How to use nix-serve with an alternative store location

nix-serve.md

This is something you might want to do if you have an existing store directory on another dataset but don't want to overlay mount it onto /nix/store.

~/shell.nix is

{
  pkgs ? import <nixpkgs> {
    overlays = [
      (self: super: {
        nix = super.nix.override {
          storeDir = "/mnt/nix/store";
          stateDir = "/mnt/nix/var";
        };
      })
    ];
  }
}: pkgs.mkShell {
  buildInputs = [
    pkgs.nix
    pkgs.nix-serve
  ];
}

nixpkgs revision: https://github.com/NixOS/nixpkgs-channels/archive/fce7562cf46727fdaf801b232116bc9ce0512049.tar.gz

~ # readlink -f /root/.nix-defexpr/channels/nixos/
/nix/store/xv5v445yf322zfh0xirb05vpw2jyjk4m-nixos-20.09pre223023.fce7562cf46/nixos

~ # nix-shell

# ...

~ # nix-serve -p 8080

# in another terminal

~ # curl http://127.0.0.1:8080/nix-cache-info
StoreDir: /mnt/nix/store
WantMassQuery: 1
Priority: 30

~ # nixos-install --option extra-binary-caches http://127.0.0.1:8080/

warning: binary cache 'http://127.0.0.1:8080' is for Nix stores with prefix '/mnt/nix/store', not '/nix/store' 🥺