There are nine basic measures that must be taken to make sure that servers are secure from unauthorized access or intercepted communications

There are nine basic measures that must be taken to make sure that servers are secure from
unauthorized access or intercepted communications:
1. Use secure and encrypted communication.
2. Disable root login and use sudo.
3. Remove unused software, open only required ports.
4. Update the OS and installed software.
5. Use a properly-configured firewall.
6. Make sure log files are populated and rotated.
7. Monitor logins and block suspect IP addresses.
8. Use SELinux (Security-Enhanced Linux).