{
  time.timeZone = "Asia/Shanghai";
  security.sudo.wheelNeedsPassword = false;
  networking.firewall.enable = false;
  networking.nameservers = [
    "223.5.5.5"
    "223.6.6.6"
    "1.1.1.1"
    "8.8.8.8"

    "2400:3200::1"
    "2400:3200:baba::1"
  ];

  # Select internationalisation properties.
  i18n = {
    defaultLocale = "zh_CN.UTF-8";
    extraLocaleSettings = {
      LC_ADDRESS = "zh_CN.UTF-8";
      LC_IDENTIFICATION = "zh_CN.UTF-8";
      LC_MEASUREMENT = "zh_CN.UTF-8";
      LC_MONETARY = "zh_CN.UTF-8";
      LC_NAME = "zh_CN.UTF-8";
      LC_NUMERIC = "zh_CN.UTF-8";
      LC_PAPER = "zh_CN.UTF-8";
      LC_TELEPHONE = "zh_CN.UTF-8";
      LC_TIME = "zh_CN.UTF-8";
    };
  };

  nix.settings = {
    auto-optimise-store = true;
    experimental-features = [
      "nix-command"
      "flakes"
    ];

    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/"
    ];

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

  nix.gc = {
    automatic = true;
    dates = "weekly";
    options = "--delete-older-than 1w";
  };
}