Divide by Zero Error on Boot

Hi Ryan,
As requested I've now found the time to gather more data you asked for.
I can now confirm that after the server boots, it shows the boot menu briefly, then for a fraction of a second the "Welcome to Grub" black screen shows. You have to be fast to catch it though as it's so quick. Normally after that it switches to the TrueNas blue bootloader screen for a second and then starts booting Linux. However, once the crash occurs after the very fast Grub screen shows it goes straight ot he red "Divide By Zero" screen instead of the usual Turneas blue bootloader screen.

This additional information would seem to prove it is not the server's firmware having this issue as suspected above as far as I can tell, but happy to be corrected if you think that is possible even after the Welcome to Grub screen.

A few more relevant pieces of information I have found:
1) This error only occurs if I select Reboot from the Truenas shutdown menu. If I select Shutdown and then turn the server back on again all is fine (I have tested this over half a dozen times now so confidence is high that is safe now).
2) This error also affects the new 21.08 BETA2 in the same way.

So to summarise, this issue is avoidable usually if I remember to never use the Reboot option. Unfortunately upgrading to higher releases from the GUI is out of the question as this automatically reboots afterwards instead of shutting down so causes the issue.
A fresh install from USB stick is fine as that gives the option to shutdown once completed instead of reboot.

N.B. Once the Divide By Zero error has occurred once, it never boots again even if power down/up completely, as Divide By Zero comes back every single time. Also once you have rebooted and got that error, the usb boot upgrade previous installation always fails so you can only install it fresh while choosing the format the boot device option.
I have not yet tried a full shutdown and then boot to new version on USB and then an upgrade via that method but I suspect it would work. I will try it when 21.10 is out.

Thanks!

Unfortunately I don't think there's anything we can do to resolve this issue other than hope it is an issue that gets fixed upstream somewhere. There's nothing useful for me to go off of and it doesn't seem to be a common issue other people experience either.

Hi,
Up to June 2021 it was running Ubuntu 20.04 fine since around mid 2020. Prior to that it was running Windows years ago then Linux Mint for a few years, never with any issues. At that point switched to SCALE 21.06 and that also was fine the few times I rebooted it since.

I've not tried another OS since upgrading to 21.08 and seeing this error as this system is in use so difficult to find the time to do that, but will do if useful at some point.
Interesting that you say it's not from Linux, I hadn't considered that as assumed the OS as that was the only thing that had changed, and it had rebooted fine many times including a few times right before the upgrade but it could be true and just a case of coincidental timing I guess?
The server goes though the usual POST checks and all passes and then get to the point where the bootloader would normally show briefly, but while the screen goes black right before the RSOD it is too quick to read it even so no chance of switching the boot option.

If it is a firmware bug could it be something that 21.08 is doing differently that past OS's have not that could explain it? Can i provide any logs before the reboot to help?

@Paul Hawker Does this machine still work with other operating systems? You say you ran Ubuntu and a previous scale version fine before, but what about after?

This error doesn't come from the Linux kernel, it looks like it comes from the machine's firmware.

At what point do you see this message? Is it before or after the GRUB boot menu? Can you choose the 21.06 boot environment from the boot menu to boot successfully?