For users, The UNIX Programming Environment by Kernighan and Pike is the book that got me going. There are a few things in there that don't exist now but it is

For users, The UNIX Programming Environment by Kernighan and Pike is the book that got me going. There are a few things in there that don't exist now but it is the most concise easy-to-read book for new *nix users. For administration the UNIX System Administration Handbook by Nemeth, Snyder, Seebass, and Hein is how I got started. Newer editions of this book cover Linux specifically.