CyBOK
Awais Rashid & Howard Chivers & George Danezis & Emil Lupu & Andrew Martin
Pluggable Authentication Modules
Kenneth Geisshirt
Linux Networking Cookbook
Carla Schroder
Mastering Linux Administration
Alexandru Calcatinge & Julian Balog
Bash Idioms: Write Powerful, Flexible, Readable Shell Scripts
Carl Albing & J P Vossen