Booting, or "bootstrapping" for us older folk, is that deeply mysterious sequence of operations performed by your computer between the moment when you switch it on and the moment it's ready for you to log in. During this time, all kinds of incomprehensible messages scroll up the screen, but they're not something you usually take much notice of, and most linux distros cover them up with a pretty splash screen and a nice encouraging progress bar. This is all fine, of course, until it stops working. In this tutorial we'll examine the boot process in more detail, looking in particular at what can go wrong, and how to diagnose and fix the problem.