Beginning Linux book?

[Peter Kahle]

A co-worker of mine is going on vacation and planning on bringing a
laptop with a knoppix CD (actually, I've got him set up with Knoppix,
KANOTIX, and knoppix-std) and wants to try to learn about linux. So he'd
like to get a basic linux book. Anybody know a good beginning book? He's
computer literate, and knows programming, but is pretty much a novice
when it comes to Unix.

Thanks,
P