Limit concurrent logins to multiple desktops on LDAP Linux network?

After searching it doesn't look like LDAP or Kerberos will do this. Apparently there is no attribute for it in LDAP and there really is no way for it to work from an LDAP perspective. There's no logout from LDAP, so it would never be able to decrement the login count.

Given this, it appears that the solution will have to be ad hoc.

You'll need a service that monitors /var/run/utmp or the command w (shows users currently logged in) on each machine and reports it to a central server by some mechanism (nfs mount + text file, for example).

Then, you'll need a login script that kicks the user out if they've exceeded the limit of concurrent logins. The login script would read from the central server what the current login count is. Alternatively, you could have a service that modifies the maxlogins in /etc/security/limits.conf based on the value of the login count retrieved from the central server.

maxlogins = $total_logins - $current_logins

Basically, the most important consideration is that the users don't have permission to change the login count themselves or they could just manually change the value to allow more logins.