Create Cron Jobs on Linux

Cron is a time-based scheduler commonly used on Linux and Unix-like systems. It can run backups, cleanup scripts, reports, maintenance commands, and other recurring tasks automatically.

Cron Syntax

A user crontab entry has five schedule fields followed by the command:

* * * * * /path/to/command
- - - - -
| | | | |
| | | | +----- day of week (0-7, Sunday=0 or 7)
| | | +------- month (1-12)
| | +--------- day of month (1-31)
| +----------- hour (0-23)
+------------- minute (0-59)

Edit Your User Crontab

crontab -e

For example, run a backup every day at 02:30:

30 2 * * * /home/user/bin/backup.sh

List current entries:

crontab -l

Common Schedules

Every hour:

0 * * * * /path/to/script.sh

Every day at midnight:

0 0 * * * /path/to/daily-task.sh

Every Monday at 17:00:

0 17 * * 1 /path/to/weekly-task.sh

On the 1st and 15th of every month:

0 0 1,15 * * /path/to/task.sh

System-Wide Cron Entries

/etc/crontab and files under /etc/cron.d/ usually include an additional user field:

30 2 * * * root /usr/local/sbin/system-backup

Use distribution conventions and appropriate permissions when creating system-wide entries.

Cron Has a Minimal Environment

A command that works in your interactive shell can fail under cron because the working directory, PATH, shell, and environment variables may differ. Prefer absolute paths and set required environment variables explicitly.

PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
30 2 * * * /home/user/bin/backup.sh >> /home/user/log/backup.log 2>&1

Troubleshooting

If a job does not run:

• verify it appears in crontab -l;
• use absolute paths;
• check script permissions and the interpreter shebang;
• capture stdout and stderr to a log while debugging;
• inspect cron logs, commonly via journalctl, /var/log/syslog, or /var/log/cron depending on the distribution.

Conclusion

Cron is a simple and dependable scheduler for recurring Linux tasks. Define the schedule carefully, use explicit paths and environments, and capture errors so automated jobs remain observable.