How to rollback to a previous generation? (Pi5)

[DerRockWolf]

I have a Pi5 without uboot as I'm booting from a NVMe SSD.
After updating my configuration and running nixos-rebuild switch the Pi was working fine, but after a small power outage a week later it stopped booting up. No output on HDMI, not responding to ICMP.

I suspect that some update caused this and I'm now wondering how I can boot into a previous generation.

I've already tried to connect the SSD to my PC and use nixos-enter to then change the default generation using switch-to-generation. I wasn't able to get nixos-enter to work, I always got:

sudo nixos-enter --root /run/media/xxx/NIXOS_SD
chroot: failed to run command ‘/nix/var/nix/profiles/system/activate’: No such file or directory
chroot: failed to run command ‘/nix/var/nix/profiles/system/sw/bin/bash’: No such file or directory

I also tried to set --system which resulted in the same errors (with slightly different paths).

Was someone smarter than me already able to boot into a previous generation? Any tips are highly appreciated. 🙂

[DerRockWolf]

I was able to recover, although not by booting into a previous generation.
I got hit by the breaking change introduced in #79 as I didn't pin to a release.

I just needed to re-add root, rootfstype & rootwait to cmdline.txt. And the Pis boot loader doesn't support multiple boot entries.
It could still have been useful if old versions of cmdline.txt and config.txt were retained for easier rollback.