Questions[sysrq](ubuntu)

I am using Ubuntu 20.04 on Dell vostro 7500. But the whole system crash frequently. The symptom is the screen shows no response to keyboard event and mouse event(mouse cannot move or click), but the screen is still light and showing the graphic contents(but everything including the time is stuck). SysRq+REISUB, which works in normal time on my machine, is invalid when crashing. And /var/log/syslog contains nothing after the crash. So it should be a kernel crash. Does anybody encounter this problem ever? I have reported this on launchpad https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1909381. Please vote on it if you also share the same problem.

After the crash, I updated my BIOS and fully tested my hardware and found no hardware error. Switching my kernel from 5.4.0-58-generic back to 5.4.0-42-generic also does not solve this problem.

I searched the contents in syslog just before the crash, but I found no much similar pattern. But the following line appears before both of the two crashes:

Dec 22 19:09:12 ofSimon kernel: [  878.796035] sof-audio-pci 0000:00:1f.3: error: no reply expected, received 0x0

I do not know what it means, and I noticed that this line also appear in tty every time when I shutdown my computer. Can anyone explain it to me?

Hey there I am doing yet another edit with newly gathered information. So far there has been few responses here, so this will probably be the last one.

I am running a ThinkPad P14s with Ubuntu 20.04. Some times the machine freezes completely and I have to hard reset it.

I am almost sure this does not happen because I am running out of RAM or the machine getting to hot.

Of course I want to track the root of the problem, but I also want to learn more about how to approach these problems in general as I have little knowledge of Ubuntu and Linux in general. So what log file and setting should I look at? What am I looking for? Maybe there are also guides that you could link me to. Although I get overwhelmed by those quite fast. A similar question has been asked here (Tracking down a random freeze?) and /var/log/syslog is mentioned there but the question of what to look for was not answered.

I have gathered some additional information that hopefully can enable some one to help me.

Occurrences and graphics card

I am not 100% certain but I think the freezes occur exclusively when

• watching a DvD / Blueray
• streaming videos
• during games

I changed what graphics card is used with prime-select [nvidia | intel]. But the freezes occur in both setups.

no REISUB

When a freeze occurs I cannot reboot the system with SysRq + R E I S U B. From what I understand that is not the case for "most" system crashes. Does that lead towards some possible problems more that towards others?

memtest

I tried to to do the steps here but holding Shift did not open GRUB. After some searching I found that I can change /etc/default/grub such that I have:

GRUB_TIMEOUT_STYLE=menu
GRUB_TIMEOUT=10

Now GRUB opens on every reboot, but there is no option memtest86+ available. I checked that /etc/grub.d/ contains the executable file 20_memtest86+ and I also checked all options under "advanced" in GRUB.

What else could I try in order to run memtest?

psensor

I do not think my problem comes from overheating. The last couple of freezes happened when my Laptop felt relatively cool. I use "psensor" to constantly track the temperature.

problems on reboot

This may or may not be related. I recently was trying to load a save game of some game but the game crashed every time. I decided to reboot the system to see if that helps but the reboot could not be completed! Instead the following was printed:

Virtual device wlp0s20f3 asks to queue paket!
sytemmd-shutdown[1]: Could not detach Dm /dev/dm-0: Device or resource busy
sytemmd-shutdown[1]: Failed to finalize DM devices, ignoring
sof-audio-pci 0000:00:1f.3: error: no reply expected, received 0x0
xhci_hcd 0000:2b:00.0: Host halt failed, -19

I had to hard reset after this. What does that mean?

https://en.wikipedia.org/wiki/Magic_SysRq_key

According to this it's very important. What I can do? Can I rebind this key to something else?

The magic SysRq key does not work on my Ubuntu 16.04 desktop. I imagine it's now disabled by default. My attempts to enable it did not work, and the only thing Google finds is a 2007 forum post from when it was apparently enabled by default.

Can I enable it? If so, how?

[Added the following after the first answer:]

According to https://en.wikipedia.org/wiki/Magic_SysRq_key "In Ubuntu the combination of Alt+SysReq acts as "print screen" command." This is in fact the behaviour I observe on a non-hung system, even after doing sudo sysctl -w kernel.sysrq=1 I get some kind of screen capture on my desktop. Not what I want.

It's not practical to write to /proc/sysrq-trigger from a system that's basically hung, trying to get information to debug the problem.

On occasion, my laptop has become stuck so I've used the magic key combination of Alt + SysRq + REISUB to perform a safe reboot. However, it doesn't seem to work for me as when I press the B key to complete the magic key command it simply says, "resetting..." and doesn't do anything.

All of the other keys seem to work fine as it resets the keyboard layout, kills all tasks etc., but it doesn't seem to complete with a reboot.

I was under the impression that my laptop should reboot after the magic keys have all been pressed in the order of REISUB.