mirror of
https://github.com/NixOS/nixpkgs.git
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885 lines
28 KiB
XML
885 lines
28 KiB
XML
<chapter xmlns="http://docbook.org/ns/docbook"
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xmlns:xlink="http://www.w3.org/1999/xlink">
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<title>Development</title>
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<para>This chapter describes how you can modify and extend
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NixOS.</para>
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<!--===============================================================-->
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<section>
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<title>Getting the sources</title>
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<para>By default, NixOS’s <command>nixos-rebuild</command> command
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uses the NixOS and Nixpkgs sources provided by the
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<literal>nixos-unstable</literal> channel (kept in
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<filename>/nix/var/nix/profiles/per-user/root/channels/nixos</filename>).
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To modify NixOS, however, you should check out the latest sources from
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Git. This is done using the following command:
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<screen>
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$ nixos-checkout <replaceable>/my/sources</replaceable>
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</screen>
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or
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<screen>
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$ mkdir -p <replaceable>/my/sources</replaceable>
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$ cd <replaceable>/my/sources</replaceable>
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$ nix-env -i git
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$ git clone git://github.com/NixOS/nixpkgs.git
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</screen>
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This will check out the latest NixOS sources to
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<filename><replaceable>/my/sources</replaceable>/nixpkgs/nixos</filename>
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and the Nixpkgs sources to
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<filename><replaceable>/my/sources</replaceable>/nixpkgs</filename>.
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(The NixOS source tree lives in a subdirectory of the Nixpkgs
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repository.) If you want to rebuild your system using your (modified)
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sources, you need to tell <command>nixos-rebuild</command> about them
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using the <option>-I</option> flag:
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<screen>
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$ nixos-rebuild switch -I nixpkgs=<replaceable>/my/sources</replaceable>/nixpkgs
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</screen>
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</para>
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<para>If you want <command>nix-env</command> to use the expressions in
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<replaceable>/my/sources</replaceable>, use <command>nix-env -f
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<replaceable>/my/sources</replaceable>/nixpkgs</command>, or change
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the default by adding a symlink in
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<filename>~/.nix-defexpr</filename>:
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<screen>
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$ ln -s <replaceable>/my/sources</replaceable>/nixpkgs ~/.nix-defexpr/nixpkgs
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</screen>
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You may want to delete the symlink
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<filename>~/.nix-defexpr/channels_root</filename> to prevent root’s
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NixOS channel from clashing with your own tree.</para>
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<!-- FIXME: not sure what this means.
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<para>You should not pass the base directory
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<filename><replaceable>/my/sources</replaceable></filename>
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to <command>nix-env</command>, as it will break after interpreting expressions
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in <filename>nixos/</filename> as packages.</para>
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-->
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</section>
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<!--===============================================================-->
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<section>
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<title>Writing NixOS modules</title>
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<para>NixOS has a modular system for declarative configuration. This
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system combines multiple <emphasis>modules</emphasis> to produce the
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full system configuration. One of the modules that constitute the
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configuration is <filename>/etc/nixos/configuration.nix</filename>.
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Most of the others live in the <link
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xlink:href="https://github.com/NixOS/nixpkgs/tree/master/nixos/modules"><filename>nixos/modules</filename></link>
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subdirectory of the Nixpkgs tree.</para>
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<para>Each NixOS module is a file that handles one logical aspect of
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the configuration, such as a specific kind of hardware, a service, or
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network settings. A module configuration does not have to handle
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everything from scratch; it can use the functionality provided by
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other modules for its implementation. Thus a module can
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<emphasis>declare</emphasis> options that can be used by other
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modules, and conversely can <emphasis>define</emphasis> options
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provided by other modules in its own implementation. For example, the
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module <link
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xlink:href="https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/security/pam.nix"><filename>pam.nix</filename></link>
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declares the option <option>security.pam.services</option> that allows
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other modules (e.g. <link
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xlink:href="https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/services/networking/ssh/sshd.nix"><filename>sshd.nix</filename></link>)
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to define PAM services; and it defines the option
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<option>environment.etc</option> (declared by <link
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xlink:href="https://github.com/NixOS/nixpkgs/blob/master/nixos/modules/system/etc/etc.nix"><filename>etc.nix</filename></link>)
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to cause files to be created in
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<filename>/etc/pam.d</filename>.</para>
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<para xml:id="para-module-syn">In <xref
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linkend="sec-configuration-syntax"/>, we saw the following structure
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of NixOS modules:
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<programlisting>
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{ config, pkgs, ... }:
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{ <replaceable>option definitions</replaceable>
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}
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</programlisting>
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This is actually an <emphasis>abbreviated</emphasis> form of module
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that only defines options, but does not declare any. The structure of
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full NixOS modules is shown in <xref linkend='ex-module-syntax' />.</para>
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<example xml:id='ex-module-syntax'><title>Structure of NixOS modules</title>
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<programlisting>
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{ config, pkgs, ... }: <co xml:id='module-syntax-1' />
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{
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imports =
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[ <replaceable>paths of other modules</replaceable> <co xml:id='module-syntax-2' />
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];
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options = {
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<replaceable>option declarations</replaceable> <co xml:id='module-syntax-3' />
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};
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config = {
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<replaceable>option definitions</replaceable> <co xml:id='module-syntax-4' />
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};
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}</programlisting>
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</example>
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<para>The meaning of each part is as follows.
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<calloutlist>
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<callout arearefs='module-syntax-1'>
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<para>This line makes the current Nix expression a function. The
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variable <varname>pkgs</varname> contains Nixpkgs, while
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<varname>config</varname> contains the full system configuration.
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This line can be omitted if there is no reference to
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<varname>pkgs</varname> and <varname>config</varname> inside the
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module.</para>
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</callout>
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<callout arearefs='module-syntax-2'>
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<para>This list enumerates the paths to other NixOS modules that
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should be included in the evaluation of the system configuration.
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A default set of modules is defined in the file
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<filename>modules/module-list.nix</filename>. These don't need to
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be added in the import list.</para>
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</callout>
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<callout arearefs='module-syntax-3'>
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<para>The attribute <varname>options</varname> is a nested set of
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<emphasis>option declarations</emphasis> (described below).</para>
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</callout>
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<callout arearefs='module-syntax-4'>
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<para>The attribute <varname>config</varname> is a nested set of
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<emphasis>option definitions</emphasis> (also described
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below).</para>
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</callout>
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</calloutlist>
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</para>
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<para><xref linkend='locate-example' /> shows a module that handles
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the regular update of the “locate” database, an index of all files in
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the file system. This module declares two options that can be defined
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by other modules (typically the user’s
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<filename>configuration.nix</filename>):
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<option>services.locate.enable</option> (whether the database should
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be updated) and <option>services.locate.period</option> (when the
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update should be done). It implements its functionality by defining
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two options declared by other modules:
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<option>systemd.services</option> (the set of all systemd services)
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and <option>services.cron.systemCronJobs</option> (the list of
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commands to be executed periodically by <command>cron</command>).</para>
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<example xml:id='locate-example'><title>NixOS module for the “locate” service</title>
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<programlisting>
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{ config, pkgs, ... }:
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with pkgs.lib;
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let locatedb = "/var/cache/locatedb"; in
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{
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options = {
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services.locate = {
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enable = mkOption {
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type = types.bool;
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default = false;
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description = ''
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If enabled, NixOS will periodically update the database of
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files used by the <command>locate</command> command.
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'';
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};
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period = mkOption {
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type = types.str;
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default = "15 02 * * *";
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description = ''
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This option defines (in the format used by cron) when the
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locate database is updated. The default is to update at
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02:15 at night every day.
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'';
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};
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};
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};
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config = {
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systemd.services.update-locatedb =
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{ description = "Update Locate Database";
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path = [ pkgs.su ];
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script =
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''
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mkdir -m 0755 -p $(dirname ${locatedb})
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exec updatedb --localuser=nobody --output=${locatedb} --prunepaths='/tmp /var/tmp /media /run'
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'';
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};
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services.cron.systemCronJobs = optional config.services.locate.enable
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"${config.services.locate.period} root ${config.systemd.package}/bin/systemctl start update-locatedb.service";
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};
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}</programlisting>
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</example>
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<section><title>Option declarations</title>
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<para>An option declaration specifies the name, type and description
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of a NixOS configuration option. It is illegal to define an option
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that hasn’t been declared in any module. A option declaration
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generally looks like this:
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<programlisting>
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options = {
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<replaceable>name</replaceable> = mkOption {
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type = <replaceable>type specification</replaceable>;
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default = <replaceable>default value</replaceable>;
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example = <replaceable>example value</replaceable>;
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description = "<replaceable>Description for use in the NixOS manual.</replaceable>";
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};
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};
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</programlisting>
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</para>
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<para>The function <varname>mkOption</varname> accepts the following arguments.
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<variablelist>
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<varlistentry>
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<term><varname>type</varname></term>
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<listitem>
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<para>The type of the option (see below). It may be omitted,
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but that’s not advisable since it may lead to errors that are
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hard to diagnose.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>default</varname></term>
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<listitem>
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<para>The default value used if no value is defined by any
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module. A default is not required; in that case, if the option
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value is ever used, an error will be thrown.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>example</varname></term>
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<listitem>
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<para>An example value that will be shown in the NixOS manual.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>description</varname></term>
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<listitem>
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<para>A textual description of the option, in DocBook format,
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that will be included in the NixOS manual.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</para>
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<para>Here is a non-exhaustive list of option types:
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<variablelist>
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<varlistentry>
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<term><varname>types.bool</varname></term>
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<listitem>
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<para>A Boolean.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>types.int</varname></term>
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<listitem>
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<para>An integer.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>types.str</varname></term>
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<listitem>
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<para>A string.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>types.lines</varname></term>
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<listitem>
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<para>A string. If there are multiple definitions, they are
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concatenated, with newline characters in between.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>types.path</varname></term>
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<listitem>
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<para>A path, defined as anything that, when coerced to a
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string, starts with a slash. This includes derivations.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>types.listOf</varname> <replaceable>t</replaceable></term>
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<listitem>
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<para>A list of elements of type <replaceable>t</replaceable>
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(e.g., <literal>types.listOf types.str</literal> is a list of
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strings). Multiple definitions are concatenated together.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>types.attrsOf</varname> <replaceable>t</replaceable></term>
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<listitem>
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<para>A set of elements of type <replaceable>t</replaceable>
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(e.g., <literal>types.attrsOf types.int</literal> is a set of
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name/value pairs, the values being integers).</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><varname>types.nullOr</varname> <replaceable>t</replaceable></term>
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<listitem>
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<para>Either the value <literal>null</literal> or something of
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type <replaceable>t</replaceable>.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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You can also create new types using the function
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<varname>mkOptionType</varname>. See
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<filename>lib/types.nix</filename> in Nixpkgs for details.</para>
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</section>
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<section><title>Option definitions</title>
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<para>Option definitions are generally straight-forward bindings of values to option names, like
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<programlisting>
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config = {
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services.httpd.enable = true;
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};
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</programlisting>
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However, sometimes you need to wrap an option definition or set of
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option definitions in a <emphasis>property</emphasis> to achieve
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certain effects:</para>
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<simplesect><title>Delaying conditionals</title>
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<para>If a set of option definitions is conditional on the value of
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another option, you may need to use <varname>mkIf</varname>.
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Consider, for instance:
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<programlisting>
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config = if config.services.httpd.enable then {
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environment.systemPackages = [ <replaceable>...</replaceable> ];
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<replaceable>...</replaceable>
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} else {};
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</programlisting>
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This definition will cause Nix to fail with an “infinite recursion”
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error. Why? Because the value of
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<option>config.services.httpd.enable</option> depends on the value
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being constructed here. After all, you could also write the clearly
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circular and contradictory:
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<programlisting>
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config = if config.services.httpd.enable then {
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services.httpd.enable = false;
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} else {
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services.httpd.enable = true;
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};
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</programlisting>
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The solution is to write:
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<programlisting>
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config = mkIf config.services.httpd.enable {
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environment.systemPackages = [ <replaceable>...</replaceable> ];
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<replaceable>...</replaceable>
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};
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</programlisting>
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The special function <varname>mkIf</varname> causes the evaluation of
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the conditional to be “pushed down” into the individual definitions,
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as if you had written:
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<programlisting>
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config = {
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environment.systemPackages = if config.services.httpd.enable then [ <replaceable>...</replaceable> ] else [];
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||
<replaceable>...</replaceable>
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||
};
|
||
</programlisting>
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||
|
||
</para>
|
||
|
||
</simplesect>
|
||
|
||
<simplesect><title>Setting priorities</title>
|
||
|
||
<para>A module can override the definitions of an option in other
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modules by setting a <emphasis>priority</emphasis>. All option
|
||
definitions that do not have the lowest priority value are discarded.
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||
By default, option definitions have priority 1000. You can specify an
|
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explicit priority by using <varname>mkOverride</varname>, e.g.
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|
||
<programlisting>
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services.openssh.enable = mkOverride 10 false;
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||
</programlisting>
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|
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This definition causes all other definitions with priorities above 10
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to be discarded. The function <varname>mkForce</varname> is
|
||
equal to <varname>mkOverride 50</varname>.</para>
|
||
|
||
</simplesect>
|
||
|
||
<simplesect><title>Merging configurations</title>
|
||
|
||
<para>In conjunction with <literal>mkIf</literal>, it is sometimes
|
||
useful for a module to return multiple sets of option definitions, to
|
||
be merged together as if they were declared in separate modules. This
|
||
can be done using <varname>mkMerge</varname>:
|
||
|
||
<programlisting>
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||
config = mkMerge
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||
[ # Unconditional stuff.
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||
{ environment.systemPackages = [ <replaceable>...</replaceable> ];
|
||
}
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||
# Conditional stuff.
|
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(mkIf config.services.bla.enable {
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||
environment.systemPackages = [ <replaceable>...</replaceable> ];
|
||
})
|
||
];
|
||
</programlisting>
|
||
|
||
</para>
|
||
|
||
</simplesect>
|
||
|
||
</section>
|
||
|
||
|
||
<section><title>Important options</title>
|
||
|
||
<para>NixOS has many options, but some are of particular importance to
|
||
module writers.</para>
|
||
|
||
<variablelist>
|
||
|
||
<varlistentry>
|
||
<term><option>environment.etc</option></term>
|
||
<listitem>
|
||
<para>This set defines files in <filename>/etc</filename>. A
|
||
typical use is:
|
||
<programlisting>
|
||
environment.etc."os-release".text =
|
||
''
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||
NAME=NixOS
|
||
<replaceable>...</replaceable>
|
||
'';
|
||
</programlisting>
|
||
which causes a file named <filename>/etc/os-release</filename>
|
||
to be created with the given contents.</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><option>system.activationScripts</option></term>
|
||
<listitem>
|
||
<para>A set of shell script fragments that must be executed
|
||
whenever the configuration is activated (i.e., at boot time, or
|
||
after running <command>nixos-rebuild switch</command>). For instance,
|
||
<programlisting>
|
||
system.activationScripts.media =
|
||
''
|
||
mkdir -m 0755 -p /media
|
||
'';
|
||
</programlisting>
|
||
causes the directory <filename>/media</filename> to be created.
|
||
Activation scripts must be idempotent. They should not start
|
||
background processes such as daemons; use
|
||
<option>systemd.services</option> for that.</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><option>systemd.services</option></term>
|
||
<listitem>
|
||
<para>This is the set of systemd services. Example:
|
||
<programlisting>
|
||
systemd.services.dhcpcd =
|
||
{ description = "DHCP Client";
|
||
wantedBy = [ "multi-user.target" ];
|
||
after = [ "systemd-udev-settle.service" ];
|
||
path = [ dhcpcd pkgs.nettools pkgs.openresolv ];
|
||
serviceConfig =
|
||
{ Type = "forking";
|
||
PIDFile = "/run/dhcpcd.pid";
|
||
ExecStart = "${dhcpcd}/sbin/dhcpcd --config ${dhcpcdConf}";
|
||
Restart = "always";
|
||
};
|
||
};
|
||
</programlisting>
|
||
which creates the systemd unit
|
||
<literal>dhcpcd.service</literal>. The option
|
||
<option>wantedBy</option> determined which other units pull this
|
||
one in; <literal>multi-user.target</literal> is the default
|
||
target of the system, so <literal>dhcpcd.service</literal> will
|
||
always be started. The option
|
||
<option>serviceConfig.ExecStart</option> provides the main
|
||
command for the service; it’s also possible to provide pre-start
|
||
actions, stop scripts, and so on.</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><option>users.extraUsers</option></term>
|
||
<term><option>users.extraGroups</option></term>
|
||
<listitem>
|
||
<para>If your service requires special UIDs or GIDs, you can
|
||
define them with these options. See <xref
|
||
linkend="sec-user-management"/> for details.</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
|
||
</variablelist>
|
||
|
||
</section>
|
||
|
||
|
||
</section>
|
||
|
||
|
||
<!--===============================================================-->
|
||
|
||
<section>
|
||
|
||
<title>Building specific parts of NixOS</title>
|
||
|
||
<para>With the command <command>nix-build</command>, you can build
|
||
specific parts of your NixOS configuration. This is done as follows:
|
||
|
||
<screen>
|
||
$ cd <replaceable>/path/to/nixpkgs/nixos</replaceable>
|
||
$ nix-build -A config.<replaceable>option</replaceable></screen>
|
||
|
||
where <replaceable>option</replaceable> is a NixOS option with type
|
||
“derivation” (i.e. something that can be built). Attributes of
|
||
interest include:
|
||
|
||
<variablelist>
|
||
|
||
<varlistentry>
|
||
<term><varname>system.build.toplevel</varname></term>
|
||
<listitem>
|
||
<para>The top-level option that builds the entire NixOS system.
|
||
Everything else in your configuration is indirectly pulled in by
|
||
this option. This is what <command>nixos-rebuild</command>
|
||
builds and what <filename>/run/current-system</filename> points
|
||
to afterwards.</para>
|
||
|
||
<para>A shortcut to build this is:
|
||
|
||
<screen>
|
||
$ nix-build -A system</screen>
|
||
</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>system.build.manual.manual</varname></term>
|
||
<listitem><para>The NixOS manual.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>system.build.etc</varname></term>
|
||
<listitem><para>A tree of symlinks that form the static parts of
|
||
<filename>/etc</filename>.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>system.build.initialRamdisk</varname></term>
|
||
<term><varname>system.build.kernel</varname></term>
|
||
<listitem>
|
||
<para>The initial ramdisk and kernel of the system. This allows
|
||
a quick way to test whether the kernel and the initial ramdisk
|
||
boot correctly, by using QEMU’s <option>-kernel</option> and
|
||
<option>-initrd</option> options:
|
||
|
||
<screen>
|
||
$ nix-build -A config.system.build.initialRamdisk -o initrd
|
||
$ nix-build -A config.system.build.kernel -o kernel
|
||
$ qemu-system-x86_64 -kernel ./kernel/bzImage -initrd ./initrd/initrd -hda /dev/null
|
||
</screen>
|
||
|
||
</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>system.build.nixos-rebuild</varname></term>
|
||
<term><varname>system.build.nixos-install</varname></term>
|
||
<term><varname>system.build.nixos-generate-config</varname></term>
|
||
<listitem>
|
||
<para>These build the corresponding NixOS commands.</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>systemd.units.<replaceable>unit-name</replaceable>.unit</varname></term>
|
||
<listitem>
|
||
<para>This builds the unit with the specified name. Note that
|
||
since unit names contain dots
|
||
(e.g. <literal>httpd.service</literal>), you need to put them
|
||
between quotes, like this:
|
||
|
||
<screen>
|
||
$ nix-build -A 'config.systemd.units."httpd.service".unit'
|
||
</screen>
|
||
|
||
You can also test individual units, without rebuilding the whole
|
||
system, by putting them in
|
||
<filename>/run/systemd/system</filename>:
|
||
|
||
<screen>
|
||
$ cp $(nix-build -A 'config.systemd.units."httpd.service".unit')/httpd.service \
|
||
/run/systemd/system/tmp-httpd.service
|
||
$ systemctl daemon-reload
|
||
$ systemctl start tmp-httpd.service
|
||
</screen>
|
||
|
||
Note that the unit must not have the same name as any unit in
|
||
<filename>/etc/systemd/system</filename> since those take
|
||
precedence over <filename>/run/systemd/system</filename>.
|
||
That’s why the unit is installed as
|
||
<filename>tmp-httpd.service</filename> here.</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
|
||
</variablelist>
|
||
|
||
</para>
|
||
|
||
</section>
|
||
|
||
|
||
<!--===============================================================-->
|
||
|
||
<section>
|
||
|
||
<title>Building your own NixOS CD</title>
|
||
|
||
<para>Building a NixOS CD is as easy as configuring your own computer. The
|
||
idea is to use another module which will replace
|
||
your <filename>configuration.nix</filename> to configure the system that
|
||
would be installed on the CD.</para>
|
||
|
||
<para>Default CD/DVD configurations are available
|
||
inside <filename>nixos/modules/installer/cd-dvd</filename>. To build them
|
||
you have to set <envar>NIXOS_CONFIG</envar> before
|
||
running <command>nix-build</command> to build the ISO.
|
||
|
||
<screen>
|
||
$ nix-build -A config.system.build.isoImage -I nixos-config=modules/installer/cd-dvd/installation-cd-minimal.nix</screen>
|
||
|
||
</para>
|
||
|
||
<para>Before burning your CD/DVD, you can check the content of the image by mounting anywhere like
|
||
suggested by the following command:
|
||
|
||
<screen>
|
||
$ mount -o loop -t iso9660 ./result/iso/cd.iso /mnt/iso</screen>
|
||
|
||
</para>
|
||
|
||
</section>
|
||
|
||
|
||
<!--===============================================================-->
|
||
|
||
<section>
|
||
|
||
<title>Testing the installer</title>
|
||
|
||
<para>Building, burning, and
|
||
booting from an installation CD is rather
|
||
tedious, so here is a quick way to see if the installer works
|
||
properly:
|
||
|
||
<screen>
|
||
$ nix-build -A config.system.build.nixos-install
|
||
$ dd if=/dev/zero of=diskimage seek=2G count=0 bs=1
|
||
$ yes | mke2fs -j diskimage
|
||
$ mount -o loop diskimage /mnt
|
||
$ ./result/bin/nixos-install</screen>
|
||
|
||
</para>
|
||
|
||
</section>
|
||
|
||
|
||
|
||
<!--===============================================================-->
|
||
|
||
<section><title>Whole-system testing using virtual machines</title>
|
||
|
||
<para>Complete NixOS GNU/Linux systems can be tested in virtual
|
||
machines (VMs). This makes it possible to test a system upgrade or
|
||
configuration change before rebooting into it, using the
|
||
<command>nixos-rebuild build-vm</command> or <command>nixos-rebuild
|
||
build-vm-with-bootloader</command> command.</para>
|
||
|
||
<!-- The following is adapted from
|
||
http://wiki.nixos.org/wiki/NixOS_VM_tests, by Eelco Dolstra. -->
|
||
<para>The <filename>tests/</filename> directory in the NixOS source
|
||
tree contains several <emphasis>whole-system unit tests</emphasis>.
|
||
These tests can be run<footnote><para>NixOS tests can be run both from
|
||
NixOS and from a non-NixOS GNU/Linux distribution, provided the Nix
|
||
package manager is installed.</para></footnote> from the NixOS source
|
||
tree as follows:
|
||
|
||
<screen>
|
||
$ nix-build tests/ -A nfs.test
|
||
</screen>
|
||
|
||
This performs an automated test of the NFS client and server
|
||
functionality in the Linux kernel, including file locking semantics
|
||
(e.g., whether locks are maintained across server crashes). It will
|
||
first build or download all the dependencies of the test (e.g., all
|
||
packages needed to run a NixOS VM). The test is defined in <link
|
||
xlink:href="https://nixos.org/repos/nix/nixos/trunk/tests/nfs.nix">
|
||
<filename>tests/nfs.nix</filename></link>. If the test succeeds,
|
||
<command>nix-build</command> will place a symlink
|
||
<filename>./result</filename> in the current directory pointing at the
|
||
location in the Nix store of the test results (e.g., screenshots, test
|
||
reports, and so on). In particular, a pretty-printed log of the test
|
||
is written to <filename>log.html</filename>, which can be viewed using
|
||
a web browser like this:
|
||
|
||
<screen>
|
||
$ firefox result/log.html
|
||
</screen>
|
||
</para>
|
||
|
||
<para>It is also possible to run the test environment interactively,
|
||
allowing you to experiment with the VMs. For example:
|
||
|
||
<screen>
|
||
$ nix-build tests/ -A nfs.driver
|
||
$ ./result/bin/nixos-run-vms
|
||
</screen>
|
||
|
||
The script <command>nixos-run-vms</command> starts the three virtual
|
||
machines defined in the NFS test using QEMU/KVM. The root file system
|
||
of the VMs is created on the fly and kept across VM restarts in
|
||
<filename>./</filename><varname>hostname</varname><filename>.qcow2</filename>.</para>
|
||
|
||
<para>Finally, the test itself can be run interactively. This is
|
||
particularly useful when developing or debugging a test:
|
||
|
||
<screen>
|
||
$ nix-build tests/ -A nfs.driver
|
||
$ ./result/bin/nixos-test-driver
|
||
starting VDE switch for network 1
|
||
>
|
||
</screen>
|
||
|
||
Perl statements can now be typed in to start or manipulate the VMs:
|
||
|
||
<screen>
|
||
> startAll;
|
||
(the VMs start booting)
|
||
> $server->waitForJob("nfs-kernel-nfsd");
|
||
> $client1->succeed("flock -x /data/lock -c 'sleep 100000' &");
|
||
> $client2->fail("flock -n -s /data/lock true");
|
||
> $client1->shutdown;
|
||
(this releases client1's lock)
|
||
> $client2->succeed("flock -n -s /data/lock true");
|
||
</screen>
|
||
|
||
The function <command>testScript</command> executes the entire test
|
||
script and drops you back into the test driver command line upon its
|
||
completion. This allows you to inspect the state of the VMs after the
|
||
test (e.g. to debug the test script).</para>
|
||
|
||
<para>This and other tests are continuously run on <link
|
||
xlink:href="http://hydra.nixos.org/jobset/nixos/trunk">the Hydra
|
||
instance at <literal>nixos.org</literal></link>, which allows
|
||
developers to be notified of any regressions introduced by a NixOS or
|
||
Nixpkgs change.</para>
|
||
|
||
<para>The actual Nix programming interface to VM testing is in NixOS,
|
||
under <link
|
||
xlink:href="https://nixos.org/repos/nix/nixos/trunk/lib/testing.nix">
|
||
<filename>lib/testing.nix</filename></link>. This file defines a
|
||
function which takes an attribute set containing a
|
||
<literal>nixpkgs</literal> attribute (the path to a Nixpkgs checkout),
|
||
and a <literal>system</literal> attribute (the system type). It
|
||
returns an attribute set containing several utility functions, among
|
||
which the main entry point is <literal>makeTest</literal>.
|
||
</para>
|
||
|
||
<para>The <literal>makeTest</literal> function takes a function
|
||
similar to that found in <link
|
||
xlink:href="https://nixos.org/repos/nix/nixos/trunk/tests/nfs.nix">
|
||
<filename>tests/nfs.nix</filename></link> (discussed above). It
|
||
returns an attribute set containing (among others):
|
||
|
||
<variablelist>
|
||
|
||
<varlistentry>
|
||
<term><varname>test</varname></term>
|
||
<listitem><para>A derivation containing the test log as an HTML
|
||
file, as seen above, suitable for presentation in the Hydra
|
||
continuous build system.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>report</varname></term>
|
||
<listitem><para>A derivation containing a code coverage report, with
|
||
meta-data suitable for Hydra.</para></listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term><varname>driver</varname></term>
|
||
<listitem><para>A derivation containing scripts to run the VM test or
|
||
interact with the VM network interactively, as seen above.</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
|
||
</variablelist>
|
||
|
||
</para>
|
||
|
||
</section>
|
||
|
||
|
||
</chapter>
|