rc script to execute command(s) when system is up or down. Note the header lines which is required to have.

sysupdown

#!/bin/bash

### BEGIN INIT INFO
# Provides:       <your service name>
# Required-Start:    $network $syslog
# Required-Stop:     $network $syslog
# Default-Start:     2 3 4 5
# Default-Stop:      0 6
# Short-Description: execute commands when system is up or down
# Description:       execute commands when system is up or down
### END INIT INFO

case "$1" in
        start)
                <do something here when system is up>
                ;;
        stop)
                <do something here when system is down>
                ;;
esac

exit 0