Bash Pocket Reference
Arnold Robbins
Time Management for System Administrators
Thomas A. Limoncelli
Gray Hat Hacking the Ethical Hacker's Handbook, Fourth Edition
Daniel Regalado & Shon Harris & Allen Harper & Chris Eagle & Jonathan Ness & Branko Spasojevic & Ryan Linn & Stephen Sims
Crypto101
Laurens Van Houtven
How Linux Works: What Every Superuser Should Know
Brian Ward
Ruby Under a Microscope: An Illustrated Guide to Ruby Internals
Pat Shaughnessy
Black Hat Python: Python Programming for Hackers and Pentesters
Justin Seitz
Absolute FreeBSD: The Complete Guide to FreeBSD, 2nd Edition
Michael W. Lucas
The Linux Programming Interface
Michael Kerrisk
Learn You Some Erlang for Great Good!: A Beginner's Guide
Fred Hébert
The Art of Assembly Language
Randall Hyde
The Book of PF: A No-Nonsense Guide to the OpenBSD Firewall
Peter N. M. Hansteen
The GNU Make Book
John Graham-Cumming
Android Security Internals: An In-Depth Guide to Android's Security ...
Nikolay Elenkov
Hacking VoIP: Protocols, Attacks, and Countermeasures
Himanshu Dwivedi