I prefer LASG from Kurt Seifried, also after reading maximum linux security.
Thanks.
LASG is free and writes about the most important topics/basics. Why would you pay for a book if there's an alternative book which is also free?
Some books are worth buying because the online docs suck ass, or the book is so incredibly good (like say DNS&BIND from oreilly, that book is a must have). Having said that the LASG is out of date (I haven't worked on it in ages). The LSKB is it's replacement. It's all DocumentGPL licensed, contributors are welcome. I'm almost done hacking up content into articles and dumping it into the LSKB, once that's done I'll be adding more original content, tidying up existing content, etc.
That saves money you can spend on other books ;)
Or beer.
Kind regards, S.G. Zijl
-Kurt