Automatic shutdown if system temp is high?

There are a few ways to do it, but the easiest is to run the 'sensors' command from the lm_sensors package, but I prefer the simplicity of the acpi command

For example,

[fedora ~]$ acpi -t Thermal 0: ok, 20.0 degrees C

So you could do:

#!/usr/bin/bash

if [ $(acpi -t | cut -d" " -f4 | cut -d"." -f1) -gt 80 ]; then
        # halt?  shutdown? reboot?  It's up to you.
fi

The second way is to use your BIOS settings to see if you can adjust the trip temperature. On my system,

[fedora ~]# sensors

which means the system will auto-shutdown at 110.0 degrees.

You can see that this happens at https://elixir.bootlin.com/linux/latest/source/drivers/thermal/thermal_core.c#L316

The best option is likely creating a script in user scripts as you can tune that as you please. Having a quick look on Unraid, there may be an option: https://forums.unraid.net/topic/39111-feature-request-perform-a-clean-shutdown-if-disk-reaches-critical-temp/?do=findComment&comment=898761

I know it's possible to get the system temperature from sensors. Which gets the info from /sys/class/thermal

You could probably write a wrapper around the temperature from there and when it gets to 100? Perform a shutdown