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<refentry xmlns="http://docbook.org/ns/docbook"
xmlns:xlink="http://www.w3.org/1999/xlink"
xmlns:xi="http://www.w3.org/2001/XInclude">
<refmeta>
<refentrytitle><command>nixos-generate-config</command></refentrytitle>
<manvolnum>8</manvolnum>
<refmiscinfo class="source">NixOS</refmiscinfo>
<!-- <refmiscinfo class="version"><xi:include href="version.txt" parse="text"/></refmiscinfo> -->
</refmeta>
<refnamediv>
<refname><command>nixos-generate-config</command></refname>
<refpurpose>generate NixOS configuration modules</refpurpose>
</refnamediv>
<refsynopsisdiv>
<cmdsynopsis>
<command>nixos-generate-config</command>
<arg><option>--force</option></arg>
<arg>
<arg choice='plain'><option>--root</option></arg>
<replaceable>root</replaceable>
</arg>
<arg>
<arg choice='plain'><option>--dir</option></arg>
<replaceable>dir</replaceable>
</arg>
</cmdsynopsis>
</refsynopsisdiv>
<refsection><title>Description</title>
<para>This command writes two NixOS configuration modules:
<variablelist>
<varlistentry>
<term><option>/etc/nixos/hardware-configuration.nix</option></term>
<listitem>
<para>This module sets NixOS configuration options based on your
current hardware configuration. In particular, it sets the
<option>fileSystem</option> option to reflect all currently
mounted file systems, the <option>swapDevices</option> option to
reflect active swap devices, and the
<option>boot.initrd.*</option> options to ensure that the
initial ramdisk contains any kernel modules necessary for
mounting the root file system.</para>
<para>If this file already exists, it is overwritten. Thus, you
should not modify it manually. Rather, you should include it
from your <filename>/etc/nixos/configuration.nix</filename>, and
re-run <command>nixos-generate-config</command> to update it
whenever your hardware configuration changes.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>/etc/nixos/configuration.nix</option></term>
<listitem>
<para>This is the main NixOS system configuration module. If it
already exists, it’s left unchanged. Otherwise,
<command>nixos-generate-config</command> will write a template
for you to customise.</para>
</listitem>
</varlistentry>
</variablelist>
</para>
</refsection>
<refsection><title>Options</title>
<para>This command accepts the following options:</para>
<variablelist>
<varlistentry>
<term><option>--root</option></term>
<listitem>
<para>If this option is given, treat the directory
<replaceable>root</replaceable> as the root of the file system.
This means that configuration files will be written to
<filename><replaceable>root</replaceable>/etc/nixos</filename>,
and that any file systems outside of
<replaceable>root</replaceable> are ignored for the purpose of
generating the <option>fileSystems</option> option.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--dir</option></term>
<listitem>
<para>If this option is given, write the configuration files to
the directory <replaceable>dir</replaceable> instead of
<filename>/etc/nixos</filename>.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--force</option></term>
<listitem>
<para>Overwrite
<filename>/etc/nixos/configuration.nix</filename> if it already
exists.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--no-filesystems</option></term>
<listitem>
<para>Omit everything concerning file systems and swap devices
from the hardware configuration.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><option>--show-hardware-config</option></term>
<listitem>
<para>Don't generate <filename>configuration.nix</filename> or
<filename>hardware-configuration.nix</filename> and print the
hardware configuration to stdout only.</para>
</listitem>
</varlistentry>
</variablelist>
</refsection>
<refsection><title>Examples</title>
<para>This command is typically used during NixOS installation to
write initial configuration modules. For example, if you created and
mounted the target file systems on <filename>/mnt</filename> and
<filename>/mnt/boot</filename>, you would run:
<screen>
$ nixos-generate-config --root /mnt
</screen>
The resulting file
<filename>/mnt/etc/nixos/hardware-configuration.nix</filename> might
look like this:
<programlisting>
# Do not modify this file! It was generated by ‘nixos-generate-config’
# and may be overwritten by future invocations. Please make changes
# to /etc/nixos/configuration.nix instead.
{ config, pkgs, ... }:
{
imports =
[ <nixos/modules/installer/scan/not-detected.nix>
];
boot.initrd.availableKernelModules = [ "ehci_hcd" "ahci" ];
boot.kernelModules = [ "kvm-intel" ];
boot.extraModulePackages = [ ];
fileSystems."/" =
{ device = "/dev/disk/by-label/nixos";
fsType = "ext3";
options = [ "rw" "data=ordered" "relatime" ];
};
fileSystems."/boot" =
{ device = "/dev/sda1";
fsType = "ext3";
options = [ "rw" "errors=continue" "user_xattr" "acl" "barrier=1" "data=writeback" "relatime" ];
};
swapDevices =
[ { device = "/dev/sda2"; }
];
nix.maxJobs = 8;
}
</programlisting>
It will also create a basic
<filename>/mnt/etc/nixos/configuration.nix</filename>, which you
should edit to customise the logical configuration of your system.
This file includes the result of the hardware scan as follows:
<programlisting>
imports = [ ./hardware-configuration.nix ];
</programlisting>
</para>
<para>After installation, if your hardware configuration changes, you
can run:
<screen>
$ nixos-generate-config
</screen>
to update <filename>/etc/nixos/hardware-configuration.nix</filename>.
Your <filename>/etc/nixos/configuration.nix</filename> will
<emphasis>not</emphasis> be overwritten.</para>
</refsection>
</refentry>
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