All of the sudden gksu stopped working for me:
~$ gksu gparted (gpartedbin:24252): Gtk-WARNING **: cannot open display: :0
The same happens with
~$ gparted-pkexec No protocol specified (gpartedbin:25454): Gtk-WARNING **: cannot open display: :0
What could possibly be causing this?
I am not running this through SSH or VNC. This is localhost in a normal terminal window.