nixpkgs/nixos/doc/manual/installation.xml

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

<title>Installing NixOS</title>


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

<section>

<title>Obtaining NixOS</title>

<para>NixOS ISO images can be downloaded from the <link
xlink:href="http://nixos.org/nixos/download.html">NixOS
homepage</link>.  These can be burned onto a CD.  It is also possible
to copy them onto a USB stick and install NixOS from there.  For
details, see the <link
xlink:href="https://nixos.org/wiki/Installing_NixOS_from_a_USB_stick">NixOS
Wiki</link>.</para>

<para>As an alternative to installing NixOS yourself, you can get a
running NixOS system through several other means:

<itemizedlist>
  <listitem>
    <para>Using virtual appliances in Open Virtualization Format (OVF)
    that can be imported into VirtualBox.  These are available from
    the <link xlink:href="http://nixos.org/nixos/download.html">NixOS
    homepage</link>.</para>
  </listitem>
  <listitem>
    <para>Using AMIs for Amazon’s EC2.  To find one for your region
    and instance type, please refer to the <link
    xlink:href="https://github.com/NixOS/nixops/blob/master/nix/ec2-amis.nix">list
    of most recent AMIs</link>.</para>
  </listitem>
  <listitem>
    <para>Using NixOps, the NixOS-based cloud deployment tool, which
    allows you to provision VirtualBox and EC2 NixOS instances from
    declarative specifications.  Check out the <link
    xlink:href="https://github.com/NixOS/nixops">NixOps
    homepage</link> for details.</para>
  </listitem>
</itemizedlist>

</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 contains 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 networking manually
  using <command>ifconfig</command>.</para></listitem>

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

  <listitem><para>Login as <literal>root</literal> and the 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 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 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>

    The <command>vim</command> text editor is also available.</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></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 easily roll back 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>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>

</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, you should do

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

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

<warning><para>These commands must be executed as root, so you should
either run them from a root shell or by prefixing them with
<literal>sudo -i</literal>.</para></warning>

<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>You can make your configuration show up in a different submenu
of the GRUB 2 boot screen by giving it a different <emphasis>profile
name</emphasis>, e.g.

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

which causes the new configuration (and previous ones created using
<literal>-p test</literal>) to show up in the GRUB submenu “NixOS -
Profile 'test'”.  This can be useful to separate test configurations
from “stable” configurations.</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>

<para>If you have a machine that supports hardware virtualisation, you
can also test the new configuration in a sandbox by building and
running a QEMU <emphasis>virtual machine</emphasis> that contains the
desired configuration.  Just do

<screen>
$ nixos-rebuild build-vm
$ ./result/bin/run-*-vm
</screen>

The VM does not have use any data from your host system, so your
existing user accounts and home directories will not be
available.</para>

</section>


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<section xml:id="sec-upgrading">

<title>Upgrading NixOS</title>

<para>The best way to keep your NixOS installation up to date is to
use one of the NixOS <emphasis>channels</emphasis>.  A channel is a
Nix mechanism for distributing Nix expressions and associated
binaries.  The NixOS channels are updated automatically from NixOS’s
Git repository after certain tests have passed and all packages have
been built.  These channels are:

<itemizedlist>
  <listitem>
    <para>Stable channels, such as <literal
    xlink:href="http://nixos.org/channels/nixos-13.10">nixos-13.10</literal>.
    These only get conservative bug fixes and package upgrades.  For
    instance, a channel update may cause the Linux kernel on your
    system to be upgraded from 3.4.66 to 3.4.67 (a minor bug fix), but
    not from 3.4.<replaceable>x</replaceable> to
    3.11.<replaceable>x</replaceable> (a major change that has the
    potential to break things).</para>
  </listitem>
  <listitem>
    <para>The unstable channel, <literal
    xlink:href="http://nixos.org/channels/nixos-unstable">nixos-unstable</literal>.
    This corresponds to NixOS’s main development branch, and may thus
    see radical changes between channel updates.  It’s not recommended
    for production systems.</para>
  </listitem>
</itemizedlist>

To see what channels are available, go to <link
xlink:href="http://nixos.org/channels"/>.  (Note that the URIs of the
various channels redirect to a directory that contains the channel’s
latest version and includes ISO images and VirtualBox
appliances.)</para>

<para>When you first install NixOS, you’re automatically subscribed to
the NixOS channel that corresponds to your installation source.   For
instance, if you installed from a 13.10 ISO, you will be subscribed to
the <literal>nixos-13.10</literal> channel.  To see which NixOS
channel you’re subscribed to, run the following as root:

<screen>
$ nix-channel --list | grep nixos
nixos https://nixos.org/channels/nixos-unstable
</screen>

To switch to a different NixOS channel, do

<screen>
$ nix-channel --add http://nixos.org/channels/<replaceable>channel-name</replaceable> nixos
</screen>

(Be sure to include the <literal>nixos</literal> parameter at the
end.)  For instance, to use the NixOS 13.10 stable channel:

<screen>
$ nix-channel --add http://nixos.org/channels/nixos-13.10 nixos
</screen>

But it you want to live on the bleeding edge:

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

</para>

<para>You can then upgrade NixOS to the latest version in your chosen
channel by running

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

which is equivalent to the more verbose <literal>nix-channel --update
nixos; nixos-rebuild switch</literal>.</para>

<warning><para>It is generally safe to switch back and forth between
channels.  The only exception is that a newer NixOS may also have a
newer Nix version, which may involve an upgrade of Nix’s database
schema.  This cannot be undone easily, so in that case you will not be
able to go back to your original channel.</para></warning>

</section>

</chapter>