Help on user login restrictions

[dud]

I want to prevent some logins in my linux box. I have some users that I do not want to log in directly to the box (only "su user" after logged in).
How can I do that?
I cannot change the user shell to /dev/null ´cause then I cannot su to it...
How can I restrict some users login in my Linux Box?

[X_console]

Perhaps you could tell us what you're trying to do exactly? Like, what is the purpose for doing this? Because I can think of a few ways. One is to remove or change the user's password, but I don't know if your users need to access a service that reads the /etc/passwd file for them to be able to login. Please provide more information.

[dud]

I have some privileged users on my system, and I don´t want anyone to log in with those users. The box has a lot of "real" users, people that I can identify. So I want to log when those "real" ppl make a su to anyone of those privileged users.
How can I deny directly login to those privileged users?
(I want to deny EVERY access, like any service (telnet, ftp, ssh))
Thanks in Advance.

[dud]

Hey X_Console, there is no way to do it?