Absolute FreeBSD, 3rd Edition: The Complete Guide to FreeBSD

FreeBSD Mastery: ZFS (IT Mastery) (Volume 7)

FreeBSD Mastery: Jails (IT Mastery)

SSH Mastery: OpenSSH, PuTTY, Tunnels and Keys (IT Mastery) (Volume 12)

The Design and Implementation of the FreeBSD Operating System (2nd Edition)

FreeBSD Mastery: Advanced ZFS (IT Mastery) (Volume 9)

Absolute OpenBSD: Unix for the Practical Paranoid

UNIX and Linux System Administration Handbook (5th Edition)

The Book of PF: A No-Nonsense Guide to the OpenBSD Firewall

FreeBSD Device Drivers: A Guide for the Intrepid

How Linux Works, 2nd Edition: What Every Superuser Should Know