Disable/Ban certain users to connect from ssh

Generally after turning on the sshd service on our machines, we fail to authorize or rather restrict a set of users only to access (white-listing) the machine. The following setting in sshd_config helps you to restrict access to a select few users. The settings will take effect after restarting the sshd demon on your machine if already running.

[parag@paragcentos:/home/parag]sudo cat /etc/ssh/sshd_config  | grep -i Allow
...
##Allow the following users only to remote via ssh
AllowUsers root parag
...
...
[parag@paragcentos:/home/parag]

Also please read this post on more tips on how to secure your ssh server.