Cron

Cron: Scheduling Tasks on Unix-like Systems

Overview

cron is a time-based job scheduler in Unix-like operating systems. It allows users to schedule jobs (commands or scripts) to run periodically at fixed times, dates, or intervals.

Crontab Syntax

The crontab file is a configuration file that specifies shell commands to run periodically on a given schedule. Each line of a crontab file represents a job, and follows this format:

- - - - - command_to_run
--
| | | | | | | | | +---- Day of the week (0 - 7) (Sunday is both 0 and 7) | | | +------ Month (1 - 12) | | +-------- Day of the month (1 - 31) | +---------- Hour (0 - 23) +------------ Minute (0 - 59)

Special Strings

In addition to the standard format, cron also supports special strings:

• @reboot : Run once, at startup.
• @yearly : Run once a year, 0 0 1 1 *.
• @annually : Same as @yearly.
• @monthly : Run once a month, 0 0 1 * *.
• @weekly : Run once a week, 0 0 * * 0.
• @daily : Run once a day, 0 0 * * *.
• @midnight : Same as @daily.
• @hourly : Run once an hour, 0 * * * *.

Editing Crontab

To edit the crontab for the current user, use the command:

crontab -e

This opens the crontab file in the default text editor.

Viewing Crontab

To view the crontab entries for the current user:

crontab -l

Removing Crontab

To remove the crontab file for the current user: