Roconnor mentioned some problems on irc about that... I've had /nix off the /root partition in many computers. You simply need to mark in fileSystems the partition as: neededForBoot = true; I also had the 'nix' directory inside the /home partition, and then I bind-mounted /home/nix to /nix, also using the neededForBoot mounts. Regards, Lluís.