path: root/man1p/crontab.1p

.\" Copyright (c) 2001-2003 The Open Group, All Rights Reserved 
.TH "CRONTAB" P 2003 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\" crontab 
.SH NAME
crontab \- schedule periodic background work
.SH SYNOPSIS
.LP
\fBcrontab\fP \fB[\fP\fIfile\fP\fB]\fP\fB
.br
.sp
crontab\fP \fB[\fP \fB-e | -l | -r\fP \fB]\fP\fB\fP
\fB
.br
\fP
.SH DESCRIPTION
.LP
The \fIcrontab\fP utility shall create, replace, or edit a user's
crontab entry; a crontab entry is a list of commands and the
times at which they shall be executed. The new crontab entry can be
input by specifying \fIfile\fP or input from standard input if
no \fIfile\fP operand is specified, or by using an editor, if \fB-e\fP
is specified.
.LP
Upon execution of a command from a crontab entry, the implementation
shall supply a default environment, defining at least the
following environment variables:
.TP 7
\fIHOME\fP
A pathname of the user's home directory.
.TP 7
\fILOGNAME\fP
The user's login name.
.TP 7
\fIPATH\fP
A string representing a search path guaranteed to find all of the
standard utilities.
.TP 7
\fISHELL\fP
A pathname of the command interpreter. When \fIcrontab\fP is invoked
as specified by this volume of
IEEE\ Std\ 1003.1-2001, the value shall be a pathname for \fIsh\fP.
.sp
.LP
The values of these variables when \fIcrontab\fP is invoked as specified
by this volume of IEEE\ Std\ 1003.1-2001 shall
not affect the default values provided when the scheduled command
is run.
.LP
If standard output and standard error are not redirected by commands
executed from the crontab entry, any generated output or
errors shall be mailed, via an implementation-defined method, to the
user.
.LP
Users shall be permitted to use \fIcrontab\fP if their names appear
in the file \fB/usr/lib/cron/cron.allow\fP. If that file does
not exist, the file \fB/usr/lib/cron/cron.deny\fP shall be checked
to determine whether the user shall be denied access to
\fIcrontab\fP. If neither file exists, only a process with appropriate
privileges shall be allowed to submit a job. If only
\fBcron.deny\fP exists and is empty, global usage shall be permitted.
The \fBcron.allow\fP and \fBcron.deny\fP files shall
consist of one user name per line. 
.SH OPTIONS
.LP
The \fIcrontab\fP utility shall conform to the Base Definitions volume
of IEEE\ Std\ 1003.1-2001, Section 12.2, Utility Syntax Guidelines.
.LP
The following options shall be supported:
.TP 7
\fB-e\fP
Edit a copy of the invoking user's crontab entry, or create an empty
entry to edit if the crontab entry does not exist. When
editing is complete, the entry shall be installed as the user's crontab
entry.
.TP 7
\fB-l\fP
(The letter ell.) List the invoking user's crontab entry.
.TP 7
\fB-r\fP
Remove the invoking user's crontab entry.
.sp
.SH OPERANDS
.LP
The following operand shall be supported:
.TP 7
\fIfile\fP
The pathname of a file that contains specifications, in the format
defined in the INPUT FILES section, for crontab
entries.
.sp
.SH STDIN
.LP
See the INPUT FILES section.
.SH INPUT FILES
.LP
In the POSIX locale, the user or application shall ensure that a crontab
entry is a text file consisting of lines of six fields
each. The fields shall be separated by <blank>s. The first five fields
shall be integer patterns that specify the
following:
.IP " 1." 4
Minute [0,59]
.LP
.IP " 2." 4
Hour [0,23]
.LP
.IP " 3." 4
Day of the month [1,31]
.LP
.IP " 4." 4
Month of the year [1,12]
.LP
.IP " 5." 4
Day of the week ([0,6] with 0=Sunday)
.LP
.LP
Each of these patterns can be either an asterisk (meaning all valid
values), an element, or a list of elements separated by
commas. An element shall be either a number or two numbers separated
by a hyphen (meaning an inclusive range). The specification of
days can be made by two fields (day of the month and day of the week).
If month, day of month, and day of week are all asterisks,
every day shall be matched. If either the month or day of month is
specified as an element or list, but the day of week is an
asterisk, the month and day of month fields shall specify the days
that match. If both month and day of month are specified as an
asterisk, but day of week is an element or list, then only the specified
days of the week match. Finally, if either the month or
day of month is specified as an element or list, and the day of week
is also specified as an element or list, then any day matching
either the month and day of month, or the day of week, shall be matched.
.LP
The sixth field of a line in a crontab entry is a string that shall
be executed by \fIsh\fP
at the specified times. A percent sign character in this field shall
be translated to a <newline>. Any character preceded by
a backslash (including the \fB'%'\fP ) shall cause that character
to be treated literally. Only the first line (up to a
\fB'%'\fP or end-of-line) of the command field shall be executed by
the command interpreter. The other lines shall be made
available to the command as standard input.
.LP
Blank lines and those whose first non- <blank> is \fB'#'\fP shall
be ignored.
.LP
The text files \fB/usr/lib/cron/cron.allow\fP and \fB/usr/lib/cron/cron.deny\fP
shall contain zero or more user names, one per
line, of users who are, respectively, authorized or denied access
to the service underlying the \fIcrontab\fP utility. 
.SH ENVIRONMENT VARIABLES
.LP
The following environment variables shall affect the execution of
\fIcrontab\fP:
.TP 7
\fIEDITOR\fP
Determine the editor to be invoked when the \fB-e\fP option is specified.
The default editor shall be \fIvi\fP.
.TP 7
\fILANG\fP
Provide a default value for the internationalization variables that
are unset or null. (See the Base Definitions volume of
IEEE\ Std\ 1003.1-2001, Section 8.2, Internationalization Variables
for
the precedence of internationalization variables used to determine
the values of locale categories.)
.TP 7
\fILC_ALL\fP
If set to a non-empty string value, override the values of all the
other internationalization variables.
.TP 7
\fILC_CTYPE\fP
Determine the locale for the interpretation of sequences of bytes
of text data as characters (for example, single-byte as
opposed to multi-byte characters in arguments and input files).
.TP 7
\fILC_MESSAGES\fP
Determine the locale that should be used to affect the format and
contents of diagnostic messages written to standard
error.
.TP 7
\fINLSPATH\fP
Determine the location of message catalogs for the processing of \fILC_MESSAGES
\&.\fP 
.sp
.SH ASYNCHRONOUS EVENTS
.LP
Default.
.SH STDOUT
.LP
If the \fB-l\fP option is specified, the crontab entry shall be written
to the standard output.
.SH STDERR
.LP
The standard error shall be used only for diagnostic messages.
.SH OUTPUT FILES
.LP
None.
.SH EXTENDED DESCRIPTION
.LP
None.
.SH EXIT STATUS
.LP
The following exit values shall be returned:
.TP 7
\ 0
Successful completion.
.TP 7
>0
An error occurred.
.sp
.SH CONSEQUENCES OF ERRORS
.LP
The user's crontab entry is not submitted, removed, edited, or listed.
.LP
\fIThe following sections are informative.\fP
.SH APPLICATION USAGE
.LP
The format of the crontab entry shown here is guaranteed only for
the POSIX locale. Other cultures may be supported with
substantially different interfaces, although implementations are encouraged
to provide comparable levels of functionality.
.LP
The default settings of the \fIHOME ,\fP \fILOGNAME ,\fP \fIPATH ,\fP
and \fISHELL\fP variables that are given to the
scheduled job are not affected by the settings of those variables
when \fIcrontab\fP is run; as stated, they are defaults. The
text about "invoked as specified by this volume of IEEE\ Std\ 1003.1-2001"
means that the implementation may provide
extensions that allow these variables to be affected at runtime, but
that the user has to take explicit action in order to access
the extension, such as give a new option flag or modify the format
of the crontab entry.
.LP
A typical user error is to type only \fIcrontab\fP; this causes the
system to wait for the new crontab entry on standard input.
If end-of-file is typed (generally <control>-D), the crontab entry
is replaced by an empty file. In this case, the user
should type the interrupt character, which prevents the crontab entry
from being replaced.
.SH EXAMPLES
.IP " 1." 4
Clean up \fBcore\fP files every weekday morning at 3:15 am:
.sp
.RS
.nf

\fB15 3 * * 1-5 find $HOME -name core 2>/dev/null | xargs rm -f
\fP
.fi
.RE
.LP
.IP " 2." 4
Mail a birthday greeting:
.sp
.RS
.nf

\fB0 12 14 2 * mailx john%Happy Birthday!%Time for lunch.
\fP
.fi
.RE
.LP
.IP " 3." 4
As an example of specifying the two types of days:
.sp
.RS
.nf

\fB0 0 1,15 * 1
\fP
.fi
.RE
.LP
would run a command on the first and fifteenth of each month, as well
as on every Monday. To specify days by only one field, the
other field should be set to \fB'*'\fP ; for example:
.sp
.RS
.nf

\fB0 0 * * 1
\fP
.fi
.RE
.LP
would run a command only on Mondays.
.LP
.SH RATIONALE
.LP
All references to a \fIcron\fP daemon and to \fIcron\fP \fIfiles\fP
have been omitted. Although historical implementations
have used this arrangement, there is no reason to limit future implementations.
.LP
This description of \fIcrontab\fP is designed to support only users
with normal privileges. The format of the input is based on
the System V \fIcrontab\fP; however, there is no requirement here
that the actual system database used by the \fIcron\fP daemon
(or a similar mechanism) use this format internally. For example,
systems derived from BSD are likely to have an additional field
appended that indicates the user identity to be used when the job
is submitted.
.LP
The \fB-e\fP option was adopted from the SVID as a user convenience,
although it does not exist in all historical
implementations.
.SH FUTURE DIRECTIONS
.LP
None.
.SH SEE ALSO
.LP
\fIat\fP
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .