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Linux in a Nutshell

This directory of Linux commands is from Linux in a Nutshell, 5th Edition.

Click on any of the 687 commands below to get a description and list of available options. All links in the command summaries point to the online version of the book on Safari Bookshelf.

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crontab [options] [file]

View, install, or uninstall your current crontab file. A privileged user can run crontab for another user by supplying -u user. A crontab file is a list of commands, one per line, that will execute automatically at a given time. Numbers are supplied before each command to specify the execution time. The numbers appear in five fields, as follows:

Minute 0-59 Hour 0-23 Day of month1-31 Month 1-12 Jan, Feb, Mar, ... Day of week 0-6, with 0 = Sunday Sun, Mon, Tue, ...

Use a comma between multiple values, a hyphen to indicate a range, and an asterisk to indicate all possible values. For example, assuming these crontab entries:

59 3 * * 5 find / -print | backup_program 0 0 1,15 * * echo "Timesheets due" | mail user

the first command backs up the system files every Friday at 3:59 a.m., and the second command mails a reminder on the 1st and 15th of each month.

The superuser can always issue the crontab command. Other users must be listed in the file /etc/cron.allow if it exists; otherwise, they must not be listed in /etc/cron.deny. If neither file exists, only the superuser can issue the command.


The -e, -l, and -r options are not valid if any files are specified.


Edit the user's current crontab file (or create one).


Display the user's crontab file on standard output.


Delete the user's crontab file.

-u user

Indicate which user's crontab file will be acted upon.

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