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Diffstat (limited to 'nixos/modules/misc/nixos.xml')
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diff --git a/nixos/modules/misc/nixos.xml b/nixos/modules/misc/nixos.xml new file mode 100644 index 000000000000..f8d3b4bc6e33 --- /dev/null +++ b/nixos/modules/misc/nixos.xml @@ -0,0 +1,84 @@ +<chapter xmlns="http://docbook.org/ns/docbook" + xmlns:xlink="http://www.w3.org/1999/xlink" + xmlns:xi="http://www.w3.org/2001/XInclude" + version="5.0" + xml:id="module-misc-nixos"> + +<title>NixOS Reentry</title> + +<!-- FIXME: render nicely --> + +<!-- FIXME: source can be added automatically --> +<para><emphasis>Source:</emphasis> <filename>modules/misc/nixos.nix</filename></para> + +<!-- FIXME: more stuff, like maintainer? --> + +<para>NixOS reentry can be used for both pinning the evaluation to a +specific version of NixOS, and to dynamically add additional modules into +the Module evaluation.</para> + +<section><title>NixOS Version Pinning</title> + +<para>To pin a specific version of NixOS, you need a version that you can +either clone localy, or that you can fetch remotely.</para> + +<para>If you already have a cloned version of NixOS in the directory +<filename>/etc/nixos/nixpkgs-16-03</filename>, then you can specify the +<option>nixos.path</option> with either the path or the relative path of +your NixOS clone. For example, you can add the following to your +<filename>/etc/nixos/configuration.nix</filename> file: + +<programlisting> +nixos.path = ./nixpkgs-16-03/nixos; +</programlisting> +</para> + +<para>Another option is to fetch a specific version of NixOS, with either +the <literal>fetchTarball</literal> builtin, or the +<literal>pkgs.fetchFromGithub</literal> function and use the result as an +input. + +<programlisting> +nixos.path = "${builtins.fetchTarball https://github.com/NixOS/nixpkgs/archive/1f27976e03c15183191d1b4aa1a40d1f14666cd2.tar.gz}/nixos"; +</programlisting> +</para> + +</section> + + +<section><title>Adding Module Dynamically</title> + +<para>To add additional module, the recommended way is to use statically +known modules in the list of imported arguments as described in <xref +linkend="sec-modularity" />. Unfortunately, this recommended method has +limitation, such that the list of imported files cannot be selected based on +the content of the configuration. + +Fortunately, NixOS reentry system can be used as an alternative to register +new imported modules based on the content of the configuration. To do so, +one should define both <option>nixos.path</option> and +<option>nixos.extraModules</option> options. + +<programlisting> +nixos.path = <nixos>; +nixos.extraModules = + if config.networking.hostName == "server" then + [ ./server.nix ] else [ ./client.nix ]; +</programlisting> + +Also note, that the above can be reimplemented in a different way which is +not as expensive, by using <literal>mkIf</literal> at the top each +configuration if both modules are present on the file system (see <xref +linkend="sec-option-definitions" />) and by always inmporting both +modules.</para> + +</section> + +<section><title>Options</title> + +<para>FIXME: auto-generated list of module options.</para> + +</section> + + +</chapter> |