I'd like to conditionally disable interactive logins in ubuntu in the event that a user attempts to login to an ssh shell with an invalid username.
Say I have a user 'bob' on my server, but the user 'fred; is not a valid user.
When bob logs in with
I want an interactive login
When someone signs in with
I don't want any interactive login and the login attempt to terminate.
How can one do this in Ubuntu?