FWIW, I’ve just had to rollback a second time (discourse topic), and I discovered /run/current-system/bin/switch-to-configuration boot which is better than sudo nixos-rebuild switch --rollback.
Rollback rolls you back from the current, broken generation, to the previous one, which is hopefully working. This isn’t an ideal workflow, because:
- you need to be booted up into the broken gen,
- you need to remember that the previous gen is OK (which it might actually not be)
What switch-to-configuration does is it makes the current configuration default. So the workflow is:
- you do upgrade
- you reboot
- you notice stuff is broken
- you reboot into the generation which works for you (not necessary the previous one)
- you verify that it indeed works
- you make it current by running
/run/current-system/bin/switch-to-configuration boot