The idea is very simple you want to limit who can use sshd based on a list of users. The text file contains a list of users that may not log in (or allowed to log in) using the SSH server. This is used for improving security.

 

 

 

PAM (Pluggable authentication modules) allows you to define flexible mechanism for authenticating users. My previous post demonstrated how to deny or allow users using sshd configuration option. However, if you want to block or deny a large number of users, use PAM configuration.

A note for new sys admins

1. Backup all data and PAM configuration files before any modification