CRONTAB(5)							File Formats Manual							CRONTAB(5)

NAME

       crontab - tables for driving cron (ISC Cron V4.1)

DESCRIPTION

       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 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.   Simi-
       larly, 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.  HOME and SHELL 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.  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.

       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  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 at least one of the two day fields (day of month, or day of week)  match
       the  current time (see ``Note'' below).	Note that this means that non-existent times, such as "missing hours" during daylight savings con-
       version, will never match, causing jobs scheduled during the "missing times" not to be run.  Similarly, times that  occur  more	than  once
       (again, during daylight savings conversion) will cause matching jobs to be run twice.

       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 ``*/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 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.

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"

FILES

       /etc/crontab   System crontab file

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.

       If the uid of the owner is 0 (root), he can put a "-" as first character of a crontab entry. This will prevent cron from writing  a  syslog
       message about this command getting executed.

       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).

       These special time specification "nicknames" are supported, which replace the 5 initial time and date fields, and are prefixed by  the  '@'
       character:
       @reboot	  :    Run once, at startup.
       @yearly	  :    Run once a year, ie.  "0 0 1 1 *".
       @annually  :    Run once a year, ie.  "0 0 1 1 *".
       @monthly   :    Run once a month, ie. "0 0 1 * *".
       @weekly	  :    Run once a week, ie.  "0 0 * * 0".
       @daily	  :    Run once a day, ie.   "0 0 * * *".
       @hourly	  :    Run once an hour, ie. "0 * * * *".

CAVEATS

       In this version of cron, /etc/crontab must not be writable by any user other than root.	No crontab files may be links, or linked to by any
       other file.  No crontab files may be executable, or be writable by any user other than their owner.

AUTHOR

       Paul Vixie <vixie@isc.org>

4th Berkeley Distribution					  24 January 1994							CRONTAB(5)