wiki/docs/nix/pkgs-tools-reference.md

---
title: Nixpkgs Tools
description: An overview of the various functions unrelated to building source code available in Nixpkgs.
published: true
date: 2024-06-29T14:50:41.540Z
tags: nix, nixpkgs
editor: markdown
dateCreated: 2024-06-22T16:41:59.925Z
---

# Introduction to Nixpkgs' tools

This page is an overview of various functionality included in Nixpkgs, that is not directly related to building packages from source code. 

## Fetchers (`pkgs.fetch*`)

Fetchers such as `pkgs.fetchurl` allow to download content such as package sources, by specifying an expected hash of the content.

Resources: 

- [Nixpkgs manual](https://nixos.org/manual/nixpkgs/stable/#chap-pkgs-fetchers)

## Wrappers (`pkgs.runCommand*`, `pkgs.write*`)

Functions such as `pkgs.runCommand` or `pkgs.writeShellScript` are use-case specific wrappers around `pkgs.stdenv` with simple arguments.
Not to be confused with `pkgs.writers`.

Resources:

- [Nixpkgs manual](https://nixos.org/manual/nixpkgs/stable/#chap-trivial-builders)

## Data Formats (`pkgs.writers`)

Data format or application focussed writers that transform Nix expressions into the respective format.
Not to be confused with `pkgs.write*`.

Resource:

- [Nixpkgs source](https://github.com/NixOS/nixpkgs/blob/master/pkgs/build-support/writers)

## Config File Formats (`pkgs.formats`)

Produce various config file formats from nix expressions.

Resources:

- [Nixpkgs source](https://github.com/NixOS/nixpkgs/blob/master/pkgs/pkgs-lib/formats.nix)

## Custom Build Environments (`pkgs.mkShell`)

Convenience wrapper around `mkDerivation` for usage with `nix-shell` / `nix develop`.

Resources:

- [Nixpkgs manual](https://nixos.org/manual/nixpkgs/stable/#sec-pkgs-mkShell)

## Creating Hooks (`pkgs.makeSetupHook`)

Helper to produce hooks for the `stdenv` build phases. 
(For more info on hooks in general, see [Language/Framework Specific Builders in Nixpkgs#Hooks](./pkgs-languages-frameworks#hooks)).

Resources:

- [Nixpkgs manual](https://nixos.org/manual/nixpkgs/stable/#sec-pkgs.makeSetupHook)

## Test Utilities (`pkgs.testers`)

Derivation builders for testing various properties of other derivations.

Resources:

- [Nixpkgs manual](https://nixos.org/manual/nixpkgs/stable/#chap-testers)
- [nix.dev Tutorial: Integration testing with NixOS virtual machines](https://nix.dev/tutorials/nixos/integration-testing-using-virtual-machines)

## `fakeNss`

Including this *derivation* in, e.g. docker images or other environments without them, provides a simplistic set of user/group entries, to allow binaries expecting them to exist to work.

Resources:

- [Nixpkgs manual](https://nixos.org/manual/nixpkgs/stable/#sec-fakeNss)

## Standard Filesystem Layout Wrapper (`buildFHSEnv`)

Wraps binaries that expect a [FHS](https://en.wikipedia.org/wiki/Filesystem_Hierarchy_Standard)-compatible filesystem layout to run unpatched on NixOs.

Resources:

- [Nixpkgs manual](https://nixos.org/manual/nixpkgs/stable/#sec-fhs-environments)

## Run AppImages (`pkgs.appimageTools`)

A set of functions to run or extract [AppImages](https://appimage.org/).

Resources:

- [Nixpkgs manual](https://appimage.org/)

## Docker Images (`pkgs.dockerTools`)

A set of functions to create, modify, import or export docker images.

Resources:

- [Nixpkgs manual](https://nixos.org/manual/nixpkgs/stable/#sec-pkgs-dockerTools)
- [Xe Iaso's Talk: Nix is a better Docker image builder than Docker's image builder (Transcript & Recording)](https://xeiaso.net/talks/2024/nix-docker-build/)
- [nix.dev Tutorial: Building and running Docker images)](https://nix.dev/tutorials/nixos/building-and-running-docker-images.html)
- [Xe Iaso's Blog Post: Nix Flakes: Packages and How to Use Them](https://xeiaso.net/blog/nix-flakes-2-2022-02-27/)


## Build OCI Containers (`pkgs.ociTools`)

A set of function to create [OCI containers](https://github.com/opencontainers/runtime-spec/blob/v1.0.0/spec.md).

Resources:

- [Nixpkgs manual](https://nixos.org/manual/nixpkgs/stable/#sec-pkgs-ociTools)

## Build Portable Services (`pkgs.portableService`)

A function to create [systemd's Portable Services](https://systemd.io/PORTABLE_SERVICES/).

Resources:

- [Nixpkgs manual](https://nixos.org/manual/nixpkgs/stable/#sec-pkgs-portableService)
- [Xe Iaso's Blog Post: Nix Flakes: Packages and How to Use Them](https://xeiaso.net/blog/nix-flakes-2-2022-02-27/)

## Build Disk Images (`make-disk-image.nix`)

This function creates disk images in various formats (e.g. raw, QCOW2 (QEMU), VDI (VirtualBox), etc.).

Resources:

- [Nixpkgs manual](https://nixos.org/manual/nixpkgs/stable/#sec-make-disk-image)

## Run Derivations inside a VM (`pkgs.vmTools`)

Various tools to run derivations inside a Qemu/KVM backed virtual machine.

Resources: 

- [Nixpkgs manual](https://nixos.org/manual/nixpkgs/stable/#sec-vm-tools)

## Incremental Builds (`pkgs.checkpointBuildTools`)

Resources:

- [Nixpkgs manual](https://nixos.org/manual/nixpkgs/stable/#sec-checkpoint-build)

## Flat-file Binary Cache (`pkgs.mkBinaryCache`)

Create Nix flat-file binary caches.

Resources:

- [Nixpkgs manual](https://nixos.org/manual/nixpkgs/stable/#sec-pkgs-binary-cache)