Lightdm crashes when lightdm.conf is inconsistent

[Lonepsi]

On a system which was well running, I set the line
greeter-setup-script=/usr/bin/numlockx on
in lightdm.conf
but I forgot to install numlockx.

At the next boot, I got a low resolution screen and no possibility of login
(with a kind of message from probably server X it doesn't recognise the graphic card )
I verified this by toggling between the initial lightdm.conf and the modified lightdm.conf.

Perhaps this kind of error of the user in the file should not lead to this kind of crash. At best, nothing, at worse, an error message, not a crash.

uname -a gives :
Linux A64 3.5.0-36-generic #57~precise1-Ubuntu SMP Thu Jun 20 18:21:09 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux - the graphic card is nvidia 7100 GS

[Lonepsi (imho)]

Here are the backup log I got at boot (archive log option).

[Robert Ancell (robert-ancell)]

This is the correct behaviour. LightDM hasn't crashed, it has just exited with an error code (you can see this in /var/log/lightdm/lightdm.log). Ubuntu then shows you a failsafe mode to prompt you to fix your system.

I'll reassign this to xdiagnose which is the failsafe mode you are seeing - it would be nice if it could provide more accurate information on what has happened.