Linux Firewalls

This is undoubtedly the best introductory security book I've read. Note that I specifically didn't say "best introductory Linux security book". Yes, the focus is on Linux, and the packet filter examples are all ipchains, but more than 99% of the advice and explanation here applies to any Unix system, and if your aim is to understand why and how you are filtering rather than just blindly typing in someone else's rules, this is the book.

This is a practical book: there are detailed explanations and specific examples given for the typical situations facing anyone with Internet access. More importantly, there are complete explanations of just about every service likely to be available on a Unix box, and the security implications of each.

As with several recent books, I note that at least one Amazon reviewer complained about typos. I noticed one, and that was just a pluralization in a context that should have been singular- hardly disturbing.