The book that I recommended is free, you can save it to your hard drive.
If you don't like that book, here's where you can find more resources:
http://www.lpi.org/exam-preparation
The official LPI site, you can find books under "Books", and the book that I recommended is under "Free Study Resources" . There are other free books there, but the one that I recommended is my favorite because it's not purely technicial, it also touches on the history of linux and linux distros, and it talks about open source and free software. Like I've said, the exercises are really fun, they aren't dry, and some not even technical at all.
As far as other books go, I cannot recommend any, sorry. I haven't finished reading all the free books yet :)
EDIT: Forgot to mention this, I don't know if you are aware of this, but linux is just the kernel (the part of the operating system that communicates with the hardware), and when it was first released, it was released together with the GNU operating system, which was missing the kernel at the time (now they have developed their own microkernel, Hurd). I recommend you take a look at their website, especially the philosphy section.
https://gnu.org/
You should also watch one of Richard Stallman's videos:
http://audio-video.gnu.org/video/
I'm not suggesting this because I agree or disagree with Richard Stallman, I'm recommending it because his views (and the views of the Free Software Foundation) are interesting, and people should be aware of them if only because, historically speaking, GNU is a very important part of linux.