crontab

Additional Notes

crontab manages scheduled recurring jobs for users. Cron jobs run commands at specified minutes, hours, days, months, or weekdays.

Use cron for repeated tasks such as backups, cleanup, reports, and maintenance scripts.

Syntax

crontab [options]
crontab file

Parameters

• file: File containing crontab entries to install.
• options: Edit, list, remove, and user controls.

Common Options

• -e: Edit the current user's crontab.
• -l: List the current user's crontab.
• -r: Remove the current user's crontab.
• -u USER: Manage another user's crontab as root.
• -i: Prompt before removing with -r on some systems.

Cron Time Format

• Field 1: Minute, 0-59.
• Field 2: Hour, 0-23.
• Field 3: Day of month, 1-31.
• Field 4: Month, 1-12.
• Field 5: Day of week, 0-7 where 0 and 7 often mean Sunday.

Examples

crontab -l

List your scheduled jobs.

crontab -e

Edit your crontab.

0 2 * * * /usr/local/bin/backup.sh

Run a backup every day at 02:00.

*/15 * * * * /usr/local/bin/check-service.sh

Run a command every 15 minutes.

Practical Notes

• Use absolute paths inside cron jobs.
• Cron has a smaller environment than your interactive shell.
• Redirect output to a log file when you need diagnostics.
• For complex system jobs, systemd timers may be easier to monitor.