<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>
 <para>
  NixOS can be installed on BIOS or UEFI systems. The procedure for a UEFI
  installation is by and large the same as a BIOS installation. The differences
  are mentioned in the steps that follow.
 </para>
 <orderedlist>
  <listitem>
   <para>
    Boot from the CD.
   </para>
   <variablelist>
    <varlistentry>
     <term>
      UEFI systems
     </term>
     <listitem>
      <para>
       You should boot the live CD in UEFI mode (consult your specific
       hardware's documentation for instructions). You may find the
       <link xlink:href="http://www.rodsbooks.com/refind">rEFInd boot
       manager</link> useful.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </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)
    or by running <command>nixos-help</command>.
   </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>systemctl
    start display-manager</command> to start KDE. If you want to continue on
    the terminal, you can use <command>loadkeys</command> to switch to your
    preferred keyboard layout. (We even provide neo2 via <command>loadkeys de
    neo</command>!)
   </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>
   <para>
    To manually configure the wifi on the minimal installer, run
    <command>wpa_supplicant -B -i interface -c &lt;(wpa_passphrase 'SSID'
    'key')</command>.
   </para>
  </listitem>
  <listitem>
   <para>
    If you would like to continue the installation from a different machine you
    need to activate the SSH daemon via <literal>systemctl start
    sshd</literal>. In order to be able to login you also need to set a
    password for <literal>root</literal> using <literal>passwd</literal>.
   </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>.
<screen>
# fdisk /dev/sda # <lineannotation>(or whatever device you want to install on)</lineannotation>
-- for UEFI systems only
> n      # <lineannotation>(create a new partition for /boot)</lineannotation>
> 3      # <lineannotation>(make it a partition number 3)</lineannotation>
>        # <lineannotation>(press enter to accept the default)</lineannotation>
> +512M  # <lineannotation>(the size of the UEFI boot partition)</lineannotation>
> t      # <lineannotation>(change the partition type ...)</lineannotation>
> 3      # <lineannotation>(... of the boot partition ...)</lineannotation>
> 1      # <lineannotation>(... to 'UEFI System')</lineannotation>
-- for BIOS or UEFI systems
> n      # <lineannotation>(create a new partition for /swap)</lineannotation>
> 2      # <lineannotation>(make it a partition number 2)</lineannotation>
>        # <lineannotation>(press enter to accept the default)</lineannotation>
> +8G    # <lineannotation>(the size of the swap partition, set to whatever you like)</lineannotation>
> n      # <lineannotation>(create a new partition for /)</lineannotation>
> 1      # <lineannotation>(make it a partition number 1)</lineannotation>
>        # <lineannotation>(press enter to accept the default)</lineannotation>
>        # <lineannotation>(press enter to accept the default and use the rest of the remaining space)</lineannotation>
> a      # <lineannotation>(make the partition bootable)</lineannotation>
> x      # <lineannotation>(enter expert mode)</lineannotation>
> f      # <lineannotation>(fix up the partition ordering)</lineannotation>
> r      # <lineannotation>(exit expert mode)</lineannotation>
> w      # <lineannotation>(write the partition table to disk and exit)</lineannotation></screen>
      </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>. For example:
<screen>
# mkswap -L swap /dev/sda2</screen>
      </para>
     </listitem>
     <listitem>
      <variablelist>
       <varlistentry>
        <term>
         UEFI systems
        </term>
        <listitem>
         <para>
          For creating boot partitions: <command>mkfs.fat</command>. Again
          it’s recommended to assign a label to the boot partition:
          <option>-n <replaceable>label</replaceable></option>. For example:
<screen>
# mkfs.fat -F 32 -n boot /dev/sda3</screen>
         </para>
        </listitem>
       </varlistentry>
      </variablelist>
     </listitem>
     <listitem>
      <para>
       For creating LVM volumes, the LVM commands, e.g.,
       <command>pvcreate</command>, <command>vgcreate</command>, and
       <command>lvcreate</command>.
      </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>
   <variablelist>
    <varlistentry>
     <term>
      UEFI systems
     </term>
     <listitem>
      <para>
       Mount the boot file system on <filename>/mnt/boot</filename>, e.g.
<screen>
# mkdir -p /mnt/boot
# mount /dev/disk/by-label/boot /mnt/boot
</screen>
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </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.
<screen>
# swapon /dev/sda2</screen>
   </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>
   <variablelist>
    <varlistentry>
     <term>
      BIOS systems
     </term>
     <listitem>
      <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>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term>
      UEFI systems
     </term>
     <listitem>
      <para>
       You <emphasis>must</emphasis> set the option
       <option>boot.loader.systemd-boot.enable</option> to
       <literal>true</literal>. <command>nixos-generate-config</command> should
       do this automatically for new configurations when booted in UEFI mode.
      </para>
      <para>
       You may want to look at the options starting with
       <option>boot.loader.efi</option> and
       <option>boot.loader.systemd-boot</option> as well.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
   <para>
    If there are other operating systems running on the machine before
    installing NixOS, the <option>boot.loader.grub.useOSProber</option> option
    can be set to <literal>true</literal> to automatically add them to the grub
    menu.
   </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>
  </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>
    <note>
     <para>
      To prevent the password prompt, set <code>users.mutableUsers =
      false;</code> in <filename>configuration.nix</filename>, which allows
      unattended installation necessary in automation.
     </para>
    </note>
   </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>
-- for UEFI systems only
> n      # <lineannotation>(create a new partition for /boot)</lineannotation>
> 3      # <lineannotation>(make it a partition number 3)</lineannotation>
>        # <lineannotation>(press enter to accept the default)</lineannotation>
> +512M  # <lineannotation>(the size of the UEFI boot partition)</lineannotation>
> t      # <lineannotation>(change the partition type ...)</lineannotation>
> 3      # <lineannotation>(... of the boot partition ...)</lineannotation>
> 1      # <lineannotation>(... to 'UEFI System')</lineannotation>
-- for BIOS or UEFI systems
> n      # <lineannotation>(create a new partition for /swap)</lineannotation>
> 2      # <lineannotation>(make it a partition number 2)</lineannotation>
>        # <lineannotation>(press enter to accept the default)</lineannotation>
> +8G    # <lineannotation>(the size of the swap partition)</lineannotation>
> n      # <lineannotation>(create a new partition for /)</lineannotation>
> 1      # <lineannotation>(make it a partition number 1)</lineannotation>
>        # <lineannotation>(press enter to accept the default)</lineannotation>
>        # <lineannotation>(press enter to accept the default and use the rest of the remaining space)</lineannotation>
> a      # <lineannotation>(make the partition bootable)</lineannotation>
> x      # <lineannotation>(enter expert mode)</lineannotation>
> f      # <lineannotation>(fix up the partition ordering)</lineannotation>
> r      # <lineannotation>(exit expert mode)</lineannotation>
> w      # <lineannotation>(write the partition table to disk and exit)</lineannotation>
# mkfs.ext4 -L nixos /dev/sda1
# mkswap -L swap /dev/sda2
# swapon /dev/sda2
# mkfs.fat -F 32 -n boot /dev/sda3        # <lineannotation>(for UEFI systems only)</lineannotation>
# mount /dev/disk/by-label/nixos /mnt
# mkdir -p /mnt/boot                      # <lineannotation>(for UEFI systems only)</lineannotation>
# mount /dev/disk/by-label/boot /mnt/boot # <lineannotation>(for UEFI systems only)</lineannotation>
# 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";   # <lineannotation>(for BIOS systems only)</lineannotation>
  boot.loader.systemd-boot.enable = true; # <lineannotation>(for UEFI systems only)</lineannotation>

  # 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-usb.xml" />
 <xi:include href="installing-pxe.xml" />
 <xi:include href="installing-virtualbox-guest.xml" />
 <xi:include href="installing-from-other-distro.xml" />
</chapter>
