Differences between version 3 and predecessor to the previous major change of crontab(5).
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| Newer page: | version 3 | Last edited on Tuesday, January 21, 2003 9:31:52 pm | by CraigBox | Revert |
| Older page: | version 1 | Last edited on Tuesday, June 4, 2002 12:30:36 am | by perry | Revert |
@@ -1,230 +1,136 @@
-CRONTAB
-!!!CRONTAB
-NAME
-DESCRIPTION
-EXAMPLE CRON FILE
-EXAMPLE SYSTEM CRON FILE
-SEE ALSO
-EXTENSIONS
-AUTHOR
-----
!!NAME
+crontab - tables for driving cron
-
-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.
-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,
-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.
+ name = value
-
-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.
-Several environment variables are set up automatically by
-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
-''
+(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.
-(Another note:
the LOGNAME variable is sometimes called USER
-on BSD systems
... on these systems
, USER
will be set
-also
.)
+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
('). 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
.
-In addition to LOGNAME, HOME, and SHELL,
cron(8) will
-look at MAILTO if it has any reason to send mail as a result
-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=
-
+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)
-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.
+A field may be an asterisk (*), which always stands for ''first-last''.
-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:
+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''.
-field allowed
values
------ --------------
-minute
-59
-hour
-23
-day of month 1-31
-month 1-
12 (or names
, see below
)
-day of week -7 (0 or 7 is Sun
, or
use names)
+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, ''
-23/2'' can be used in the hours field to specify command execution every other hour (the
+alternative in the V7 standard is ''
,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.
-A
field may be an asterisk
(*
), which always stands for
-``first
-last''
.
+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.
-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.
+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,
-Lists are allowed. A list is a set of numbers (or ranges)
-separated by commas. Examples: ``1,2,5,9'',
-``
-4,8
-12''.
+-----
-
-Step values can be used in conjunction with ranges.
-Following a range with ``/
-
-
-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
-# 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.
-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 * * 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
-
-# /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 * * 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
+cron(8), crontab(1)
-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).
-When specifying day
of week, both day 0 and day 7 will be
-considered Sunday. BSD and ATT seem to disagree about
-this
.
+All
of the `@' commands that can appear in place of the first five fields are extensions
.
-
-Lists and ranges are allowed to co-exist in the same field.
-
-
-Ranges can include
-
-
-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
-----
