virtualisation = {
              host.pkgs = pkgs;
              darwin-builder.workingDirectory = "/var/lib/darwin-builder";
              darwin-builder.hostPort = 22;
            };
          }
        ];
      };
    in
    {

      darwinConfigurations = {
        machine1 = darwinSystem {
          inherit system;
          modules = [
            {
              nix.distributedBuilds = true;
              nix.buildMachines = [
                {
                  hostName = "localhost";
                  sshUser = "builder";
                  sshKey = "/etc/nix/builder_ed25519";
                  system = linuxSystem;
                  maxJobs = 4;
                  supportedFeatures = [
                    "kvm"
                    "benchmark"
                    "big-parallel"
                  ];
                }
              ];

              launchd.daemons.darwin-builder = {
                command = "${darwin-builder.config.system.build.macos-builder-installer}/bin/create-builder";
                serviceConfig = {
                  KeepAlive = true;
                  RunAtLoad = true;
                  StandardOutPath = "/var/log/darwin-builder.log";
                  StandardErrorPath = "/var/log/darwin-builder.log";
                };
              };
            }
          ];
        };
      };

    };
}
```

## Reconfiguring the remote builder {#sec-darwin-builder-reconfiguring}

Initially you should not change the remote builder configuration else you will not be
able to use the binary cache. However, after you have the remote builder running locally
you may use it to build a modified remote builder with additional storage or memory.

To do this, you just need to set the `virtualisation.darwin-builder.*` parameters as
in the example below and rebuild.

```nix
{
  darwin-builder = nixpkgs.lib.nixosSystem {
    system = linuxSystem;
    modules = [
      "${nixpkgs}/nixos/modules/profiles/nix-builder-vm.nix"
      {
        virtualisation.host.pkgs = pkgs;
        virtualisation.darwin-builder.diskSize = 5120;
        virtualisation.darwin-builder.memorySize = 1024;
        virtualisation.darwin-builder.hostPort = 33022;
        virtualisation.darwin-builder.workingDirectory = "/var/lib/darwin-builder";
      }
    ];
  };
}
```

You may make any other changes to your VM in this attribute set. For example,
you could enable Docker or X11 forwarding to your Darwin host.

## Troubleshooting the generated configuration {#sec-darwin-builder-troubleshoot}

The `linux-builder` package exposes the attributes `nixosConfig` and `nixosOptions` that allow you to inspect the generated NixOS configuration in the `nix repl`. For example:

```
$ nix repl --file ~/src/nixpkgs --argstr system aarch64-darwin

nix-repl> darwin.linux-builder.nixosConfig.nix.package
«derivation /nix/store/...-nix-2.17.0.drv»

nix-repl> :p darwin.linux-builder.nixosOptions.virtualisation.memorySize.definitionsWithLocations
[ { file = "/home/user/src/nixpkgs/nixos/modules/profiles/nix-builder-vm.nix"; value = 3072; } ]

```