In addition to all the really great advice already submitted, I really like using Lynis[0] for scanning my servers to get an idea of obvious vulnerabilities and

In addition to all the really great advice already submitted, I really like using Lynis[0] for scanning my servers to get an idea of obvious vulnerabilities and a baseline for hardening ssh. It's absolutely not a substitute for a security expert, but in about 10 minutes of setup you can get an idea of what action items you need to add to the top of your queue. [0] https://cisofy.com/lynis/ https://cisofy.com/lynis/