FAQ/zh: Difference between revisions

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为了避免重复回答那些经常被问到的问题以及处理新手常遇到的麻烦，这些问题被收录在这里。

<span id="Why_is_there_a_new_wiki?_What_is_with_nixos.wiki?"></span>

旧的 wiki（nixos.wiki）存在以下几个问题：

* 维基的基础设施本应在上线后公开，但最终未能公开。

另请参阅：

<span id="Why_is_Nix_written_in_C++_rather_than_a_functional_language_like_Haskell?"></span>

主要是因为 Nix 旨在轻量级、易于学习且具有良好的可移植性（零依赖）。

<span id="How_to_keep_build-time_dependencies_around_/_be_able_to_rebuild_while_being_offline?"></span>

<syntaxhighlight lang="nix"># /etc/nixos/configuration.nix

{ config, pkgs, lib, ... }:

   };

}</syntaxhighlight>

Check 'man configuration.nix' for these options. Rebuild for these options to take effect:

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List all store paths that form the system closure and realise them:

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<syntaxhighlight lang="bash">

nix-store -qR $(nix-instantiate '<nixpkgs/nixos>' -A system) | xargs nix-store -r

warning: you did not specify `--add-root'; the result might be removed by the garbage collector

<build output and list of successfully realised paths>

</syntaxhighlight>

Repeat for your user and further profiles:

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The warning can be ignored for profiles that are listed/linked in ''/nix/var/nix/profiles/'' or one of its subdirectories.

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<span id="Why_-_instead_of_-?"></span>

在少数需要深入查看 /nix/store 的情况下，将哈希值的前几位放在开头更方便记忆和使用。

</div>

<syntaxhighlight lang="bash">

q0yi2nr8i60gm2zap46ryysydd2nhzhp-automake-1.11.1/

xvs7y09jf7j48p6l0p87iypgpq470jqw-nixos-build-vms/

</syntaxhighlight>

<span id="I&#039;ve_updated_my_channel_and_something_is_broken,_how_can_I_rollback_to_an_earlier_channel?"></span>

查看可用的各代 channel：

20  2014-08-12 19:09:20  (current)

</syntaxhighlight>

<syntaxhighlight lang="bash">

nix-env --rollback -p /nix/var/nix/profiles/per-user/root/channels

switching from generation 20 to 19

</syntaxhighlight>

<syntaxhighlight lang="bash">

nix-env --switch-generation 18 -p /nix/var/nix/profiles/per-user/root/channels

switching from generation 20 to 18

</syntaxhighlight>

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You can replace callPackage with callPackage_i686 to build the 32-bit version of your package on a 64-bit system if you want to test that.

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<syntaxhighlight lang="bash">nix-build -E 'with import <nixpkgs> { }; enableDebugging fooPackage'</syntaxhighlight>

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<syntaxhighlight lang="bash">sudo nix-build --check -A ncdu</syntaxhighlight>

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<ol style="list-style-type: decimal;">

<syntaxhighlight lang="nix">

with (import <nixpkgs> {});

}

</syntaxhighlight></li>

<syntaxhighlight lang="bash">nix-env -iA userPackages -f '<nixpkgs>'</syntaxhighlight></li></ol>

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Another way is using [[Home Manager]].

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Binaries normally do not work out of the box when you download them because they normally just assume that libraries can be found in hardcoded paths such as <code>/lib</code>. However this assumption is incorrect on NixOS systems due to the inner workings of <code>nix</code> - there is no default path, everything gets set to the corresponding version on compile time.

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<syntaxhighlight lang="nix">

programs.nix-ld = {

   libraries = [ pkgs.zlib pkgs.openssl ];

};</syntaxhighlight>

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<syntaxhighlight lang="nix">

programs.nix-ld = {

   enable = true;

};</syntaxhighlight>

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</div>

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<syntaxhighlight lang="nix">

# mybinaryprogram.nix

   '';

}</syntaxhighlight>

This can be built with:

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And run with:

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Another possibility is using a FHS-compatible Sandbox with [https://nixos.org/nixpkgs/manual/#sec-fhs-environments buildFHSUserEnv]

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<syntaxhighlight lang="nix">

# fhsUser.nix

   runScript = "bash";

}).env</syntaxhighlight>

the sandbox can be entered with

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If your target application can't find shared libraries inside buildFHSUserEnv, you may run [https://github.com/lexleogryfon/de-generate nix-de-generate] for target application inside FHS, which will generate newenv.nix file, an nix-expression of buildFHSUserEnv with resolved dependencies for shared libraries.

{{main|Channel branches}}

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If you want to know where <nixpkgs> is located:

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To know the commit, open the .version-suffix file in the nixpkgs location. The hash after the dot is the git commit.

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Branches on the nixpkgs repo have a relationship with channels, but that relationship is not 1:1.

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<syntaxhighlight lang="command">

NIX_PATH=nixpkgs=https://github.com/NixOS/nixpkgs/archive/release-17.09.tar.gz nix-shell -p $software

</syntaxhighlight>

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start a new shell with a private mount namespace (Linux-only)

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remount the filesystem with write privileges (as root)

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update the file

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exit to shell where /nix/store is still mounted read-only

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Be sure to [https://github.com/NixOS/nixpkgs/issues report the incorrect url] or [https://github.com/NixOS/nixpkgs/pulls fix it yourself].

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<syntaxhighlight lang="bash">nix-prefetch-git https://git.zx2c4.com/password-store</syntaxhighlight>

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<syntaxhighlight lang="bash">nixos-rebuild switch --option binary-caches ''</syntaxhighlight>

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<syntaxhighlight lang="nix">

# /etc/nix/nix.conf

build-sandbox-paths = $(nix-store -qR $(nix-build '<nixpkgs>' -A bash) | xargs echo /bin/sh=$(nix-build '<nixpkgs>' -A bash)/bin/bash)

</syntaxhighlight>

On NixOS set the following in ''configuration.nix'':

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<syntaxhighlight lang="nix">

nix.settings.sandbox = true;

</syntaxhighlight>

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<syntaxhighlight lang="bash">nix-shell -I nixpkgs=channel:nixpkgs-unstable -p somepackage</syntaxhighlight>

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It is possible to have multiple nix-channels simultaneously. To add the unstable channel with the specifier ''unstable'',

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After updating the channel

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queries via <code>nix-env</code> will show packages from both ''stable'' and ''unstable''. Use this to install unstable packages into your user environment. The following snippet shows how this can be done in ''configuration.nix''.

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<syntaxhighlight lang="nix">

{ config, pkgs, ... }:

}

</syntaxhighlight>

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This only changes what version of <code>PACKAGE_NAME</code> is available on <code>$PATH</code>. If the package you want to take from unstable is installed through a NixOS module, you must use [[overlays]]:

<syntaxhighlight lang="nix">

{ config, pkgs, ... }:

}

</syntaxhighlight>

Note that this will rebuild all packages depending on the overlaid package, which may be a lot. Some modules offer a <code>services.foo.package</code> to change the actual derivation used by the module without and overlay, and without recompiling dependencies ([https://nixos.org/manual/nixos/stable/options.html#opt-services.gvfs.package example]).

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If you want to install unfree packages from unstable you need to also set allowUnfree by replacing the import statment above with:

<syntaxhighlight lang="nix">

import <nixos-unstable> { config = { allowUnfree = true; }; }

</syntaxhighlight>

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<syntaxhighlight lang="bash">su nano /etc/nixos/configuration.nix</syntaxhighlight>

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Add this line to your configuration file.

<syntaxhighlight lang="bash">boot.extraModulePackages = [ config.boot.kernelPackages.exfat-nofuse ];</syntaxhighlight>

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<syntaxhighlight lang="bash">nixos-rebuild switch</syntaxhighlight>

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The name <code>Nix</code> comes from the Dutch word [https://en.wiktionary.org/wiki/nix niks] which means ''nothing''. It reflects the fact that Nix derivations do not have access to anything that has not been explicitly declared as an input.<ref>Eelco Dolstra et al. “Nix: A Safe and Policy-Free System for Software Deployment.” LiSA (2004), https://pdfs.semanticscholar.org/5fd8/8f89bd8738816e62808a1b7fb12d3ab14a2f.pdf</ref>

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Immutability is a property of data, in general, which means that the data cannot be modified after it is created. In the context of an operating system, it really means that certain parts of the system have this property. In the case of Nix and NixOS, that includes the Nix store, where files can be created but not modified after the time they are created. It does not apply to every part of the operating system, in that users can still modify their own files in their home directory, for example.

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