I have an odd problem. I have tried to use Synaptic so I can install a package. The system asks for the root password but won't accept it. I can start a terminal window and start 'su'su with the root password and start Synaptic in 'su'su and it comes just fine. The same for Apper except it won't start in 'su'su for GUI reasons.
What must I do to correct this?
I am using Debian 9 stretch with KDE.
 
                