## Start using home-manager

As I mentioned earlier, NixOS can only manage system-level configuration, to manage the Home directory(user-level configuration), we need to install home-manager.

According to the official document [Home Manager Manual](https://nix-community.github.io/home-manager/index.html), in order to install home-manager as a module of NixOS, we need to create `/etc/nixos/home.nix` first, an example content shown below:

```nix
{ config, pkgs, ... }:

{
  # TODO please change the username & home direcotry to your own
  home.username = "ryan";
  home.homeDirectory = "/home/ryan";

  # link the configuration file in current directory to the specified location in home directory
  # home.file.".config/i3/wallpaper.jpg".source = ./wallpaper.jpg;

  # link all files in `./scripts` to `~/.config/i3/scripts`
  # home.file.".config/i3/scripts" = {
  #   source = ./scripts;
  #   recursive = true;   # link recursively
  #   executable = true;  # make all files executable
  # };

  # encode the file content in nix configuration file directly
  # home.file.".xxx".text = ''
  #     xxx
  # '';

  # set cursor size and dpi for 4k monitor
  xresources.properties = {
    "Xcursor.size" = 16;
    "Xft.dpi" = 172;
  };

  # basic configuration of git, please change to your own
  programs.git = {
    enable = true;
    userName = "Ryan Yin";
    userEmail = "xiaoyin_c@qq.com";
  };

  # Packages that should be installed to the user profile.
  home.packages = [
    # here is some command line tools I use frequently
    # feel free to add your own or remove some of them

    neofetch
    nnn # terminal file manager

    # archives
    zip
    xz
    unzip
    p7zip

    # utils
    ripgrep # recursively searches directories for a regex pattern
    jq # A lightweight and flexible command-line JSON processor
    yq-go # yaml processer https://github.com/mikefarah/yq
    exa # A modern replacement for ‘ls’
    fzf # A command-line fuzzy finder

    # networking tools
    mtr # A network diagnostic tool
    iperf3
    dnsutils  # `dig` + `nslookup`
    ldns # replacement of `dig`, it provide the command `drill`
    aria2 # A lightweight multi-protocol & multi-source command-line download utility
    socat # replacement of openbsd-netcat
    nmap # A utility for network discovery and security auditing
    ipcalc  # it is a calculator for the IPv4/v6 addresses

    # misc
    cowsay
    file
    which
    tree
    gnused
    gnutar
    gawk
    zstd
    gnupg

    # nix related
    #
    # it provides the command `nom` works just like `nix
    # with more details log output
    nix-output-monitor

    # productivity
    hugo # static site generator
    glow # markdown previewer in terminal

    btop  # replacement of htop/nmon
    iotop # io monitoring
    iftop # network monitoring

    # system call monitoring
    strace # system call monitoring
    ltrace # library call monitoring
    lsof # list open files

    # system tools
    sysstat
    lm_sensors # for `sensors` command
    ethtool
    pciutils # lspci
    usbutils # lsusb
  ];

  # starship - an customizable prompt for any shell
  programs.starship = {
    enable = true;
    settings = {
      add_newline = false;
      aws.disabled = true;
      gcloud.disabled = true;
      line_break.disabled = true;
    };
  };

  # alacritty - a cross-platform, GPU-accelerated terminal emulator
  programs.alacritty = {
    enable = true;
      env.TERM = "xterm-256color";
      font = {
        size = 12;
        draw_bold_text_with_bright_colors = true;
      };
      scrolling.multiplier = 5;
      selection.save_to_clipboard = true;
  };

  programs.bash = {
    enable = true;
    enableCompletion = true;
    bashrcExtra = ''
      export PATH="$PATH:$HOME/bin:$HOME/.local/bin:$HOME/go/bin"
    '';

    # set some aliases, feel free to add more or remove some
    shellAliases = {
      urldecode = "python3 -c 'import sys, urllib.parse as ul; print(ul.unquote_plus(sys.stdin.read()))'";
      urlencode = "python3 -c 'import sys, urllib.parse as ul; print(ul.quote_plus(sys.stdin.read()))'";
      httpproxy = "export https_proxy=http://127.0.0.1:7890; export http_proxy=http://127.0.0.1:7890;";
    };
  };

  # This value determines the home Manager release that your
  # configuration is compatible with. This helps avoid breakage
  # when a new home Manager release introduces backwards
  # incompatible changes.
  #
  # You can update home Manager without changing this value. See
  # the home Manager release notes for a list of state version
  # changes in each release.
  home.stateVersion = "22.11";

  # Let home Manager install and manage itself.
  programs.home-manager.enable = true;
}
```

After adding `/etc/nixos/home.nix`, you need to import this new configuration file in `/etc/nixos/flake.nix` to make use of it, use the following command to generate an example in the current folder for reference:

```shell
nix flake new example -t github:nix-community/home-manager#nixos
```

After adjusting the parameters, the content of `/etc/nixos/flake.nix` is as follows:

```nix
{
  description = "NixOS configuration";

  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
    home-manager.url = "github:nix-community/home-manager";
    home-manager.inputs.nixpkgs.follows = "nixpkgs";
  };

  outputs = inputs@{ nixpkgs, home-manager, ... }: {
    nixosConfigurations = {
      # TODO please change the hostname to your own
      nixos-test = nixpkgs.lib.nixosSystem {
        system = "x86_64-linux";
        modules = [
          ./configuration.nix

          # make home-manager as a module of nixos
          # so that home-manager configuration will be deployed automatically when executing `nixos-rebuild switch`
          home-manager.nixosModules.home-manager
          {
            home-manager.useGlobalPkgs = true;
            home-manager.useUserPackages = true;

            # TODO replace ryan with your own username
            home-manager.users.ryan = import ./home.nix;

            # Optionally, use home-manager.extraSpecialArgs to pass arguments to home.nix
          }
        ];
      };
    };
  };
}
```

Then run `sudo nixos-rebuild switch` to apply the configuration, and home-manager will be installed automatically.

After the installation, all user-level packages and configuration can be managed through `/etc/nixos/home.nix`. When running `sudo nixos-rebuild switch`, the configuration of home-manager will be applied automatically. (**It's not necessary to run `home-manager switch` manually**!)

To find the options we can use in `home.nix`, referring to the following documents:

- [Home Manager - Appendix A. Configuration Options](https://nix-community.github.io/home-manager/options.html): A list of all options, it is recommended to search for keywords in it.
- [home-manager](https://github.com/nix-community/home-manager): Some options are not listed in the official documentation, or the documentation is not clear enough, you can directly search and read the corresponding source code in this home-manager repo.