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LightDM is installed and running by default as a part of the Beta release. Yet, LightDM is not displayed at login time, rather a primitive, GDM like manager is the one we find at login time.

I tried the command sudo dpkg-reconfigure lightdm

which gave the result :

dpkg-maintscript-helper: warning: environment variable DPKG_MAINTSCRIPT_NAME missing dpkg-maintscript-helper: warning: environment variable DPKG_MAINTSCRIPT_PACKAGE missing


sudo stop gdm gives stop: Unknown job: gdm (as GDM is not installed in the Beta Release)

sudo start lightdm gives start: Job is already running: lightdm

So now, how do we make LightDM appear at login time?

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Can you show a screenshot? I suppose what you call "a primitive GDM-like display manager" is exactly LightDM. – enzotib Sep 4 '11 at 13:20
I have already used LightDM in alpha 3. It isnt like it at all. Rather like the one default in Alpha 1 – Shiv Sep 4 '11 at 18:16

Run the following in a terminal:

sudo apt-get update && sudo apt-get install lightdm

That should resolve your issue.

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There is a bug for this issue.
If lightdm starts sucessfully on your machine, the workaround is to manually set absolute path to lightdm in the /etc/X11/default-display-manager file:

sudo su
echo "/usr/sbin/lightdm" > /etc/X11/default-display-manager

(when I experienced this problem on my installation, there was only the binary name lightdm in the file.)

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Exactly what I needed to sort out my problem. – tardomatic Nov 27 '11 at 13:50
This did not work for me. My default manager is already set to lightdm, but my screen is still blank. – Cerin Feb 19 '12 at 12:51

LightDM is installed but I suppose it's still using the greeter from the alpha. Just apt-get purge lightdm and lightdm-gtk-something (it will also remove ubuntu-desktop). Then install again ubuntu-desktop and unity-greater will be installed alongside lightdm.

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Don't do that! Purging your display manager is not good. – James Sep 9 '11 at 15:27

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