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nixpkgs/nixos/doc/manual/man-nixos-generate-config.xml

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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>
<prompt>$ </prompt>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 =
[ &lt;nixos/modules/installer/scan/not-detected.nix&gt;
];
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>
<prompt>$ </prompt>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>