who

Displays list of all users currently logged on

$ who
Username console  Oct 12 08:20
Username ttys000  Oct 20 09:35

The who utility displays a list of all users currently logged on, showing for each user the login name, tty name, the date and time of login, and hostname if not local.

Available options with examples:

-a Same as -bdlprTtu. This command processes the system database used for user information.

-b Time of last system boot.

$ who -b
reboot ~ Oct 12 8:20

-d Print dead processes. This command shows the zombie processes or processes that have already been executed.

-H Write column headings above the regular output.

-l Print system login processes (unsupported). This command shows the terminals where a user can log in.

-m Only print information about the current terminal. This is the POSIX way of saying who am i.

$ who -m
Norinlava ttys000  Oct 29 18:35

-p Print active processes spawned by launchd(8) (unsupported).

-q Quick mode: List only the names and the number of users currently logged on. When this option is used, all other options are ignored.

-r Print the current runlevel. This is meaningless on Mac OS X.

-s List only the name, line and time fields. This is the default.

-T Print a character after the user name indicating the state of the terminal line: ‘+’ if the terminal is writable; ‘-‘ if it is not; and ‘?’ if a bad line is encountered.

$ who -T
Username - console  Oct 12 08:20
Username + ttys000  Oct 20 20:04

-t Print last system clock change (unsupported).

-u Print the idle time for each user, and the associated process ID.

$ who -u
Username console  Oct 12 08:20  old  	    99
Username ttys000  Oct 20 20:04   .   	 87780

am I Returns the invoker’s real user name.

file By default, who gathers information from the file /var/run/utmpx. An alternative file may be specified.