nixpkgs/doc/manual/installation.xml

<chapter xmlns="http://docbook.org/ns/docbook"
         xmlns:xlink="http://www.w3.org/1999/xlink">

<title>Installation</title>


<!--===============================================================-->

<section>

<title>Building the installation CD</title>

<para>Instead of building an installation CD, you could just download
one from <link xlink:href="http://nixos.org/nixos/"/>.  If you want
(or need) to build it yourself:

<orderedlist>

  <listitem><para>Make sure that you have a <emphasis>very</emphasis>
  recent pre-release version of Nix installed (<link
  xlink:href="http://nixos.org/releases/nix/nix-unstable/"/>).
  The NixOS Nix expressions frequently use bleeding-edge features.  If
  you get any kind of expression evaluation error, try to upgrade your
  Nix.</para></listitem>

  <listitem><para>Optional but strongly recommended (and currently
  <emphasis>required</emphasis> for building the
  <literal>x86_64</literal> ISO): subscribe/pull from the Nixpkgs
  channel to speed up building, i.e.,

<screen>
$ nix-channel --add http://nixos.org/releases/nixpkgs/channels/nixpkgs-unstable
$ nix-channel --update</screen>

  </para></listitem>

  <listitem><para>Check out NixOS from <link
  xlink:href="https://svn.nixos.org/repos/nix/nixos/trunk"/> as
  <literal>nixos</literal>.</para></listitem>

  <listitem><para>If you don’t already have Nixpkgs checkout, Check
  out Nixpkgs from <link
  xlink:href="https://svn.nixos.org/repos/nix/nixos/trunk"/> as
  <literal>nixpkgs</literal>.</para></listitem>

  <listitem><para>In the directory <literal>nixos</literal>, make a
  symbolic link <literal>pkgs</literal> to the <literal>pkgs</literal>
  directory of the Nixpkgs tree, e.g.,

<screen>
$ ln -s nixpkgs/pkgs nixos/</screen>

  </para></listitem>

  <listitem><para>Build the ISO image:

<screen>
$ nix-build configuration/rescue-cd.nix -A rescueCD</screen>

  If everything goes well, you’ll end up with an ISO image in
  <filename>./result/iso/nixos-<replaceable>version</replaceable>-<replaceable>platform</replaceable>.iso</filename>
  that you can burn onto a CD or attach to a virtual CD-ROM drive in
  your favourite virtual machine software.</para></listitem>

</orderedlist>
  
</para>

</section>


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<section>

<title>Installation</title>

<orderedlist>

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

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

  <listitem><para>The NixOS manual is available on virtual console 7
  (press Alt+F7 to access).</para></listitem>

  <listitem><para>Login as <literal>root</literal>, empty
  password.</para></listitem>

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

  <itemizedlist>

    <listitem><para>For partitioning:
    <command>fdisk</command>.</para></listitem>
    
    <listitem><para>For initialising Ext2/Ext3 partitions:
    <command>mke2fs</command>.  Ext3 is recommended; use the
    <option>-j</option> to create a journalled file system.  It is
    also recommended that you assign a unique symbolic label to the
    file system using the option <option>-L
    <replaceable>label</replaceable></option>.  This will make the
    file system configuration independent from device
    changes.</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>

    Possibly you’ll need to do <userinput>initctl start
    lvm</userinput> after this (TODO: check whether this is
    needed).</para></listitem>

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

  </itemizedlist>

  </para></listitem>
    
  <listitem><para>Mount the target file system on
  <filename>/mnt</filename>.</para></listitem>

  <listitem>

    <para>The installation is declarative; you need to write a
    description of the configuration that you want to be built and
    activated.  The configuration is specified in a Nix expression and
    must be stored <emphasis>on the target file system</emphasis> in
    <filename>/mnt/etc/nixos/configuration.nix</filename>.  See
    <filename>/etc/nixos/nixos/doc/config-examples</filename> for
    example machine configurations.  You can copy and edit one of
    those (e.g., copy
    <filename>/etc/nixos/nixos/doc/config-examples/basic.nix</filename>
    to <filename>/mnt/etc/nixos/configuration.nix</filename>).  See
    <xref linkend="ch-options"/> for a list of the available
    configuration options.  The text editors <command>nano</command>
    and <command>vim</command> are available.</para>

    <para>In particular you need to specify a root file system in
    <option>fileSystems</option> and the target device for the Grub
    boot loader in <option>boot.grubDevice</option>.</para>

    <para>The command <command>nixos-hardware-scan</command> can
    generate an initial configuration file for you, i.e.,

<screen>
$ mkdir -p /mnt/etc/nixos
$ nixos-hardware-scan > /mnt/etc/nixos/configuration.nix</screen>

    It tries to figure out the modules necessary for mounting the root
    device, as well as various other hardware characteristics.
    However, it doesn’t try to figure out the
    <option>fileSystems</option> option yet.</para>

    <para>More examples of NixOS configurations for some actual
    machines can be found at <link
    xlink:href="https://svn.nixos.org/repos/nix/configurations/trunk/"/>.</para>

    <note><para>It is very important that you specify in the option
    <option>boot.initrd.extraKernelModules</option> all 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 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>.)
    <command>nixos-hardware-scan</command> should figure out the
    required modules in most cases.</para></note>

  </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>Optionally, you can run

<screen>
$ nixos-checkout</screen>

  to make the installer use the latest NixOS/Nixpkgs sources from the
  Subversion repository, rather than the sources on CD.</para></listitem>

  <listitem><para>Do the installation:

<screen>
$ nixos-install</screen>

    Cross fingers.</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 <xref
    linkend="sec-changing-config" />), a new item appears in the menu.
    This allows you to go back easily to another 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><xref linkend="ex-install-sequence" /> shows a typical sequence
of commands for installing NixOS on an empty hard drive (here
<filename>/dev/sda).  <xref linkend="ex-config" /> shows a
corresponding configuration Nix expression.</filename>

</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>
$ mke2fs -j -L nixos /dev/sda1 <lineannotation>(idem)</lineannotation>
$ mkswap -L swap /dev/sda2 <lineannotation>(idem)</lineannotation>
$ mount LABEL=nixos /mnt
$ mkdir -p /mnt/etc/nixos
$ nixos-hardware-scan > /mnt/etc/nixos/configuration.nix
$ nano /mnt/etc/nixos/configuration.nix
<lineannotation>(in particular, set the fileSystems and swapDevices options)</lineannotation>
$ nixos-install
$ reboot</screen>
</example>

<example xml:id='ex-config'><title>NixOS configuration</title>
<screen>
{
  boot = {
    initrd = {
      extraKernelModules = [ "ata_piix" ];
    };
    grubDevice = "/dev/sda";
  };

  fileSystems = [
    { mountPoint = "/";
      label = "nixos";
    }
  ];

  swapDevices = [
    { label = "swap"; }
  ];
  
  services = {
    sshd = {
      enable = true;
    };
  };
}</screen>
</example>

</section>



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<section xml:id="sec-changing-config">

<title>Changing the configuration</title>

<para>The file <filename>/etc/nixos/configuration.nix</filename>
contains the current configuration of your machine.  Whenever you’ve
changed something to that file, or to the NixOS/Nixpkgs sources in
<filename>/etc/nixos/nixos</filename> and
<filename>/etc/nixos/nixpkgs</filename>, respectively, you should do

<screen>
$ nixos-rebuild switch</screen>

to build the new configuration, make it the default configuration for
booting, and try to effect the configuration in the running system
(e.g., by restarting system services).</para>

<para>You can also do 

<screen>
$ nixos-rebuild test</screen>

to build the configuration and switch the running system to it, but
without making it the boot default.  So if (say) the configuration
locks up your machine, you can just reboot to get back to a working
configuration.</para>

<para>There is also 

<screen>
$ nixos-rebuild boot</screen>

to build the configuration and make it the boot default, but not
switch to it now (so it will only take effect after the next
reboot).</para>

<para>Finally, you can do 

<screen>
$ nixos-rebuild build</screen>

to build the configuration but nothing more.  This is useful to see
whether everything compiles cleanly.</para>

</section>



<!--===============================================================-->

<section>

<title>Keeping NixOS up to date</title>

<para>The currently best way to keep your NixOS installation up to
date is to track the NixOS Subversion repository.  You should replace
the static NixOS/Nixpkgs sources installed in
<filename>/etc/nixos</filename> with a Subversion checkout.  The
program <command>nixos-checkout</command> does that for you (and it
also installs Subversion into your current profile).</para>

<para>To build the latest and greatest, do

<screen>
$ svn up /etc/nixos/nixos
$ svn up /etc/nixos/nixpkgs
$ nixos-rebuild switch</screen>

(Or instead of <literal>switch</literal>, use any of the alternatives
shown in <xref linkend="sec-changing-config"/>.)</para>


</section>




</chapter>