First I tried to install synaptic and found that even though it was installed, it didn't appear in the whisker menu. I tried creating a shortcut in the usr/share/applications folder,but giving the order EXEC= pkexec synaptic , It opened the box for me to write the password but it was never executed-run synaptic...when I tried to execute this command through a terminal it said the following.... $ pkexec synaptic (synaptic:32881): Gtk-WARNING **: 16:29:27.236: cannot open display: finally the shortcut ran only through terminal with the command below xfce4-terminal --hold -e "sudo synaptic"