324 lines
8.7 KiB
Groff
324 lines
8.7 KiB
Groff
.\"/* Copyright 1988,1990,1993,1994 by Paul Vixie
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.\" * All rights reserved
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.\" *
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.\" * Distribute freely, except: don't remove my name from the source or
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.\" * documentation (don't take credit for my work), mark your changes (don't
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.\" * get me blamed for your possible bugs), don't alter or remove this
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.\" * notice. May be sold if buildable source is provided to buyer. No
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.\" * warrantee of any kind, express or implied, is included with this
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.\" * software; use at your own risk, responsibility for damages (if any) to
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.\" * anyone resulting from the use of this software rests entirely with the
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.\" * user.
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.\" *
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.\" * Send bug reports, bug fixes, enhancements, requests, flames, etc., and
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.\" * I'll try to keep a version up to date. I can be reached as follows:
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.\" * Paul Vixie <paul@vix.com> uunet!decwrl!vixie!paul
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.\" */
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.\"
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.\" $FreeBSD$
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.\"
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.Dd April 28, 2012
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.Dt CRONTAB 5
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.Os
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.Sh NAME
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.Nm crontab
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.Nd tables for driving cron
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.Sh DESCRIPTION
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A
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.Nm
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file contains instructions to the
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.Xr cron 8
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daemon of the general form: ``run this command at this time on this date''.
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Each user has their own crontab, and commands in any given crontab will be
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executed as the user who owns the crontab.
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Uucp and News will usually have
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their own crontabs, eliminating the need for explicitly running
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.Xr su 1
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as part of a cron command.
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.Pp
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Blank lines and leading spaces and tabs are ignored.
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Lines whose first
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non-space character is a pound-sign (#) are comments, and are ignored.
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Note that comments are not allowed on the same line as cron commands, since
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they will be taken to be part of the command.
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Similarly, comments are not
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allowed on the same line as environment variable settings.
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.Pp
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An active line in a crontab will be either an environment setting or a cron
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command.
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An environment setting is of the form,
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.Bd -literal
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name = value
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.Ed
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.Pp
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where the spaces around the equal-sign (=) are optional, and any subsequent
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non-leading spaces in
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.Em value
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will be part of the value assigned to
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.Em name .
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The
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.Em value
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string may be placed in quotes (single or double, but matching) to preserve
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leading or trailing blanks.
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The
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.Em name
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string may also be placed in quote (single or double, but matching)
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to preserve leading, trailing or inner blanks.
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.Pp
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Several environment variables are set up
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automatically by the
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.Xr cron 8
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daemon.
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.Ev SHELL
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is set to
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.Pa /bin/sh ,
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.Ev PATH
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is set to
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.Pa /usr/bin:/bin ,
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and
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.Ev LOGNAME
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and
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.Ev HOME
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are set from the
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.Pa /etc/passwd
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line of the crontab's owner.
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.Ev HOME ,
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.Ev PATH
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and
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.Ev SHELL
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may be overridden by settings in the crontab;
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.Ev LOGNAME
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may not.
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.Pp
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(Another note: the
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.Ev LOGNAME
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variable is sometimes called
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.Ev USER
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on
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.Bx
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systems...
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On these systems,
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.Ev USER
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will be set also).
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.Pp
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In addition to
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.Ev LOGNAME ,
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.Ev HOME ,
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.Ev PATH ,
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and
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.Ev SHELL ,
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.Xr cron 8
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will look at
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.Ev MAILTO
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if it has any reason to send mail as a result of running
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commands in ``this'' crontab.
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If
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.Ev MAILTO
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is defined (and non-empty), mail is
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sent to the user so named.
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.Ev MAILTO
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may also be used to direct mail to multiple recipients
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by separating recipient users with a comma.
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If
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.Ev MAILTO
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is defined but empty (MAILTO=""), no
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mail will be sent.
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Otherwise mail is sent to the owner of the crontab.
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This
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option is useful if you decide on
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.Pa /bin/mail
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instead of
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.Pa /usr/lib/sendmail
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as
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your mailer when you install cron --
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.Pa /bin/mail
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does not do aliasing, and UUCP
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usually does not read its mail.
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.Pp
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The format of a cron command is very much the V7 standard, with a number of
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upward-compatible extensions.
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Each line has five time and date fields,
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followed by a user name
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(with optional ``:<group>'' and ``/<login-class>'' suffixes)
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if this is the system crontab file,
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followed by a command.
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Commands are executed by
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.Xr cron 8
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when the minute, hour, and month of year fields match the current time,
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.Em and
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when at least one of the two day fields (day of month, or day of week)
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matches the current time (see ``Note'' below).
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.Xr cron 8
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examines cron entries once every minute.
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The time and date fields are:
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.Bd -literal -offset indent
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field allowed values
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----- --------------
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minute 0-59
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hour 0-23
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day of month 1-31
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month 1-12 (or names, see below)
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day of week 0-7 (0 or 7 is Sun, or use names)
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.Ed
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.Pp
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A field may be an asterisk (*), which always stands for ``first\-last''.
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.Pp
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Ranges of numbers are allowed.
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Ranges are two numbers separated
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with a hyphen.
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The specified range is inclusive.
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For example,
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8-11 for an ``hours'' entry specifies execution at hours 8, 9, 10
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and 11.
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.Pp
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Lists are allowed.
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A list is a set of numbers (or ranges)
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separated by commas.
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Examples: ``1,2,5,9'', ``0-4,8-12''.
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.Pp
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Step values can be used in conjunction with ranges.
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Following
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a range with ``/<number>'' specifies skips of the number's value
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through the range.
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For example, ``0-23/2'' can be used in the hours
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field to specify command execution every other hour (the alternative
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in the V7 standard is ``0,2,4,6,8,10,12,14,16,18,20,22'').
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Steps are
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also permitted after an asterisk, so if you want to say ``every two
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hours'', just use ``*/2''.
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.Pp
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Names can also be used for the ``month'' and ``day of week''
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fields.
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Use the first three letters of the particular
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day or month (case does not matter).
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Ranges or
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lists of names are not allowed.
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.Pp
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The ``sixth'' field (the rest of the line) specifies the command to be
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run.
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The entire command portion of the line, up to a newline or %
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character, will be executed by
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.Pa /bin/sh
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or by the shell
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specified in the
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.Ev SHELL
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variable of the cronfile.
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Percent-signs (%) in the command, unless escaped with backslash
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(\\), will be changed into newline characters, and all data
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after the first % will be sent to the command as standard
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input.
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.Pp
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Note: The day of a command's execution can be specified by two
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fields \(em day of month, and day of week.
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If both fields are
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restricted (ie, are not *), the command will be run when
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.Em either
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field matches the current time.
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For example,
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``30 4 1,15 * 5''
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would cause a command to be run at 4:30 am on the 1st and 15th of each
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month, plus every Friday.
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.Pp
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Instead of the first five fields,
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one of eight special strings may appear:
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.Bd -literal -offset indent
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string meaning
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------ -------
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@reboot Run once, at startup of cron.
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@yearly Run once a year, "0 0 1 1 *".
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@annually (same as @yearly)
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@monthly Run once a month, "0 0 1 * *".
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@weekly Run once a week, "0 0 * * 0".
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@daily Run once a day, "0 0 * * *".
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@midnight (same as @daily)
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@hourly Run once an hour, "0 * * * *".
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@every_minute Run once a minute, "*/1 * * * *".
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@every_second Run once a second.
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.Ed
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.Sh EXAMPLE CRON FILE
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.Bd -literal
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# use /bin/sh to run commands, overriding the default set by cron
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SHELL=/bin/sh
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# mail any output to `paul', no matter whose crontab this is
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MAILTO=paul
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#
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# run five minutes after midnight, every day
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5 0 * * * $HOME/bin/daily.job >> $HOME/tmp/out 2>&1
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# run at 2:15pm on the first of every month -- output mailed to paul
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15 14 1 * * $HOME/bin/monthly
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# run at 10 pm on weekdays, annoy Joe
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0 22 * * 1-5 mail -s "It's 10pm" joe%Joe,%%Where are your kids?%
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23 0-23/2 * * * echo "run 23 minutes after midn, 2am, 4am ..., everyday"
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5 4 * * sun echo "run at 5 after 4 every sunday"
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.Ed
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.Sh SEE ALSO
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.Xr crontab 1 ,
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.Xr cron 8
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.Sh EXTENSIONS
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When specifying day of week, both day 0 and day 7 will be considered Sunday.
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.Bx
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and
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.Tn ATT
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seem to disagree about this.
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.Pp
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Lists and ranges are allowed to co-exist in the same field.
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"1-3,7-9" would
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be rejected by
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.Tn ATT
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or
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.Bx
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cron -- they want to see "1-3" or "7,8,9" ONLY.
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.Pp
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Ranges can include "steps", so "1-9/2" is the same as "1,3,5,7,9".
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.Pp
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Names of months or days of the week can be specified by name.
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.Pp
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Environment variables can be set in the crontab.
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In
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.Bx
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or
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.Tn ATT ,
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the
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environment handed to child processes is basically the one from
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.Pa /etc/rc .
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.Pp
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Command output is mailed to the crontab owner
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.No ( Bx
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cannot do this), can be
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mailed to a person other than the crontab owner (SysV cannot do this), or the
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feature can be turned off and no mail will be sent at all (SysV cannot do this
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either).
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.Pp
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All of the
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.Sq @
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commands that can appear in place of the first five fields
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are extensions.
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.Sh AUTHORS
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.An Paul Vixie Aq Mt paul@vix.com
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.Sh BUGS
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If you are in one of the 70-odd countries that observe Daylight
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Savings Time, jobs scheduled during the rollback or advance may be
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affected if
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.Xr cron 8
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is not started with the
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.Fl s
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flag.
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In general, it is not a good idea to schedule jobs during
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this period if
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.Xr cron 8
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is not started with the
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.Fl s
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flag, which is enabled by default.
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See
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.Xr cron 8
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for more details.
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.Pp
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For US timezones (except parts of AZ and HI) the time shift occurs at
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2AM local time.
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For others, the output of the
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.Xr zdump 8
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program's verbose
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.Fl ( v )
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option can be used to determine the moment of time shift.
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