mirror of
https://github.com/NixOS/nixpkgs.git
synced 2024-11-30 01:20:40 +00:00
218 lines
6.4 KiB
XML
218 lines
6.4 KiB
XML
<section 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="sec-configuration-file">
|
||
|
||
<title>NixOS Configuration File</title>
|
||
|
||
<para>The NixOS configuration file generally looks like this:
|
||
|
||
<programlisting>
|
||
{ config, pkgs, ... }:
|
||
|
||
{ <replaceable>option definitions</replaceable>
|
||
}
|
||
</programlisting>
|
||
|
||
The first line (<literal>{ config, pkgs, ... }:</literal>) denotes
|
||
that this is actually a function that takes at least the two arguments
|
||
<varname>config</varname> and <varname>pkgs</varname>. (These are
|
||
explained later.) The function returns a <emphasis>set</emphasis> of
|
||
option definitions (<literal>{ <replaceable>...</replaceable> }</literal>). These definitions have the
|
||
form <literal><replaceable>name</replaceable> =
|
||
<replaceable>value</replaceable></literal>, where
|
||
<replaceable>name</replaceable> is the name of an option and
|
||
<replaceable>value</replaceable> is its value. For example,
|
||
|
||
<programlisting>
|
||
{ config, pkgs, ... }:
|
||
|
||
{ services.httpd.enable = true;
|
||
services.httpd.adminAddr = "alice@example.org";
|
||
services.httpd.documentRoot = "/webroot";
|
||
}
|
||
</programlisting>
|
||
|
||
defines a configuration with three option definitions that together
|
||
enable the Apache HTTP Server with <filename>/webroot</filename> as
|
||
the document root.</para>
|
||
|
||
<para>Sets can be nested, and in fact dots in option names are
|
||
shorthand for defining a set containing another set. For instance,
|
||
<option>services.httpd.enable</option> defines a set named
|
||
<varname>services</varname> that contains a set named
|
||
<varname>httpd</varname>, which in turn contains an option definition
|
||
named <varname>enable</varname> with value <literal>true</literal>.
|
||
This means that the example above can also be written as:
|
||
|
||
<programlisting>
|
||
{ config, pkgs, ... }:
|
||
|
||
{ services = {
|
||
httpd = {
|
||
enable = true;
|
||
adminAddr = "alice@example.org";
|
||
documentRoot = "/webroot";
|
||
};
|
||
};
|
||
}
|
||
</programlisting>
|
||
|
||
which may be more convenient if you have lots of option definitions
|
||
that share the same prefix (such as
|
||
<literal>services.httpd</literal>).</para>
|
||
|
||
<para>NixOS checks your option definitions for correctness. For
|
||
instance, if you try to define an option that doesn’t exist (that is,
|
||
doesn’t have a corresponding <emphasis>option declaration</emphasis>),
|
||
<command>nixos-rebuild</command> will give an error like:
|
||
<screen>
|
||
The option `services.httpd.enable' defined in `/etc/nixos/configuration.nix' does not exist.
|
||
</screen>
|
||
Likewise, values in option definitions must have a correct type. For
|
||
instance, <option>services.httpd.enable</option> must be a Boolean
|
||
(<literal>true</literal> or <literal>false</literal>). Trying to give
|
||
it a value of another type, such as a string, will cause an error:
|
||
<screen>
|
||
The option value `services.httpd.enable' in `/etc/nixos/configuration.nix' is not a boolean.
|
||
</screen>
|
||
|
||
</para>
|
||
|
||
<para>Options have various types of values. The most important are:
|
||
|
||
<variablelist>
|
||
<varlistentry>
|
||
<term>Strings</term>
|
||
<listitem>
|
||
<para>Strings are enclosed in double quotes, e.g.
|
||
|
||
<programlisting>
|
||
networking.hostName = "dexter";
|
||
</programlisting>
|
||
|
||
Special characters can be escaped by prefixing them with a
|
||
backslash (e.g. <literal>\"</literal>).</para>
|
||
|
||
<para>Multi-line strings can be enclosed in <emphasis>double
|
||
single quotes</emphasis>, e.g.
|
||
|
||
<programlisting>
|
||
networking.extraHosts =
|
||
''
|
||
127.0.0.2 other-localhost
|
||
10.0.0.1 server
|
||
'';
|
||
</programlisting>
|
||
|
||
The main difference is that it strips from each line
|
||
a number of spaces equal to the minimal indentation of
|
||
the string as a whole (disregarding the indentation of
|
||
empty lines), and that characters like
|
||
<literal>"</literal> and <literal>\</literal> are not special
|
||
(making it more convenient for including things like shell
|
||
code).
|
||
See more info about this in the Nix manual <link
|
||
xlink:href="https://nixos.org/nix/manual/#ssec-values">here</link>.</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term>Booleans</term>
|
||
<listitem>
|
||
<para>These can be <literal>true</literal> or
|
||
<literal>false</literal>, e.g.
|
||
|
||
<programlisting>
|
||
networking.firewall.enable = true;
|
||
networking.firewall.allowPing = false;
|
||
</programlisting>
|
||
</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term>Integers</term>
|
||
<listitem>
|
||
<para>For example,
|
||
|
||
<programlisting>
|
||
boot.kernel.sysctl."net.ipv4.tcp_keepalive_time" = 60;
|
||
</programlisting>
|
||
|
||
(Note that here the attribute name
|
||
<literal>net.ipv4.tcp_keepalive_time</literal> is enclosed in
|
||
quotes to prevent it from being interpreted as a set named
|
||
<literal>net</literal> containing a set named
|
||
<literal>ipv4</literal>, and so on. This is because it’s not a
|
||
NixOS option but the literal name of a Linux kernel
|
||
setting.)</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term>Sets</term>
|
||
<listitem>
|
||
<para>Sets were introduced above. They are name/value pairs
|
||
enclosed in braces, as in the option definition
|
||
|
||
<programlisting>
|
||
fileSystems."/boot" =
|
||
{ device = "/dev/sda1";
|
||
fsType = "ext4";
|
||
options = [ "rw" "data=ordered" "relatime" ];
|
||
};
|
||
</programlisting>
|
||
</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term>Lists</term>
|
||
<listitem>
|
||
<para>The important thing to note about lists is that list
|
||
elements are separated by whitespace, like this:
|
||
|
||
<programlisting>
|
||
boot.kernelModules = [ "fuse" "kvm-intel" "coretemp" ];
|
||
</programlisting>
|
||
|
||
List elements can be any other type, e.g. sets:
|
||
|
||
<programlisting>
|
||
swapDevices = [ { device = "/dev/disk/by-label/swap"; } ];
|
||
</programlisting>
|
||
</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
|
||
<varlistentry>
|
||
<term>Packages</term>
|
||
<listitem>
|
||
<para>Usually, the packages you need are already part of the Nix
|
||
Packages collection, which is a set that can be accessed through
|
||
the function argument <varname>pkgs</varname>. Typical uses:
|
||
|
||
<programlisting>
|
||
environment.systemPackages =
|
||
[ pkgs.thunderbird
|
||
pkgs.emacs
|
||
];
|
||
|
||
postgresql.package = pkgs.postgresql90;
|
||
</programlisting>
|
||
|
||
The latter option definition changes the default PostgreSQL
|
||
package used by NixOS’s PostgreSQL service to 9.0. For more
|
||
information on packages, including how to add new ones, see
|
||
<xref linkend="sec-custom-packages"/>.</para>
|
||
</listitem>
|
||
</varlistentry>
|
||
|
||
</variablelist>
|
||
|
||
</para>
|
||
|
||
</section>
|