Thank you all!
@ryecoaaron: I've created/lib/systemd/system/COPS.service
However, my machine runs OMV 2: perhaps that's why
systemctl enable COPS.service
returns
-bash: systemctl: command not found
I can put your script in /etc/init.d/ folder, and then automate it with update-rc.d?
I've read something similar in Debian documentation...
In the meantime, I try the solution proposed by @macom