Q. How do I block access to root user over ssh session?
A.. sshd (OpenSSH Daemon) is the daemon program for ssh. Server side ssh configuration is defined in /etc/ssh/sshd_config file.
You need to use DenyUsers option to block access to root user.
This option can be followed by a list of user name patterns, separated by spaces. Login is disallowed for user names that match one of the patterns. Only user names are valid; a numerical user ID is not recognized. By default, login is allowed for all users. If the pattern takes the form USER@HOST then USER and HOST are separately checked, restricting logins to particular users from particular hosts.
Open /etc/ssh/sshd_config file
Use vi command:
# vi /etc/ssh/sshd_config
Deny root user access
Append or modify as follows to block root user:
If you want to block additional user just append names to DenyUsers
DenyUsers root, user2, user3
Save and close the file. Restart sshd service: