The ssh server configuration file in most Linux distribution is located at: /etc/ssh/sshd_config
Note: The client system-wide configuration is located at /etc/ssh/ssh_config
1. Change the ssh port
Open sshd_config with an editor and uncomment and change this line:
#Port 22
Change the number to a different port you'd like to use.
2. Restrict root access.
Note: Some UNIX based OS's like solaris, openindiana, opensolaris, and the BSD's disable root access by default.
Uncomment this line and change its attribute to "no"
#PermitRootLogin yes
3. Allow only specific users
If you want to allow only user1 and user2 to access the server via ssh, add this line to sshd_config
AllowUsers user1 user2
Ssh needs to be restarted for any changes to take effect.