Introduction to Nix (and NixOS)

Suvash Thapaliya ~ @suvash

25th February 2015

Disclaimer

I'm pretty sure I don't know a lot things.

But, please feel free to ask questions !

The Problem

Some solutions....?

Configuration

Management

Declarative

Purely Functional

Nix(OS) Family

Things we won't quite cover...

Nix expressions

(language)

Hydra

Nix Build System

NixOps

NixOS + Operations tooling

Why Nix ?

Origin

Philosophy

• Nix is a system for software deployment
• Components(a set of files/tree in a filesystem) are the basic units of deployment
• Nix stores components in a component store, called the Nix store (usually /nix/store)
• The names of the components contain a cryptographic hash of all the inputs involved in building the component. (eg. /nix/store/b6q64986n0smwwfwrhg655lcg3pxhk56-git-2.1.4 )
• The collision resistant name is what provides Nix the ability to prevent undeclared dependencies and a component interface

Components & Closures

Demo

# nix-env manages user-environments 
# which are 'views' into the available components

$ nix-env -i cowsay

$ which cowsay

$ ls -lah $(which cowsay)

$ realpath $(which cowsay)

$ readlink -f $(which cowsay)

$ nix-env --list-generation

$ nix-env --rollback

$ which cowsay

$ nix-env --switch-generation X

$ which cowsay

$ nix-env --uninstall cowsay

$ nix-env --delete-generations 10d

$ nix-collect-garbage

More Demo

# pick the symlink to ~/.nix-profile

$ ls -l ~/
$ ls -l ~/.nix-profile

# up the profile directory
$ ls -l <symlink-to-nix-profile-without-the-profile-directory-at-the-end>

# where is it located actually (can be seen above too) ?
$ realpath ~/.nix-profile

# Custom profile
$ which cowsay

$ cd <some-dir>

$ nix-env -i cowsay -p custom-profile

$ ls -l

$ ./custom-profile/bin/cowsay -f dragon Nix is awesome

$ realpath ./custom-profile

$ which sl

$ nix-env -i sl -p custom-profile

$ ./custom-profile/bin/sl

$ nix-env --list-generation -p custom-profile

# compare the hash of custom profile and 'normal' profile
$ nix-env -i sl 

# uninstall sl, remove custom profile, garbage collect and path no more

Purely functional : What does it mean ?

(in this context)

Persistent Data Structures

Example Package

with import <nixpkgs> { };

stdenv.mkDerivation rec {
  pname = "mosquitto";
  version = "1.4";

  name = "${pname}-${version}";

  src = fetchurl {
    url = http://mosquitto.org/files/source/mosquitto-1.4.tar.gz;
    sha256 = "1imw5ps0cqda41b574k8hgz9gdr8yy58f76fg8gw14pdnvf3l7sr";
  };

  buildInputs = [ openssl libuuid ];

  buildFlags = "mosquitto";

  installPhase = ''
    mkdir -p $out/bin
    cp src/mosquitto $out/bin/
  '';

  meta = {
    homepage = http://mosquitto.org/;
    description = "An open source MQTT v3.1/3.1.1 broker";
    platforms = stdenv.lib.platforms.linux;
    license = stdenv.lib.licenses.epl10;
  };
}

Custom Package Demo ?

# nix-build

$ nix-build ./mosquitto.nix

$ ls -l

$ ./result/bin/mosquitto



# nix-shell

$ nix-shell ./mosquitto.nix

nix-shell $ echo $src

nix-shell $ echo $out

nix-shell $ make / make install / etc..



# same idea can be used for development environments

# add cowsay, sl to the buildInputs :)

This all is pretty neat

Configuration with NixOS

More NixOS demo

$ ls -l /run

# booted / current system

$ ls -l current-system-path

$ ls -l current-system-path/sw/bin

$ ls -l current-system-path/etc

# Profiles

# same as ~/.nix-profile
$ ls -l /nix/var/nix/profiles/per-user/user

$ ls -l /nix/var/nix/profiles/

$ nix-channel (--list | --add | --update... )

$ nixos-rebuild (switch | test | boot | --rollback )  # --upgrade

# compare /nix/var/nix/profiles/ after a rebuild

$ nix-env --list-generations

$ nix-env --switch-generation N -p /nix/var/nix/profiles/system

$ nix-env --remove-generations 10d -p /nix/var/nix/profiles/system

$ nix-store --optimise

$ nixos-option

Development with Nix

nix-shell + cabal example

# Scenario 1 : Your project already has a working .cabal file

$ cabal2nix ./. > default.nix

# Since the generated file above is supposed to be used for Nix packages, few changes are required

# Replace the list of function parameters with below

{ haskellPackages ? (import <nixpkgs> {}).haskellPackages }:

# Prepend the following to the expression body

with haskellPackages;

# Add cabal as the build tool for the project

buildTools = [cabalInstall];

# Based on dependencies not present on Nixpkgs, more other configuration can be done

$ nix-shell --pure

# OMG, no need for sandboxes

[nix-shell] $ cabal build


# Scenario 2 : Start out with a nix expression directly

Development/... environments with Nix

that's it for now...

Hopefully I've got you interested in Nix

and NixOS.

There's a lot more interesting stuff to explore.

Lots of help at #nixos and ##nix-darwin

@suvash

Sources

• http://nixos.org/
• http://nixos.org/nixos/manual/
• https://nixos.org/wiki/Main_Page
• http://www.infoq.com/articles/configuration-management-with-nix
• http://nixos.org/~eelco/pubs/phd-thesis.pdf
• http://nixos.org/~eelco/pubs/nixos-jfp-final.pdf
• http://nixer.ghost.io/why/
• https://www.domenkozar.com/2014/01/02/getting-started-with-nix-package-manager/
• http://www.pavelkogan.com/2014/07/09/haskell-development-with-nix/
• https://ocharles.org.uk/blog/posts/2014-02-04-how-i-develop-with-nixos.html
• https://nixos.org/wiki/Develop_software_with_unique_profiles_using_Nix