So, you have a directory full of super-secret files that only a very few people need to see, and you want to know when unauthorized people try to see them. Or, maybe you want to see when a certain file gets changed, or you want to see when people log into the system and what they're doing once they do log in. For all this and more, you have the auditd system. It's a really cool system, and I think that you'll like it.
One of the beauties of auditd is that it works at the Linux kernel level, rather than at the user-mode level. This makes it much harder for attackers to subvert.
On Red Hat-type systems, auditd comes installed and enabled by default. So, you'll find it already there on your CentOS machine. On Ubuntu, it won't be installed, so you'll have to do it yourself:
sudo apt install auditd
On Ubuntu, you can control...