I never pass up an opportunity to recommend the Cyber Plumber's Handbook: https://github.com/opsdisk/the_cyber_plumbers_handbook

Goes over similar content as TFA, in perhaps a little more depth. Indispensable sysadmin knowledge.

Appreciate the mention wbadart!

Not mentioning the ssh -w option in that book should be a crime.

so good, I learn new things.