Ubuntu – What does ‘(:0)’ in the output of the command ‘who’ mean

command linewhoxorg

When I type who in terminal I get this output:

$USER      tty2         2017-01-12 12:50 (:1)

What does this smiley (:1) mean ?

Sometimes this smiley looks like (:0.0). What does it mean in this case?

Where is an overview about these different brackets?

Best Answer

As you can find out in the manpage by typing man who, you can enable column headings with the -H option:

$ who -H
NAME          LINE         TIME             COMMENT
bytecommander tty7         2017-01-12 15:26 (:0)
guest-c62iz5  tty8         2017-01-12 15:40 (:1)

I have to agree this is not very helpful though, and the manpage also doesn't contain any explanation of the values.

However, I think I can tell you what these columns mean anyway:

  • NAME is the username of each logged in user.
  • LINE seems to contain the TTY through which the user is logged in (TTY1-6 are terminals, TTY7-12 are used by the X display server to show graphical desktops; you switch between them using Ctrl+Alt+F1 - F12).
  • TIME is the date and time when the user logged in to their current session.
  • COMMENT in our cases shows the content of the $DISPLAY environment variable (normally :0) in braces, which is also used by the X display server. Only graphical TTYs should have such a value, this column is empty for me on the terminal TTYs.

    You can check the value of this variable using the command echo $DISPLAY. What exactly it means is described e.g. in What does DISPLAY=:0.0 actually mean? and What is DISPLAY=:0?.