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I have a new system on my laptop (Ubuntu Gnome 16.04) and first week or so it was great, but then it started to (seemingly randomly) freeze every now and then (about once a day, sometimes more; it's a complete system freeze, where the only option so far was to force shutdown). I was looking at some system logs (kern.log, syslog and dmesg) and found this in /var/log/syslog at the timestamp of the most recent freeze: screenshot of the syslog file

The complete syslog is here, the weird line is at 14582.

Does anybody have any hints on what could be the culprit of the freezes? Should I look at other logs? I tried to search for some advice on how to debug system crashes, but the information I found was rather scarce and not very helpful. For instance the Ubuntu wiki guide tells me to replicate the issue on CLI, but I don't know how since I don't know what is crashing. I hoped to find something in the logs but the ones recommended for checking show nothing of interest to my non-expert eye.

I want to try the SysRq method described in the Ubuntu wiki, however it rather conflicts with the Wikipedia article on this topic. This is why I hesitated to use it so far. If anybody has any advice on this, it would be also greatly apreciated.

Here is my system info:

$ uname -a
Linux ultrabook 4.13.0-31-generic #34~16.04.1-Ubuntu SMP Fri Jan 19 17:11:01 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux

Update

Today it freezed again, todays log with just errors (outputed by grep -i Error* /var/log/syslog), as suggested by Elder Geek can be found here. The timestamp of the crash is before 11:30:24, which is the time of new booting.

Thanks for any help.

jena
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  • Can you describe the problem in some more details. Is it a crash or a freeze, or both? When do they happen? Also, if you want to show us a particular piece of text, copy/paste it, instead of taking a screenshot of a window of a program with that text inside, and then uploding it. – mikewhatever Jan 25 '18 at 19:23
  • It's a complete system freeze, only option is to force shutdown (I want to try SysRq next time it happens). I didn't notice any pattern, so far it seems random to me. I uploaded a screenshot because the weird part is more obvious in it (furthermore, copy-pasting changed the symbols). The full log as copied from gedit editor is in the link provided. – jena Jan 26 '18 at 15:41
  • Not much help, but I have had this problem. In my case it was fixed by blacklisting a driver, btsdio. I can't give any advice whatsoever on figuring out which driver, if any, could be the culprit in your case; I had read that this driver should be blacklisted on my hardware (which is a basketcase) for a completely different minor reason, and incidentally figured out it was to blame for these terrible freezes. Try testing with different kernels you have installed – Zanna Feb 01 '18 at 22:20
  • The character you see is a text rendering of a control character. In your case it is the NULL character ( 00 ). – ravery Feb 05 '18 at 11:15
  • Regarding your syslog: TL;DR replacing the thousands of lines of log file provided with the output of grep Error* /var/log/syslog would likely be more direct and to the point. – Elder Geek Feb 05 '18 at 17:50
  • @ElderGeek Ok i could do that, but in every documantation manual it's advised to post the full logs because context can be important. – jena Feb 06 '18 at 10:47
  • Have you tried booting a previous kernel? – Elder Geek Feb 06 '18 at 13:55
  • I had no previous kernel to boot from (I like to clean my SSD with apt autoremove once in a while) and I got really frustrated by the freezes, so I reinstalled the whole system (first to same version, then to Ubuntu 17.10, as the LTS had issues, as if my ~/.config folder survived disk formating & reinstall, weird). Now the freezes are gone, even though I run the same kernel as before (because new HWE policies). Of course I didn't install so much software yet, as I still suspect it was one of the programs I installed that caused all this.. – jena Feb 12 '18 at 20:56
  • daaamn it happened again :( there was a kernel update last week and i probably rebooted and it freezed again yesterday :( nothing in the logs again, all just stop reporting before the freeze.. now i have two kernels: 4.13.0-32 and -21, the older one is probably ok, because there was no freeze for a week. But now i don't know how to boot into it, holding shift during boot does nothing on my Dell Latitude 6430u :/ and i'm not really comfortable with editing some system config files - any other option? – jena Feb 15 '18 at 12:32
  • so it's also freezing on the older kernel (4.13.0-21) - i'm lost now :( – jena Feb 21 '18 at 12:31
  • I upgraded last week to 18.04 LTS (with 4.15.0-20 kernel) and the freezes still occur, I'm sending the laptop to repair service. I will probably include this thread into the report. – jena May 14 '18 at 11:59
  • @jena I'm having those freezes as well, luckily I found your post because my syslog also contains @^@^@^@^@^@^@^@^@^@^@^@ at the moment of the freeze. Did you finally find a culprit by any chance ? – Wadih M. Nov 25 '20 at 13:38
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    @WadihM. well the service replaced my ssd and the freezes mostly stopped (I experienced only 3 since, always under heavy load) so I think I had a HW issue.. – jena Nov 25 '20 at 14:28
  • @jena Thanks so much! I will also test my RAM, perhaps it's related to that. Because I added RAM that had different speeed recently, perhaps it has to do with that. – Wadih M. Nov 25 '20 at 17:21
  • As an update to everyone, the issue stopped after I disconnected the slower ram and moved the remaining RAM to another RAM slot, I also unplugged and re-plugged the disk. It has happened only once since after a few months, big improvement from once every night before! But I'm still wondering why it happened that one extra time after though, seems I might still be missing part of the picture. I'm starting to think it might have to do with swap on disk getting corrupt. – Wadih M. Jan 05 '21 at 13:35
  • I was also wondering about the 3 freezes, as the load wasn't that heavy (well there was gnome and lot of apps). But since the laptop was actually refurbished (Dell ultrabook for quite a cheap buck) I guess it will never be as new. Switching to elementaryOS helped with performance a lot and I didn't get any freeze since, for about a year now. – jena Jan 05 '21 at 17:12
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    @Jena Believe I found the reason, confident enough to post it as an answer, because I undid my previously mentioned attempts to fix it to go back to square one, and the kernel parameter alone was the end-all solution, going from a daily crash for months to no crashing at all. Now been a few months without crash, so coming back to post the solution. Cheers! – Wadih M. Feb 17 '21 at 21:57

1 Answers1

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It might be hard to confirm from your past case, but I believe this was the reason, and others will be able to upvote if this worked for them.

I found out there are a certain number of NVME SSD disks that don't play well with linux because of power related matters.

After many months of troubleshooting, I found the reason Ubuntu was suddenly freezing for no reason was because of that.

The solution was to add the following kernel parameter:

nvme_core.default_ps_max_latency_us=0

To do so, modify /etc/default/grub, and add the above to your GRUB_CMDLINE_LINUX_DEFAULT= string, e.g. mine looked like that:

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash nvme_core.default_ps_max_latency_us=0"

Then save, and run update-grub.

And reboot the system.

I have had a 100% success rate since, e.g. 0 crashes, not even an odd crash once in a while.

@Jena, if you still have your original NVME SSD disk that was causing the issue, it would be nice to have a full circle confirmation.

References:

Official kernel bug report: https://bugzilla.kernel.org/show_bug.cgi?id=195039

Wadih M.
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