NixOS/zh: Difference between revisions

==== 32位 x86 架构 ====

对于32位 x86 架构(即 <code>i686</code>)的支持正在减少。大多数包仍然可以编译和运行，但它们的缓存可用性显著降低<ref>https://discourse.nixos.org/t/limited-cache-availability-for-i686-32-bits-x86-architecture/37626</ref>。32位 x86 架构不再提供预构建的 ISO 镜像文件，但其仍可手动构建。

==== 64位 x86 架构 ====

==== 32位 ARM 架构 ====

==== 64位 ARM 架构 ====

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 [[Special:MyLanguage/Nix#Nix store|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 [[Special:MyLanguage/Nix#Profiles|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.

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=== 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 [[Special:MyLanguage/NixOS_modules|module system]] for editing all required configurations. Users should first use [https://search.nixos.org/options the option search tool] to check if the option they need 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 Nixpkgs and the same <code>/etc/nixos/configuration.nix</code> you will get the exact same system state.

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=== Modules ===

The [[Special:MyLanguage/NixOS modules|NixOS module system]] as defined in  [[Special:MyLanguage/Nixpkgs|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.

All module configuration is generally performed by adding options to <code>/etc/nixos/configuration.nix</code>. Most of the examples in the wiki show how this file can be used to configure the OS.

The NixOS module system implements a typing system which allows typechecking of option settings. It also enables options defined in multiple places to be merged automatically. This allows you to spread your configuration over multiple files, and the options you set across all of those files will be merged together:

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

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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.

$ nix-env --rollback              # roll back a user environment

$ nixos-rebuild switch --rollback  # roll back a system environment

NixOS also places entries for previous generations in the bootloader menu, so as a last resort you can always revert to a previous configuration by rebooting. To set the currently booted generation as the default run

Because NixOS keeps previous generations of system state available in case rollback is desired, old package versions aren't deleted from your system immediately after an update. You can delete old generations manually:

# delete generations older than 30 days

# delete ALL previous generations - you can no longer rollback after running this

# as root

# as root switch to generation 204

# as root delete broken generations 205 and 206  

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You can configure automatic garbage collection by setting the [https://search.nixos.org/options?query=nix.gc nix.gc] options in <code>/etc/nixos/configuration.nix</code>. This is recommended, as it keeps the size of the Nix store down.

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== See also ==

* [[Special:MyLanguage/NixOS modules|NixOS modules]], a library for modular [[Special:MyLanguage/Overview of the Nix Expression Language#Expressions|Nix expressions]] which powers [[#declarative-configuration|the declarative configuration of NixOS]].

* [[Special:MyLanguage/NixOS VM tests|NixOS VM tests]], a library for creating reproducible infrastructure tests, based on [[Special:MyLanguage/Nixpkgs|Nixpkgs]], [[Special:MyLanguage/NixOS|NixOS]], QEMU and Perl.

* [https://github.com/ryan4yin/nixos-and-flakes-book NixOS & Flakes Book] (Ryan4yin, 2023) - 🛠️ ❤️ An unofficial NixOS & Flakes book for beginners.