2004-11-03 13:51:07 +00:00
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.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved
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2007-06-20 22:33:04 +00:00
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.TH "CRONTAB" 1P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
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2004-11-03 13:51:07 +00:00
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.\" crontab
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2007-09-20 06:03:25 +00:00
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.SH PROLOG
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This manual page is part of the POSIX Programmer's Manual.
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The Linux implementation of this interface may differ (consult
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the corresponding Linux manual page for details of Linux behavior),
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or the interface may not be implemented on Linux.
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2004-11-03 13:51:07 +00:00
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.SH NAME
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crontab \- schedule periodic background work
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.SH SYNOPSIS
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.LP
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\fBcrontab\fP \fB[\fP\fIfile\fP\fB]\fP\fB
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.br
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.sp
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crontab\fP \fB[\fP \fB-e | -l | -r\fP \fB]\fP\fB\fP
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\fB
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.br
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\fP
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.SH DESCRIPTION
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.LP
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The \fIcrontab\fP utility shall create, replace, or edit a user's
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crontab entry; a crontab entry is a list of commands and the
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times at which they shall be executed. The new crontab entry can be
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input by specifying \fIfile\fP or input from standard input if
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no \fIfile\fP operand is specified, or by using an editor, if \fB-e\fP
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is specified.
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.LP
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Upon execution of a command from a crontab entry, the implementation
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shall supply a default environment, defining at least the
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following environment variables:
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.TP 7
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\fIHOME\fP
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A pathname of the user's home directory.
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.TP 7
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\fILOGNAME\fP
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The user's login name.
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.TP 7
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\fIPATH\fP
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A string representing a search path guaranteed to find all of the
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standard utilities.
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.TP 7
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\fISHELL\fP
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A pathname of the command interpreter. When \fIcrontab\fP is invoked
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as specified by this volume of
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IEEE\ Std\ 1003.1-2001, the value shall be a pathname for \fIsh\fP.
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.sp
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.LP
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The values of these variables when \fIcrontab\fP is invoked as specified
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by this volume of IEEE\ Std\ 1003.1-2001 shall
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not affect the default values provided when the scheduled command
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is run.
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.LP
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If standard output and standard error are not redirected by commands
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executed from the crontab entry, any generated output or
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errors shall be mailed, via an implementation-defined method, to the
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user.
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.LP
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Users shall be permitted to use \fIcrontab\fP if their names appear
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in the file \fB/usr/lib/cron/cron.allow\fP. If that file does
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not exist, the file \fB/usr/lib/cron/cron.deny\fP shall be checked
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to determine whether the user shall be denied access to
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\fIcrontab\fP. If neither file exists, only a process with appropriate
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privileges shall be allowed to submit a job. If only
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\fBcron.deny\fP exists and is empty, global usage shall be permitted.
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The \fBcron.allow\fP and \fBcron.deny\fP files shall
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consist of one user name per line.
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.SH OPTIONS
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.LP
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The \fIcrontab\fP utility shall conform to the Base Definitions volume
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of IEEE\ Std\ 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
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.LP
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The following options shall be supported:
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.TP 7
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\fB-e\fP
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Edit a copy of the invoking user's crontab entry, or create an empty
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entry to edit if the crontab entry does not exist. When
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editing is complete, the entry shall be installed as the user's crontab
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entry.
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.TP 7
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\fB-l\fP
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(The letter ell.) List the invoking user's crontab entry.
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.TP 7
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\fB-r\fP
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Remove the invoking user's crontab entry.
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.sp
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.SH OPERANDS
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.LP
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The following operand shall be supported:
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.TP 7
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\fIfile\fP
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The pathname of a file that contains specifications, in the format
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defined in the INPUT FILES section, for crontab
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entries.
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.sp
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.SH STDIN
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.LP
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See the INPUT FILES section.
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.SH INPUT FILES
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.LP
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In the POSIX locale, the user or application shall ensure that a crontab
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entry is a text file consisting of lines of six fields
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each. The fields shall be separated by <blank>s. The first five fields
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shall be integer patterns that specify the
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following:
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.IP " 1." 4
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Minute [0,59]
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.LP
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.IP " 2." 4
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Hour [0,23]
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.LP
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.IP " 3." 4
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Day of the month [1,31]
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.LP
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.IP " 4." 4
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Month of the year [1,12]
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.LP
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.IP " 5." 4
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Day of the week ([0,6] with 0=Sunday)
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.LP
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.LP
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Each of these patterns can be either an asterisk (meaning all valid
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values), an element, or a list of elements separated by
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commas. An element shall be either a number or two numbers separated
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by a hyphen (meaning an inclusive range). The specification of
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days can be made by two fields (day of the month and day of the week).
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If month, day of month, and day of week are all asterisks,
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every day shall be matched. If either the month or day of month is
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specified as an element or list, but the day of week is an
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asterisk, the month and day of month fields shall specify the days
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that match. If both month and day of month are specified as an
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asterisk, but day of week is an element or list, then only the specified
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days of the week match. Finally, if either the month or
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day of month is specified as an element or list, and the day of week
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is also specified as an element or list, then any day matching
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either the month and day of month, or the day of week, shall be matched.
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.LP
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The sixth field of a line in a crontab entry is a string that shall
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be executed by \fIsh\fP
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at the specified times. A percent sign character in this field shall
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be translated to a <newline>. Any character preceded by
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a backslash (including the \fB'%'\fP ) shall cause that character
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to be treated literally. Only the first line (up to a
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\fB'%'\fP or end-of-line) of the command field shall be executed by
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the command interpreter. The other lines shall be made
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available to the command as standard input.
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.LP
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Blank lines and those whose first non- <blank> is \fB'#'\fP shall
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be ignored.
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.LP
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The text files \fB/usr/lib/cron/cron.allow\fP and \fB/usr/lib/cron/cron.deny\fP
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shall contain zero or more user names, one per
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line, of users who are, respectively, authorized or denied access
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to the service underlying the \fIcrontab\fP utility.
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.SH ENVIRONMENT VARIABLES
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.LP
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The following environment variables shall affect the execution of
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\fIcrontab\fP:
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.TP 7
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\fIEDITOR\fP
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Determine the editor to be invoked when the \fB-e\fP option is specified.
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The default editor shall be \fIvi\fP.
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.TP 7
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\fILANG\fP
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Provide a default value for the internationalization variables that
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are unset or null. (See the Base Definitions volume of
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IEEE\ Std\ 1003.1-2001, Section 8.2, Internationalization Variables
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for
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the precedence of internationalization variables used to determine
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the values of locale categories.)
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.TP 7
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\fILC_ALL\fP
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If set to a non-empty string value, override the values of all the
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other internationalization variables.
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.TP 7
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\fILC_CTYPE\fP
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Determine the locale for the interpretation of sequences of bytes
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of text data as characters (for example, single-byte as
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opposed to multi-byte characters in arguments and input files).
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.TP 7
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\fILC_MESSAGES\fP
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Determine the locale that should be used to affect the format and
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contents of diagnostic messages written to standard
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error.
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.TP 7
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\fINLSPATH\fP
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Determine the location of message catalogs for the processing of \fILC_MESSAGES
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\&.\fP
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.sp
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.SH ASYNCHRONOUS EVENTS
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.LP
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Default.
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.SH STDOUT
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.LP
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If the \fB-l\fP option is specified, the crontab entry shall be written
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to the standard output.
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.SH STDERR
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.LP
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The standard error shall be used only for diagnostic messages.
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.SH OUTPUT FILES
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.LP
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None.
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.SH EXTENDED DESCRIPTION
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.LP
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None.
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.SH EXIT STATUS
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.LP
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The following exit values shall be returned:
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.TP 7
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\ 0
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Successful completion.
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.TP 7
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>0
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An error occurred.
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.sp
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.SH CONSEQUENCES OF ERRORS
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.LP
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The user's crontab entry is not submitted, removed, edited, or listed.
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.LP
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\fIThe following sections are informative.\fP
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.SH APPLICATION USAGE
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.LP
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The format of the crontab entry shown here is guaranteed only for
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the POSIX locale. Other cultures may be supported with
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substantially different interfaces, although implementations are encouraged
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to provide comparable levels of functionality.
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.LP
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2007-09-20 06:41:41 +00:00
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The default settings of the \fIHOME\fP, \fILOGNAME\fP, \fIPATH\fP,
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2004-11-03 13:51:07 +00:00
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and \fISHELL\fP variables that are given to the
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scheduled job are not affected by the settings of those variables
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when \fIcrontab\fP is run; as stated, they are defaults. The
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text about "invoked as specified by this volume of IEEE\ Std\ 1003.1-2001"
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means that the implementation may provide
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extensions that allow these variables to be affected at runtime, but
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that the user has to take explicit action in order to access
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the extension, such as give a new option flag or modify the format
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of the crontab entry.
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.LP
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A typical user error is to type only \fIcrontab\fP; this causes the
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system to wait for the new crontab entry on standard input.
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If end-of-file is typed (generally <control>-D), the crontab entry
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is replaced by an empty file. In this case, the user
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should type the interrupt character, which prevents the crontab entry
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from being replaced.
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.SH EXAMPLES
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.IP " 1." 4
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Clean up \fBcore\fP files every weekday morning at 3:15 am:
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.sp
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.RS
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.nf
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\fB15 3 * * 1-5 find $HOME -name core 2>/dev/null | xargs rm -f
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\fP
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.fi
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.RE
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.LP
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.IP " 2." 4
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Mail a birthday greeting:
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.sp
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.RS
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.nf
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\fB0 12 14 2 * mailx john%Happy Birthday!%Time for lunch.
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\fP
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.fi
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.RE
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.LP
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.IP " 3." 4
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As an example of specifying the two types of days:
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.sp
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.RS
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.nf
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\fB0 0 1,15 * 1
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\fP
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.fi
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.RE
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.LP
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would run a command on the first and fifteenth of each month, as well
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as on every Monday. To specify days by only one field, the
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other field should be set to \fB'*'\fP ; for example:
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.sp
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.RS
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.nf
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\fB0 0 * * 1
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\fP
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.fi
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.RE
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.LP
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would run a command only on Mondays.
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.LP
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.SH RATIONALE
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.LP
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All references to a \fIcron\fP daemon and to \fIcron\fP \fIfiles\fP
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have been omitted. Although historical implementations
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have used this arrangement, there is no reason to limit future implementations.
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.LP
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This description of \fIcrontab\fP is designed to support only users
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with normal privileges. The format of the input is based on
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the System V \fIcrontab\fP; however, there is no requirement here
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that the actual system database used by the \fIcron\fP daemon
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(or a similar mechanism) use this format internally. For example,
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systems derived from BSD are likely to have an additional field
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appended that indicates the user identity to be used when the job
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is submitted.
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.LP
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The \fB-e\fP option was adopted from the SVID as a user convenience,
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although it does not exist in all historical
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implementations.
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.SH FUTURE DIRECTIONS
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.LP
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None.
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.SH SEE ALSO
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.LP
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\fIat\fP
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.SH COPYRIGHT
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Portions of this text are reprinted and reproduced in electronic form
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from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
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-- Portable Operating System Interface (POSIX), The Open Group Base
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Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
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Electrical and Electronics Engineers, Inc and The Open Group. In the
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event of any discrepancy between this version and the original IEEE and
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The Open Group Standard, the original IEEE and The Open Group Standard
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is the referee document. The original Standard can be obtained online at
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http://www.opengroup.org/unix/online.html .
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