Lightdm sometimes fails to auto login

Bug #1250875 reported by Paulo Narciso on 2013-11-13
This bug affects 5 people
Affects Status Importance Assigned to Milestone
lightdm (Ubuntu)

Bug Description

Using ubuntu 14.04 and sometimes when I boot into ubuntu lightdm fails to auto login, and I must login manually in the unity greeter.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: lightdm 1.9.3-0ubuntu1
ProcVersionSignature: Ubuntu 3.12.0-2.7-generic 3.12.0
Uname: Linux 3.12.0-2-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.12.6-0ubuntu1
Architecture: amd64
Date: Wed Nov 13 14:33:18 2013
InstallationDate: Installed on 2013-10-10 (33 days ago)
InstallationMedia: Ubuntu 13.10 "Saucy Salamander" - Beta amd64 (20131008)
MarkForUpload: True
SourcePackage: lightdm
UpgradeStatus: Upgraded to trusty on 2013-11-04 (9 days ago)

Paulo Narciso (p-narciso) wrote :
Launchpad Janitor (janitor) wrote :

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

Changed in lightdm (Ubuntu):
status: New → Confirmed
Nick Sharp (njsharp) wrote :

Ubuntu 14.04 has just recently started doing this to me too about a week ago, today being 2015-04-22. I keep Ubuntu upgraded on this 64bit PC (Intel i5) to the latest state nearly all the time.

I wonder if this helps:

When I turn on the power (with the BIOS is set to start the PC when power resumes) I often see my desktop for an instant before the system flips to the login screen.

If however I reboot the machine without downing the power, the auto logon works OK.

Happy to do any diagnostics as directed.

Nick Sharp (njsharp) wrote :

Oh, and another 64bit machine I have with an identical motherboard but an i3 instead of an i5 DOES carry out auto login OK after power on with BIOS set to boot up on power resume. Hmmm?

Nick Sharp (njsharp) wrote :

More: creating a new 'test' account on the i5 machine and changing auto login to that account results in auto login working OK for 'test'.

That seems to suggest that a fault has somehow arisen in my usual account's control files. I'm hoping someone will discover such a fault and how to correct it by a tiny action.

I am reluctant to go through the process of trying to ensure I have saved all my normal account's files and settings, then deleting and recreating that account! I try only to do that when I totally reload a machine and then only with a new LTS, which will not be until 16.04.

I'd be pleased to receive via this forum requests for diagnostic information.

Nick Sharp (njsharp) wrote :

Problem now gone at:

uname -a
Linux u1404tv 3.13.0-51-generic #84-Ubuntu SMP Wed Apr 15 12:08:34 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux


Nick Sharp (njsharp) wrote :

Humph! Problem returned at:

Linux u1404tv 3.13.0-52-generic #86-Ubuntu SMP Mon May 4 04:32:59 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux


Nick Sharp (njsharp) wrote :

I have just noticed this:

I created a second account (administrative) and gave it a distinct desktop background. Both accounts were set autologin=NO.

On rebooting from a complete power off (at the wall), I of course got the login screen, BUT if I dropped down to the second account, its distinctive desktop background was displayed, whereas on returning up to my usual sole account, the background went to the standard purple, instead of my account's distinctive desktop background.

I guess there is some sort of corruption in my account's files. I expect that complete removal of my account, followed by its exact re-creation might remove this problem. I am tempted to try, after the appropriate backups of course.

By the way, am I talking to myself here, or is anybody who might be able to solve this also listening?

Sitsofe Wheeler (sitsofe) wrote :

I've just seen this on Ubuntu 16.04 on an EeePC and in one start up configuration it always happens and autologin always fails.

It seems to be highly dependent on what else is happening as lightdm is starting. When the problem occurs looking at the lightdm log shows that it is trying to log using a normal PAM lightdm session rather than an autologin PAM session. This leads to failure because the account being authenticated has a password and no password is being passed to PAM and the user is intentionally absent from the nopasswdlogin group.

Attaching /etc/lightdm/lilghtdm.conf, /var/log/lightdm/lightdm.log and PAM's /var/log/auth.log .

Sitsofe Wheeler (sitsofe) wrote :
Sitsofe Wheeler (sitsofe) wrote :
Sitsofe Wheeler (sitsofe) wrote :

Further investigation on what I was seeing showed this to be a race between X starting and the intel i915 graphics kernel module being loaded (because it's not built into the kernel).

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