When I try to update Nix itself on a non-NixOS system (Linux in this case), I get this error:
$ nix upgrade-nix
error: directory '/home/cv/.nix-profile/bin' does not appear to be part of a Nix profile
Which makes no sense:
$ readlink -q ~/.nix-profile
/nix/var/nix/profiles/per-user/cv/profile
How much more of a profile can this be?