Here is a document that I wrote to have some general initial security practices for first starting off a linux server. If you are planning to run a Stake Pool, or just want to verify things, check this out (grab it below). I will add a disclaimer that it is not all encompassing, I did use information from other sites to help, and if there is any improvement you see, just message me. Places like coincashew and other awesome site have a lot of good information as well. I just wanted to formally write this up and share it out.
If you would like to verify this file is the correct file I posted, use the hash values below
sha256sum SecurityBestPractices.txt
519d5de41d800fe96b62a5f3ade8ac1f418d8d299b08772e8d7c3e2ec1b57c66 SecurityBestPractices.txt
md5sum SecurityBestPractices.txt
276fa425773894fc221017c7e668ec02 SecurityBestPractices.txt