I don't have much to add to Vladimir Ivanovic's review, except to echo that this is an outstanding book in the style of Stevens' (and Rago's) beloved classic Advanced Programming in the UNIX Environment. I am now recommending it to my friends and colleagues over Stevens. Covers the same territory as Stevens and more, since it contains the entire Linux system call interface. The treatment of each system call is very thorough, indicating deviations from the Single UNIX Specification and comparisons with various Unix flavors.
This is not a "how to program" book, but you will definitely learn a lot about programming from it. I would recommend it to anyone who is serious about Linux/Unix programming in C, or actually in any language.