[snip]
> > # DISPLAY=<that thing you got>  synaptic
>
> # echo $DISPLAY
>
> :1.0
>
> # DISPLAY=1.0 synaptic
>
> (synaptic:15881): Gtk-WARNING **: cannot open display: 1.0
>
>
> but:
> $ sux -
> (enter root password)
> # synaptic
>
> DOES WORK.


just one try:

$ echo $DISPLAY
$ sux
# echo $DISPLAY