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# Configuration Syntax {#sec-configuration-syntax}

     

       
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The NixOS configuration file `/etc/nixos/configuration.nix` is actually

     

       
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a *Nix expression*, which is the Nix package manager's purely functional

     

       
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language for describing how to build packages and configurations. This

     

       
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means you have all the expressive power of that language at your

     

       
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disposal, including the ability to abstract over common patterns, which

     

       
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is very useful when managing complex systems. The syntax and semantics

     

       
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of the Nix language are fully described in the [Nix

     

       
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manual](https://nixos.org/nix/manual/#chap-writing-nix-expressions), but

     

       
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here we give a short overview of the most important constructs useful in

     

       
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NixOS configuration files.

     

       
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```{=docbook}

     

       
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<xi:include href="config-file.section.xml" />

     

       
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<xi:include href="abstractions.section.xml" />

     

       
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<xi:include href="modularity.section.xml" />

     

       
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<xi:include href="summary.section.xml" />

     

       
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```

     

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<chapter xmlns="http://docbook.org/ns/docbook"

     

       
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         xmlns:xlink="http://www.w3.org/1999/xlink"

     

       
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         xmlns:xi="http://www.w3.org/2001/XInclude"

     

       
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         version="5.0"

     

       
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         xml:id="sec-configuration-syntax">

     

       
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 <title>Configuration Syntax</title>

     

       
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 <para>

     

       
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  The NixOS configuration file

     

       
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  <filename>/etc/nixos/configuration.nix</filename> is actually a <emphasis>Nix

     

       
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  expression</emphasis>, which is the Nix package manager’s purely functional

     

       
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  language for describing how to build packages and configurations. This means

     

       
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-
       
  you have all the expressive power of that language at your disposal,

     

       
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-
       
  including the ability to abstract over common patterns, which is very useful

     

       
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-
       
  when managing complex systems. The syntax and semantics of the Nix language

     

       
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-
       
  are fully described in the

     

       
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  <link

     

       
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xlink:href="https://nixos.org/nix/manual/#chap-writing-nix-expressions">Nix

     

       
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  manual</link>, but here we give a short overview of the most important

     

       
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  constructs useful in NixOS configuration files.

     

       
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 </para>

     

       
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 <xi:include href="../from_md/configuration/config-file.section.xml" />

     

       
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 <xi:include href="../from_md/configuration/abstractions.section.xml" />

     

       
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 <xi:include href="../from_md/configuration/modularity.section.xml" />

     

       
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 <xi:include href="../from_md/configuration/summary.section.xml" />

     

       
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</chapter>

     

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   effect after you run <command>nixos-rebuild</command>.

     

       
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  </para>

     

       
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 </partintro>

     

       
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 <xi:include href="config-syntax.xml" />

     

       
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 <xi:include href="../from_md/configuration/config-syntax.chapter.xml" />

     

       
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 <xi:include href="package-mgmt.xml" />

     

       
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 <xi:include href="../from_md/configuration/user-mgmt.chapter.xml" />

     

       
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 <xi:include href="file-systems.xml" />

     

···

       
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<chapter xmlns="http://docbook.org/ns/docbook"  xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xi="http://www.w3.org/2001/XInclude" xml:id="sec-configuration-syntax">

     

       
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  <title>Configuration Syntax</title>

     

       
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  <para>

     

       
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    The NixOS configuration file

     

       
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    <literal>/etc/nixos/configuration.nix</literal> is actually a

     

       
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    <emphasis>Nix expression</emphasis>, which is the Nix package

     

       
7
       
7
       
+
       
    manager’s purely functional language for describing how to build

     

       
8
       
8
       
+
       
    packages and configurations. This means you have all the expressive

     

       
9
       
9
       
+
       
    power of that language at your disposal, including the ability to

     

       
10
       
10
       
+
       
    abstract over common patterns, which is very useful when managing

     

       
11
       
11
       
+
       
    complex systems. The syntax and semantics of the Nix language are

     

       
12
       
12
       
+
       
    fully described in the

     

       
13
       
13
       
+
       
    <link xlink:href="https://nixos.org/nix/manual/#chap-writing-nix-expressions">Nix

     

       
14
       
14
       
+
       
    manual</link>, but here we give a short overview of the most

     

       
15
       
15
       
+
       
    important constructs useful in NixOS configuration files.

     

       
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  </para>

     

       
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  <xi:include href="config-file.section.xml" />

     

       
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  <xi:include href="abstractions.section.xml" />

     

       
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  <xi:include href="modularity.section.xml" />

     

       
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  <xi:include href="summary.section.xml" />

     

       
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</chapter>