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!!NAME
crontab - tables for driving cron

!!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 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 ''*/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.

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,
 @annually   (same as @yearly)
 @monthly    Run once a month,
 @weekly     Run once a week,
 @daily      Run once a day,
 @midnight   (same as @daily)
 @hourly     Run once an hour,

-----

!!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

!!EXAMPLE SYSTEM CRON FILE

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.
 SHELL=/bin/sh
 PATH=/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin
 # m   h  dom mon dow usercommand
   42  6  *   *   *   rootrun-parts --report /etc/cron.daily
   47  6  *   *   7   rootrun-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

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
6 pages link to crontab(5):
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Last edited on Tuesday, January 21, 2003 9:33:51 pm by CraigBox
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