Using Hydra to build custom images

Building custom images

You can build images with either the legacy (non-flake) and flake method, there are a few great resources such as nix.dev and NixOS Wiki. For example if we wanted a minimal (CLI only) ISO for x86_64 with helix and git we can do that here:

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{
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  description = "Minimal NixOS installation media";
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  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-25.05";
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  outputs = { self, nixpkgs }: {
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    nixosConfigurations = {
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      exampleIso = nixpkgs.lib.nixosSystem {
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        system = "x86_64-linux";
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        modules = [
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          ({ pkgs, modulesPath, ... }: {
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            imports = [ (modulesPath + "/installer/cd-dvd/installation-cd-minimal.nix") ];
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            environment.systemPackages with pkgs; = [ helix git ];
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          })
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        ];
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      };
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    };
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  };
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}

We would build the image like this using flakes:

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git init
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git add flake.nix
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nix build .#nixosConfigurations.exampleIso.config.system.build.images.iso

I started my own nixos live disk repository recently for building images for my Pi 4, Pi 5 and x86_64 minimal CLI versions.

If we want to build an image for aarch64-linux with the graphical installer for GNOME with the latest kernel, hostname set and helix.

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{
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  description = "Minimal NixOS installation media";
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  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-25.05";
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  outputs = {self, nixpkgs }: {
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    nixosConfigurations = {
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      drack = nixpkgs.lib.nixosSystem {
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        system = "aarch64-linux";
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        modules = [
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          ({ pkgs, lib, modulesPath, ... }: {
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            imports = [ "${modulesPath}/installer/cd-dvd/installation-cd-graphical-calamares-gnome.nix" ];
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            boot.kernelPackages = pkgs.linuxPackages_latest;
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            boot.supportedFilesystems = lib.mkForce [ "btrfs" "reiserfs" "vfat" "f2fs" "xfs" "ntfs" "cifs" ];
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            environment.systemPackages = with pkgs; [ helix ];
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            networking.hostName = "drack";
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            services.openssh.enable = true;
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            system.stateVersion = "25.05";
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          })
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        ];
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      };
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    };
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  };
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}

Having Hydra get a job

With the following in the flake we can have Hydra start building the images:

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    hydraJobs = {
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      images = {
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        vetra = self.nixosConfigurations.vetra.config.system.build.sdImage;
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        sidera = self.nixosConfigurations.sidera.config.system.build.sdImage;
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        drack = self.nixosConfigurations.drack.config.system.build.isoImage;
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        test-gui = self.nixosConfigurations.test-gui.config.system.build.isoImage;
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        test-cli = self.nixosConfigurations.test-cli.config.system.build.isoImage;
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      };
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    };

Other questions

Reach out to me on Mastodon for questions!