Who (Unix)
The standard Unix command
who displays a list of users who are currently logged into the computer.The
who command is related to the command, which provides the same information but also displays additional data and statistics.History
A command that displays the names of users logged in was first implemented for the CTSS operating system by Noel Morris in 1965. This inspired Tom Van Vleck to write a Multics version. Later, it appeared in Version 1 Unix and became part of the X/Open Portability Guide since issue 2 of 1987. It was inherited by the first version of POSIX.1 and the Single Unix Specification.The existence of presupposes the existence of an online group of users in a shared collegial environment with a need to communicate with each other.
The version of
who bundled in GNU coreutils was written by Joseph Arceneaux, David MacKenzie, and Michael Stone.Specification
The Single UNIX Specification specifies thatwho 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.The command can be invoked with the arguments
am i or am I, showing information about the current terminal only.Usage
The SUS without extensions only specifies the following-m, -T, and -u options, all other options are specified in the XSI extension.Other Unix and Unix-like operating systems may add extra options. GNU includes a
-i option behaving similarly to -u and a -w option displaying whether the user listed accepts messages, yet GNU who and BSD who both omit a number of the above options ; GNU who instead uses -l to perform DNS lookups on hostnames listed.