who

Display the username, line, and time of all currently logged-in sessions

$ who

$ who [[-a|--all]]

$ who [[-aH|--all --heading]]

who [options] [file]

-a, --all
    Print all information

-b, --boot
    Time of last system boot

-H, --heading
    Print column headers

-q, --count
    All login names and count

-r, --runlevel
    Print current runlevel

-u, --users
    List users logged in

am i
    Print info about current user

who displays information about users currently logged into the system. It shows usernames, terminal lines, login times, and remote hosts. who reads the utmp file to get login information.

Shows terminal sessions, may not include all remote sessions. Information comes from utmp/wtmp files.

w(1), users(1), last(1), whoami(1), finger(1)