Here is description of program/utility to display the currently logged in user in a Linux box (tried on Fedora 13 Goddard):
Whowatch is an interactive console utility that displays informations about the users currently logged on to the machine, in real time. Besides standard information (login, tty, host, user\’s process) you can see type of login (ie. ssh, telnet). You can also see selected user\’s processes tree or all system processes tree. In the process tree mode there is ability to send INT or KILL signal to selected process.