I connect from UBUNTU on a PC to two raspbery pi computers via rdesktop, not both at the same time, say to rasp1 and rasp2.
In the remote desktop I open a terminal and issue "echo $DISPLAY".
On rasp1 I get :10.0 and can start programs that use a GUI, e.g., gparted.
On rasp2 I get :0.0 and trying to start gparted I get "cannot open display: :0.0". However, "DISPLAY=:10.0 gparted" works fine.

So the question: why sets rdesktop the DISPLAY variable sometimes, sometimes not. Where comes :10.0 from?

rasp1 and rasp2 run the same OS: ubuntu mate.

Thanks for enlightenment,

ulrich

Hi (and welcome here).
At first, it is not the desktop which sets the variable DISPLAY.
When you start the graphical environment (this is usually the startx command) you may need to specify the DISPLAY you use. The usual default is :0 (or :0.0).
When you log in (connect) from a remote host (using ssh, rdesktop or something similar) you will get a virtual DISPLAY which is valid during the given remote session. :10 is usually connected to :0 (usually 10 is added to the original DISPLAY).
when you make a remote connection you can specify if you want to use DISPLAY or not (therefore you can configure if you want to set DISPLAY at all).


https://support.objectplanet.com/esu...kbarticleid=17
https://unix.stackexchange.com/quest...t-is-display-0
https://askubuntu.com/questions/4322...nment-variable

I still do not understand why connecting to two - as far as I know - identical target hosts gives different results.
I looked at /etc/alternatives/vncserver on both machines: they are identical. The same holds for /etc/X11/Xsession.
Something must be different, but what?