NixOS: Difference between revisions

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~~{{Expansion|This article is incomplete.}}~~

[https://nixos.org/ NixOS] is a Linux distribution based on the [[Nix Package Manager]]. It supports reproducible and declarative system-wide configuration management as well as atomic upgrades and rollbacks, although it can additionally support imperative package and user management. In NixOS, all components of the distribution — including the kernel, installed packages and system configuration files — are built by [[Nix Package Manager|Nix]] from purely functional (that is, [[Wikipedia:Pure function|side-effect free]]) [[Nix Expression Language|Nix expressions]].

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== Internals ==

=== ~~Comparsion to~~ traditional Linux Distributions ===

=== Comparison with traditional Linux Distributions ===

~~''See also: [[Nix vs. Linux Standard Base]]''~~

The main difference between to Linux Distribution is that NixOS does not follow the [https://en.wikipedia.org/wiki/Linux_Standard_Base Linux Standard Base] file system structure. On LSB-compliant systems software is stored under <code>/{,usr}/{bin,lib,share}</code> and configuration is generally stored in <code>/etc</code>.

Software binaries are available in the user environment if they are placed in one of the LSB's <code>bin</code> directories. When a program references dynamic libraries it will search for the required libraries in the LSB folders (<code>/lib</code>, <code>/usr/lib</code>).

In NixOS however <code>/lib</code> and <code>/usr/lib</code> do not exist. Instead all system libraries, binaries, kernels, firmware and configuration files are stored beneath <code>/nix/store</code>. The files and directories in <code>/nix/store</code> are named by hashes of the information describing the built data. All of the files and directories placed in the Nix ~~store are immutable~~.

''Main Article: [[Nix vs. Linux Standard Base]]''

<code>/bin</code> and <code>/~~usr/bin~~</code> are ~~almost absent:~~ they ~~contain only~~ <code>/bin/sh</code> ~~and~~ <code>/usr/~~bin/env~~</code> ~~respectively, to provide minimal compatibility with existing scripts using shebang lines~~.

The main difference between NixOS and other Linux distributions is that NixOS does not follow the [https://en.wikipedia.org/wiki/Linux_Standard_Base Linux Standard Base] file system structure. On LSB-compliant systems software is stored under <code>/{,usr}/{bin,lib,share}</code> and configuration is generally stored in <code>/etc</code>. Software binaries are available in the user environment if they are placed in one of the LSB's <code>/bin</code> directories. When a program references dynamic libraries it will search for the required libraries in the LSB folders (<code>/lib</code>, <code>/usr/lib</code>).

Structuring the system in this way is how NixOS obtains its key advantages over conventional Linux distributions, such as atomicity and rollback support. Every item inside the store is the product of the evaluation of a pure function in Nix called a ''derivation'' (essentially a build). Essentially, the store is the reification of the pure, functional description of the system, which is consumed by Nix and used to generate the contents of the store.

In NixOS however <code>/lib</code> and <code>/usr/lib</code> do not exist. Instead all system libraries, binaries, kernels, firmware and configuration files are placed in the [[Nix Package Manager:Nix Store]]. The files and directories in <code>/nix/store</code> are named by hashes of the information describing the built data. All of the files and directories placed in the Nix store are immutable. <code>/bin</code> and <code>/usr/bin</code> are almost absent: they contain only <code>/bin/sh</code> and <code>/usr/bin/env</code> respectively, to provide minimal compatibility with existing scripts using shebang lines. User-level environments are implemented using a large number of symbolic links to all required packages and auxiliary files. These environments are called [[Nix Package Manager: profiles]] and are stored in <code>/nix/var/nix/profiles</code>, each user having their own profiles. Structuring the system in this way is how NixOS obtains its key advantages over conventional Linux distributions, such as atomicity and rollback support.

~~User-level environments are implemented using a large number~~ of ~~symbolic links to all required packages and auxiliary files. These environments are stored in <code>/nix/var/nix/profiles</code>. Each user has their own environment.~~

=== Usage of the Nix store ===

~~=== Usage of the Nix Store ===~~

A lot of confusion for newcomers arises from the fact that configuration is stored in the read-only <code>/nix/store</code> tree along with all the installed packages. This fact makes it impossible to manually edit system configuration; all configuration changes must be performed by editing the <code>/etc/nixos/configuration.nix</code> file and executing <code>nixos-rebuild switch</code>. NixOS provides the [[NixOS Modules System|modules system]] for editing all required configurations. Users should first [https://nixos.org/nixos/options.html# check if an option] for the configuration they require already exists before attempting to manually add files or configuration via low-level NixOS features like activation scripts.

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=== Modules ===

~~''See also: [https://nixos.org/nixos/manual/index.html#sec-writing-modules Modules (NixOS Manual)]''~~

The NixOS module system as defined in [[Nixpkgs]] provides the means necessary to customize the configuration of the OS. It is used to enable and customize services such as nginx, enable firmware and customize the kernel.

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}

</syntaxHighlight>

See the [https://nixos.org/nixos/manual/index.html#sec-writing-modules Modules section of the NixOS Manual] for more details.

=== Generations ===

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-{{Expansion|This article is incomplete.}}
 [https://nixos.org/ NixOS] is a Linux distribution based on the [[Nix Package Manager]]. It supports reproducible and declarative system-wide configuration management as well as atomic upgrades and rollbacks, although it can additionally support imperative package and user management. In NixOS, all components of the distribution &mdash; including the kernel, installed packages and system configuration files &mdash; are built by [[Nix Package Manager|Nix]] from purely functional (that is, [[Wikipedia:Pure function|side-effect free]]) [[Nix Expression Language|Nix expressions]].
@@ Line 160: / Line 158: @@
 == Internals ==
-=== Comparsion to traditional Linux Distributions ===
+=== Comparison with traditional Linux Distributions ===
-''See also: [[Nix vs. Linux Standard Base]]''
-The main difference between to Linux Distribution is that NixOS does not follow the [https://en.wikipedia.org/wiki/Linux_Standard_Base Linux Standard Base] file system structure. On LSB-compliant systems software is stored under <code>/{,usr}/{bin,lib,share}</code> and configuration is generally stored in <code>/etc</code>.
-Software binaries are available in the user environment if they are placed in one of the LSB's <code>bin</code> directories. When a program references dynamic libraries it will search for the required libraries in the LSB folders (<code>/lib</code>, <code>/usr/lib</code>).
-In NixOS however <code>/lib</code> and <code>/usr/lib</code> do not exist. Instead all system libraries, binaries, kernels, firmware and configuration files are stored beneath <code>/nix/store</code>. The files and directories in <code>/nix/store</code> are named by hashes of the information describing the built data. All of the files and directories placed in the Nix store are immutable.
+''Main Article: [[Nix vs. Linux Standard Base]]''
-<code>/bin</code> and <code>/usr/bin</code> are almost absent: they contain only <code>/bin/sh</code> and <code>/usr/bin/env</code> respectively, to provide minimal compatibility with existing scripts using shebang lines.
+The main difference between NixOS and other Linux distributions is that NixOS does not follow the [https://en.wikipedia.org/wiki/Linux_Standard_Base Linux Standard Base] file system structure. On LSB-compliant systems software is stored under <code>/{,usr}/{bin,lib,share}</code> and configuration is generally stored in <code>/etc</code>. Software binaries are available in the user environment if they are placed in one of the LSB's <code>/bin</code> directories. When a program references dynamic libraries it will search for the required libraries in the LSB folders (<code>/lib</code>, <code>/usr/lib</code>).
-Structuring the system in this way is how NixOS obtains its key advantages over conventional Linux distributions, such as atomicity and rollback support. Every item inside the store is the product of the evaluation of a pure function in Nix called a ''derivation'' (essentially a build). Essentially, the store is the reification of the pure, functional description of the system, which is consumed by Nix and used to generate the contents of the store.
+In NixOS however <code>/lib</code> and <code>/usr/lib</code> do not exist. Instead all system libraries, binaries, kernels, firmware and configuration files are placed in the [[Nix Package Manager:Nix Store]]. The files and directories in <code>/nix/store</code> are named by hashes of the information describing the built data. All of the files and directories placed in the Nix store are immutable. <code>/bin</code> and <code>/usr/bin</code> are almost absent: they contain only <code>/bin/sh</code> and <code>/usr/bin/env</code> respectively, to provide minimal compatibility with existing scripts using shebang lines. User-level environments are implemented using a large number of symbolic links to all required packages and auxiliary files. These environments are called [[Nix Package Manager: profiles]] and are stored in <code>/nix/var/nix/profiles</code>, each user having their own profiles. Structuring the system in this way is how NixOS obtains its key advantages over conventional Linux distributions, such as atomicity and rollback support.
-User-level environments are implemented using a large number of symbolic links to all required packages and auxiliary files. These environments are stored in <code>/nix/var/nix/profiles</code>. Each user has their own environment.
+=== Usage of the Nix store ===
-=== Usage of the Nix Store ===
 A lot of confusion for newcomers arises from the fact that configuration is stored in the read-only <code>/nix/store</code> tree along with all the installed packages. This fact makes it impossible to manually edit system configuration; all configuration changes must be performed by editing the <code>/etc/nixos/configuration.nix</code> file and executing <code>nixos-rebuild switch</code>. NixOS provides the [[NixOS Modules System|modules system]] for editing all required configurations. Users should first [https://nixos.org/nixos/options.html# check if an option] for the configuration they require already exists before attempting to manually add files or configuration via low-level NixOS features like activation scripts.
@@ Line 182: / Line 173: @@
 === Modules ===
-''See also: [https://nixos.org/nixos/manual/index.html#sec-writing-modules Modules (NixOS Manual)]''
 The NixOS module system as defined in  [[Nixpkgs]] provides the means necessary to customize the configuration of the OS. It is used to enable and customize services such as nginx, enable firmware and customize the kernel.
@@ Line 217: / Line 206: @@
 }
 </syntaxHighlight>
+See the [https://nixos.org/nixos/manual/index.html#sec-writing-modules Modules section of the NixOS Manual] for more details.
 === Generations ===