Not sure if this is a security or networking issue, but here goes:

We have a number of Redhat 7.3 Linux PC's on our network.
Until now, they have only been used via remote logins from Sun Workstations for the purpose of distributed processing.

Therefore until now, the only login on the actual console has only ever been with root.

Now, due to a change of requirements, the Linux PC's have been deployed on desktops and the users require local logins.

However, the Redhat Login screen on each PC will not allow this - the screen simply blinks and returns to the login prompt for anything but root. No errors are logged in the message file.

If we do log in as root, we can easily use the su command to change to any other account - but why can we not do this from the initial console login?

You do have regular users already added to the system or not?
login as root first and then type login and it should prompt for username/password. try that and see if it will let you login as a regular user.

I just tried that - I logged into the console as root then I launched a new shell and typed "login".

The shell just dies immediately.

Is the user information stored locally, or is it retrieved from a remote database such as NIS or LDAP? If the latter, you want to verify that those settings are correct. For instance. most NIS hosts keep root in the local passwd file (so it can log on in case of a network outage) but get all other user info from NIS.

Our main server (Sun) holds the NIS info.

I am starting to suspect that it may be a permissions problem - however, it's strange that we can rlogin and rsh fine on Linux.

My first suspicion is that in converting these machines to desktops you somehow broke the NIS configuration, which would explain why user logins fail but root can login OK. You might also want to make sure that the permissions on /bin/login are correct or that there isn't something weird going on with PAM. It might help to make a list of what all you've changed moving these from cluster to desktop usage. Or, maybe whoever set up the cluster denied normal users the ability to login from console thinking that it would never be needed. I *think* there are ways to do this through PAM, so it may be an avenue to explore.

I think we figured out the problem.

The user accounts are hosted on a Sun server and each user has a rather complex login script used for setting up their environment and so forth.

It would seem that on Linux certain commands in that script are conflicting with the KDE startup - my systems administrator is currently probing this deeper to create a workaround...

If we succeed, I will post the deatils.

Thanks for everyone's help!