<chapter xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink" xml:id="sec-x11">
  <title>X Window System</title>
  <para>
    The X Window System (X11) provides the basis of NixOS’ graphical
    user interface. It can be enabled as follows:
  </para>
  <programlisting language="bash">
services.xserver.enable = true;
</programlisting>
  <para>
    The X server will automatically detect and use the appropriate video
    driver from a set of X.org drivers (such as <literal>vesa</literal>
    and <literal>intel</literal>). You can also specify a driver
    manually, e.g.
  </para>
  <programlisting language="bash">
services.xserver.videoDrivers = [ &quot;r128&quot; ];
</programlisting>
  <para>
    to enable X.org’s <literal>xf86-video-r128</literal> driver.
  </para>
  <para>
    You also need to enable at least one desktop or window manager.
    Otherwise, you can only log into a plain undecorated
    <literal>xterm</literal> window. Thus you should pick one or more of
    the following lines:
  </para>
  <programlisting language="bash">
services.xserver.desktopManager.plasma5.enable = true;
services.xserver.desktopManager.xfce.enable = true;
services.xserver.desktopManager.gnome.enable = true;
services.xserver.desktopManager.mate.enable = true;
services.xserver.windowManager.xmonad.enable = true;
services.xserver.windowManager.twm.enable = true;
services.xserver.windowManager.icewm.enable = true;
services.xserver.windowManager.i3.enable = true;
services.xserver.windowManager.herbstluftwm.enable = true;
</programlisting>
  <para>
    NixOS’s default <emphasis>display manager</emphasis> (the program
    that provides a graphical login prompt and manages the X server) is
    LightDM. You can select an alternative one by picking one of the
    following lines:
  </para>
  <programlisting language="bash">
services.xserver.displayManager.sddm.enable = true;
services.xserver.displayManager.gdm.enable = true;
</programlisting>
  <para>
    You can set the keyboard layout (and optionally the layout variant):
  </para>
  <programlisting language="bash">
services.xserver.layout = &quot;de&quot;;
services.xserver.xkbVariant = &quot;neo&quot;;
</programlisting>
  <para>
    The X server is started automatically at boot time. If you don’t
    want this to happen, you can set:
  </para>
  <programlisting language="bash">
services.xserver.autorun = false;
</programlisting>
  <para>
    The X server can then be started manually:
  </para>
  <programlisting>
# systemctl start display-manager.service
</programlisting>
  <para>
    On 64-bit systems, if you want OpenGL for 32-bit programs such as in
    Wine, you should also set the following:
  </para>
  <programlisting language="bash">
hardware.opengl.driSupport32Bit = true;
</programlisting>
  <section xml:id="sec-x11-auto-login">
    <title>Auto-login</title>
    <para>
      The x11 login screen can be skipped entirely, automatically
      logging you into your window manager and desktop environment when
      you boot your computer.
    </para>
    <para>
      This is especially helpful if you have disk encryption enabled.
      Since you already have to provide a password to decrypt your disk,
      entering a second password to login can be redundant.
    </para>
    <para>
      To enable auto-login, you need to define your default window
      manager and desktop environment. If you wanted no desktop
      environment and i3 as your your window manager, you'd define:
    </para>
    <programlisting language="bash">
services.xserver.displayManager.defaultSession = &quot;none+i3&quot;;
</programlisting>
    <para>
      Every display manager in NixOS supports auto-login, here is an
      example using lightdm for a user <literal>alice</literal>:
    </para>
    <programlisting language="bash">
services.xserver.displayManager.lightdm.enable = true;
services.xserver.displayManager.autoLogin.enable = true;
services.xserver.displayManager.autoLogin.user = &quot;alice&quot;;
</programlisting>
  </section>
  <section xml:id="sec-x11--graphics-cards-intel">
    <title>Intel Graphics drivers</title>
    <para>
      There are two choices for Intel Graphics drivers in X.org:
      <literal>modesetting</literal> (included in the xorg-server
      itself) and <literal>intel</literal> (provided by the package
      xf86-video-intel).
    </para>
    <para>
      The default and recommended is <literal>modesetting</literal>. It
      is a generic driver which uses the kernel
      <link xlink:href="https://en.wikipedia.org/wiki/Mode_setting">mode
      setting</link> (KMS) mechanism. It supports Glamor (2D graphics
      acceleration via OpenGL) and is actively maintained but may
      perform worse in some cases (like in old chipsets).
    </para>
    <para>
      The second driver, <literal>intel</literal>, is specific to Intel
      GPUs, but not recommended by most distributions: it lacks several
      modern features (for example, it doesn't support Glamor) and the
      package hasn't been officially updated since 2015.
    </para>
    <para>
      The results vary depending on the hardware, so you may have to try
      both drivers. Use the option
      <xref linkend="opt-services.xserver.videoDrivers" /> to set one.
      The recommended configuration for modern systems is:
    </para>
    <programlisting language="bash">
services.xserver.videoDrivers = [ &quot;modesetting&quot; ];
</programlisting>
    <para>
      If you experience screen tearing no matter what, this
      configuration was reported to resolve the issue:
    </para>
    <programlisting language="bash">
services.xserver.videoDrivers = [ &quot;intel&quot; ];
services.xserver.deviceSection = ''
  Option &quot;DRI&quot; &quot;2&quot;
  Option &quot;TearFree&quot; &quot;true&quot;
'';
</programlisting>
    <para>
      Note that this will likely downgrade the performance compared to
      <literal>modesetting</literal> or <literal>intel</literal> with
      DRI 3 (default).
    </para>
  </section>
  <section xml:id="sec-x11-graphics-cards-nvidia">
    <title>Proprietary NVIDIA drivers</title>
    <para>
      NVIDIA provides a proprietary driver for its graphics cards that
      has better 3D performance than the X.org drivers. It is not
      enabled by default because it’s not free software. You can enable
      it as follows:
    </para>
    <programlisting language="bash">
services.xserver.videoDrivers = [ &quot;nvidia&quot; ];
</programlisting>
    <para>
      Or if you have an older card, you may have to use one of the
      legacy drivers:
    </para>
    <programlisting language="bash">
services.xserver.videoDrivers = [ &quot;nvidiaLegacy390&quot; ];
services.xserver.videoDrivers = [ &quot;nvidiaLegacy340&quot; ];
services.xserver.videoDrivers = [ &quot;nvidiaLegacy304&quot; ];
</programlisting>
    <para>
      You may need to reboot after enabling this driver to prevent a
      clash with other kernel modules.
    </para>
  </section>
  <section xml:id="sec-x11--graphics-cards-amd">
    <title>Proprietary AMD drivers</title>
    <para>
      AMD provides a proprietary driver for its graphics cards that is
      not enabled by default because it’s not Free Software, is often
      broken in nixpkgs and as of this writing doesn't offer more
      features or performance. If you still want to use it anyway, you
      need to explicitly set:
    </para>
    <programlisting language="bash">
services.xserver.videoDrivers = [ &quot;amdgpu-pro&quot; ];
</programlisting>
    <para>
      You will need to reboot after enabling this driver to prevent a
      clash with other kernel modules.
    </para>
  </section>
  <section xml:id="sec-x11-touchpads">
    <title>Touchpads</title>
    <para>
      Support for Synaptics touchpads (found in many laptops such as the
      Dell Latitude series) can be enabled as follows:
    </para>
    <programlisting language="bash">
services.xserver.libinput.enable = true;
</programlisting>
    <para>
      The driver has many options (see <xref linkend="ch-options" />).
      For instance, the following disables tap-to-click behavior:
    </para>
    <programlisting language="bash">
services.xserver.libinput.touchpad.tapping = false;
</programlisting>
    <para>
      Note: the use of <literal>services.xserver.synaptics</literal> is
      deprecated since NixOS 17.09.
    </para>
  </section>
  <section xml:id="sec-x11-gtk-and-qt-themes">
    <title>GTK/Qt themes</title>
    <para>
      GTK themes can be installed either to user profile or system-wide
      (via <literal>environment.systemPackages</literal>). To make Qt 5
      applications look similar to GTK ones, you can use the following
      configuration:
    </para>
    <programlisting language="bash">
qt5.enable = true;
qt5.platformTheme = &quot;gtk2&quot;;
qt5.style = &quot;gtk2&quot;;
</programlisting>
  </section>
  <section xml:id="custom-xkb-layouts">
    <title>Custom XKB layouts</title>
    <para>
      It is possible to install custom
      <link xlink:href="https://en.wikipedia.org/wiki/X_keyboard_extension">
      XKB </link> keyboard layouts using the option
      <literal>services.xserver.extraLayouts</literal>.
    </para>
    <para>
      As a first example, we are going to create a layout based on the
      basic US layout, with an additional layer to type some greek
      symbols by pressing the right-alt key.
    </para>
    <para>
      Create a file called <literal>us-greek</literal> with the
      following content (under a directory called
      <literal>symbols</literal>; it's an XKB peculiarity that will help
      with testing):
    </para>
    <programlisting language="bash">
xkb_symbols &quot;us-greek&quot;
{
  include &quot;us(basic)&quot;            // includes the base US keys
  include &quot;level3(ralt_switch)&quot;  // configures right alt as a third level switch

  key &lt;LatA&gt; { [ a, A, Greek_alpha ] };
  key &lt;LatB&gt; { [ b, B, Greek_beta  ] };
  key &lt;LatG&gt; { [ g, G, Greek_gamma ] };
  key &lt;LatD&gt; { [ d, D, Greek_delta ] };
  key &lt;LatZ&gt; { [ z, Z, Greek_zeta  ] };
};
</programlisting>
    <para>
      A minimal layout specification must include the following:
    </para>
    <programlisting language="bash">
services.xserver.extraLayouts.us-greek = {
  description = &quot;US layout with alt-gr greek&quot;;
  languages   = [ &quot;eng&quot; ];
  symbolsFile = /yourpath/symbols/us-greek;
};
</programlisting>
    <note>
      <para>
        The name (after <literal>extraLayouts.</literal>) should match
        the one given to the <literal>xkb_symbols</literal> block.
      </para>
    </note>
    <para>
      Applying this customization requires rebuilding several packages,
      and a broken XKB file can lead to the X session crashing at login.
      Therefore, you're strongly advised to <emphasis role="strong">test
      your layout before applying it</emphasis>:
    </para>
    <programlisting>
$ nix-shell -p xorg.xkbcomp
$ setxkbmap -I/yourpath us-greek -print | xkbcomp -I/yourpath - $DISPLAY
</programlisting>
    <para>
      You can inspect the predefined XKB files for examples:
    </para>
    <programlisting>
$ echo &quot;$(nix-build --no-out-link '&lt;nixpkgs&gt;' -A xorg.xkeyboardconfig)/etc/X11/xkb/&quot;
</programlisting>
    <para>
      Once the configuration is applied, and you did a logout/login
      cycle, the layout should be ready to use. You can try it by e.g.
      running <literal>setxkbmap us-greek</literal> and then type
      <literal>&lt;alt&gt;+a</literal> (it may not get applied in your
      terminal straight away). To change the default, the usual
      <literal>services.xserver.layout</literal> option can still be
      used.
    </para>
    <para>
      A layout can have several other components besides
      <literal>xkb_symbols</literal>, for example we will define new
      keycodes for some multimedia key and bind these to some symbol.
    </para>
    <para>
      Use the <emphasis>xev</emphasis> utility from
      <literal>pkgs.xorg.xev</literal> to find the codes of the keys of
      interest, then create a <literal>media-key</literal> file to hold
      the keycodes definitions
    </para>
    <programlisting language="bash">
xkb_keycodes &quot;media&quot;
{
 &lt;volUp&gt;   = 123;
 &lt;volDown&gt; = 456;
}
</programlisting>
    <para>
      Now use the newly define keycodes in <literal>media-sym</literal>:
    </para>
    <programlisting language="bash">
xkb_symbols &quot;media&quot;
{
 key.type = &quot;ONE_LEVEL&quot;;
 key &lt;volUp&gt;   { [ XF86AudioLowerVolume ] };
 key &lt;volDown&gt; { [ XF86AudioRaiseVolume ] };
}
</programlisting>
    <para>
      As before, to install the layout do
    </para>
    <programlisting language="bash">
services.xserver.extraLayouts.media = {
  description  = &quot;Multimedia keys remapping&quot;;
  languages    = [ &quot;eng&quot; ];
  symbolsFile  = /path/to/media-key;
  keycodesFile = /path/to/media-sym;
};
</programlisting>
    <note>
      <para>
        The function
        <literal>pkgs.writeText &lt;filename&gt; &lt;content&gt;</literal>
        can be useful if you prefer to keep the layout definitions
        inside the NixOS configuration.
      </para>
    </note>
    <para>
      Unfortunately, the Xorg server does not (currently) support
      setting a keymap directly but relies instead on XKB rules to
      select the matching components (keycodes, types, ...) of a layout.
      This means that components other than symbols won't be loaded by
      default. As a workaround, you can set the keymap using
      <literal>setxkbmap</literal> at the start of the session with:
    </para>
    <programlisting language="bash">
services.xserver.displayManager.sessionCommands = &quot;setxkbmap -keycodes media&quot;;
</programlisting>
    <para>
      If you are manually starting the X server, you should set the
      argument <literal>-xkbdir /etc/X11/xkb</literal>, otherwise X
      won't find your layout files. For example with
      <literal>xinit</literal> run
    </para>
    <programlisting>
$ xinit -- -xkbdir /etc/X11/xkb
</programlisting>
    <para>
      To learn how to write layouts take a look at the XKB
      <link xlink:href="https://www.x.org/releases/current/doc/xorg-docs/input/XKB-Enhancing.html#Defining_New_Layouts">documentation
      </link>. More example layouts can also be found
      <link xlink:href="https://wiki.archlinux.org/index.php/X_KeyBoard_extension#Basic_examples">here
      </link>.
    </para>
  </section>
</chapter>
