When I first started learning FreeBSD I picked up Michael Lucas’s book named “Absolute FreeBSD” which is a great read. This book tells about lots of FreeBSD internals and touches on some interesting topics you wouldn’t find easily. He is also the author of a couple of other books and the latest one is “Network Flow Analysis” which is about Netflow and how we can use open source tools to collect, view, and analyze NetFlow data from our network devices without using commercial tools. I have put it in my reading queue! Sounds a good book with unique info I assume!
If you are curious to meet this guy check this out: “BSD Needs Books“