Crontab -e

Create a cron task

ref:https://linuxtools-rst.readthedocs.io/zh_CN/latest/tool/crontab.html

Edit crontab

$ crontab -e

Line:

0,30 * * * *    /path/to/command

Restart cron service

$ sudo service cron reload
[ ok ] Reloading configuration files for periodic command scheduler: cron.

$ sudo service cron restart