Nix Guides and Information

Nix Language basics

Nix Language Basics

The Nix language is used to declare packages and configurations to be built by Nix. It is a domain-specific, purely functional, lazily evaluated, dynamically typed programming language.

Uses of Nix language:

Nixpkgs: software distribution
NixOS: Linux distribution that can be configured declaratively and based on Nix and Nixpkgs

Use Cases of NixOS and Beginning Install

Source: NIX OS: the BEST package manager on the MOST SOLID Linux distribution - The Linux Experiment - YouTube

Install with Live ISO, graphical install
Can modify /etc/nixos/ configuration files - configuration.nix
- Functional descriptions (everything is declared) of
  - hardware
  - bootloader
  - operating system, managers
  - options, services, users, apps
- File can be used rebuild system with sudo nixos-rebuild switch
  - New “generation” is created
  - Rebuild will check for issues in configuration file
Packages can use different channel like stable, unstable has newer packages with some risks
- Update channel: sudo nix-channel --update
- Rebuild to upgrade: sudo nixos-rebuild switch

Other Cases

Flakes - reproducible environments
Home Manager - declarative configuration for user directory

NixOS: Everything Everywhere All at Once

Source: NixOS: Everything Everywhere All at Once

Hardware and system configurations are separated to allow reuse of system configurations on multiple hardware platform
System configuration can configure things like:
- Packages and their configuration
- Variables
- Bootloader
- EFI
- Networking
- Timezone
- Users
- File system
- Fonts
- Sound
- Hardware
- and more
Portability and reproducibility: can be used to roll back to previous generations, customize a live NixOS USB

NixOS Rebuild Script - Allows easily visible changes and error handling to configuration changes

./rebuild

#!/bin/bash
set -e
pushd ~/dotfiles/nixos/
# Edit changes
nvim oatman-pc.nix
# Format nix file with alejandra
alejandra . &>/dev/null
# Show what changed
git diff -U0 *.nix
echo "NixOS Rebuilding..."
# Make changes, show relevant errors
sudo nixos-rebuild switch &>nixos-switch.log || (
 cat nixos-switch.log | grep --color error && false)
gen=$(nixos-rebuild list-generations | grep current)
# Check in configuration change under the Nix generation name
git commit -am "$gen"
popd

Channel Use

All Unstable

$ nix-channel --add \
https://nixos.org/channels/nixos-unstable nixos
$ nixos-rebuild switch --upgrade

Some Unstable

environment.systemPackages = with pkgs; [
  unstable.neovim  # bleeding-edge nvim
  emacs            # stable emacs
];

Auto Upgrade in Background on Schedule, Run linked executables, Systemd services,

# Auto Upgrade in Background on Schedule
system.autoUpgrade = {
  enable = true;
  flake = inputs.self.outPath;
  flags = [
    "--update-input"
    "nixpkgs"
    "-L"
  ];
  dates = "09:00";
  randomizedDelaySec = "45min";
};

# LD Fix, Allow NixOS to run dynamically linked executables \
# and binaries for Generic Linux

programs.nix-ld.enable = true;
programs.nix-ld.libraries = with pkgs; [
  # Add any missing dynamic libraries for unpackaged
  # programs here, NOT in environment.systemPackages
];

# Configure systemd services

systemd.services.irc = {

  serviceConfig = {
    Type = "simple";
    User = "oatman";
    ExecStart = "screen -dmS irc irssi";
    ExecStop = "screen -S irc -X quit";
  };

  wantedBy = ["multi-user.target"];
};

Reproducible, Dotfiles, Condition Config, Packages

nix flakes = package.lock for reproducible environment
home manager = dotfiles management
Turing-complete config = use if statements etc
All packages get their own independent dependency tree
Nix good for development setup

NixOS Guide, Flakes, Home-manager, Config Structuring

Source: Ultimate NixOS Guide | Flakes | Home-manager

NixOS Guide

Uses declarative configuration (default at /etc/nixos/*.nix), allow reuse across different systems, allows roll back
Use man configuration.nix to discover/search for configuration settings
All Nix packages, info stored in /nix/store
sudo nixos-rebuild switch does not update packages, updates are relative to a system’s channel’s commit

Flakes

flake.nix declarative configuration of packages and versions with flake.lock
- It will have a reproducible environment that will not depend on a system’s channel
Use of flakes requires activation of experimental feature
Starter configuration for integrating flakes into NixOS: https://github.com/vimjoyer/flake-starter-config

About Nix Modules

Nix modules = like a function that takes in input and specifies output
- For example, set up users in a main-user.nix and specific options and its config
- Can be imported / reused in other nix configuration files

Home-Manager Use Case

Install user programs, user programs’ config, font, theme, shell
Set up /home/user directory
Read home-manager options with man home-configuration.nix
Works on Unix, Linux distributions

Config Structuring

/etc/nixos - could be moved to user’s home directory
- configuration.nix
- hardware-configuration.nix
- home.nix
- flake.nix
- flake.lock
- modules/ - reusable modules, for example to configure specific programs, parts of system
  - nixos/
    - nvidia.nix
  - home-manager/
    - neovim.nix
    - terminals/
    - alacritty.nix
    - kitty.nix
- hosts/ - different system configurations
  - default/
    - configuration.nix
    - hardware-configuration.nix
    - home.nix
  - workmachine:
    - configuration.nix
    - hardware-configuration.nix
    - home.nix
Reference default configuration in flake.nix modules, then add additional configurations for specific machines in modules
Choose which configuration to use with sudo nixos-rebuild switch --flake /etc/nixos/#workmachine

What Nix Can Do (Docker Can’t)

Source: Matthew Croughan - What Nix Can Do (Docker Can’t) - SCaLE 20x. Taught by Matthew Croughan from Nix Camp

What Nix Can Do

Use case: “Anyone should be able to compile my code”

Other users can use the same code
- CI/CD, different user machines all run the same
- Manage dependencies and prevent conflicts with them
- Use old programs that may be difficult to run

Features
- Infrastructure as Code
- Reproducibility
- Software supply chain security
- Software Bill of Materials
1. Example Usage
  - Servers, personal devices defined by nix: https://github.com/MatthewCroughan/nixcfg
  - Nix flake for running AI: https://nixified.ai/
  - Could replace other package managers, dotfiles, dockerfiles, makefiles, helper scripts, version managers
About
- Example companies using nix: replit, Anduril, Target
  - Some companies use Nix and view as a competitive advantage
- Nix is a small C++ program
  - Can be copied to another machine to use just the binary
- Functional programming language
- Package manager
- Method of compiling software from source
1. Communicating
  - nixpkgs repository
  - NixOS Discourse

Nixpkgs

A repository, collection of packages
- Nix code of reproducible recipes (derivations)
- Automated
- Largest and most up to date collection of packages compared to other package managers
Packaging can be done by writing nix instructions for building the program and patching any non-Nix specific items like an output directory in a Makefile

NixOS

Built from Nix language, packages and nixpkgs
Declarative

Container Images

Nix can build OCI compliant images

Demonstrations

nix-shell and python3.withPackage

# Start repl
nix repl
# Load nixpkgs. a path to repository
:l <nixpkgs>
# See derivation of python3
python3
# See function
python3.withPackages
# See python with packages
python3.withPackages (p: [p.numpy])
python3.withPackages (p: [p.jupyter])

# Exit repl

# See configurations
cd /etc/nixos
ls
# Edit configuration.nix and activate changes
nixos-rebuild switch
# Observe what is being built

Flakes

All inputs and outputs are defined
Exampe: make reproducible shell for projects with exact same version of all tools, stack
nix will use nix cache if the requested output has been built before and stored
Can use to override existing build attributes like pkgs.packagename.overrideAttrs (old : ….)

# Edit flake.nix

# See changes
nix flake show
# Go into shell
nix develop .#devShell.x86_64-linux

# Cross compilations, see tab for architectures
nix build nixpkgs#pkgsCross.<tab>
# Binary can be run with nix emulated architectures enabled
# using: boot.binfmt.registrations
# e.g. boot.binfmt.emulatedSystems = ["risc64..."]

# Run programs
nix run <https:/...>

# Run VM with QEMU
nix-shell -p nixos-shell
# In vm.nix, specific state, Linux kernel services
nixos-shell vm.nix

Tests
- Using nix, specific creation of VMs with services
- Start VMs, run tests, check results
Docker
- Enable in configuration.nix with virtualization.docker.enable = true;
- Using a nix file, build Docker image, docker load the image for running using Nix’s dockerTools build.

Nix Guides and Information

Nix Language basics

Use Cases of NixOS and Beginning Install

NixOS: Everything Everywhere All at Once

NixOS Rebuild Script - Allows easily visible changes and error handling to configuration changes

Channel Use

Auto Upgrade in Background on Schedule, Run linked executables, Systemd services,

Reproducible, Dotfiles, Condition Config, Packages

NixOS Guide, Flakes, Home-manager, Config Structuring

NixOS Guide

Flakes

About Nix Modules

Home-Manager Use Case

Config Structuring

What Nix Can Do (Docker Can’t)

What Nix Can Do

Nixpkgs

NixOS

Container Images

Demonstrations

See Also

Resources