It’s not often that a simple comic will make me laugh for several minutes, but I thought this one was great.
I found it at http://www.redhat.com/magazine/025nov06/features/gifts/xkcd.jpg
“sudo” is Linux program that allows regular users to execute certain commands as root. Often, when working as a non-root user, you will type one command, and it complain that you need to be root to run it. You would then quickly add “sudo” to the beginning of the command and execute it again, this time running as root, and the command will run successfully.