Resolved store paths

Nix resolves all valid derivations to a store path. Here’s an example:

nix path-info "https://flakehub.com/f/NixOS/nixpkgs/*#coreutils"

That command evaluates a specific flake reference from Nixpkgs and returns a store path of this form (it will differ on your system):

/nix/store/1. Nix store prefix
sglc12hc6pc68w5ppn2k56n6jcpaci162. Hash part
-
coreutils-9.53. Package name

Evaluating store paths is an expensive operation in Nix, and one that’s preferably avoided on resource-constrained devices or when Nix is not available on the host system. For situations like this, FlakeHub can resolve store paths for you, persist them, and make them available via the fh resolve and fh apply commands.

Resolving paths using fh

You can use the fh resolve command to fetch resolved store paths from FlakeHub. Here’s an example:

fh resolve "https://flakehub.com/f/my-org/my-flake/0.1#nixosConfigurations.auth-server"

That would return a store path like this:

/nix/store/
5yg2v0iz3dl27rwaw3brzadwfj702b89
-
auth-server-0.1.4

What’s noteworthy here, though, is that Nix isn’t resolving the store path; instead, fh is making an HTTP request to the FlakeHub API to fetch the store path (and that request is automatically authenticated if the flake is private). The store path is available this way because flakehub-push already generated it during the flake’s publishing process (see How to pre-resolve store paths below to see how to enable this).

Applying system configurations using fh

You can apply full system configurations for NixOS, Home Manager, and nix-darwin from resolved store paths using the fh apply. Here are some examples:

fh apply nixos "my-org/my-nixos-config-flake/*"

fh apply home-manager "my-org/my-home-manager-config-flake/*"

fh apply nix-darwin "my-org/my-nix-darwin-config-flake/*"

In all these cases, Nix doesn’t need to evaluate the flake reference to determinate the store path; the store path is already available and Nix can copy the closure at that path directly from FlakeHub Cache. This can make some deployment scenarios far less resource intensive than those involving standard nix build commands.

How to pre-resolve store paths

You can make FlakeHub resolve and persist store paths when publishing your flakes by adding a single line to your flakehub-push configuration:

- name: Publish to FlakeHub
  uses: DeterminateSystems/flakehub-push@main
  with:
    include-output-paths: true

Once you’ve added this configuration, subsequent releases of your flake will have resolved store paths available to fh resolve. If you’re using FlakeHub Cache, then you can use fh apply to apply NixOS, Home Manager, and nix-darwin system configurations.