Mastering Linux Network Administration
Jay LaCroix
Asterisk: The Definitive Guide
Jim Van Meggelen & Russell Bryant & Leif Madsen
Linux iptables Pocket Reference
Gregor N. Purdy
Practical LXC and LXD
Senthil Kumaran S.
Bash Idioms: Write Powerful, Flexible, Readable Shell Scripts
Carl Albing & J P Vossen