Disable multiple login[FC or *NIX]?

[Deepak Shrestha]

Hi,

Is there a way to limit the particular user login only once in FC (or
*nix)??or disabling the double logins. Currently a user can log in
from different terminals using same account at same time and do
various things. I have tried also Putty and able to login using same
login name from windows machines. This is good for troubleshooting
purposes like when situation goes wrong, user can log in from
different terminal and fix it, but this also brings the anomali of two
persons being present at the different place at the same time.

I guess this is not an concern for desktop users but exposing as
server might need considering this. At present my question is more on
a curiosity than of practical use.

Thanks!