File: crontab.1

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.\"/* Copyright 1988,1990,1993 by Paul Vixie
.\" * All rights reserved
.\" *
.\" * Distribute freely, except: don't remove my name from the source or
.\" * documentation (don't take credit for my work), mark your changes (don't
.\" * get me blamed for your possible bugs), don't alter or remove this
.\" * notice.  May be sold if buildable source is provided to buyer.  No
.\" * warrantee of any kind, express or implied, is included with this
.\" * software; use at your own risk, responsibility for damages (if any) to
.\" * anyone resulting from the use of this software rests entirely with the
.\" * user.
.\" *
.\" * Send bug reports, bug fixes, enhancements, requests, flames, etc., and
.\" * I'll try to keep a version up to date.  I can be reached as follows:
.\" * Paul Vixie          <paul@vix.com>          uunet!decwrl!vixie!paul
.\" */
.\"
.\" $Id: crontab.1,v 2.4 1993/12/31 10:47:33 vixie Exp $
.\"
.TH CRONTAB 1 "29 December 1993"
.UC 4
.SH NAME
crontab \- maintain crontab files for individual users (V3)
.SH SYNOPSIS
crontab [ -u user ] file
.br
crontab [ -u user ] { -l | -r | -e }
.SH DESCRIPTION
.I crontab
is the program used to install, deinstall or list the tables
used to drive the
.IR cron (8)
daemon in Vixie Cron.  Each user can have their own crontab, and though
these are files in /var/spool/cron/crontabs,
they are not intended to be edited directly.
.PP
If the
.I /etc/cron.allow
file exists, then you must be listed therein in order to be allowed to use
this command.  If the
.I /etc/cron.allow
file does not exist but the
.I /etc/cron.deny
file does exist, then you must \fBnot\fR be listed in the
.I /etc/cron.deny
file in order to use this command.  If neither of these files exists, then
depending on site-dependent configuration parameters, only the super user
will be allowed to use this command, or all users will be able to use this
command. For standard Debian systems, all users may use this command.
.PP
If the
.I -u
option is given, it specifies the name of the user whose crontab is to be
tweaked.  If this option is not given,
.I crontab
examines "your" crontab, i.e., the crontab of the person executing the
command.  Note that
.IR su (8)
can confuse
.I crontab
and that if you are running inside of
.IR su (8) 
you should always use the
.I -u
option for safety's sake.
.PP
The first form of this command is used to install a new crontab from some
named file or standard input if the pseudo-filename ``-'' is given.
.PP
The
.I -l
option causes the current crontab to be displayed on standard output. See
the note under 
.B DEBIAN SPECIFIC
below.
.PP
The
.I -r
option causes the current crontab to be removed.
.PP
The
.I -e
option is used to edit the current crontab using the editor specified by
the \s-1VISUAL\s+1 or \s-1EDITOR\s+1 environment variables.
The specified editor
.B must
edit the file in place;
any editor that unlinks the file and recreates it cannot be used.
After you exit
from the editor, the modified crontab will be installed automatically.
.SH DEBIAN SPECIFIC
The "out-of-the-box" behaviour for
.I crontab -l
is to display the three line "DO NOT EDIT THIS FILE" header 
that is placed at the
beginning of the crontab when it is installed. The problem is that
it makes the sequence
.PP
crontab -l | crontab -
.PP
non-idempotent -- you keep adding copies of the header. This causes
pain to scripts that use sed to edit a crontab. Therefore, the default
behaviour of the 
.B -l
option has been changed to not output such header. You may obtain the
original behaviour by setting the environment variable 
.B CRONTAB_NOHEADER
to 'N', which will cause the
.I crontab -l
command to emit the extraneous header.
.SH "SEE ALSO"
crontab(5), cron(8)
.SH FILES
.nf
/etc/cron.allow
/etc/cron.deny
.fi
.SH STANDARDS
The
.I crontab
command conforms to IEEE Std1003.2-1992 (``POSIX'').  This new command syntax
differs from previous versions of Vixie Cron, as well as from the classic
SVR3 syntax.

.SH DIAGNOSTICS
A fairly informative usage message appears if you run it with a bad command
line.

.SH BUGS
Although cron requires that each entry in a crontab end in a newline
character, the neither the crontab command nor the cron daemon will
detect this error. Instead, the crontab will appear load
normally. However, the command will never run. The best choice is to
ensure that your crontab has a blank line at the end.

.SH AUTHOR
.nf
Paul Vixie <paul@vix.com>