Nix package manager: Difference between revisions

Latest revision as of 20:11, 15 April 2024

Nix is a package manager and build system that parses reproducible build instructions specified in the Nix Expression Language, a pure functional language with lazy evaluation. Nix expressions are pure functions^[1]taking dependencies as arguments and producing a derivation specifying a reproducible build environment for the package. Nix stores the results of the build in unique addresses specified by a hash of the complete dependency tree, creating an immutable package store (aka the nix store) that allows for atomic upgrades, rollbacks and concurrent installation of different versions of a package, essentially eliminating dependency hell.

Usage

Installation

NixOS: Nix is being installed while you install NixOS.

If you intend to utilize Nix on a different Linux distribution or a Mac computer, you can perform a standalone installation: The installation section of the Nix manual describes the installation of standalone Nix from binary or source.

Nix commands

The Nix commands are documented in the Nix reference manual: main commands, utilities and experimental commands. Prior to version 2.0 (released in February 2018) there have been different commands.

Configuration

On NixOS, Nix is configured through the nix option.

Standalone Nix is configured through nix.conf (usually found in /etc/nix/), which defines a number of settings relating to evaluation, builds, garbage collection, sandboxing, and user permissions. Details on the available options are found in the Nix reference manual.

Even further configuration is possible with Home Manager to manage declarative environments for a single user. For system-wide configuration on Linux, you can use System Manager. For system-wide configuration on macOS, nix-darwin is the preferred solution.

Internals

Nix store

Packages built by Nix are placed in the read-only Nix store, normally found in /nix/store. Each package is given a unique address specified by a cryptographic hash followed by the package name and version, for example /nix/store/nawl092prjblbhvv16kxxbk6j9gkgcqm-git-2.14.1. These prefixes hash all the inputs to the build process, including the source files, the full dependency tree, compiler flags, etc. This allows Nix to simultaneously install different versions of the same package, and even different builds of the same version, for example variants built with different compilers. When adding, removing or updating a package, nothing is removed from the store; instead, symlinks to these packages are added, removed or changed in profiles.

Profiles

In order to construct a coherent user or system environment, Nix symlinks entries of the Nix store into profiles. These are the front-end by which Nix allows rollbacks: since the store is immutable and previous versions of profiles are kept, reverting to an earlier state is simply a matter of change the symlink to a previous profile. To be more precise, Nix symlinks binaries into entries of the Nix store representing the user environments. These user environments are then symlinked into labeled profiles stored in /nix/var/nix/profiles, which are in turn symlinked to the user's ~/.nix-profile.

Sandboxing

When sandbox builds are enabled, Nix will setup an isolated environment for each build process. It is used to remove further hidden dependencies set by the build environment to improve reproducibility. This includes access to the network during the build outside of fetch* functions and files outside the Nix store. Depending on the operating system access to other resources are blocked as well (ex. inter process communication is isolated on Linux); see nix.conf section in the Nix manual for details.

Sandboxing is enabled by default on Linux, and disabled by default on macOS. In pull requests for Nixpkgs people are asked to test builds with sandboxing enabled (see Tested using sandboxing in the pull request template) because in official Hydra builds sandboxing is also used.

To configure Nix for sandboxing, set sandbox = true in /etc/nix/nix.conf; to configure NixOS for sandboxing set nix.useSandbox = true; in configuration.nix. The nix.useSandbox option is true by default since NixOS 17.09.

Alternative Interpreters

There is an ongoing effort to reimplement Nix, from the ground up, in Rust.

tvix

Earlier attempts can be found on riir-nix

Notes

↑ Values cannot change during computation. Functions always produce the same output if their input does not change.

[1] Values cannot change during computation. Functions always produce the same output if their input does not change.

[1]

@@ Line 1: / Line 1: @@
-Nix is a package manager and build system that parses reproducible build instructions specified in the [[Nix Expression Language]], a pure functional language with lazy evaluation. Nix expressions are pure functions taking dependencies as arguments and producing ''derivation'' specifying a reproducible build environment for the package. Nix stores the results of the build in unique addresses specified by a hash of the complete dependency tree, creating an immutable package store that allows for atomic upgrades, rollbacks and concurrent installation of different versions of a package, essentially eliminating [https://en.wikipedia.org/wiki/Dependency_hell dependency hell].
+Nix is a package manager and build system that parses reproducible build instructions specified in the [[Nix Expression Language]], a pure functional language with lazy evaluation. Nix expressions are pure functions<ref>Values cannot change during computation. Functions always produce the same output if their input does not change. </ref>taking dependencies as arguments and producing a ''derivation'' specifying a reproducible build environment for the package. Nix stores the results of the build in unique addresses specified by a hash of the complete dependency tree, creating an immutable package store (aka the [[#Nix store|nix store]]) that allows for atomic upgrades, rollbacks and concurrent installation of different versions of a package, essentially eliminating [https://en.wikipedia.org/wiki/Dependency_hell dependency hell].
 == Usage ==
 === Installation ===
+NixOS: Nix is being installed while you install NixOS.
-The [https://nixos.org/nix/manual/#chap-installation installation section of the Nix manual] describes how to install Nix from binary or source on Linux and Mac systems for a user with root privileges; it is easiest to install Nix for a single user, but steps are also included for setting up a multiuser installation. For an extensive guide on various methods for installing Nix - including how to install Nix without root privileges - see the [[Nix Installation Guide]].
+If you intend to utilize Nix on a different Linux distribution or a Mac computer, you can perform a standalone installation:  The [https://nixos.org/manual/nix/stable/installation/ installation section of the Nix manual] describes the installation of standalone Nix from binary or source.
 === Nix commands ===
-Since nix 2.0 there is a new style of commands. Those are [https://nixos.org/manual/nix/stable/command-ref/experimental-commands.html documented in the official manual].
+The [[Nix command|Nix commands]] are documented in the [https://nixos.org/manual/nix/stable/command-ref/ Nix reference manual]: main commands, utilities and experimental commands. Prior to version 2.0 (released in February 2018) there have been different commands.
-See [[Nix command]] for additional information.
-=== Declarative Configuration ===
+=== Configuration ===
-The only configuration file officially associated with Nix is <code>nix.conf</code> (usually found in <code>/etc/nix/</code>), which defines a number of settings relating to how Nix, including build, garbage collection, sandboxing, and user permissions. Details on the available options are found in the [https://nixos.org/nix/manual/#sec-conf-file|nix.conf section of the manual].
+On NixOS, Nix is configured through the [https://search.nixos.org/options?query=nix. <code>nix</code> option].
-Since most scenarios involve using [[Nixpkgs]], configuration of <code>~/.config/nixpkgs/config.nix</code> is often also helpful; here package overrides can be specified.
+Standalone Nix is configured through <code>nix.conf</code> (usually found in <code>/etc/nix/</code>), which defines a number of settings relating to evaluation, builds, garbage collection, sandboxing, and user permissions. Details on the available options are [https://nixos.org/manual/nix/stable/command-ref/conf-file found in the Nix reference manual].
-[[Home Manager]] is the preferred way to manage declarative environments for a single user.
+Even further configuration is possible with [[Home Manager]] to manage declarative environments for a single user. For system-wide configuration on Linux, you can use [https://github.com/numtide/system-manager System Manager]. For system-wide configuration on macOS, [https://github.com/LnL7/nix-darwin nix-darwin] is the preferred solution.
-For system configuration on macOS [https://github.com/LnL7/nix-darwin nix-darwin] is the preferred solution.
-=== Imperative Operations ===
-To a large extent, package and environment management in Nix is imperative; user environments - including package installation and removal - is managed with the <code>nix-env</code> command, while <code>nix-channels</code> determine which version of [[Nixpkgs]] is used, and thus which version your packages will have.
-====  User Environments ====
-Nix offers an imperative package management command line tool - <code>nix-env</code> - which can be used to install packages at the user level. Packages installed using <code>nix-env</code> are only available to the given user, and do not change system state.
-{|  class="wikitable"
-|+ Common <code>nix-env</code> Commands
-|-
-|Searching for packages
-|<code>nix search nixpkgs packagename</code>
-|-
-|Installing a package
-|<code>nix-env -iA packagename</code>
-|-
-|List installed packages
-|<code>nix-env -q</code>
-|-
-|Uninstall packages
-|<code>nix-env -e packagename</code>
-|-
-|Upgrade packages
-|<code>nix-env -u</code>
-|}
-==== Channels ====
-Nix packages are distributed through a number of Nix channels: mechanisms for distributing Nix expressions as well as the associated binary caches for them. These channels are what determine which versions your packages have, and they can be broadly categorized into ''stable'' and ''unstable'' channels. Most users will want the stable channel, currently <code>nixos-22.05</code>. For more information on channels and how to choose them, see the [[Nix Channels]] article.
-{| class="wikitable"
-|+ Common nix-channel commands
-|-
-|Listing current channels
-|<code>nix-channel --list</code>
-|-
-| Adding a primary channel
-|<code><nowiki>nix-channel --add https://nixos.org/channels/channel-name nixos</nowiki></code>
-|-
-| Adding other channels
-|<code><nowiki>nix-channel --add https://some.channel/url my-alias</nowiki></code>
-|-
-| Remove a channel
-|<code>nix-channel --remove channel-alias</code>
-|-
-| Updating a channel
-|<code>nix-channel --update channel-alias</code>
-|-
-| Updating all channels
-|<code>nix-channel --update</code>
-|}
 == Internals ==
@@ Line 78: / Line 24: @@
 === Nix store ===
-Packages built by Nix are placed in the read-only ''Nix store'', normally found in <code>/nix/store</code>. Each package is given a unique address specified by a cryptographic hash followed by the package name and version, for example <code>/nix/store/nawl092prjblbhvv16kxxbk6j9gkgcqm-git-2.14.1</code>. These prefixes hash all the inputs to the build process, including the source files, the full dependency tree, compiler flags, etc. This allows Nix to simultaneously install different versions of the same package, and even different builds of the same version, for example variants built with different compilers. When adding, removing or updating a package, nothing is removed from the store; instead, it symlinks to these packages are added, removed or changed in ''profiles''.
+Packages built by Nix are placed in the read-only ''Nix store'', normally found in <code>/nix/store</code>. Each package is given a unique address specified by a cryptographic hash followed by the package name and version, for example <code>/nix/store/nawl092prjblbhvv16kxxbk6j9gkgcqm-git-2.14.1</code>. These prefixes hash all the inputs to the build process, including the source files, the full dependency tree, compiler flags, etc. This allows Nix to simultaneously install different versions of the same package, and even different builds of the same version, for example variants built with different compilers. When adding, removing or updating a package, nothing is removed from the store; instead, symlinks to these packages are added, removed or changed in ''profiles''.
 === Profiles ===
@@ Line 93: / Line 39: @@
 To configure Nix for sandboxing, set <code>sandbox = true</code> in <code>/etc/nix/nix.conf</code>; to configure NixOS for sandboxing set <code>nix.useSandbox = true;</code> in <code>configuration.nix</code>. The <code>nix.useSandbox</code> option is <code>true</code> by default since NixOS 17.09.
-{{Bottom whitespace}}
+=== Alternative Interpreters ===
+There is an ongoing effort to reimplement Nix, from the ground up, in Rust.
+* [https://cs.tvl.fyi/depot/-/tree/tvix tvix]
+Earlier attempts can be found on [https://riir-nix.github.io/ riir-nix]
+==Notes==
+<references />
 [[Category:Pedias]]