By any chance if you got access to root console of your friends or other machine and you quickly want to add a root hidden user you can use this script or binary or if you want to play something malicious you can use the same binary or this custom script to add a root user on target machines . Probably this script works with all debain base linux env and few red hat base env I tested the same on ubuntu 12.x,13.x,14.x,16.x,Linux mint 16,17,18 and fedora,cent os 6,7. - View it on GitHub