Michael W. Lucas wrote a new edition to his Absolute OpenBSD book, and that second edition was published relatively recently. It’s a hefty book, nearly 500 pages in length, and I’ve needed to write a review for some time now. Not-necessarily-relevant-disclaimer: I contributed the IPv6 haiku/joke at the start of Chapter 12.
If you’re interested in OpenBSD, it’s an obvious purchase. It goes into detail for all aspects of OpenBSD, starting with a very detailed conversation about installation, then disk setup, and so on. This is not going to surprise anyone, of course. Past the initial overview, the book starts with a chapter that talks about nothing else but locating other resources to help learn OpenBSD. It seems a little counter-intuitive to start a book with advice on how to look somewhere else, but it makes sense in light of the topic.
What if you aren’t using OpenBSD, at least not right now? Something I didn’t realize until I had chewed my way through most of the book was that there’s several smaller books hidden inside. The book goes very far into individual utilities. So far, in fact, that it ends up creating mini-guides about the topics within the chapters. (or entire chapters, in the case of pf.)
There’s in fact 2 chapters for pf, initial and advanced. TCP/IP gets close to 30 pages just to itself, and topics like snmpd or chroot get an introductory section that assumes nothing about your prior knowledge. These are technologies you’re using already, no matter which BSD flavor you’re dealing with.
It works as a reference. I’m going to show the aforementioned chapter 11, on TCP/IP, to my coworker who makes a confused face every time I say “link-layer protocol.” I don’t know if he’ll make it from one end to the other, but it’s a lot better than waving a hand in the air and mumbling “You should look that up on the Internet sometime.” There’s enough detail that some of the smaller sections could probably be broken out into individual books, and I daresay that’s what is happening with Lucas’s Mastery series.
It’s comprehensive, it’s readable, and you’ll find something useful in it no matter your experience level. The book is available in printed and eBook form, from the usual online stores linked at Michael W. Lucas’s site, or directly from the publisher. It’s also available through the OpenBSD Project, which then gets a cut towards development.