Determinate Nix

Determinate Nix is Determinate Systems’ downstream distribution of Nix (flakes enabled by default, lazy-trees, its own determinate-nixd daemon). This flake used to run it on every host; it has since been removed in favour of the stock Nix that ships with nixpkgs.

This page documents how it was wired in so it can be re-enabled if ever needed — and the one gotcha (source rebuilds) that made it painful.

Why it was removed

The determinate module pins a specific determinate-nix-<version> build. That build is published as a binary on the FlakeHub cache, but this flake never listed https://cache.flakehub.com as a substituter — only its public key was present (see the gotcha below). So every version bump rebuilt Determinate Nix (and its boost etc. dependencies) from source during nh os switch, which was slow enough to not be worth it. Stock Nix already covers everything this config needs (flakes, nix-command, pipe-operators are enabled in modules/nixos/system/nix-utils.nix and modules/darwin/system/nix.nix, independent of Determinate).

How to re-enable it

Three edits, then rebuild:

Add the flake input (flake.nix):

determinate.url = "https://flakehub.com/f/DeterminateSystems/determinate/*";

Import the module for the relevant platform (systems/default.nix) — it lives in the nixosModules / darwinModules list:
```
# in nixosModules
determinate.nixosModules.default
# in darwinModules
determinate.darwinModules.default
```

Add the FlakeHub cache substituter (flake.nix → nixConfig). This is the important one — without it, Determinate Nix builds from source:

extra-substituters = [
  # …
  "https://cache.flakehub.com"
];
extra-trusted-public-keys = [
  # …
  "cache.flakehub.com-3:hJuILl5sVK4iKm86JzgdXW12Y2Hwd5G07qKtHTOcDCM="
];

Then just switch (NixOS) / just switch on the darwin host.

The gotcha: install.determinate.systems is the installer host, not a binary cache. The Determinate Nix binaries live on cache.flakehub.com. If you re-add the module but forget the substituter, you’ll compile Nix from source on every lockfile bump — the exact reason it was removed.

Platform notes

NixOS

The determinate.nixosModules.default module sets nix.package to the Determinate build and hands daemon management to determinate-nixd. Nothing else in the config depends on it — nix-command/flakes/pipe-operators come from modules/nixos/system/nix-utils.nix, so removing Determinate does not disable flakes.

darwin (`tensa`)

On darwin the module sets nix.enable = false, telling nix-darwin not to manage Nix (Determinate manages it out-of-band via determinate-nixd). It also consumes a determinateNix.customSettings option to push the shared settings into Determinate’s config.

If you run darwin on stock Nix instead, nix.enable must be true so nix-darwin manages the daemon — otherwise nothing configures Nix on that host. modules/darwin/system/nix.nix is where both live.

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