{
    sound.enable = true;
    networking.networkmanager.enable = true;
    time.timeZone = "Asia/Shanghai";
    security.sudo.wheelNeedsPassword = false;

    hardware = {
        opengl.enable = true;
    };

    # 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";
    };
}