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Following user: "coteyr's" suggestions (5.5.13) 'sudo X :2' did give me a black screen but no "X" for the mouse pointer. The log for this is apparently /var/log/X.2.log, but this did not show any errors. Also had to ctrl-alt-del out of this.

I then created a new user and could login using it, but it would not log out. I could also look into the old-user directories down about 5 levels but had no rights to look at any files. If I read your logic correctly this all means that xorg and lightdm are both ok and that it is a problem with my old user configuration.

Performed logical testing procedure thanks to coteyr and followed his advice step by step to find the personal config was "borked" for unknown reasons. Instead of deleting .config I did as suggested and typed: mv .config .config.old which I gather backs it up and allows a new .config to be created next time you boot/login. This allowed login of my original user and hence direct access to all my old files. However, there were a few "12.04 has experienced an error" windows popping up to do with: /usr/bin/gnome-session /usr/bin/gsettings /usr/bin/l2tpIPsecVpn all crashed. So in the end this was not a lightdm or xorg problem, but a unity/gnome config problem. 7th May: Since the second login on 12.04 I have not been able to get online, but have just been able to check using wifi, which works. So my DSL connection is now not recognised. I know this is not the same question but can anyone help or should I post this as an additional problem?

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Read your error logs and system messages from /var/log/ and post them if there's any errors. – Alex Apr 19 '13 at 4:34
Question that may already have your answer:… – Radu Rădeanu Apr 19 '13 at 5:26
To see whole output of a command, append ` | less` to it. For example cat /var/log/Xorg.0.log | less. After you have finished reading, press q to exit the less utility. Also, if nothing else works, you can try installing another display manager, like GDM. – user31389 Apr 29 '13 at 14:16
up vote 3 down vote accepted

Seperate your login issues from X issues.

First try logging in to a VTY. Press Ctrl + Alt + F1 and login.

Once logged in try running sudo X :2 & you should be taken to a black screen with a X for a mouse pointer. If you do then X is fine, and your problem is your configuration of either lightdm or your desktop. This is common with large upgrades.

If X doesn't start then back at the terminal (etrl + alt + f1) run cat /var/log/X.2.log | grep EE that will return all errors. We will need that to really go any further down this path.

If X did start then go back to the terminal (ctrl + alt + f1) and create a new user, then try to log in using that user. sudo adduser testing will create a new user called testing.

If you were able to log in as testing, then your personal configuration is borked. If you could not log in as testing (in X) then lightdm is borked.

To fix your login the best way is to just delete (after backing up of course) your home directory contents. Then copy back the files you need from backup. This will reset all your settings but is a sure fire way to make sure your config issue is addressed. You could also delete just the .config directory, or all the hidden directories. However make sure you have backups.

To fix lightdm, you can probably just do sudo dpkg-reconfigure lightdm. If it's still lightdm and still causing the issue, we will need the full lightdm log (/var/log/lighdm) use pastebin or something to add it to your question.

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Can now login, but cannot get on line using 12.04. So have to revert once again to the old faithful 10.04 – user133904 May 6 '13 at 14:01

once you login at the terminal, try running

sudo pkill lightdm


sudo lightdm (tell us if that fails, and if so, what error msgs)

When ever you see "Permission Denied" This means the command probably requires root permissions. use sudo to gain root permissions.

lightdm requires root to run.

if possible, post your dmesg information.
Also, have a look at this post, specifically running fail safe X. After Upgrading to 12.04 I can't get to the login screen

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