Introduction To Nix (Part III)

August 2018

by Michael Fellinger

After the install

source ~/.nix-profile/etc/profile.d/nix.sh
nix-channel --add \
  https://nixos.org/channels/nixpkgs-18.03-darwin nixpkgs
nix-channel --update

First steps

nix-channel --add https://nixos.org/channels/nixpkgs-18.03-darwin nixpkgs
nix-channel --update

nix-env -iA nixpkgs.hello

nix-env -u hello

nix-env --list-generations

nix-env --rollback

nix-env -e hello

nix-collect-garbage

Nix Store

    /nix/store/rqjf7a7i5wh7d0mryy69mzy3nr511acs-home-manager-path/bin/git

    /nix/store/6p18brdpbj91snn4zmg9dwb4yyaf1501-crystal-0.25.0/
    ├── bin
    │   └── crystal
    ├── lib
    │   └── crystal
    └── share
        ├── bash-completion
        ├── doc
        ├── licenses
        ├── man
        └── zsh

Environments

• System wide
• User owned
• Project specific
• Service specific

All reproducible and can reuse each others code!

Platform independent

Nix runs on Linux (not only NixOS), MacOS, BSD, Windows, and more. NixOS has been ported to many platforms, so it runs on i686, x86_64, MIPS, ARM, and AArch64 So you can use it on anything from Supercomputers to your Router, also MacBooks and Rasberry Pis.

You don’t have to run NixOS to use Nix, although that gives you many benefits.

What’s a Nix Package?

• A Nix source file is a function.
• The function returns “derivations”
• Dependencies are given as parameters to the function

Calling Packages

The top-level passes arguments automatically using callPackage:

    cowsay = callPackage ./pkgs/cowsay {};

The function

{ stdenv, fetchgit, perl }:

stdenv.mkDerivation {
  name = "cowsay-3.03+dfsg1-16";

  src = fetchgit {
    url = https://anonscm.debian.org/git/collab-maint/cowsay.git;
    rev = "acb946c166fa3b9526b9c471ef1330f9f89f9c8b";
    sha256 = "1ji66nrdcc8sh79hwils3nbaj897s352r5wp7kzjwiym8bm2azk6";
  };

  buildInputs = [ perl ];

  installPhase = ''
    bash ./install.sh $out
  '';

  meta = {
    description = "A program which generates ASCII pictures of a cow with a message";
    homepage = http://www.nog.net/~tony/warez/cowsay.shtml;
    platforms = stdenv.lib.platforms.all;
    maintainers = [ stdenv.lib.maintainers.rob ];
  };
}

Writing our first Nix package

{ stdenv }:

stdenv.mkDerivation {
  name = "hello";
  unpackPhase = "true";
  src = ./hello.rb;
  installPhase = ''
    install -m 0744 -D $src $out/bin/hello
  '';
}

Nix-Shell

On-demand project specific development environments:

with import (fetchTarball {
  url = https://github.com/NixOS/nixpkgs-channels/archive/98792fe35152d3470929b40ad83359b605233a76.tar.gz;
  sha256 = "1p52zqpp924nwcp534whznrwsgrfi8mas0n1wsrrh6kpsxmlh64f";
}) {};
mkShell {
  buildInputs = [
    ruby_2_5
    nodejs-9_x
    go_1_10
    elixir
    libxml2
  ];
}

Nix-Shell in practice

So the next time you work on a project, you get the exact same version of all dependencies as everybody else and don’t have to install anything manually.

This is extremely useful, especially when you come back a year later and completely forgot what’s needed (no fear of forgetting to updating docs).

Nix-Shell & Direnv

The dream-team for people who constantly switch between projects.

Given a .envrc:

use nix

You can simply change into a directory and you’ll automatically be in a nix-shell.

nix-darwin

Nix modules for darwin, /etc/nixos/configuration.nix for macOS.

{ pkgs, ... }:

{
  shellAliases = with pkgs; {
    v = "${neovim}/bin/nvim";
    g = "${gitFull}/bin/git"
    c = "clear";
  };

  environment.systemPackages = with pkgs; {
    curl di direnv emacs jq htop
  };

  environment.variables = {
    EDITOR = "nvim";
    LESS = "-M";
  };

  system.default.dock.autohide = true;
  system.defaults.finder.AppleShowAllExtensions = true;
  system.defaults.trackpad.Clicking = true;
  ...
}

NixOps

{
  server_alpha = {
    deployment.targetEnv = "virtualbox";
    services = {
      nginx.enable = true;
      kubernetes.enable = true;
      redis = {
        enable = true;
        port = 777;
      }
    };
    fileSystems."/data" = {
      fsType = "nfs4";
      device = "fileserver:/";
    };
  }
  fileserver = {
    deployment.targetEnv = "virtualbox";
    services.nfs.server.enable = true;
    services.nfs.server.exports = ''
      /exported/directory server_alpha
    '';
  };
}

nixops created -d simple network.nix
nixops deploy -d simple

NixOps Deploys To

• Amazon EC2 instances and other resources (such as S3 buckets, EC2 key pairs, elastic IPs, etc.).
• Google Cloud Engine instances and other resources (such as networks, firewalls, IPs, disks, etc.).
• VirtualBox virtual machines.
• Hetzner machines.
• NixOS containers.
• Any machine already running NixOS.

home-manager

Can manage your dotfiles and applications, here’s a little sample of my config:

{ pkgs, ... }:
{
  home.packages = with pkgs; [
    tree ripgrep ruby chromium elixir go fzy
  ];
  programs.zsh = {
    enable = true;
    enableAutosuggestions = true;
    enableCompletion = true;
    history = {
      ignoreDups = true;
      save = 1000000;
      size = 1000000;
    };
    shellAliases = {
      v = "vim";
      c = "clear";
      open = "xdg-open";
    };
    oh-my-zsh = {
      enable = true;
      theme = "flazz";
      plugins = [
        "docker"
        "git"
        "man"
        "nyan"
        "ssh-agent"
        "sudo"
        "vi-mode"
        "yarn"
        "zsh-navigation-tools"
        "systemd"
        "tmux"
      ];
    };
  };
}

more at https://github.com/manveru/dotfiles