Installing and configuring SSH on Ubuntu server (If you haven't done it during installation)
If you haven't installed SSH yet, do it now:
sudo apt-get install openssh-server
Now, edit your /etc/ssh/sshd_config file Set a list of users who can login
AllowUsers user1 user2
or deny users
DenyUsers user3 user4
Display a banner to the user:
Banner /etc/issue.net
If you want to display the same banner as to users logging in on a local console
Banner /etc/issue
To edit the banner itself:
sudo vim /etc/issue.net
And restart the ssh server
sudo service ssh restart
To secure you server, disable password authentication and use SSH keys to authenticate users instead
PasswordAuthentication no