"No protocol specified" when running a sudo/su app on Ubuntu Linux

Question

I try to run the iReport 5.6 on Ubuntu and Java 7, using the command:

$ sudo iReport-5.6.0/bin/ireport
No protocol specified.

I get an error. When I try run it without sudo, I get a permission denied error and an alert that the file Preferences on Default System are read only.

Answer 1

Newer systems by design don't allow graphical applications as root (it's a Wayland thing). Workaround:

xhost si:localuser:root

sudo   your-graphical-app

Restore the default permissions:

xhost -si:localuser:root

Answer 2

It looks like either the display port is not opened in your system or it is disabled.
Try running this command as non-root user:

xhost +

and then run the app with root.