Ubuntu – How to enable the pc power button at the lock screen

The number of processes should not be different. You have to remember when counting the pids to include the script itself and the subprocess created.

I created the following that should work for your requirements. You should alter the timeout depending on how quickly you want the multiple button presses.

#!/bin/sh
# /etc/acpi/powerbtn.sh
# Initiates a shutdown when the power putton has been
# pressed.

timeout=0.8
pid_count=$(pidof -x powerbtn.sh | wc -w)

( if [ $pid_count -eq 4 ]; then
        sleep $timeout
        /etc/acpi/sleep.sh
    else
        sleep $timeout
        pid_count_now=$(pidof -x powerbtn.sh | wc -w)
        if [ $pid_count_now -eq 2 ] && [ $pid_count -eq 2 ]; then
            poweroff
        fi
        exit
    fi
) &

You can use next command in terminal:

sudo chmod -x /sbin/shutdown

If you want to re-enable, use +x instead -x in the same command.

Anyway, by holding the power button down for several seconds the above solution will not work and I don't think that you will find a software solution for this case.