I have scoured both Askubuntu as well other sites for this and haven't found anything substantial, so I hope it's not too much of a duplicate.
In any case, I've been lately experiencing random freezes - the system locks up completely, my keyboard and mouse do not respond, the PC also disappears from active network clients (by scanning my network with nmap from a different PC) so I assume it dies completely instead of just losing the inputs. It started happening recently, after upgrading to 19.04.
I haven't been able to pinpoint the problem, and the only common denominator seems to be Chrome. However, even then there's a huge window of variation, as I can be doing anything from watching YT to just reading Latex formatting tips, so anything from high to low load. I have GPU acceleration and other experimental goodies turned off, so I don't think it's that - besides, I never had such problems before 19.04.
The following comes up in /var/log/syslog just before the freeze:
Sep 25 12:31:08 meeshbox systemd[1]: Started Run anacron jobs.
Sep 25 12:31:08 meeshbox anacron[11822]: Anacron 2.3 started on 2019-09-25
Sep 25 12:31:08 meeshbox anacron[11822]: Normal exit (0 jobs run)
Sep 25 12:31:08 meeshbox systemd[1]: anacron.service: Succeeded.
Sep 25 12:31:32 meeshbox org.gnome.Shell.desktop[1329]: Window manager warning: Window 0x3802c74 sets an MWM hint indicating it isn't resizable, but sets min size 1 x 1 and max size 2147483647 x 214748364
7; this doesn't make much sense.
Sep 25 12:31:32 meeshbox org.gnome.Shell.desktop[1329]: Window manager warning: Window 0x3802c74 sets an MWM hint indicating it isn't resizable, but sets min size 1 x 1 and max size 2147483647 x 214748364
7; this doesn't make much sense.
Sep 25 12:36:28 meeshbox org.gnome.Shell.desktop[1329]: [1:1:0925/123628.789445:ERROR:child_process_sandbox_support_impl_linux.cc(81)] FontService unique font name matching request did not receive a respo
nse.
Sep 25 12:36:28 meeshbox org.gnome.Shell.desktop[1329]: [1:1:0925/123628.791155:ERROR:child_process_sandbox_support_impl_linux.cc(81)] FontService unique font name matching request did not receive a respo
nse.
Sep 25 12:36:45 meeshbox org.gnome.Shell.desktop[1329]: Window manager warning: Window 0x38039d7 sets an MWM hint indicating it isn't resizable, but sets min size 1 x 1 and max size 2147483647 x 214748364
7; this doesn't make much sense.
Sep 25 12:36:45 meeshbox org.gnome.Shell.desktop[1329]: Window manager warning: Window 0x38039d7 sets an MWM hint indicating it isn't resizable, but sets min size 1 x 1 and max size 2147483647 x 214748364
7; this doesn't make much sense.
Sep 25 12:38:08 meeshbox org.gnome.Shell.desktop[1329]: Window manager warning: Window 0x3803b5a sets an MWM hint indicating it isn't resizable, but sets min size 1 x 1 and max size 2147483647 x 214748364
7; this doesn't make much sense.
Sep 25 12:38:08 meeshbox org.gnome.Shell.desktop[1329]: Window manager warning: Window 0x3803b5a sets an MWM hint indicating it isn't resizable, but sets min size 1 x 1 and max size 2147483647 x 2147483647; this doesn't make much sense.
Sep 25 12:38:26 meeshbox org.gnome.Shell.desktop[1329]: Window manager warning: Window 0x3803bc3 sets an MWM hint indicating it isn't resizable, but sets min size 1 x 1 and max size 2147483647 x 2147483647; this doesn't make much sense.
Sep 25 12:38:26 meeshbox org.gnome.Shell.desktop[1329]: Window manager warning: Window 0x3803bc3 sets an MWM hint indicating it isn't resizable, but sets min size 1 x 1 and max size 2147483647 x 2147483647; this doesn't make much sense.
Sep 25 12:38:40 meeshbox org.gnome.Shell.desktop[1329]: Window manager warning: Window 0x3803c21 sets an MWM hint indicating it isn't resizable, but sets min size 1 x 1 and max size 2147483647 x 2147483647; this doesn't make much sense.
Sep 25 12:38:40 meeshbox org.gnome.Shell.desktop[1329]: Window manager warning: Window 0x3803c21 sets an MWM hint indicating it isn't resizable, but sets min size 1 x 1 and max size 2147483647 x 2147483647; this doesn't make much sense.
Sep 25 12:38:41 meeshbox org.gnome.Shell.desktop[1329]: Window manager warning: Window 0x3803c35 sets an MWM hint indicating it isn't resizable, but sets min size 1 x 1 and max size 2147483647 x 2147483647; this doesn't make much sense.
Sep 25 12:38:41 meeshbox org.gnome.Shell.desktop[1329]: Window manager warning: Window 0x3803c35 sets an MWM hint indicating it isn't resizable, but sets min size 1 x 1 and max size 2147483647 x 2147483647; this doesn't make much sense.
Sep 25 12:38:42 meeshbox org.gnome.Shell.desktop[1329]: Window manager warning: Window 0x3803c49 sets an MWM hint indicating it isn't resizable, but sets min size 1 x 1 and max size 2147483647 x 2147483647; this doesn't make much sense.
Sep 25 12:38:42 meeshbox org.gnome.Shell.desktop[1329]: Window manager warning: Window 0x3803c49 sets an MWM hint indicating it isn't resizable, but sets min size 1 x 1 and max size 2147483647 x 2147483647; this doesn't make much sense.
Sep 25 12:38:51 meeshbox org.gnome.Shell.desktop[1329]: Window manager warning: Window 0x3803ca1 sets an MWM hint indicating it isn't resizable, but sets min size 1 x 1 and max size 2147483647 x 2147483647; this doesn't make much sense.
Sep 25 12:38:51 meeshbox org.gnome.Shell.desktop[1329]: Window manager warning: Window 0x3803ca1 sets an MWM hint indicating it isn't resizable, but sets min size 1 x 1 and max size 2147483647 x 2147483647; this doesn't make much sense.
Sep 25 12:39:02 meeshbox org.gnome.Shell.desktop[1329]: Window manager warning: Window 0x3803d01 sets an MWM hint indicating it isn't resizable, but sets min size 1 x 1 and max size 2147483647 x 2147483647; this doesn't make much sense.
Sep 25 12:39:02 meeshbox org.gnome.Shell.desktop[1329]: Window manager warning: Window 0x3803d01 sets an MWM hint indicating it isn't resizable, but sets min size 1 x 1 and max size 2147483647 x 2147483647; this doesn't make much sense.
Sep 25 12:40:09 meeshbox smartd[910]: Device: /dev/sdb [SAT], SMART Usage Attribute: 190 Airflow_Temperature_Cel changed from 68 to 67
Sep 25 12:40:09 meeshbox smartd[910]: Device: /dev/sdb [SAT], SMART Usage Attribute: 194 Temperature_Celsius changed from 32 to 33
Sep 25 12:41:14 meeshbox systemd-resolved[803]: Server returned error NXDOMAIN, mitigating potential DNS violation DVE-2018-0001, retrying transaction with reduced feature level UDP.
Nothing of interest in kern.log. Never had this problem with 18.04. It's not very common, but quite irritating once it happens - for example now, I lost a pretty substantial chunk of code I was writing, as I was dumb enough not to save it. It also never happened when, for example, playing games, even with other stuff in the background. I cannot really pinpoint it properly. However, scouring logs from the last week for when the freezes happened, I found that lines like this:
[1:1:0925/123628.789445:ERROR:child_process_sandbox_support_impl_linux.cc(81)] FontService unique font name matching request did not receive a response.
are often seen shortly before a freeze - but not immediately before it, more like 3-4 minutes.
What other logs can be relevant to check?
Enable systemd multi-boot message logs
The best solution is to enable multi-boot message logging and then displaying the last messages of the previous boot:
In your case the messages won't show a normal shutdown but rather the last recorded messages just before the system crashed.
Analyzing the messages you found so far
The first error message is addressed here:
The solution is to use:
The second error message is generated by nvidia:
The answers posted are only helpful for the software developer, not the end user. For end users running chrome other solutions exist:
System lockups can be notoriously hard to diagnose, particularly when nothing shows in syslog. You could check journalctl as suggested in the other answer but my guess is it won't show anything more informative.
If you are able to find a way to reliably trigger the freeze, then running
dmesg --follow --humanin a window may show something useful. However, much of the time the freeze occurs so suddenly nothing actually gets logged. And a lot of time these 'random freezes' are difficult to narrow to any specific cause.System freezes can be caused by an issue in the hardware itself (e.g. bad memory, overloaded power supply, ...), a defected in the BIOS, or a bug in the kernel or it's hardware drivers (GPU drivers particularly). Sometimes it's most time efficient to first try upgrading/downgrading the kernel, then see if there is a BIOS update available and if so update it, then do some hardware diagnostics and/or replacements.
GPU lockups are a common type of system freeze. For Intel graphics there are tools to get dumps off the video card itself following a freeze (see docs for intel-gpu-tools), but it can be hit or miss to get useful enough information. Often best case is to keep updating your bios, kernel, and/or hardware until the issue goes away.
I had crashes every few minutes with my AMD Ryzen 3800 + Ubuntu 18.04 + Gigabyte B450, very annoying stuff.
What seems to have done the trick was tweaking a few BIOS settings.
Under Advanced CPU Settings: - SMT -> disabled - Power Supply Idle Control -> Typical current idle - Global C-State control -> disabled