It seems like there is a lot of buzz lately around Nix and NixOS. It keeps popping up more and more as a topic of discussion, especially with software developers. However, looking at it's surface and trying to understand what Nix even is can be a struggle. Nix is expansive and knowing what problems it solves and how to even begin to approach the ecosystem can be challenging. This guide is intended to be an introduction and brief exploration into what Nix/NixOS is and how it can benefit you as a developer.

Table of Contents

• What is Nix?
  • Difference Between Nix and NixOS
• System Management
  • User
    • Home Manager
    • Nixos-Generators
  • Server
• Nixpkgs
  • Packaging Software
    • Flakes
• Development Environment
  • Devshell
• Learning Nix

What is Nix?

Nix is a purely functional package manager and operating system deployment tool. It was designed to manage the configuration and installation of software on a variety of operating systems, including Linux, and macOS.

Nix's distinguishing feature is its functional approach to package management. Instead of the traditional approach of installing packages into a global system directory, Nix packages are built in isolation and stored in a per-user store. This means that multiple versions of a package can coexist on the same system, and dependencies are managed in a consistent and predictable way.

Here are some reasons why someone might want to use Nix:

• Reproducible builds: Nix ensures that every package build is isolated and uses exactly the same dependencies, making it easy to reproduce builds across different machines.

• Multiple versions: Nix allows you to have multiple versions of the same package installed at the same time, which is useful for development and testing.

• Declarative package management: Nix uses a declarative language to describe package dependencies and configurations, making it easy to specify exactly what you want installed on a system.

• Rollbacks: Nix allows you to roll back to a previous system configuration if something goes wrong, which can be a lifesaver in production environments.

• Cross-platform support: Nix works on a variety of operating systems, so you can use the same package management tool across different machines.

• Massive package repository: Nix has a huge repository of pre-built packages, which can save time and effort in setting up a new system or developing software. See how nixpkgs compares to your package manager.

Difference Between Nix and NixOS

Nix is a package manager for Linux and other Unix-like systems that allows for declarative, reproducible, and isolated software installation and configuration.

NixOS, on the other hand, is a Linux distribution that uses Nix as its package manager and is built around the principles of declarative system configuration and functional package management. NixOS uses a declarative language (also confusingly called Nix) to describe system configuration, including the installation and configuration of packages, users, network interfaces, and other system components. This makes it easy to reproduce a system's configuration and to roll back to a previous configuration if necessary.

In other words, while Nix is a package manager that can be used on any Linux or Unix-like system, NixOS is a complete Linux distribution that uses Nix as its package manager and has a unique approach to system configuration.

System Management

One of the most appealing features of Nix/NixOS that tends to draw new users in is the ability to have your entire system configuration written out and version controlled. This means that your entire fully configured system is ready to deploy anytime, anywhere right from a git repository. This even includes things like SSH or PGP keys by using agenix.

User

Using Nix as a package manager and configuring your home applications with home-manager means that your configuration can be deployed outside of NixOS. Nix can reproduce a configuration on Ubuntu, Fedora, etc. as well as macOS. This can allow users to leverage some strengths of Nix without diving all the way into the ecosystem.

Home Manager

Home-manager is a tool for managing user-specific configuration files on top of the Nix package manager. It allows users to declaratively manage their user environment, including their shell configuration, editor configuration, and other user-specific settings.

Home-manager extends the power of NixOS system management to user management letting you declaratively configure your home applications.

Some examples of what you can do with Home Manager include:

• Configuring your shell (e.g. zsh or bash or nushell) with custom settings and plugins
• Installing and configuring your favorite text editor (e.g. Neovim or VSCode) with custom settings and plugins
• Configuring your development tools (e.g. Git or Docker) with custom settings and aliases

Nixos-Generators

Nixos-generators can be used to generate a plethora of formats including ISO. Meaning you can keep a configuration that's specific to your needs and have it handy on a thumb drive.

You can also build a server configuration and have a cloud image (digitalocean, aws, etc) uploaded and ready to deploy on-demand.

Server

NixOS really shines when used to build application infrastructure. Things like firewalls, databases, reverse-proxies, and environment variables can all be configured using NixOS declarative module system.

Using NixOS for server configuration provides several other benefits, including:

• Declarative configuration: NixOS modules provide a declarative way to describe server configuration, allowing you to specify exactly what software should be installed, how it should be configured, and what services should be running on the server. This makes it easy to reproduce server configurations across different machines, and ensures that server configuration is always consistent and predictable.

• Modularity: NixOS modules are designed to be modular, with each module responsible for configuring a specific aspect of the server. This makes it easy to manage complex server configurations, and allows you to reuse configuration across different servers.

• Reusability: NixOS modules can be reused across different server configurations, making it easy to share configuration between different projects and teams.

• Versioning: NixOS modules are versioned, making it easy to track changes to server configuration over time and to roll back to previous configurations if necessary.

• Safety: NixOS modules are designed to be safe, with built-in checks to prevent invalid configurations and to ensure that server configuration is consistent and predictable.

Nixpkgs

Nixpkgs currently has more software packages than any other package repository (excluding the npm madhouse). The packages also tend to be very fresh and up-to-date thanks to the community and projects like nixpkgs-update.

Packaging Software

Packaging software for Nix involves creating a Nix derivation, which is an expression that describes how to build and install the software. In this expression you provide a list of dependencies as well as instructions on how the software should be built. There are many helpful tools to make building common project types like cargo, poetry, or go projects much simpler.

Flakes

Nix Flakes is a new feature that was introduced in Nix version 2.4. It's a way to make Nix more composable and modular, and to simplify the process of managing and distributing Nix configurations as well as achieving strict reproducibility through a lock file.

At a high level, Nix Flakes allow you to specify a set of inputs (e.g. Nix packages or other Flakes) and a set of outputs (e.g. a configuration for a specific system or environment). You can then use these inputs to build your outputs, and share your configuration as a single, self-contained unit that can be easily distributed and reused.

Flakes have created somewhat of a schism in the Nix community although adoption continues to increase as Flakes reduce or eliminate many of the pain-points experienced while working with Nix.

Development Environment

Nix is a developers dream. There is a staggering amount of tooling, utility, and clever mechanisms that can provide enormous amounts of value and productivity to a project. Using Nix, Flakes, and Devshells can eliminate the worry of dependencies and versions inside a developers' environment.

Devshell

Devshells are a feature of Nix that allow you to create a shell environment with all the dependencies and environment variables needed for a particular project or task. Devshells are useful for developers who work on multiple projects or who need to switch between different programming languages or development environments frequently.

They're also useful as a means of unifying dependencies and development environments in a consistent and reproducible way. By defining the dependencies and environment in a Nix expression, you can ensure that all developers on your team are using the same versions of libraries and tools, and that the environment can be easily recreated on different machines or platforms.

This can be further extended into automation environments like CI/CD pipelines and even into production.

Combined with Flakes, Devshell dependencies can all be pinned to specific versions for extremely consistent reproducibility which virtually eliminates the 'works on my machine' dilemma.

Learning Nix

Overall, Nix and NixOS offer many benefits for developers, including reproducible builds, isolation, easy package management, and rollback capabilities. These features can help developers be more productive and efficient, and make it easier to collaborate on software projects with others.

However, Nix has a pretty notorious reputation for being difficult to grasp. The learning curve for Nix and NixOS can be steep, especially for developers who are new to functional programming and declarative configuration management.

Documentation for NixOS is mostly adequate in 2023 although oftentimes scattered around the internet.

Despite these challenges, many developers find that the benefits of using Nix and NixOS outweigh the learning curve. Once developers become proficient with Nix and NixOS, they can enjoy the benefits of reproducible builds, isolation, easy package management, and rollback capabilities, among others.

Links:

• awesome-nix: Officially curated list of Nix resources.
• nixpkgs: Software repository for Nix.
• wiki: Official NixOS wiki.
• discourse: NixOS community discussion.
• nixos-search: Search nixpkgs from the web.