Dissagree (Score 5, Informative)

No, I dissagree. Essential System Administration, 3rd Edition is an excellent book, As is the one by Nemeth/Snyder et all. Both do a superb job of showing you what you need in the Unix world. I'd recommend that you get both, actually, as each has its strong and week points.

However both do a very cursory overview of security measures, if you ask me. While both are great for an administration standpont (and that's their goal, of course) much more is needed on the security front.

I'd suggest getting a copy of Hacking Linux Exposed (good for all Unix operating systems) and Building Secure Servers with Linux (more Linux specific, but still has some good any-unix tips and tricks.) These will help round out your administration bookshelf.