Annoying problem with GTK apps

[Piero Piutti <chromewave@gmail.com>]

Hi,
I have recently moved to Debian Sarge from "another" distro and I like it a 
lot, besides a few problems that I'm trying to fix on the way.

One of these is one related to GTK apps: every time I try to run one from the 
console as root I receive the same error. For istance, if I try to run 
Synaptics this happens:

adam:~# synaptic

(synaptic:17058): Gtk-WARNING **: cannot open display:

Another example, this time with firefox:

adam:~# firefox

(firefox-bin:17451): Gtk-WARNING **: cannot open display:

Needless to say, if I launch firefox as a normal user, it shows up as 
expected.

I'm not sure wether or not this problem is strictly related to GTK as it also 
happens with other X apps, not necessarily GTK-based, such as xpdf which 
gives me this slightly different error message:

adam:~# xpdf
Error: Can't open display:

(xpdf works nicely if launched as normal user)

I have searched the web and the ML archive for a solution but no joy. Any help 
would be very much appreciated.

-- 
Piero Piutti
------------
Debian Linux - KDE 3 - Firefox - Gmail