I use the Dia tool for all my diagramming work. I have worked with many tools, but find Dia the easiest to use and is the most responsive, apart from it being a great OpenSource tool :).

I recently upgraded to the new Mac Operating System Yosemite and I could no longer use Dia. Each time I clicked on the Dia icon, it would jump up & down and do nothing. I finally tried opening the app via the command line, which gave me the following error:

The domain/default pair of (.GlobalPreferences, AppleCollationOrder) does not exist

The error trace ended with GTK warning - could not open display.

I could not find anything on the internet that was Dia specific, so I thought of writing this blog, in hope of helping someone in the same situation as me. So here is what I did:

1. Goto your Applications directory where Dia.app exists (mine was located at: /Applications)
2. Right click the icon and click on Show Package Contents
3. Goto the directory Dia.app/Contents/Resources/bin
4. Edit the file dia, in your favourite text editor.
5. After line 39, add the line: export DISPLAY=:0
6. Save and exit.
7. Close XQuartz if its running.
8. Now Dia should come up.
9. If it does not come up, try restarting your computer.

If not, try and add the line - export DISPLAY=:0 to your ~/.bash_profile, re-login and hopefully you should have Dia working once again. 

Let me know if this helped you out :)

The red rectangle shows where I put the DISPLAY variable for Dia to start responding.