How do I upgrade my existing Nix installation? After updating the nixpkgs-unstable channel, nixpkgs.nix is still 1.11.16 (and nixpkgs.nixUnstable is a 2.0 pre-release).

Look up channels status here:

http://howoldis.herokuapp.com

It will prob take like 5 hours to be updated. Run nix-channel --update then reinstall nix.

Would it be safe to run `curl https://nixos.org/nix/install | sh` (safe as in it won't screw with my existing installed packages), and if so, will that get me Nix 2.0? Or do I still have to wait for nixpkgs-unstable to rebuild?

The easiest way is probably to do following:

  git clone https://github.com/nixos/nixpkgs
  cd nixpkgs
  git checkout origin/nix-2.0
  nix-env -i $(nix-build --no-out-link . -A nix)