The standard Unix command who displays a list of users who are currently logged into the computer.

A who command that displays the names of users logged in was first implemented within Multics.

[3] The version of who bundled in GNU coreutils was written by Joseph Arceneaux, David MacKenzie, and Michael Stone.

[4] The Single UNIX Specification (SUS) specifies that who should list information about accessible users.

The XSI extension also specifies that the data of the username, terminal, login time, process ID, and time since last activity occurred on the terminal, furthermore, an alternate system database used for user information can be specified as an optional argument to who.