I would assume that’s the case and that the Fn key would continue to work in the event of a kernel hang. I’ve never had a keyboard where Print Screen was on a secondary layer so I can’t say for sure, but you could enable it, try it out, and report back to let others with Librem laptops know.
Update: the magic key combination is actually: Fn Alt PrtSc to invoke Sysrq. That’s because Sysrq is shared with PrtSc so you need Alt PrtSc to invoke it. Then you can use the magic sysrq key to forcibly tell the kernel to reboot, by holding Fn Alt PrtSc then typing R E I S U B, which, of course, stands for “Reboot Even If System Utterly Broken”
Does it reboot if you hit Alt + Fn + PrtSc + B ?
That works for me (L13 v3).
I’m not sure if the order is important, but I always press Fn directly before PrtSc, as it needs to apply to this key.
When I do REISUB, I also release all keys in between (I think it didn’t work for me otherwise).
I usually don’t need to release Fn Alt PrtSc when I REISUB… I also don’t think the modifier order matters, as long as Fn and Alt are pressed beforePrtSc.
That’s kind of nasty advice to give to people, for the record. The b shortcut is super aggressive – it sends a CPU reset instructions that causes an immediate reboot without any other operation, which can lead to data loss and filesystem corruption. That’s why you run the entire sequence.
A safer way to test this is to monitor your kernel logs, for example, in a terminal, with:
sudo dmesg -w
Then trying a shortcut like Fn Alt PrtSc a, which should print a usage like this: