TheGhost is correct. I installed Ubuntu, got fed up with Unity, and installed kubuntu-desktop. polkit-kde-1 did not get installed when I did that. Also, rubik-cube's advice does indeed work (once polkit-kde-1 is installed), although the dialog is a bit slow to appear, so I didn't think it worked at first.
TheGhost is correct. I installed Ubuntu, got fed up with Unity, and installed kubuntu-desktop. polkit-kde-1 did not get installed when I did that. Also, rubik-cube's advice does indeed work (once polkit-kde-1 is installed), although the dialog is a bit slow to appear, so I didn't think it worked at first.