<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="sec-installation">

<title>Installing NixOS</title>

<orderedlist>

  <listitem><para>Boot from the CD.</para></listitem>

  <listitem><para>The CD contains a basic NixOS installation.  (It
  also contains Memtest86+, useful if you want to test new hardware).
  When it’s finished booting, it should have detected most of your
  hardware.</para></listitem>

  <listitem><para>The NixOS manual is available on virtual console 8
  (press Alt+F8 to access).</para></listitem>

  <listitem><para>You get logged in as <literal>root</literal>
  (with empty password).</para></listitem>

  <listitem><para>If you downloaded the graphical ISO image, you can
  run <command>start display-manager</command> to start KDE.</para></listitem>

  <listitem><para>The boot process should have brought up networking (check
  <command>ip a</command>).  Networking is necessary for the
  installer, since it will download lots of stuff (such as source
  tarballs or Nixpkgs channel binaries).  It’s best if you have a DHCP
  server on your network. Otherwise configure networking manually
  using <command>ifconfig</command>.</para>
  <para>To manually configure the network on the graphical installer,
  first disable network-manager with
  <command>systemctl stop network-manager</command>.</para></listitem>

  <listitem><para>The NixOS installer doesn’t do any partitioning or
  formatting yet, so you need to do that yourself.  Use the following
  commands:

  <itemizedlist>

    <listitem><para>For partitioning:
    <command>fdisk</command>.</para></listitem>

    <listitem><para>For initialising Ext4 partitions:
    <command>mkfs.ext4</command>.  It is recommended that you assign a
    unique symbolic label to the file system using the option
    <option>-L <replaceable>label</replaceable></option>, since this
    makes the file system configuration independent from device
    changes.  For example:

<screen>
$ mkfs.ext4 -L nixos /dev/sda1</screen>

    </para></listitem>

    <listitem><para>For creating swap partitions:
    <command>mkswap</command>.  Again it’s recommended to assign a
    label to the swap partition: <option>-L
    <replaceable>label</replaceable></option>.</para></listitem>

    <listitem><para>For creating LVM volumes, the LVM commands, e.g.,

<screen>
$ pvcreate /dev/sda1 /dev/sdb1
$ vgcreate MyVolGroup /dev/sda1 /dev/sdb1
$ lvcreate --size 2G --name bigdisk MyVolGroup
$ lvcreate --size 1G --name smalldisk MyVolGroup</screen>

    </para></listitem>

    <listitem><para>For creating software RAID devices, use
    <command>mdadm</command>.</para></listitem>

  </itemizedlist>

  </para></listitem>

  <listitem><para>Mount the target file system on which NixOS should
  be installed on <filename>/mnt</filename>, e.g.

<screen>
$ mount /dev/disk/by-label/nixos /mnt
</screen>

  </para></listitem>

  <listitem><para>If your machine has a limited amount of memory, you
  may want to activate swap devices now (<command>swapon
  <replaceable>device</replaceable></command>).  The installer (or
  rather, the build actions that it may spawn) may need quite a bit of
  RAM, depending on your configuration.</para></listitem>

  <listitem>

    <para>You now need to create a file
    <filename>/mnt/etc/nixos/configuration.nix</filename> that
    specifies the intended configuration of the system.  This is
    because NixOS has a <emphasis>declarative</emphasis> configuration
    model: you create or edit a description of the desired
    configuration of your system, and then NixOS takes care of making
    it happen.  The syntax of the NixOS configuration file is
    described in <xref linkend="sec-configuration-syntax"/>, while a
    list of available configuration options appears in <xref
    linkend="ch-options"/>.  A minimal example is shown in <xref
    linkend="ex-config"/>.</para>

    <para>The command <command>nixos-generate-config</command> can
    generate an initial configuration file for you:

<screen>
$ nixos-generate-config --root /mnt</screen>

    You should then edit
    <filename>/mnt/etc/nixos/configuration.nix</filename> to suit your
    needs:

<screen>
$ nano /mnt/etc/nixos/configuration.nix
</screen>

    If you’re using the graphical ISO image, other editors may be
    available (such as <command>vim</command>). If you have network
    access, you can also install other editors — for instance, you can
    install Emacs by running <literal>nix-env -i
    emacs</literal>.</para>

    <para>You <emphasis>must</emphasis> set the option
    <option>boot.loader.grub.device</option> to specify on which disk
    the GRUB boot loader is to be installed.  Without it, NixOS cannot
    boot.</para>

    <para>Another critical option is <option>fileSystems</option>,
    specifying the file systems that need to be mounted by NixOS.
    However, you typically don’t need to set it yourself, because
    <command>nixos-generate-config</command> sets it automatically in
    <filename>/mnt/etc/nixos/hardware-configuration.nix</filename>
    from your currently mounted file systems.  (The configuration file
    <filename>hardware-configuration.nix</filename> is included from
    <filename>configuration.nix</filename> and will be overwritten by
    future invocations of <command>nixos-generate-config</command>;
    thus, you generally should not modify it.)</para>

    <note><para>Depending on your hardware configuration or type of
    file system, you may need to set the option
    <option>boot.initrd.kernelModules</option> to include the kernel
    modules that are necessary for mounting the root file system,
    otherwise the installed system will not be able to boot.  (If this
    happens, boot from the CD again, mount the target file system on
    <filename>/mnt</filename>, fix
    <filename>/mnt/etc/nixos/configuration.nix</filename> and rerun
    <filename>nixos-install</filename>.)  In most cases,
    <command>nixos-generate-config</command> will figure out the
    required modules.</para></note>

    <para>Examples of real-world NixOS configuration files can be
    found at <link
    xlink:href="https://nixos.org/repos/nix/configurations/trunk/"/>.</para>

  </listitem>

  <listitem><para>Do the installation:

<screen>
$ nixos-install</screen>

    Cross fingers.  If this fails due to a temporary problem (such as
    a network issue while downloading binaries from the NixOS binary
    cache), you can just re-run <command>nixos-install</command>.
    Otherwise, fix your <filename>configuration.nix</filename> and
    then re-run <command>nixos-install</command>.</para>

    <para>As the last step, <command>nixos-install</command> will ask
    you to set the password for the <literal>root</literal> user, e.g.

<screen>
setting root password...
Enter new UNIX password: ***
Retype new UNIX password: ***
</screen>

    </para>

  </listitem>

  <listitem><para>If everything went well:

<screen>
$ reboot</screen>

  </para></listitem>

  <listitem>

    <para>You should now be able to boot into the installed NixOS. The
    GRUB boot menu shows a list of <emphasis>available
    configurations</emphasis> (initially just one). Every time you
    change the NixOS configuration (see <link
    linkend="sec-changing-config">Changing Configuration</link> ), a
    new item is added to the menu. This allows you to easily roll back
    to a previous configuration if something goes wrong.</para>

    <para>You should log in and change the <literal>root</literal>
    password with <command>passwd</command>.</para>

    <para>You’ll probably want to create some user accounts as well,
    which can be done with <command>useradd</command>:

<screen>
$ useradd -c 'Eelco Dolstra' -m eelco
$ passwd eelco</screen>

    </para>

    <para>You may also want to install some software.  For instance,

<screen>
$ nix-env -qa \*</screen>

    shows what packages are available, and

<screen>
$ nix-env -i w3m</screen>

    install the <literal>w3m</literal> browser.</para>

  </listitem>

</orderedlist>

<para>To summarise, <xref linkend="ex-install-sequence" /> shows a
typical sequence of commands for installing NixOS on an empty hard
drive (here <filename>/dev/sda</filename>).  <xref linkend="ex-config"
/> shows a corresponding configuration Nix expression.</para>

<example xml:id='ex-install-sequence'><title>Commands for Installing NixOS on <filename>/dev/sda</filename></title>
<screen>
$ fdisk /dev/sda # <lineannotation>(or whatever device you want to install on)</lineannotation>
$ mkfs.ext4 -L nixos /dev/sda1
$ mkswap -L swap /dev/sda2
$ swapon /dev/sda2
$ mount /dev/disk/by-label/nixos /mnt
$ nixos-generate-config --root /mnt
$ nano /mnt/etc/nixos/configuration.nix
$ nixos-install
$ reboot</screen>
</example>

<example xml:id='ex-config'><title>NixOS Configuration</title>
<screen>
{ config, pkgs, ... }:

{
  imports =
    [ # Include the results of the hardware scan.
      ./hardware-configuration.nix
    ];

  boot.loader.grub.device = "/dev/sda";

  # Note: setting fileSystems is generally not
  # necessary, since nixos-generate-config figures them out
  # automatically in hardware-configuration.nix.
  #fileSystems."/".device = "/dev/disk/by-label/nixos";

  # Enable the OpenSSH server.
  services.sshd.enable = true;
}</screen>
</example>

<xi:include href="installing-uefi.xml" />
<xi:include href="installing-usb.xml" />

</chapter>