Reddit mentions of Introduction to Unix and Linux

I wouldn't recommend starting off with metasploit, what you want to do is learn the basics on linux, I would recommend this book: http://www.amazon.com/Introduction-Unix-Linux-John-Muster/dp/0072226951

After that, learn some info sec theories (boring, but important if you want to make a career out of it.)

these two books are what I used: http://www.amazon.com/Computer-Security-Fundamentals-William-Easttom/dp/0131711296

http://www.amazon.com/Information-Security-Principles-Mark-Merkow/dp/0131547291/ref=pd_sim_b_2

The first book is mostly intro to basic concepts such as port scanning, firewalls, networking, etc. the second is info sec theories

This would most likely be your next book to buy, its a little more advanced, and has some challenging content in it.

http://www.amazon.com/Analyzing-Computer-Security-Vulnerability-Countermeasure/dp/0132789469

Finally grab this bad boy http://www.amazon.com/Metasploit-The-Penetration-Testers-Guide/dp/159327288X

you should have some decent knowledge about network security by then.