Securing Linux at the OS Level

Recap:

Linux often enters organizations due to applications that run on it.
It is not uncommon for those servers to be neglected from patching and proper permissions. This increases an organization's attack surface.
Encrypting the server disks is recommended for all servers.
Disable root SSH access.
No 777 permissions!
Just like with Windows Services, evaluate if there are any Daemons that can be disabled.
Linux Permissions work similar to windows, practice the Principle of Least Privilege after performing an audit of existing permissions.

Daemons: are a small computer program that runs as a background process, rather than being under the direct control of an interactive user.
777 Permissions: Is a level of Linux permissions that means making the file readable, writable, and executable by everyone.

systemctl list-units --type service --all

Use the command above to evaluate the services or daemons that are running on CentOS.