This is one of the most forgotten steps. After you have configured or reconfigured something, it is a good idea to stop, check, and see whether it works as it should. Here is a list of suggested checks:
Check important files (such as /etc/passwd and /etc/shadow) periodically.
Check account usage data for unusual patterns (strange connection times, places, and so on).
Check newly installed systems for correct configuration. Pay special attention to security-related settings.
Categorize systems into different categories by importance (normal, high, maximum), and check whether security is appropriate for each group.
Make sure authentication and authorization work as expected, for both local and remote ...