slug
/health

Nix Health

nix-health¹ is a program that checks the health of your Nix install. Furthermore, individual projects can configure their own health checks in their flake.nix. For example, the nammayatri project checks that the cachix cache is in use.

Checks performed

Check	Configurable in flake.nix?
Flakes are enabled	-
Nix version is not too old	Yes
Nix runs natively (no rosetta)2	Yes
Builds use multiple cores (max-jobs)	Yes
Nix Caches in use	Yes
$USER is in trusted-users	-
Direnv: installed and activated	Yes
Min RAM / Disk space	Yes

Note that some checks are considered non-essential. For eg., the disk space check looks for 1TB+ disk space, but if the user is on a laptop with 256GB SSD, the check will report a warning instead of failing. This can also be configured in per-project basis from flake.nix (see below).

Usage

Note

nix-health 0.3.0 is available on nixpkgs.

To run the development version,

# NOTE: You may have to add `--extra-experimental-features "flakes nix-command"`
# if flakes are not already enabled
nix --accept-flake-config run github:juspay/nix-health

To run nix-health along with health check configuration specified in a project flake, pass that flake as an argument. For eg., to run nix-health with additional checks from the nammayatri project, run:

# The argument can be any flake URL (including a local path)
nix --accept-flake-config run github:juspay/nix-health github:nammayatri/nammayatri

Configuring in flake.nix {#conf}

To add project specific health checks or configure health checks, add the following flake output:

{
  outputs = inputs: {
    nix-health.default = {
      # Add configuration here
      caches.required = [ "https://ourproject.cachix.org" ];
    };
  };
}

To see all available configuration options, run nix-health --dump-schema. This will dump the schema of the configuration in JSON format. Convert that to a Nix attrset to see what can be added under the nix-health.default attrset of your flake.

$ nix-health --dump-schema > schema.json
$ nix eval --impure --expr 'builtins.fromJSON (builtins.readFile ./schema.json)' | nix run nixpkgs#alejandra -- --quiet
{
  caches = {required = ["https://cache.nixos.org/"];};
  direnv = {
    enable = true;
    required = false;
  };
  flake-enabled = {};
  max-jobs = {};
  nix-version = {min-required = "2.13.0";};
  rosetta = {
    enable = true;
    required = true;
  };
  system = {
    enable = true;
    min_disk_space = "1024.0 GB";
    min_ram = null;
    required = false;
  };
  trusted-users = {};
}

Adding devShell check

You can automatically run nix-health whenever your Nix dev shell starts. To do this, import the flake module in your flake and use it in your devShell:

{
  inputs = {
    # NOTE: refers to ./module flake.
    nix-health.url = "github:juspay/nix-health?dir=module";
  };
  outputs = inputs:
    inputs.flake-parts.lib.mkFlake { inherit inputs; } {
      imports = [
        inputs.nix-health.flakeModule
      ];
      perSystem = { config, pkgs, ... }: {
        devShells.default = pkgs.mkShell {
          inputsFrom = [
            config.nix-health.outputs.devShell
          ]
        };
      };
    };
}

Now suppose you have Nix 2.18 installed, but your project requires 2.19 or above due to the following config in its flake.nix:

flake.nix-health.default = {
  nix-version.min-required = "2.19.0";
};

you can expect the devShell to print a giant message like this:

Note that you will still be dropped into the Nix dev shell (there's no way to abrupt the launching of a dev Shell).

Footnotes

1. nix-health originally began as a script https://github.com/srid/nix-health which is now deprecated. ↩

2. This check is only performed on macOS with Apple Silicon. ↩