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。

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=== 如何保留构建时依赖/在离线状态下重新构建？ ===

<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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<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：

<syntaxhighlight lang="bash">

nix-env --list-generations -p /nix/var/nix/profiles/per-user/root/channels

</syntaxhighlight>

回滚到上一代的方法如下：

<syntaxhighlight lang="bash">

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

switching from generation 20 to 19

</syntaxhighlight>

To switch to a particular generation:

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<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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=== I'm working on a new package, how can I build it without adding it to nixpkgs? ===

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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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As root you can run nix-build with the --check flag:

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=== How can I manage software with nix-env like with configuration.nix? ===

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<syntaxhighlight lang="nix">

with (import <nixpkgs> {});

}

</syntaxhighlight></li>

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

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=== I've downloaded a binary, but I can't run it, what can I do? ===

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 = {

   libraries = pkgs.steam-run.args.multiPkgs pkgs;

};</syntaxhighlight>

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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.

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=== What are channels and how do they get updated? ===

{{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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=== Nixpkgs branches ===

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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=== What does it mean to say that NixOS is "immutable" ===

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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{{:FAQ/Libraries}}

{{:FAQ/nix-env -iA}}

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