just ran into this myself a few days ago when updating to bionic. It was pure luck that I discovered the problem and fix.
** Tags added: bionic ** Changed in: lightdm (Ubuntu) Importance: Undecided => High -- You received this bug notification because you are a member of Ubuntu Touch seeded packages, which is subscribed to lightdm in Ubuntu. https://bugs.launchpad.net/bugs/1268283 Title: Lightdm doesn't give any error message when .XAutority is owned by root Status in lightdm package in Ubuntu: Confirmed Bug description: (Orignal problem at the end) I understood the problem : As I had to sudo startx previously, .XAutority was owned by root. So Lightdm wasn't able to log me in. But Lightdm doesn't display any error message explaining why it can't log me in, as there was previously in GDM. HOW to reproduce : made root the owner of the .XAutority file at the root of your personal home, then try to login via Lightdm. It doesn't display any message but it doesn't log you. ---------------------Original problem :------------------------ So here is what happened : To test if an old bug with menus is still present in Trusty I updated to it, but it went very wrong (no screen at all, I filed this bug by going to recovery mode and FailsafeX). So I tried installing Trusty "from scratch", but I kept my /home. I used the same ID and Password during the installation as I do each reinstall. Reinstall corrected the problem of no screen : I was on lightdm login screen. Then, impossible to log me in : It tried and immediately go back to login screen. I changed the password from tty1 but same problem. But I can open the guest session (from which I make this bug report). What I expected : To be able to login from lightdm as I do each time I have to reinstall the system. ProblemType: Bug DistroRelease: Ubuntu 14.04 Package: lightdm 1.9.5-0ubuntu1 ProcVersionSignature: Ubuntu 3.13.0-1.16-generic 3.13.0-rc7 Uname: Linux 3.13.0-1-generic x86_64 ApportVersion: 2.13.1-0ubuntu1 Architecture: amd64 CurrentDesktop: Unity Date: Sun Jan 12 11:50:36 2014 InstallationDate: Installed on 2014-01-12 (0 days ago) InstallationMedia: Ubuntu 14.04 LTS "Trusty Tahr" - Alpha amd64 (20140111) ProcEnviron: TERM=xterm PATH=(custom, no user) XDG_RUNTIME_DIR=<set> LANG=fr_FR.UTF-8 SHELL=/bin/bash SourcePackage: lightdm UpgradeStatus: No upgrade log present (probably fresh install) To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/lightdm/+bug/1268283/+subscriptions -- Mailing list: https://launchpad.net/~touch-packages Post to : email@example.com Unsubscribe : https://launchpad.net/~touch-packages More help : https://help.launchpad.net/ListHelp