SSH warning banners and welcome messages are necessary when organization wishes to prosecute an unauthorized user or just give out some information or announcement.
Display SSH Warning Message BEFORE the Login
Pre login SSH warning banner shows before the password prompt, during an interactive session using SSH. It usually uses for legal warnings to establish the terms and conditions by which someone is allowed to use the system.
The SSH warning messages are commonly located in the files ‘/etc/issue’ and ‘/etc/issue.net’, but you can also use your custom file like ‘/etc/ssh/sshd-banner’. The content of the specified file is sent to the remote user before authentication.
Create an SSH login banner file:
$ vi /etc/ssh/sshd-banner
Append some Warning text:
WARNING: Unauthorized access to this system is forbidden and will be prosecuted by law. By accessing this system, you agree that your actions may be monitored if unauthorized usage is suspected.
Open the sshd_config file:
$ vi /etc/ssh/sshd_config
Edit the path to the banner file:
Save the file and reload the sshd:
$ service sshd reload
Display SSH Welcome Message AFTER the Login
The content of the file ‘/etc/motd’ is displayed after successful authentication, but just before the shell. It is used for system announcements and other important information, that you want authenticated users to know about before they start using the system.
Edit the file ‘/etc/motd’:
$ vi /etc/motd
Place the announcement message and save the file.
Now this message will be shown after the successful authentication through SSH.