Recommended Books
The following books are from my own personal library of books I've read and keep using as reference books, I highly recommend them to anyone interested in learning more on the following topics:
Unix Network Programming, Volume 1: The Sockets Networking API (3rd Edition) (Addison-Wesley Professional Computing Series)
I like this book because of its original content and complete information how to build real client-server applications from the ground up in a Unix environment. A bit hard to read from start to end but once you understand some fundamentals you will appreciate its layout.
Linux Administration Handbook (2nd Edition)
This has to be my all time favourite book to read since it deals directly with Linux Administration, its a must have book for anyone looking to become a system administrator or wants to brush up their skills. Its a joy to read, very useful for me as it helps me in my day to day tasks to run my server.
Running Linux
Another great book in my collection since its more of a generic catch-all Linux book, meaning it covers a lot of topics giving you a taste of what Linux is and some of the things it can do. Great if you want an overview of Linux with a good understanding of its main applications.
C Programming Language (2nd Edition) (Prentice Hall Software)
As a C language fan this is a must have book for understanding basic and intermediate programming concepts of the C language. As you probably know, Linux was developed in C so any application you write in C are closely tied to the Operating System itself.