It’s rather easy to run a command or a script on boot without going through the full Sys V style init stuff. /etc/rc.local is executed after the init scripts on boot, but unlike BSD, Linux doesn’t have a rc.shutdown.

So how can we execute a command on shutdown? Usually, /etc/init.d/halt is used for shutting down, which calls /sbin/halt.local (if it exists). So we simply add our commands to /sbin/halt.local:

# echo "YOUR_COMMAND" >> /sbin/halt.local

Note that if the file does not exist, you have to add a shebang (e.g. #!/bin/sh) and make it executable (chmod +x /sbin/halt.local)