Format
Min Hour Day Mon Weekday
* * * * * command to be executed
┬ ┬ ┬ ┬ ┬
│ │ │ │ └─ Weekday (0=Sun .. 6=Sat)
│ │ │ └────── Month (1..12)
│ │ └─────────── Day (1..31)
│ └──────────────── Hour (0..23)
└───────────────────── Minute (0..59)
Examples
| Expression | Meaning |
|---|---|
0 * * * * |
every hour |
*/15 * * * * |
every 15 mins |
0 */2 * * * |
every 2 hours |
0 0 * * 0 |
every Sunday midnight |
@reboot |
every reboot |
Crontab
Check crontab of a user (default=root) user:
sudo crontab -l [-u user]
Edit the crontab of the root user:
sudo crontab -e
Import new crontab:
crontab /etc/cron.d/mongodb-consistent-backup
If the cron execution is logged via syslog:
sudo less +G /var/log/cron
Or systemd journal:
sudo journalctl _COMM=cron
# or
journalctl _COMM=cron --since="date" --until="date"
cron @reboot run as startup
Tools:
- https://crontab-generator.org/