LPI Linux Certification in a Nutshell

One of the better reference books out there is the "LPI Linux Certification in a Nutshell"by Jeffrey Dean. The book is broken into two parts to match up with each test. At the end of each section is a test which can be used to judge how well prepared you are for the actual test. The first section is broken into 5 sections as follows: Gnu and Unix Commands; Devices, Linux Filesystems, and the Filesystem Hierarchy Standard; Boot, Initialization, Shutdown, and Runlevels; Documentation; and Administrative Tasks.
The second half of the book is broken into 9 sections: Hardware and Architecture; Linux Instalation and Package Management; Kernel; Text-Editing, Processing, and Printing; Shells, Scripting, Programming, and Compiling; X; Network Fundamentals;Network Services; and Security.

Anyone going for certification through the LPI should spend some time going through this book even if it's borrowed from the Library mostly because after you have your certification most certification books sit on a far back shelf.