The Linux kernel occasionally sends messages to your screen. The following is a list of some of these messages and what they mean. Frequently, these messages indicate something is wrong. Some of these messages are critical, which means the operating system (and all your programs!) stops working. When these messages occur, you should write them down and what you where doing at the time, and send them to Linus. See Section 12.2.2.
Luckily, some of these messages are merely informational--hopefully, you'll see them more often!