who - who is on the system
who [ who-file ] [ am I ]
Who, without an argument, lists the login name, terminal name, and login time for each
current UNIX user.
Without an argument, who examines the /etc/utmp file to obtain its information. If a file
is given, that file is examined. Typically the given file will be /usr/adm/wtmp, which
contains a record of all the logins since it was created. Then who lists logins, logouts,
and crashes since the creation of the wtmp file. Each login is listed with user name,
terminal name (with `/dev/' suppressed), and date and time. When an argument is given,
logouts produce a similar line without a user name. Reboots produce a line with `x' in
the place of the device name, and a fossil time indicative of when the system went down.
With two arguments, as in `who am I' (and also `who are you'), who tells who you are
logged in as.