"Unix for Programmers and Users" by Graham Glass and King Ables. Really great book that took you through the basics of Unix, the various shells, all the way to programming with system calls, sockets etc. Even dove into filesystem design, inodes etc. All in one reasonably compact book. I love books that can explain complex stuff in few words and do it well. I got it as part of my studies and I had worked through it already by the time I got the class :)

Later he made a special edition for this newfangled "Linux" stuff :) But the one I had was for the original Unix. Linux was already around at that time but still very much beta quality. At college we mainly used HP-UX and Sequent.