Who is a classic command on Unix operating systems, which displays a list of currently logged on to the system user. who is standardized in the Single Unix Specification. The GNU implementation is an element of the GNU core utilities.
Who belongs to the historically oldest commands in Unix environments. Because the command from a time dated before graphical user interfaces, the display is on some platforms so far not complete, will not be considered as a virtual X11 terminals such as xterm.
With the standardization by the Single Unix Specification was determined that who should spend at least a list of logged-in user. The XSI extension also stipulates that data on the user name, terminal used, the time of login, the process ID of the login shell as well as the time since the last activity in the terminal ( idle time) to be output.
The call of who on a Linux system on which the user bob is logged on multiple virtual terminals, could look like this:
$ who bob pts / 1 2008-05-18 12:30 ( p57a6d3a7: S.0 ) bob pts / 2 2008-07-20 18:18 ( p57a6d3a7: p.1) bob pts / 4 2008-05-18 22:59 ( p57a6d3a7: p.3) bob pts / 3 2008-05-18 12:53 ( p57a6d3a7: p.2 ) bob pts / 5 2008-07-26 23:20 ( p57a6d3a7: p.4 ) In this case, the first column the user name again, the second of the login terminals, the third the login time and behind it, in parentheses, is connected from which host the user (via SSH)
The who command is similar to the Unix command- w, which to the information of who also outputs additional data, such as the last command executed by any user.
If who is called with the parameters am i, there like the Unix command whoami the name of the logged on user, but in addition, the terminal name, the time of login and the computer name from whom comes the login.