On an HP ProBook 6470b with Intel HD 4000 graphics, adding the following line to /usr/share/X11/xorg.conf.d/20-intel.conf resolved this issue in addition to fixing the resolution of my external monitor at the login screen:
Option "ReprobeOutputs" "true" -- You received this bug notification because you are a member of Desktop Packages, which is subscribed to xserver-xorg-video-intel in Ubuntu. https://bugs.launchpad.net/bugs/1531224 Title: lightdm-gtk-greeter flickers once little after lightdm starts Status in LightDM GTK+ Greeter: New Status in xserver-xorg-video-intel package in Ubuntu: Confirmed Bug description: Bug context: · Arch Linux x86_64 4.3.3-2-ARCH · systemd 228-3 (using lightdm-plymouth.service) · plymouth 0.9.2-8 (compiled from AUR) · lightdm 1:1.16.6-2 · lightdm-gtk-greeter 1:2.0.1-2 At the end of boot process, right after plymouth splash, lightdm starts normally and the GTK+ greeter login screen is shown for about 1 second, but then the screen instantly flickers (goes black) and the greeter is redrawn. From here on, everything works flawlessly, but the brief flickering is certainly annoying. This happens every time and no other greeter I have tried presents this issue, so I can confirm it is lightdm-gtk-greeter-related. To manage notifications about this bug go to: https://bugs.launchpad.net/lightdm-gtk-greeter/+bug/1531224/+subscriptions -- Mailing list: https://launchpad.net/~desktop-packages Post to : desktop-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~desktop-packages More help : https://help.launchpad.net/ListHelp