Home-manager installation questions

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If you want to rigorously separate system configuration from user configuration - for example to make your user environment portable to machines which you don’t control - you have to install home-manager in the user environment. It is not required to do this with nix-env or using nix-channel. You can also instantiate a nix-shell with the same version of home-manager that will handle your environment.

Let’s say your files live in ~/.config and the entry point to your configuration is ~/.config/home.nix. Then we can define a version of home-manager in sources.nix:

{ pkgs ? import <nixpkgs> {} }:
with pkgs;
{
  home-manager = let
    src = builtins.fetchGit {
      name = "home-manager";
      url = https://github.com/rycee/home-manager;
      ref = "release-20.03";
    };
  # `path` is required for `home-manager` to find its own sources
  in callPackage "${src}/home-manager" { path = "${src}"; };
}

Then you can instantiate your configuration in nix-shell by importing that definition:

$ nix-shell -E \
"with import <nixpkgs> {}; mkShell { buildInputs = [ (callPackage ./sources.nix {}).home-manager ]; }" \
--run "home-manager -f ~/.config/home.nix switch"

Of course your home.nix includes the same home-manager in the environment:

{ pkgs, ... }:
with pkgs;
let
  home-manager = writeShellScriptBin "home-manager" ''
    # `toString` is required to impurely track your configuration instead of copying it to `/nix/store`
    exec ${(callPackage ../home-sources.nix {}).home-manager}/bin/home-manager -f ${toString ./home.nix} $@
  '';
in
{
    home.packages = [ home-manager ];
}

That way you can update home-manager in sources.nix and just run home-manager switch to have it available.

This simplified version uses the system’s nixpkgs, but you could just as well specify one just for that user environment. Don’t forget that home-manager’s release number should match that of your nixpkgs, otherwise you may get weird errors due to incompatible package definitions. On my machines I have the nix-shell invocation as part of an installation script, and also parameterize home-manager over different machine-specific configurations.

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