" is the same as "1,3,5,7,9".

       Names of months or days of the week can be specified by name.

       Environment variables can be set in the crontab.  In BSD  or  ATT,  the
       environment  handed  to  child  processes  is  basically  the  one from
       /etc/rc.

       Command output is mailed to the crontab owner (BSD can't do this),  can
       be  mailed  to  a  person  other  than the crontab owner (SysV can't do
       this), or the feature can be turned off and no mail will be sent at all
       (SysV can't do this either).

       All  of  the  `@'  commands  that can appear in place of the first five
       fields are extensions.

AUTHOR
       Paul Vixie <paul@vix.com>



4th Berkeley Distribution       24 January 1994                     CRONTAB(5)

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