Cannot connect to X server :0.0 with a Qt application

Question

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,

Answer 1

The general causes for this are as follows:

1. DISPLAY not set in the environment.
   Solution:

   export DISPLAY=:0.0 ./myQtCmdHere 

   ( 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.  

Answer 2

Also, if you'd like your X server to be able to receive connection over TCP, these days you must almost always explicitly enable this. To test whether you're server is allowing remote TCP connections try:

telnet 127.0.0.1 6000

If telnet is able to connect, then your X server is listening. If it can't, then neither will any remote X application and you need to enable remote TCP connections on your server.