Debian 10 cannot open display:

Question

I have a Debian 10 system with a desktop environment installed and running. When I open a terminal and try to run any GUI application , such as gedit, from the command line, it fails to open with the following messages:

# gedit
Unable to init server: Could not connect: Connection refused

(gedit:3575): Gtk-WARNING **: 12:26:48.311: cannot open display: 

This happens with any user, not just root.

I have tried running the following based on suggestions to no avail:

 export DISPLAY=:0
 export DISPLAY=:1
 export DISPLAY=:2
 export DISPLAY=:3
 export DISPLAY=:4
 export DISPLAY=:5
 export DISPLAY=:6




xhost +

Anyone have any idea whats wrong here?

EDIT:

If I run export DISPLAY=:0 as a normal user, then the normal user can run GUI programs from the command line, however whenever I try the same with root it fails with the messages:

No protocol specified
Unable to init server: Could not connect: Connection refused
No protocol specified
Unable to init server: Could not connect: Connection refused
No protocol specified
Unable to init server: Could not connect: Connection refused

(gedit:3609): Gtk-WARNING **: 12:33:16.307: cannot open display: :0

Answer 1

The display belongs to the user. So, if you want to allow another user to draw on it (think of it as a printer) you have to grant permissions.

There are many ways to do that, but the simplest is probably to open the graphic terminal and run:

$ xhost +

That will allow connections to the server from other users.

Then, from the other user you can run:

$ export DISPLAY=:0

It could be another display, such as :1 ...

If you want to avoid those two steps, you can ssh into the other user, with the -X flag (that forwards the display):

$ ssh -X -l other_user localhost

Answer 2

I just added switch -E after sudo command.

for example:

sudo -E gedit /etc/apt/sources.list