Terug naar DocumentatieCron jobs allow you to execute commands or scripts automatically based on a defined schedule. They are used for backups, cleanup, updates, sending emails and much more.
Modify the crontab
Each user has their own crontab. To modify it:
crontab -e
The first time it will ask which editor to use (choose nano if unsure).
To view active cron jobs:
crontab -l
To delete all cron jobs:
crontab -r
Crontab syntax
# ┌───────── minute (0-59)
# │ ┌───────── hour (0-23)
# │ │ ┌───────── day of month (1-31)
# │ │ │ ┌───────── month (1-12)
# │ │ │ │ ┌───────── day of week (0=Sunday, 6=Saturday)
# │ │ │ │ │
# * * * * * command
Practical examples
# Every minute
# Every hour (at minute 0)
0 * * * * /path/script.sh
# Every day at 03:00
0 3 * * * /path/script.sh
# Every Monday at 08:30
30 8 * * 1 /path/script.sh
# First of the month at midnight
0 0 1 * * /path/script.sh
# Every 5 minutes
*/5 * * * * /path/script.sh
# Every 6 hours
0 */6 * * * /path/script.sh
# Monday-Friday at 09:00
0 9 * * 1-5 /path/script.sh
- /path/script.sh
Real-world usage examples
Database backup every night at 02:00
0 2 * * * mysqldump -u root -pPASSWORD database > /backups/db_$(date +\%Y\%m\%d).sql
Clean up logs every Sunday
0 4 * * 0 journalctl --vacuum-time=30d
Automatic SSL renewal
0 3 * * * certbot renew --quiet
Synchronize with rsync every hour
0 * * * * rsync -az /var/www/ backup@IP_BACKUP:/backups/www/
Automatically restart a service if down
*/5 * * * * systemctl is-active --quiet nginx || systemctl restart nginx
Save the output of cron jobs
By default cron job output is sent via email to the system user. To save it to a file:
# Save stdout and stderr to file
0 3 * * * /path/script.sh >> /var/log/my-cron.log 2>&1
# Discard all output
0 3 * * * /path/script.sh > /dev/null 2>&1
System crontab
Besides user crontab, you can use files in /etc/cron.d/ or these directories:
Just put an executable script in these directories:
nano /etc/cron.daily/my-backup
chmod +x /etc/cron.daily/my-backup
- /etc/cron.hourly/: scripts run every hour
- /etc/cron.daily/: scripts run every day
- /etc/cron.weekly/: scripts run every week
- /etc/cron.monthly/: scripts run every month
Verify that cron works
# See cron logs (Debian/Ubuntu)
grep CRON /var/log/syslog | tail -20
# With journald
journalctl -u cron -n 20
# Verify the service is active
systemctl status cron # Debian/Ubuntu
systemctl status crond # CentOS/AlmaLinux
Online tool to generate cron
If you don't remember the syntax, use crontab.guru to generate and verify cron expressions visually.
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