[Nix-dev] Cannot upgrade old NixOS

[Michael Raskin]

>> The feature isn't used too much yet, so I suggest to comment out the
>> offending lines in <nixpkgs>/pkgs/top-level/all-packages.nix (until you
>> switch to upgraded version).
>
>Thanks. That helped a bit. Now I have a problem:
>
>error: `This version on Nixpkgs requires Nix >= 1.2, please upgrade`
>
>Is it possible to recover from this point?
>I tried `nix-env -u nix` - error stays.

I guess you have to go to hydra.nixos.org and download closure of 
a reasonably fresh NixPkgs Nix.