How do I troubleshoot random freezes, where the system does not accept any input?

I have a computer that used to run Ubuntu a few years back without any problems (I don't know wether any hardware has changed). Recently, no matter which Linux distribution I install, it will randomly freeze to a point where the cursor is frozen and it doesn't respond to any keyboard input, including alt+sysrq (when the system isn't frozen I can alt+sysrq REISUB and it will reboot). There are no answers in What should I do when Ubuntu freezes? that appear to 'work' in this situation.

I've triggered the freeze with the following systems: Ubuntu 12.04, Ubuntu 14.04, Ubuntu 14.10, Ubuntu 15.04, Ubuntu 15.10, as well as Fedora 22 and 23 (all 64 bit versions). It happens with XFCE, Unity and even Gnome, it happens with nouveau and different versions of the proprietary nvidia driver. It can freeze even as early as during the installation, or during a live session. Sometimes the system will run for 5 minutes before freezing and sometimes two hours. The same hardware can run a Windows operating system for days without issues.

I have tried setting up Kernel Crash Dump, but it doesn't seem to trigger when the system freezes. There are no entries in syslog or kern.log that appear to have been written just before the freeze. On some freezes, the last entry in syslog or kern.log was 30 minutes earlier.

Update: I have disconnected a wireless network card as well as a USB webcam, will let the machine run over night to see if one of those is causing it. Will update with results.

Update 2: It froze again. I'm literally out of ideas. Any suggestions are welcome.

Update3: Some hardware specs that might be relevant:

Motherboard: Sabertooth 990FX R2.0

CPU: AMD FX-8350 Black Edition

GPU: GeForce GTX 660


I have recently upgraded the bios of the Sabertooth 990FX R2.0 to Version 2501 (the latest version currently available), without any luck.

Update 4:

I've ran a memtest for 9 hours, several passes and not a single error. There are two DIMMS seated in slot 2 and 4 on the motherboard. I have now tried removing the one from slot 4, and will see if I can reproduce the freeze. Will swap them around afterwards.

Update 5:

It has run for many hours without freezing so far, I'm finding it hard to believe myself. It might be solved, but I don't understand why. I guess I'll try and give it a few days to be sure.

Update 6:

There have been no freezes, and I must conclude that they were caused by faulty memory. Since the memtest didn't show any errors, chances are I would've never figured out what was wrong had I not started disconnecting 'random' parts. Is this the best approach really? If someone can write up a more systematic way to go at something like this, perhaps with troubleshooting from within Ubuntu, I will award them the bounty.

closed as off-topic by Eric Carvalho, David Foerster, Luís de Sousa, kos, Fabby Feb 15 '16 at 21:35

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "This describes a problem that can't be reproduced that seemingly went away on its own or was only relevant to a very specific period of time. It's off-topic as it's unlikely to help future readers." – Eric Carvalho, David Foerster, Luís de Sousa, Fabby
If this question can be reworded to fit the rules in the help center, please edit the question.

  • This seems to me like a hardware issue. Did you try unplugging all the external devices? Also check the hard drive for errors and failing. – Gayan Weerakutti Nov 10 '15 at 12:10
  • 1
    I haven't tried unplugging everything yet, but how would hard drive errors be causing this when it happens during a live session as well? – Tobias Nov 10 '15 at 12:12
  • Yup my bad. It isn't a hard drive problem then. – Gayan Weerakutti Nov 10 '15 at 12:15
  • Well I just looked at what's plugged in. And the only thing I can unplug is a USB webcam that hasn't been plugged in the whole time. Other than that, there's only a USB keyboard, a USB bluetooth thingy for wireless keyboard, network and hdmi for the monitor. Internally, I could disconnect a wireless network card and multiple storage devices. But should that matter? – Tobias Nov 10 '15 at 12:17
  • I'm not really sure, BTW. – Gayan Weerakutti Nov 10 '15 at 12:20

Here is what works for me .

Whenever Ubuntu freezes and no keyboard or mouse input works for me I launch a fullscreen login terminal ( I don't know the proper name) by pressing Ctrl+Alt+F1.

After the terminal is launched I again press Ctrl+Alt+F7. And it brings me back to my original GUI Ubuntu working environment.

And Ubuntu unfreezes.

Additional Info

After launching that terminal you can logout or restart or do whatever you want to do in a traditional terminal.

You can use any of the buttons F1 to F6 using the combination above to launch the terminals. And can launch the GUI environment using F7 as described above.

  • I'm sorry but I think you misunderstood the question. When I say that keyboard and mouse input doesn't work, that includes the Ctrl+Alt+F1 keypress. Alt+sysrq is usually the next thing to try, and that is why it is mentioned in the title rather than 'Ctrl+Alt+F1'. – Tobias Dec 23 '15 at 12:29

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