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What free ebooks do you recommend to learn more about Ubuntu?
One book per answer, please – vote answers up/down as you feel appropriate. If you feel the book is biased towards/good for particular tasks, please mention them.
Getting Started with Ubuntu (The Ubuntu Manual)
Bash - Guide for beginners (On the command line used in Linux, PDF)
Linux - Inside the boot process (IBM manual in HTML and PDF)
Linux - Network Administration guide
And if you're a masochist, don't forget the ultimate manual for Linux: Linux - Advanced Administration (Kernel, local/network/server admin, ... 545 pages of knowledge! :-))