5.6. Who else is on? What are people doing?
5.6.1. who
If you want to shut the computer down, communicate quickly with a
friend, or are worried about intruders logging on as root, you might
want a list of all users logged on to your machine. The who
command will print such a list. In its simplest form, who prints a
user's name once for every time that user is logged in (so that one
user may have many entries), along with the session's tty
(without the /dev/ path prefixed) and the date the session
began. Since it reports the date, who can be useful for checking
on runaway sessions.
5.6.2. w
Some Unix systems provide another command, w, that can be used to list
not only users, but the processes they are running. Each user
may be listed several times, once per process. w also lists
statistics about CPU usage. w is especially useful for
tracking down so-called zombie processes--ones that persist
even after they should have died--and killing them by hand.