I really would not want to mess something and not be able to log into my server box at all, so, because I have never changed the default shell, could you please indicatme precise instructions for changing the shell on a per-user basis? Or maybe point me somewhere on the internet where I can find those instructions? It is important to remind that the user that I created at install time should be allowed to log in, but just not the others.
I have found a number of posts and web pages talking about such a change on Ubuntu desktops, but not so for servers.
Your idea seems to me like a perfect solution.
Million thanks for your help.