Been wanting to mess around with pen testing sort of stuff for a while now with a possible look to trying to make a career from it in the future. So far I have got two books Grey Hat Hacking and Professional Penetration Testing.. one more to get a basic intro to the theory and one hopefully for more practical stuff. However though, there is one big gap in my knowledge which needs sorting.. LINUX!

All my life I've unfortunately been confined to Windows for convenience as I'm completely new to anything other than Windows. My friend lent me a book on Ubuntu but tbh it's aimed at complete computer novices so isn't of much use.

What books would people recommend to give me a solid foundation in Linux while at the same time allowing me to expand further on various areas if I so choose?  I guess I'll be getting Backtrack for pentesting and so far have a copy of Ubuntu I'm messing around with on my older computer so don't know how much those will effect book choices.

So far the two books I'm looking at are Linux command line and shell scriptiong bible and Backtrack 4 assuring security through penetration testing. Are both good choices? Is it even worth getting the Backtrack 4 book when Backtrack 5 is out? 

The books I like for learning are:
Running Linux
Linux System Administration
Linux in a Nutshell
and
Unix and Linux System Administration Handbook

really learn the CLI, build a vm without a gui attached. Ubuntu Server LTS, Debian, CentOS (you'll have to set it up that way).

And this happens to be one of my biggest pet peeves for someone looking to learn especially in this arena (security). The issue with "support" when learning in this environment is that the learner will learn to skip truly learning as support is readily available. That type of reliance is a moot point when faced with making mission critical and time sensitive decisions in the real world.

I think someone learning Linux should learn as much as they can by trial and error. You WILL NOT HAVE books in the field when performing penetration testing in say a client's environment. So the best bet is to aim to learn it as best as one can understand it on their own accord. Avoid using package managers (yum, YaST, apt-get, pkg_add) and configure things from scratch. Get used to the commands, get used to trouble shooting based on what you see. Imagine NOT being able to connect to a support forum. What then?

Linux, BSD, Solaris, etc., are not difficult at all and too many people have used forums as a form of crutch. We all use forums but its better to learn it from the ground up. Make scenarios for yourself and understand what you are doing. E.g. week one create your own webserver. Do this without package managers. Week 2, make it a virtual hosting server (multiple domains), following week, add email, next add say monitoring. And so on and so on.

Get used to doing things on your own by setting up tasks. you end up familiarizing yourself with tips and tricks not often found in books and your reliance on forums and or books will diminish as experience grows

@sil
For the most part I agree, but with ebook readers / tablets / laptops, and ebook versions, you may have the book with you.

However the books I recommended, if you read through them, you'll get an understanding not a cookie cutter approach (at east that was true with the last versions I read).

I could have recommend the Hacks series, but those are more reference on a regular basis book.

I agree though, people who want to learn linux need to get their hands dirty.

Wanted to throw this one out there (Linux Administration: A Beginner's Guide).
You can read about it here -->> http://www.linuxinsider.com/rsstory/74933.html
The writer assumes that the reader have a familiarity with Windows Servers.
I've added this one to my Amazon wish list.
Happy reading.