C++ Crash Course
Josh Lospinoso
SSH Mastery: OpenSSH, PuTTY, Tunnels and Keys
Michael W Lucas
Bash Scripting
Moaml Mohmmed & Max Beerbohm
Electronics for Beginners
Jonathan Bartlett
sed & awk
Dale Dougherty & Arnold Robbins
Linux iptables Pocket Reference
Gregor N. Purdy
Effective DevOps
Jennifer Davis & Ryn Daniels