Linux – Cannot connect to X server :0.0 with a Qt application


Compiling on Fedora 10.

I have just started my first qt GUI application. I used all the default settings.

Its just a simple form. It builds OK without any errors. But when I try and run the application. I get the following message:

Starting /home/rob/projects/qt/test1/test1/test1...
No protocol specified
test1: cannot connect to X server :0.0

Thanks for any advice,

Best Solution

The general causes for this are as follows:

  1. DISPLAY not set in the environment.

    export DISPLAY=:0.0

    ( This one doesn't appear to be the one at fault though, as its saying which X display its trying to connect to. Also, its not always 0.0, but most of the time it is )

  2. Non-Authorised User trying to run the X Application
    Solution ( as X owning user, ie: yourself )

    xhost +local:root   # where root is the local user you want to grant access to.