Login problem

[jamespetts]

My parents' computer I set up for them some time ago (a 32-bit Athlon based system, originally built in 2002 and originally running Windows XP Home) now runs Ubuntu 8.10. However, a week or two ago, it developed a problem that I have not been able to understand or solve: the login system is totally broken, both, it seems, for local and remote logins.

The symptoms are that it will boot and reach the graphical login screen correctly, but, when a valid username/password pair are entered, the system will, after a very short delay, return to the graphical login prompt again. The behaviour is identical no matter which session is selected, including "failsafe". When I use CTRL+ALT+F1 to get to a text login prompt, the symptoms are similar: entering a valid username/password pair produces a short delay, following which the login prompt is simply repeated (along with version information, if I recall correctly) immediately below the last one. Entering an invalid username/password pair, as I did to test it several times, produces the correct error message, so the system does discriminate between valid and invalid username/password pairs. Attempting to access the system remotely in any way gives authentication errors.

The problem first arose quite suddenly - I was investigating why the computer in the kitchen (also running Ubuntu 8.10) could not print to it, after I thought that I had set up the printing before and tested it successfully. It was giving a login/authentication error of some type: I cannot now recall in detail what the message was. I spent a long time trying to resolve the problem, including trying to access it from the bedroom computer (also running Ubuntu, but this time, 8.04), and using the web interface for CUPS (I could not access the web interface for CUPS on the computer in question remotely, but could use the CUPS web interface on the bedroom to try to print to the problem computer).

That also failed, so I returned to the problem computer and tried to restart the CUPS server via the command line. That returned a "segmentation fault" error message. Thinking that something had gone rather wrong, I tried to reboot - issuing the command via the command line also lead to a "segmentation fault" error message, so I rebooted using the graphical interface, which worked. On the next login, the problem described above occurred, and has occurred consistently ever since. (If I recall correctly, I think that also, by that point, trying to access the CUPS web interface locally failed with an HTTP error that I cannot now recall - possibly in the 500s, though).

I initially thought that the problem might be hardware related. I ran MemTest86+ for 15 or so hours: 0 errors were produced. I successfully booted from an Ubuntu 8.10 Live CD, mounted the main hard drive, and accessed files on it without any discernible difficulty, so there is no evidence of hard drive failure (and the system behaviour seems too consistent for a hard drive fault in any case). The system has been running with no apparent fault from the Live CD ever since, but, obviously, that is nothing like having the computer running properly set up.

Any clues as to what the problem might be, or how to diagnose/solve it would be very welcome.

[hazel]

As you are not getting any error messages, it looks as if the system is logging you in successfully and then immediately logging you out again. Could you have done something that affects the gdm login scripts?

[D-cat]

This happened to me after installing LDAP for Samba authentication (it came as part of a remote web administration package). Nothing I did would fix it. Unfortunately, the only way I could fix it was to reinstall Ubuntu.

[jamespetts]

Thank you both for your replies

Hazel, I am not aware of doing anything that might have affected the login scripts. There had been some automatic Ubuntu updates installed shortly beforehand, but no system reconfiguration other than one or two settings to do with the CUPS server.

D-cat, I did not, as far as I recall (and I think it quite unlikely that my memory is mistaken in that respect) install any new software for some considerable time preceding the problem, although, as stated above, there were some of the automatic updates installed a short while beforehand.

[Ziplock]

Have you run an fsck on the offending partition from the Live CD? Should give you a better idea if there is a problem with the filesystem.

[jamespetts]

Ahh, yes, forgot to mention in the original post: I did run an fsck on the disk, albeit not from the Live CD (I can't imagine that that would make a difference). There was no change in behaviour before and after the FSCK run. The files on the disk can be accessed with no trouble when the system is running from the Live CD. The filesystem is Ext3.

[Ziplock]

Hi there,

Was one of the Ubuntu updates the kernel? Do you have a specific third-party graphics card? Just wondering if it is driver related. Also, if it is all running fine on the Live CD, then the only difference seems to be the kernel?

Can you update the kernel and try again?

[jamespetts]

Hi there,

Was one of the Ubuntu updates the kernel? Do you have a specific third-party graphics card? Just wondering if it is driver related. Also, if it is all running fine on the Live CD, then the only difference seems to be the kernel?

Can you update the kernel and try again?

Thank you for your reply I don't recall specifically now whether a kernel update was involved, although I seem to remember not having to reboot, so probably not. The graphics card is a NVidea GeForce 6800, connected via the AGP. I use the proprietary driver that is automatically accessible if one selects the tool for using non-free drivers.

As to updating the kernel - how can I do that if I can't login?

[D-cat]

As to updating the kernel - how can I do that if I can't login?

You can log into your computer as root by booting up in the recovery console, no password required. May have issues with starting some hardware though, since the prompt is issued to you prior to any init scripts.

[Ziplock]

Thank you for your reply I don't recall specifically now whether a kernel update was involved, although I seem to remember not having to reboot, so probably not. The graphics card is a NVidea GeForce 6800, connected via the AGP. I use the proprietary driver that is automatically accessible if one selects the tool for using non-free drivers.

As to updating the kernel - how can I do that if I can't login?

If you can get in and mount up the drives with the rescue/live cd, you should then be able to cd into the directory that was '/' and do a 'chroot .' which will put you in the same directory structure as your underlying installation. From there, you will probably be able to do something like:

apt-get update kernel

Don't know if this is exactly the right command, but it may help. Once this is installed, you should be able to update the NVidia driver as well.