Cron

Commands#

Command	Description
crontab -e	Edit the crontab for the current user
crontab -l	List the current user's crontab
crontab -r	Remove the current user's crontab
crontab -u user -l	List the crontab for the specified user

Syntax#

Each line in a crontab file represents a scheduled task. The syntax is as follows:

* * * * * <command to execute>
| | | | |
| | | | ----- Day of the week (0 - 7) [where 0 and 7 = Sunday]
| | | ------- Month (1 - 12)
| | --------- Day of the month (1 - 31)
| ----------- Hour (0 - 23)
------------- Minute (0 - 59)

Special Characters#

• * : Every value
• , : Multiple values (e.g., 1,15 means the 1st and 15th)
• - : Range of values (e.g., 1-5 means from the 1st to the 5th)
• / : Step values (e.g., */10 means every 10 units)

Special Entries#

• @reboot : Run once, at startup
• @hourly : Run once an hour
• @daily : Run once a day
• @weekly : Run once a week
• @monthly : Run once a month
• @yearly : Run once a year

Examples#

Run a Script Daily at Midnight#

0 0 * * * /home/user/scripts/backup.shbash

Various Frequencies#

# Every 5 minutes
*/5 * * * * <command>

# Every Sunday at 10:15 PM
15 22 * * 0 <command>

# Every weekday at 8:00 AM
0 8 * * 1-5 <command>

# On the 1st of every month at midnight
0 0 1 * * <command>

# Every other day at 3:00 AM
0 3 */2 * * <command>

# From the 1st to the 10th of every month at 3:00 AM
0 3 1-10 * * <command>bash

Useful Tools#

• crontab-generator.org: Generate crontab lines by selecting your needs.
• crontab.guru: Validate and understand crontab syntax.