CompTIA Linux+ Guide to Linux Certification
Jason Eckert
Linux Server Security
Chris Binnie
The Hacker Playbook 2: Practical Guide To Penetration Testing
Peter Kim
The Shellcoder's Handbook
Chris Anley & John Heasman & Felix Lindner & Gerardo Richarte
GPEN GIAC Certified Penetration Tester All-in-One Exam Guide
Raymond Nutting