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CRONTAB(1) General Commands Manual CRONTAB(1)
NAME
crontab - maintain crontab files for individual users (Vixie Cron)
SYNOPSIS
crontab [ -u user ] file
crontab [ -u user ] [ -i ] { -e | -l | -r }
DESCRIPTION
crontab is the program used to install, deinstall or list the tables used to drive the
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.
If the /etc/cron.allow file exists, then you must be listed (one user per line) therein in
order to be allowed to use this command. If the /etc/cron.allow file does not exist but
the /etc/cron.deny file does exist, then you must not be listed in the /etc/cron.deny file
in order to use this command.
If neither of these files exists, then depending on site-dependent configuration parame‐
ters, only the super user will be allowed to use this command, or all users will be able
to use this command.
If both files exist then /etc/cron.allow takes precedence. Which means that /etc/cron.deny
is not considered and your user must be listed in /etc/cron.allow in order to be able to
use the crontab.
Regardless of the existance of any of these files, the root administrative user is always
allowed to setup a crontab. For standard Debian systems, all users may use this command.
If the -u option is given, it specifies the name of the user whose crontab is to be used
(when listing) or modified (when editing). If this option is not given, crontab examines
"your" crontab, i.e., the crontab of the person executing the command. Note that su(8)
can confuse crontab and that if you are running inside of su(8) you should always use the
-u option for safety's sake.
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.
The -l option causes the current crontab to be displayed on standard output. See the note
under DEBIAN SPECIFIC below.
The -r option causes the current crontab to be removed.
The -e option is used to edit the current crontab using the editor specified by the VISUAL
or EDITOR environment variables. After you exit from the editor, the modified crontab
will be installed automatically. If neither of the environment variables is defined, then
the default editor /usr/bin/editor is used.
The -i option modifies the -r option to prompt the user for a 'y/Y' response before actu‐
ally removing the crontab.
DEBIAN SPECIFIC
The "out-of-the-box" behaviour for 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
crontab -l | crontab -
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 -l option has been
changed to not output such header. You may obtain the original behaviour by setting the
environment variable CRONTAB_NOHEADER to 'N', which will cause the crontab -l command to
emit the extraneous header.
SEE ALSO
crontab(5), cron(8)
FILES
/etc/cron.allow
/etc/cron.deny
/var/spool/cron/crontabs
There is one file for each user's crontab under the /var/spool/cron/crontabs directory.
Users are not allowed to edit the files under that directory directly to ensure that only
users allowed by the system to run periodic tasks can add them, and only syntactically
correct crontabs will be written there. This is enforced by having the directory writable
only by the crontab group and configuring crontab command with the setgid bid set for that
specific group.
STANDARDS
The 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.
DIAGNOSTICS
A fairly informative usage message appears if you run it with a bad command line.
cron requires that each entry in a crontab end in a newline character. If the last entry
in a crontab is missing the newline, cron will consider the crontab (at least partially)
broken and refuse to install it.
AUTHOR
Paul Vixie <paul AT vix.com> is the author of cron and original creator of this manual page.
This page has also been modified for Debian by Steve Greenland, Javier Fernandez-Sanguino
and Christian Kastner.
4th Berkeley Distribution 19 April 2010 CRONTAB(1)
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