Anyone, could you tell me the best book for linux reference?
Nobody can say what is the "best" book since that depends on personal preference, and importantly what you actually want to do. What do you mean by "Linux reference"---command line reference? X/GNOME/KDE reference? Programming guide? There are so many possibilities...
If it's a CLI reference you're after, have you tried "man" that ships with every Linux distro? Just run "man COMMAND" for a given COMMAND name and it'll describe the command in a lot of detail. "info COMMAND" sometimes has even more information. I find Google very useful for discovering new commands too, as there is usually something new to discover out there. Just search for whatever it is you're trying to do, and tack "Linux" or "Unix" on the end.
Charles Lyons (SCJP 1.4, April 2003; SCJP 5, Dec 2006; SCWCD 1.4b, April 2004)
Author of OCEJWCD Study Companion for Oracle Exam 1Z0-899 (ISBN 0955160340 / AmazonAmazon UK )
You should narrow down which distribution of Linux you are using. Different distros will do things differently. Books get outdated pretty quickly. I use online resources pretty exclusively (except for man. Got to use man). I've found the Linux Documentation Project to be pretty helpful for general Linux info. You should also become familiar with your distribution's on-line documentation and help forums. For example, the ubuntu documentation and forums. They will be the most up-to-date resource.
If you are looking for a reference for Linux CLI, I recommend A Practical Guide to Linux Commands, Editors, and Shell Programming by Sobell. Most of this information is distro agnostic. I find man pages to be poorly written and no place to learn how to use the command. Once you have the basics of a command, they become useful. If you don't know the name of the command, man pages are useless. This books helps you find what you need quickly. The shell programming section is invaluable as well.
Everything in this book can be found online, but I prefer having everything in a well written book, than having to waste time searching the Internet for poorly written guides.
"Computer science is no more about computers than astronomy is about telescopes" - Edsger Dijkstra