Linux.com - https://www.linux.com/news/how-set-two-factor-authentication-linux
If you’re a Linux administrator and looking to lock down your Linux servers and desktops as tight as possible, you owe it to yourself to make use of two-factor authentication. This should be considered as “no-brainer” as they come. Why? Because by adding two-factor authentication, it becomes exponentially more difficult for malicious users to gain access to your machines. With Linux, it is possible to set up a machine so that you cannot log into the console or desktop or by way of secure shell, without having the two-factor authentication code associated with that machine.