WHO(1) General Commands Manual WHO(1)
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.