Mastering SSH
The thing about managing Linux servers is that you'll rarely use them directly on the machine.
Almost all the time, your Linux server runs on another machine and you connect to it remotely.
The defacto tool to connect to a remote Linux server is SSH, standing for Secure Shell.
This section of Linux Handbook collects numerous tips and tutorials on SSH. You'll learn to configure SSH, connect to it and then learn other tips on securing SSH, using key based authentication.
There are also some advanced SSH tips that will take your SSH skills to the ninja level.
Creator of Linux Handbook and It's FOSS. An ardent Linux user & open source promoter. Huge fan of classic detective mysteries from Agatha Christie and Sherlock Holmes to Columbo & Ellery Queen.