Command to execute on Debian shutdown (Piggybacking on existing service?)

Operating Systems & Open Source
1

I would like to execute some simple commands during the shutdown of a Debian desktop. I have 2 external drives that get power through an external USB power adapter, and they will not spin down after a normal shutdown of the desktop.

I know I should read up on systemd, but is there a service that gets executed on shutdown that I can piggyback on, with my commands? Not the cleanest solution, but probably easier for me at this point.

The commands will be to spin down the disks, after exporting the zpool that they carry

2

bash script would be the easiest i think

#!/bin/bash
'command to spin down disk'
shutdown now

set it executable and then anytime you need to shutdown use it. can be used through Cron or anything.