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I am running 12.04 LTS, fully updated. My system is configured to automatically log me in into my account. Auto-login works fine.

However, sometimes I need to access the unity-greeter/lightdm login screen. For example, this happens when I log out and then want another user want to log into their account. The interface we get is exactly the one shown on the Wikipedia page for LightDM:

  • the password prompt is grayed out and I am unable to type my password
  • the mouse moves fine but I cannot click the system icons on the top-right corner of the menu bar does not work
  • I can switch using ctrl-alt-f? to a console and login fine using the text/console login prompt. If I kill X, I am again returned to the same unusable login screen.

How can I fix this? How can a user log into their graphical environment without having to reboot the system?

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Does anything change if you click on your user name? – terdon May 9 '14 at 13:20
You can try to debug lightdm or you switch back to GDM – TuKsn May 10 '14 at 9:57

I have encountered the same on random occasions on my 14.04 LTS installation. I have not been able to reproduce it. Sometimes it just happens and I am stuck at login.

I have added this alias to to my .bash_aliases file as a workaround that have worked so far:

alias saveme="export XDG_SEAT_PATH=/org/freedesktop/DisplayManager/Seat0 && dm-tool switch-to-greeter && logout"

When login prompt is grayed out. I switch to e.g. tty1 with Ctrl+Alt+F1, login and just enter my alias: saveme.

This way you will not lose any work from open applications. When you restart lightdm you will lose everything you had running which was really annoying and something I wanted to avoid..

XDG_SEAT_PATH may not be the same for you. Check while logged in in a terminal:

env | grep -i XDG_SEAT_PATH

You can also check with:

dm-tool list-seats
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According to the bug reported at Launchpad.

The bug has been fixed in an updated version of Unity: 7.2.4+14.04.20141217-0ubuntu1. This fix should be included in 15.04 release as well.

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