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NAME    [Toc]    [Back]

       crontab - tables for driving cron

DESCRIPTION    [Toc]    [Back]

       A  crontab file contains instructions to the cron(8) daemon of the general
 form: ``run this command at this time on this date''.   Each  user
       has  their  own crontab, and commands in any given crontab will be executed
 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 hash-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, comments
 are not allowed on the same line  as  environment	variable  settings.

       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 subsequent
 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.

       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.   PATH   is  set  to
       "/usr/bin:/bin".  HOME, SHELL, and PATH may be overridden  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.

       The  format of a cron command is very much the V7 standard, with a number
 of upward-compatible extensions.  Each line has five time and  date
       fields,	followed  by  a command, followed by a newline character ('0).
       The system crontab (/etc/crontab) uses the same format, except that the
       username  for  the  command is specified after the time and date fields
       and before the command.	Note that if the line does not have a trailing
       newline	character,  the  entire  line will be silently ignored by both
       crontab and cron; the command will never be executed.

       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 specify
 command execution every other hour (the alternative in the V7 standard
 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

       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 characters,
  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  current
 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

	      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    [Toc]    [Back]

       # use /bin/sh to run commands, no matter what /etc/passwd says
       # mail any output to `paul', no matter whose crontab this is
       # 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"


       This has the username field, as used by /etc/crontab.
       # /etc/crontab: system-wide crontab
       # Unlike any other crontab you don't have to run the `crontab'
       # command to install the new version when you edit this file.
       # This file also has a username field, that none of the other crontabs do.


       # m h dom mon dow usercommand
       42 6	      * * *rootrun-parts --report /etc/cron.daily
       47 6	      * * 7rootrun-parts --report /etc/cron.weekly
       52 6	      1 * *rootrun-parts --report /etc/cron.monthly
       # Removed invocation of anacron, as this is now handled by a
       # /etc/cron.d file

SEE ALSO    [Toc]    [Back]

       cron(8), crontab(1)

EXTENSIONS    [Toc]    [Back]

       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

       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    [Toc]    [Back]

       Paul Vixie <paul@vix.com>

4th Berkeley Distribution	24 January 1994 		    CRONTAB(5)
[ Back ]
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