Auditing and checking your server to ensure that it is compliant based on your configuration and also ensuring total security is key. Many administrators get locked up with working on day to day tasks that sometimes this very important task goes undone. Here are some tools that can help automate auditing and also provide monitoring of your Linux systems.
NIX auditor is another awsome tool that is geared towards RHEL but also works on Ubuntu and other systems NIX auditor again checks the basics such as password aging and accounts as well as file systems.
I have personally used this tool and I really like it here is some sample output
The setup is pretty simple to visit their project @ https://github.com/XalfiE/Nix-Auditor
Lynis is a very well designed tool that supports nearly all versions of Linux. The developer is very approachable and very active on social media this tool includes an online dashboard. It also allows you to check your servers against a policy such as HIPPA. Check my video below on this tool this is another tool I have personally used and love. There is a free edition and a paid for edition this is another tool that is very simple to install. check out the Cisofy page @ https://cisofy.com/
Tripwire is another must have Tripwire checks the integrity of your file system and checks for changes that are not authorized. During your initial setup, you use tripwire to generate a profile of your file systems and which are in use and what you want to monitor. After that it monitors and sends you reports based on what has been changed of course there are many other features to Tripwire. You can customize it to do all sorts of things check my video below on how to install tripwire
Tiger is an open-source Linux auditing system that will check your system based on a template it will check basic things like active accounts and filesystems. It will also check for file system permissions and check for password strength also it will highlight things like aging policies for account
to install tiger on your system run the following
sudo apt-get install tiger
Check out the projects page @ https://www.openhub.net/p/tiger
UPDATE : While checking the last update of Tiger the last update I see is back in February
because of this I have bumped it down my list as auditing tools and techniques should be up to date as much as possible
see my video on how to install Tiger