I've made some progress. By setting up an xorg.conf with a modeline for the external display, I got graphics on the (lightdm) login screen to show up on it. But the login input fields weren't on this screen (it was just the background), so this was further evidence that there's monitor misdetection going on (greeter/lightdm happily thinks it's displaying the input fields on the broken internal LCD).
So I further tweaked xorg.conf to force X to ignore the internal display, and now I've got a working login screen back on the external display. I'll attach my xorg.conf below; it is a satisfactory workaround. ** Attachment added: "Internal display disabling, external display enabling xorg.conf" https://bugs.launchpad.net/ubuntu/+source/unity-greeter/+bug/1254319/+attachment/3924693/+files/xorg.conf ** Summary changed: - Black screen instead of login screen; input works + Login screen goes to broken internal display, working external display shows black (unless xorg.conf set up) -- You received this bug notification because you are a member of Desktop Packages, which is subscribed to unity-greeter in Ubuntu. https://bugs.launchpad.net/bugs/1254319 Title: Login screen goes to broken internal display, working external display shows black (unless xorg.conf set up) Status in “unity-greeter” package in Ubuntu: New Bug description: This is a laptop with a broken internal display ("LVDS1" in xrandr output), and therefore connected to a working external LCD ("VGA1"). After upgrading from Precise to Trusty, boot ends with a black screen (on the external display). The greeter sound effect is played. Typing my password (I'm the sole user) does log me in, and brings up the desktop on the display. So the login functionality is there, just the visuals are missing. And they do flash by (corrupted) when the desktop is loading; if I set automatic login for myself, I get a desktop with the login screen as the background image (I'll attach a screenshot). There are existing, similar reports but all with subtle differences from this (such as Bug #1252748, where the user only gets black screen half the time) or too vague for me to claim to be the same issue with certainty (such as Bug #1242213). A lightdm restart (such as in Bug #969489) doesn't fix this (i.e. black screen still after lightdm restart). I'm not sure whether this is a lightdm issue or a unity-greeter one, so my reporting this against the latter is just a guess. ProblemType: Bug DistroRelease: Ubuntu 14.04 Package: unity-greeter 14.04.1-0ubuntu1 ProcVersionSignature: Ubuntu 3.12.0-4.10-generic 3.12.1 Uname: Linux 3.12.0-4-generic x86_64 ApportVersion: 2.12.7-0ubuntu1 Architecture: amd64 CurrentDesktop: Unity Date: Sat Nov 23 20:53:43 2013 InstallationDate: Installed on 2012-05-25 (547 days ago) InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Release amd64 (20120425) SourcePackage: unity-greeter UpgradeStatus: Upgraded to trusty on 2013-11-17 (6 days ago) To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/unity-greeter/+bug/1254319/+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
