Linux Firewalls
Michael Rash
Linux Advanced Routing and Traffic Control HOWTO
Gregory Maxwell & Remco Mook & Martijn Oosterhout & Paul Schroeder & Jasper Spaans & Bert Hubert
The the Complete Metasploit Guide
Sagar Rahalkar & Nipun Jaswal
Ethical Hacker’s Penetration Testing Guide
Samir Kumar Rakshit
Bash Idioms: Write Powerful, Flexible, Readable Shell Scripts
Carl Albing & J P Vossen