{
  description = "NixOS configuration for Raspberry Pi 3+";

  nixConfig = rec {
    auto-optimise-store = true;
    experimental-features = [ "nix-command" "flakes" ];
    trusted-substituters = [
      "https://mirrors.ustc.edu.cn/nix-channels/store" # 中科大
      "https://mirrors.tuna.tsinghua.edu.cn/nix-channels/store" # 清华
      "https://mirrors.bfsu.edu.cn/nix-channels/store" # 北外
      "https://mirror.sjtu.edu.cn/nix-channels/store" # 交大
      "https://nixos-cn.cachix.org"
      "https://cache.nixos.org/"
    ];
    substituters = trusted-substituters;

    trusted-users = [
      "pi"
      "root"
      "@wheel"
    ];
  };

  inputs = {
    nixpkgs.url = "nixpkgs/nixos-23.05";
    impermanence.url = "github:nix-community/impermanence";
  };

  outputs = { self, nixpkgs, impermanence, ... }: {
    nixosConfigurations.default = nixpkgs.lib.nixosSystem rec {
      system = "aarch64-linux";

      specialArgs = {
        pkgs = import nixpkgs {
          system = system;
          config.allowUnfree = true;
        };
      };

      modules = [
        ./configuration.nix
        impermanence.nixosModules.impermanence
      ];
    };
  };
}