NixOS - it either works and you have a new generation, or it doesn't work and you keep the same state. If the new generation has some problems, you can switch t

NixOS - it either works and you have a new generation, or it doesn't work and you keep the same state. If the new generation has some problems, you can switch to the previous one via a single command or select the previous one from the GRUB menu when booting.