CRONTAB(1)

NAME
crontab - maintain crontab files for individual users (Vixie Cron)

SYNOPSIS

crontab [-h]

crontab [-u user] [-n] 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.

Please check that the permissions of the file /etc/cron.allow make it readable by the users which are allowed. For example, permissions rw- r-- r-- (octal 644) should be OK.

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.

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 existence 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 -h option is given, crontab shows a help message and quits immediately.

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 file, i.e., the crontab file 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.

If the -n option is given, it means "dry run": crontab examines "your" crontab for its syntax, and outputs a success message if this syntax is correct, but nothing is written to any crontab.

The -l option causes the current crontab to be displayed on standard output. See the note under the section called “DEBIAN SPECIFIC” below.

The -r option causes the current crontab to be removed.

The -e option is used to edit the current crontab using sensible-editor(1). After you exit from the editor, the modified crontab will be installed automatically.

The -i option modifies the -r option to prompt the user for a 'y/Y' response before actually 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.

HIGHLIGHTING THE OUTPUT OF CRONTAB -L

The command crontab -l outputs plain text. When a tty can support ANSI sequences to colourise this text, one can highlight the output, by calling: crontab -l | spc -t crontab when the ttybackground is dark, or crontab -l | spc -t crontab-light when this background is light.

The highlighting scheme can be modified by using customised versions of files /etc/supercat/spcrc-crontab*

One can also colourise this text with the program batcat(1) provided by the package bat, here is an example:

crontab -l | batcat --language Crontab

SEE ALSO

crontab(5), cron(8), spc(1)

FILES

/etc/cron.allow, /etc/cron.deny
    The files /etc/cron.allow and /etc/cron.deny if they exist, must be either world-readable, or readable by group ``crontab''. If they are not, then cron(8) will deny access to all users until the permissions are fixed.

/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.

LIMITATIONS

The maximum permitted length for the command field is 998 characters.

The recommended length should be less than 80 characters, like lines in readable source files. When one must use a long command, it is worth creating a dedicated script, which in turn can contain valuable comments.

DIAGNOSTICS

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

cron(8) requires that each entry in a crontab end in a newline character. If the last entry in a crontab is missing the newline, cron(8) will consider the crontab (at least partially) broken and refuse to install it.

The files under /var/spool/cron/crontabs are named based on the user's account name. Crontab jobs will not be run for users whose accounts have been renamed either due to changes in the local system or because they are managed through a central user database (external to the system, for example an LDAP directory).

AUTHORS

Paul Vixie <paul@vix.com>
    Wrote this manpage (1994).

Steve Greenland <stevegr@debian.org>
    Maintained the package (1996-2005).

Javier Fernández-Sanguino Peña <jfs@debian.org>
    Maintained the package (2005-2014).

Christian Kastner <ckk@debian.org>
    Maintained the package (2010-2016).

Georges Khaznadar <georgesk@debian.org>
    Maintained the package (2022-2024).

COPYRIGHT
Copyright © 1994 Paul Vixie

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 warranty 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.

Since year 1994, many modifications were made in this manpage, authored by Debian Developers which maintained cron(TM); above is a short list, more information can be found in the file /usr/share/doc/cron/copyright.