How to Add a Cron Job

Cron is a UNIX utility that execute programs at regular intervals. Each user and root can specify his own set of commands by creating his own crontab file.

Things You'll Need

• Linux or Unix

Instructions

1. Create a script or determine which command you want to be executed regularly and determine how often it should be run.
   For the purposes of this example, a fictional script named "backup.sh" is contained in Mary's home directory. It will run every Friday at midnight.

2. Open a terminal window. Terminal windows are found under Utilities in the Start Menu.

3. Start the crontab editor with the command:
   crontab -e

4. Enter your cron job in the form:
   Minutes Hours DayofMonth Month DayofWeek command.
   Any field not applicable to your job should have an asterisk (*) as a place holder. If you want to specify more than 1 value for any field, separate the values with a comma and no white space. The days of the week are indicated by a number with Sunday being 0.
   For example:
   0 0 * * 5 /home/Mary/backup.sh
   To run on Mondays, Wednesdays and Fridays, the entry would be:
   0 0 * * 1,3,5 /home/Mary/backup.sh

5. Save your entry and quit the editor. Cron will automatically read the file and schedule the job.

6. To make sure your entry has been issued, type the command:
   crontab -l

Tips & Warnings

• This example will add a job for 1 user. If you want to add a system-wide job, you must log in as root, or place "sudo" in front of each command.

References

• Your Unix: The Ultimate Guide; Sumitabha Das; 2001
• The Crontab Man Page
• The Cron Man Page