However, the problem finally went away after switching to the nouveau driver. (And I have no recollection of ever asking for the proprietary nvidia driver, specifically, but I may be wrong about that.)
(*) Symptoms: sddm, but also lightdm and gdm3 showing only black. startx brings up an xfce session without problems.
Same symptoms(*) here after a fresh upgrade to 18.04.
Tried installing gdm, as suggested above, and also adding "xrandr" as suggested, here: https:/ /forums. fedoraforum. org/showthread. php?316354- SDDM-shows- black-screen- with-Nvidia . Neither made a difference for me.
However, the problem finally went away after switching to the nouveau driver. (And I have no recollection of ever asking for the proprietary nvidia driver, specifically, but I may be wrong about that.)
(*) Symptoms: sddm, but also lightdm and gdm3 showing only black. startx brings up an xfce session without problems.