NixOS: Difference between revisions

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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>).

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.

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.

=== Usage of the Nix store ===

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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.

The system purity makes it possible to keep system configuration in a central place, without the need to edit multiple files. This configuration can be distributed or version controlled as desired. It also provides for determinism; if you provide the same inputs, the same version of ~~<code>nixpkgs</code>~~ and the same <code>/etc/nixos/configuration.nix</code> you will get the exact same system state.

The system purity makes it possible to keep system configuration in a central place, without the need to edit multiple files. This configuration can be distributed or version controlled as desired. It also provides for determinism; if you provide the same inputs, the same version of Nixpkgs and the same <code>/etc/nixos/configuration.nix</code> you will get the exact same system state.

=== Modules ===

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=== Generations ===

Every time the system state is rebuilt using <code>nixos-rebuild switch</code>, a new generation is created. You can revert to the previous generation at any time, which is useful if a configuration change (or system update) turns out to be detrimental.

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 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>).
-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.
+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.
 === Usage of the Nix store ===
@@ Line 170: / Line 170: @@
 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.
-The system purity makes it possible to keep system configuration in a central place, without the need to edit multiple files. This configuration can be distributed or version controlled as desired. It also provides for determinism; if you provide the same inputs, the same version of <code>nixpkgs</code> and the same <code>/etc/nixos/configuration.nix</code> you will get the exact same system state.
+The system purity makes it possible to keep system configuration in a central place, without the need to edit multiple files. This configuration can be distributed or version controlled as desired. It also provides for determinism; if you provide the same inputs, the same version of Nixpkgs and the same <code>/etc/nixos/configuration.nix</code> you will get the exact same system state.
 === Modules ===
@@ Line 210: / Line 210: @@
 === Generations ===
 Every time the system state is rebuilt using <code>nixos-rebuild switch</code>, a new generation is created. You can revert to the previous generation at any time, which is useful if a configuration change (or system update) turns out to be detrimental.