who command. It will show you the username and the terminal/pseudo terminal that they are using, as well as what time they logged in:
migs pts/0 2012-02-15 17:46 (:0)
migs pts/1 2012-02-15 17:46 (:0)
migs pts/2 2012-02-15 17:48 (:0)
Mine shows three instances of me because I've got two terminal windows open, plus my log-in to the box.
You could also use the
last command. This will show the most recently logged in people, as well as currently logged in users.
migs pts/2 :0 Wed Feb 15 17:48 still logged in
migs pts/1 :0 Wed Feb 15 17:46 still logged in
migs pts/0 :0 Wed Feb 15 17:46 still logged in