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This is not the first time that Ubuntu has froze. Last time, I checked 'recently updated files' in /var/log/ and /var/crash/ and the cause of the problem appeared to be 'LibreOffice'.

Now, it has happened again.

Nothing works, except the power-down button (based on previous experience). I can't even open tty's using Ctrl+Alt+F{1..6}

I have plenty of memory (7.7 GB), Ram (2 x 3.16Ghz) and hard drive space (100 GB on a 256GB SSD).

There is nothing I can do, except to shut down. The computer passed a memtest.

What should I look (grep) for in the logs?

Update: I have submitted a bug here: https://bugs.launchpad.net/ubuntu/+source/xorg/+bug/1023916/

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Exact duplicate here: askubuntu.com/questions/4408/… –  Tom Brossman Jun 14 '12 at 20:56
@TomBrossman similar question, except that all the answers assume some response. The [closest answer](you'll just have to power-cycle the machine. May you never reach this point.) touches on this case very briefly at the end "you'll just have to power-cycle the machine. May you never reach this point." That doesn't help me prevent the next occurrence. –  Abe Jun 14 '12 at 21:02
@TomBrossman I have updated the question to be more specific –  Abe Jun 14 '12 at 21:14

3 Answers 3

A freeze sounds a lot like an error either in Xorg or in the kernel. Have you tried to ssh to the box? Sometimes that works even if local user interfaces are all irresponsive. A working ssh connection might be very helpful debugging this kind of issue.

From the data you provided, I'd go for the kernel log. It seems libreoffice crashed for some reason, and within a second, chrome was gone as well. So there was definitely some kind of problem at that time. Have a closer look at the log around those error lines, and see whether you can identify the first error message of that event cascade. The timestamps to the left should be useful, as any event related to the freeze should be pretty close to the two I mentioned.

Just judging from the two events included in your log, it seems likely that the libreoffice crash somehow made X unstable, causing both the UI freeze and the chrome crash. You will notice that chrome crashed in an X library.

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I can indeed ssh into the box. What next? –  Abe Jun 27 '12 at 18:40
Have a look at /var/log/Xorg.0.log. Execute dmesg to see recent kernel output. Perhaps run pstree and/or ps -A to see which processes are still around. After that, you can either decide to gather more information or to see if you can restart your X server. The latter is sudo restart lightdm iirc, but I might be wrong there. –  MvG Jun 27 '12 at 18:47
Okay. After finding a few bits on ubuntu forums about the "Xorg Tainted P" message in /var/log/kern.log, I realized that I had not re-installed the proprietary ATI driver after updating to 12.04, and that this could be the issue. So I have re-installed the ATI driver. By the way, /var/log/Xorg.0.log was > 1000 lines long, all from today, so I didn't even know where to start. Thanks for the help. I will let you know what I find. –  Abe Jun 27 '12 at 19:22
Nope, installing the proprietary driver didn't fix it. –  Abe Jun 28 '12 at 0:19
Okay. I have already rebooted; but when it happens next time (note to self:) here are the instructions for reporting a "GPU lockup Bug" wiki.ubuntu.com/X/Troubleshooting/Freeze –  Abe Jun 28 '12 at 0:49

I was running in the 'vanilla' default mode, although I do have xfce and kde installed.

A vanilla installation, to my understanding means a clean installation of a distribution. Try a clean install (as in format everything, create a new user and try again). Of course, backup your important files before doing this.

Also, instead of reinstalling, you could try creating a new user. This can pin-point the problem: If the new user works, the problem is located in your home user settings. If it doesn't, it's a system problem (and reinstalling would solve it probably)

Do not install anything else. Do not use PPAs. Only update the software through update manager or apt-get, without altering/adding the sources.list. That means vanilla installation. See how the system responds for 3-4 days. Then start adding software one-by-one in order to discover the problematic package.

After a reboot, the system usually appends a ".old" or ".0" in the filename.

I'd say these log files would be informative:

tar czf mylogs.tar.gz --ignore-failed-read ~/.xsession-errors.old /var/log/Xorg.0.log.old /var/log/dmesg.0 /var/log/syslog.1 /var/log/kern.log.1 /var/log/apport.log.1 /var/log/pm-powersave.log.1
file-roller mylogs.tar.gz

...or if you prefer it separately:

cat ~/.xsession-errors.old
cat /var/log/Xorg.0.log.old
cat /var/log/dmesg.0
cat /var/log/syslog.1
cat /var/log/kern.log.1
cat /var/log/apport.log.1
cat /var/log/pm-powersave.log.1
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I meant "vanilla mode" as in selecting "ubuntu" rather than "gnome classic", "ubuntu 2D", "xubuntu", etc at login - as opposed to a "vanilla installation". Not sure what else to call it. But I will try to debug further before a re-install. –  Abe Jun 18 '12 at 18:53
Would it be helpful to post all of these logs? If so, how can I remove any private data? –  Abe Jun 18 '12 at 18:53
I don't know if it would help anyone, certainly not me. Maybe someone would be willing to look at the logs. I don't know how to clear private data from the logs, you can browse each one and decide for yourself, based on your privacy levels and concerns. Why don't you try creating a new user? If the new user works, the problem is located in your home user settings. If it doesn't, it's a system problem (and reinstalling would solve it probably) –  medigeek Jun 21 '12 at 6:41

Various applications segfault and kernel oops usually are symptoms of hardware problems. Try first to run a memtest, it will probably fail with errors.

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I already ran a memtest, and passed, but that is obviously a helpful approach to try. I have edited my question to add this information. –  Abe Jun 27 '12 at 21:53

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