Everyone knows that crontab entries look like this:
* * * * * /usr/local/bin/my-script
Which will execute command “my-script” every minute.
There are other specific entries that can prove useful: @annually, @monthly, @daily, @midnight and the best of them all @reboot.
This will execute command “my-script” every time system starts (reboot or shutdown) with environment variables, ownership and permissions of the user with this crontab entry.