FAQ: Difference between revisions

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}

</syntaxhighlight></li>

<li><p><translate>Install all specified packages using this command:</translate></p>

<li><p><translate> Install all specified packages using this command:</translate></p>

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

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Another way is using [[Home Manager]].

~~~~

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

=== 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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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.

~~~~

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

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

</translate>

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<li><translate> Once the job succeeds at a particular nixpkgs commit, '''cache.nixos.org''' will download binaries from '''hydra.nixos.org'''.</translate></li>

<li><translate>Once the above download completes, the channel updates.</translate></li>

<li><translate> Once the above download completes, the channel updates.</translate></li>

</ol>

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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.

=== Nixpkgs branches ===

~~=== Nixpkgs branches ===~~

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

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

</syntaxhighlight>

=== There's an updated version for $software on the unstable branch, but I use stable, how can I use it? ===

Before going ahead with this, note that firstly, this likely means that the package you intend to update has had a major version change. If you have used it previously, there is a chance that your existing data either will not work with the new version or will need to be migrated; If in doubt, consult the upstream documentation of the package.

Secondly, while you're less likely to run into issues on NixOS than on, for example, Debian when installing packages from different releases, it's not impossible.

Nix ensures that libraries and (usually) runtime dependencies of packages are kept separate, so that you can trivially have many versions of those dependencies installed, without affecting the versions of said dependencies used by important system components. This ensures that you cannot accidentally break your package manager by, say, updating Python, as is quite common on other distros.

Nix cannot however ensure that there will be no incompatibilities with services of which there can inherently be only one running instance. As an example, if you try to use a package from unstable on a stable system that requires a feature in systemd that is not yet present in the systemd version on stable, this package will not work; it's simply not possible to run two different versions of systemd simultaneously.

Nonetheless, it's quite uncommon that end-user facing applications rely on such singleton services, or at the very least they will typically have internal backwards compatibility. As such, mixing channels is usually unproblematic in practice, and even if not, NixOS' rollback features make it trivial to recover from problems should they occur.

==== Using channels ====

First we need to add the unstable channel to our system channels:

{{Warning|`nixos-rebuild --upgrade` will by default only update the channel named `nixos`, which this new channel is not. Use `nixos-rebuild --upgrade-all` instead.}}

</translate>

$ sudo nix-channel --add https://nixos.org/channels/nixos-unstable nixos-unstable

$ sudo nix-channel --update

</syntaxhighlight>

Then we can import this channel using the angle-bracket notation to refer to it:

</translate>

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

{

config,

pkgsUnstable,

...

}: {

# We add a new `pkgsUnstable` to the module arguments; this allows

# us to easily use `pkgsUnstable` in other modules as well, without

# having to evaluate it again.

_module.args.pkgsUnstable = import <nixos-unstable> { inherit (config.nixpkgs) config; };

environment.systemPackages = [

# Once we have created our `pkgsUnstable`, we can easily use

# packages from it wherever NixOS modules expect derivations

pkgsUnstable.hello

];

}</syntaxhighlight>

==== Using flakes ====

We simply add the unstable branch to our flake inputs, and pass them into the NixOS module system using <code>specialArgs</code>:

</translate>

# flake.nix

{

inputs = {

nixpkgs.url = "https://channels.nixos.org/nixos-25.05/nixexprs.tar.xz";

nixpkgs-unstable.url = "https://channels.nixos.org/nixos-unstable/nixexprs.tar.xz";

};

outputs = { nixpkgs, ... } @ inputs: {

# Note that the hostname "nixos" and the system tuple used here are

# examples.

nixosConfigurations."nixos" = nixpkgs.lib.nixosSystem {

system = "x86_64-linux";

modules = [

./configuration.nix

];

# Any attributes of `specialArgs` will be added to our NixOS module

# arguments.

#

# We've bound `nixpkgs-unstable` to the `inputs` variable using the `@`

# syntax; if we add any other flake inputs in the future those will also

# be added to our module arguments.

specialArgs.flake-inputs = inputs;

};

}

</syntaxhighlight>

Using this in <code>configuration.nix</code> then looks as follows:

</translate>

# configuration.nix

{

pkgs,

flake-inputs,

...

}: {

environment.systemPackages = [

flake-inputs.nixpkgs-unstable.legacyPackages.${pkgs.system}.hello

];

}

</syntaxhighlight>

=== How do I install a specific version of a package for build reproducibility etc.? ===

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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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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>

~~~~

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

=== 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.

@@ Line 198: / Line 198: @@
 }
 </syntaxhighlight></li>
-<li><p><translate>Install all specified packages using this command:</translate></p>
+<li><p><translate><!--T:137--> Install all specified packages using this command:</translate></p>
 <syntaxhighlight lang="bash">nix-env -iA userPackages -f '<nixpkgs>'</syntaxhighlight></li></ol>
@@ Line 208: / Line 208: @@
 Another way is using [[Home Manager]].
-<!--T:9-->
+=== I've downloaded a binary, but I can't run it, what can I do? === <!--T:9-->
-=== I've downloaded a binary, but I can't run it, what can I do? ===
+<!--T:138-->
 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.
@@ Line 324: / Line 324: @@
 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.
-<!--T:136-->
+=== What are channels and how do they get updated? === <!--T:136-->
-=== What are channels and how do they get updated? ===
 </translate>
@@ Line 368: / Line 367: @@
 <ol start="2" style="list-style-type: decimal;">
 <li><translate><!--T:76--> Once the job succeeds at a particular nixpkgs commit, '''cache.nixos.org''' will download binaries from '''hydra.nixos.org'''.</translate></li>
-<li><translate>Once the above download completes, the channel updates.</translate></li>
+<li><translate><!--T:139--> Once the above download completes, the channel updates.</translate></li>
 </ol>
@@ Line 390: / Line 389: @@
 To know the commit, open the .version-suffix file in the nixpkgs location. The hash after the dot is the git commit.
-<!--T:12-->
+=== Nixpkgs branches === <!--T:12-->
-=== Nixpkgs branches ===
+<!--T:140-->
 Branches on the nixpkgs repo have a relationship with channels, but that relationship is not 1:1.
@@ Line 414: / Line 413: @@
 NIX_PATH=nixpkgs=https://github.com/NixOS/nixpkgs/archive/release-17.09.tar.gz nix-shell -p $software
 </syntaxhighlight>
+<translate>
+=== There's an updated version for $software on the unstable branch, but I use stable, how can I use it? ===
+Before going ahead with this, note that firstly, this likely means that the package you intend to update has had a major version change. If you have used it previously, there is a chance that your existing data either will not work with the new version or will need to be migrated; If in doubt, consult the upstream documentation of the package.
+Secondly, while you're less likely to run into issues on NixOS than on, for example, Debian when installing packages from different releases, it's not impossible.
+Nix ensures that libraries and (usually) runtime dependencies of packages are kept separate, so that you can trivially have many versions of those dependencies installed, without affecting the versions of said dependencies used by important system components. This ensures that you cannot accidentally break your package manager by, say, updating Python, as is quite common on other distros.
+Nix cannot however ensure that there will be no incompatibilities with services of which there can inherently be only one running instance. As an example, if you try to use a package from unstable on a stable system that requires a feature in systemd that is not yet present in the systemd version on stable, this package will not work; it's simply not possible to run two different versions of systemd simultaneously.
+Nonetheless, it's quite uncommon that end-user facing applications rely on such singleton services, or at the very least they will typically have internal backwards compatibility. As such, mixing channels is usually unproblematic in practice, and even if not, NixOS' rollback features make it trivial to recover from problems should they occur.
+==== Using channels ====
+First we need to add the unstable channel to our system channels:
+{{Warning|`nixos-rebuild --upgrade` will by default only update the channel named `nixos`, which this new channel is not. Use `nixos-rebuild --upgrade-all` instead.}}
+</translate>
+<syntaxhighlight lang="console">
+$ sudo nix-channel --add https://nixos.org/channels/nixos-unstable nixos-unstable
+$ sudo nix-channel --update
+</syntaxhighlight>
+<translate>
+Then we can import this channel using the angle-bracket notation to refer to it:
+</translate>
+<syntaxhighlight lang="nixos"># configuration.nix
+{
+  config,
+  pkgsUnstable,
+  ...
+}: {
+  # We add a new `pkgsUnstable` to the module arguments; this allows
+  # us to easily use `pkgsUnstable` in other modules as well, without
+  # having to evaluate it again.
+  _module.args.pkgsUnstable = import <nixos-unstable> { inherit (config.nixpkgs) config; };
+  environment.systemPackages = [
+    # Once we have created our `pkgsUnstable`, we can easily use
+    # packages from it wherever NixOS modules expect derivations
+    pkgsUnstable.hello
+  ];
+}</syntaxhighlight>
+<translate>
+==== Using flakes ====
+We simply add the unstable branch to our flake inputs, and pass them into the NixOS module system using <code>specialArgs</code>:
+</translate>
+<syntaxhighlight lang="nix">
+# flake.nix
+{
+  inputs = {
+    nixpkgs.url = "https://channels.nixos.org/nixos-25.05/nixexprs.tar.xz";
+    nixpkgs-unstable.url = "https://channels.nixos.org/nixos-unstable/nixexprs.tar.xz";
+  };
+  outputs = { nixpkgs, ... } @ inputs: {
+    # Note that the hostname "nixos" and the system tuple used here are
+    # examples.
+    nixosConfigurations."nixos" = nixpkgs.lib.nixosSystem {
+      system = "x86_64-linux";
+      modules = [
+        ./configuration.nix
+      ];
+      # Any attributes of `specialArgs` will be added to our NixOS module
+      # arguments.
+      #
+      # We've bound `nixpkgs-unstable` to the `inputs` variable using the `@`
+      # syntax; if we add any other flake inputs in the future those will also
+      # be added to our module arguments.
+      specialArgs.flake-inputs = inputs;
+    };
+  };
+}
+</syntaxhighlight>
 <translate>
+Using this in <code>configuration.nix</code> then looks as follows:
+</translate>
+<syntaxhighlight lang="nixos">
+# configuration.nix
+{
+  pkgs,
+  flake-inputs,
+  ...
+}: {
+  environment.systemPackages = [
+    flake-inputs.nixpkgs-unstable.legacyPackages.${pkgs.system}.hello
+  ];
+}
+</syntaxhighlight>
+<translate>
 === How do I install a specific version of a package for build reproducibility etc.? === <!--T:14-->
@@ Line 589: / Line 678: @@
 <translate>
+<!--T:141-->
 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]).
@@ Line 634: / Line 724: @@
 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>
-<!--T:127-->
+=== What does it mean to say that NixOS is "immutable" === <!--T:127-->
-=== What does it mean to say that NixOS is "immutable" ===
+<!--T:142-->
 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.