Manual: crontab

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CRONTAB(1) crontab User Manual 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

Manual: crontab

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