lightdm fails to bring up X display automatically after boot

Status changed to 'Confirmed' because the bug affects multiple users.

This sounds very similar to Bug #935591. The difference seems to be that another window manager is involved.

Could you attach /var/log/lightdm/lightdm.log to confirm if lightdm is at fault?

Here are two instances of lightdm.log, before and after running lightdm as root:

lightdm.log before
lightdm1.log after

in a tar archive.

Thanks,

The relevant logs from lightdm are:
[+0.78s] DEBUG: Logging to /var/log/lightdm/x-0.log
[+0.79s] DEBUG: Launching process 1221: /usr/bin/X :0 -auth /var/run/lightdm/root/:0 -nolisten tcp vt7 -novtswitch -background none
[+2.17s] DEBUG: Process 1221 exited with return value 1

Which shows that the X server failed to start.

From Xorg.0.log-0 there is a failure (not sure if this is the correct log, /var/log/lightdm/x-0.log would tell you for sure):
[ 16.934] (II) NOUVEAU(0): NVEnterVT is called.
[ 16.961] (EE) NOUVEAU(0): failed to set mode: Invalid argument
Fatal server error:
[ 16.961] failed to create screen resources
[ 16.961]
Please consult the The X.Org Foundation support
  at http://wiki.x.org
 for help.
[ 16.961] Please also check the log file at "/var/log/Xorg.0.log" for additional information.
[ 16.961]
[ 16.961] (II) AIGLX: Suspending AIGLX clients for VT switch
[ 16.961] (II) NOUVEAU(0): NVLeaveVT is called.
[ 16.984] ddxSigGiveUp: Closing log
[ 16.985] Server terminated with error (1). Closing log file.

So it appears nouveaux has a problem starting on boot. I'll reassign this to the xorg team who can better diagnose this.

Thanks, Robert, for reviewing the lightdm.log output. I´m sure you are right - this is mainly an xorg issue. I´ve filed earlier bug reports on this hardware - see in particular Bug #707755 against development versions of Natty 11.04. :´

Ubuntu version and kernel version
 DISTRIB_ID=Ubuntu
 DISTRIB_RELEASE=11.04
 DISTRIB_CODENAME=natty
 DISTRIB_DESCRIPTION="Ubuntu natty (development branch)"
 Linux hp 2.6.37-12-generic #26-Ubuntu SMP Wed Jan 5 18:42:49 UTC 2011 i686 athlon i386 GNU/Linux
 model name : AMD Athlon(tm) 64 Processor 3800+
 cpu MHz : 1000.000

As mentioned in that bug report, I was able to come up with a workaround involving installing an xorg.conf file. Currently I´m putting that in /etc/X11/ - maybe I should try /usr/share/X11 ?

After filing comment #7, I rebooted the compaq system. As I was awaiting the system to complete booting, after the Grub2 screen closed - I was alternately hitting Alt F1 and Alt F2 and possibly Enter - somethow this time the lightdm login greeter appeared and I was able to log in. I'll attach the lightdm.log ...

I assume there is some sort of race condition in system startup.

I am also attaching Xorg.0.log

Status changed to 'Confirmed' because the bug affects multiple users.

Apparently this problem is already known:

http://ubuntuforums.org/showthread.php?t=1613132

Since I'm able to boot to a shell, what I just did was to add nomodeset to /etc/default/grub and run update-grub, as described on the ubuntuforums page above. So now the altered line in /etc/default/grub looks like

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash nomodeset"

#11 is a good workaround, but not really a fix to the nouveau driver bug.