<chapter xmlns="http://docbook.org/ns/docbook"
         xmlns:xlink="http://www.w3.org/1999/xlink"
         xml:id="chap-gnome">
 <title>GNOME Desktop</title>
 <para>
  GNOME provides a simple, yet full-featured desktop environment with a focus on productivity. Its Mutter compositor supports both Wayland and X server, and the GNOME Shell user interface is fully customizable by extensions.
 </para>

 <section xml:id="sec-gnome-enable">
  <title>Enabling GNOME</title>

  <para>
   All of the core apps, optional apps, games, and core developer tools from GNOME are available.
  </para>

  <para>
   To enable the GNOME desktop use:
  </para>

<programlisting>
<xref linkend="opt-services.xserver.desktopManager.gnome.enable"/> = true;
<xref linkend="opt-services.xserver.displayManager.gdm.enable"/> = true;
</programlisting>

  <note>
   <para>
    While it is not strictly necessary to use GDM as the display manager with GNOME, it is recommended, as some features such as screen lock <link xlink:href="#sec-gnome-faq-can-i-use-lightdm-with-gnome">might not work</link> without it.
   </para>
  </note>

  <para>
   The default applications used in NixOS are very minimal, inspired by the defaults used in <link xlink:href="https://gitlab.gnome.org/GNOME/gnome-build-meta/blob/40.0/elements/core/meta-gnome-core-utilities.bst">gnome-build-meta</link>.
  </para>

  <section xml:id="sec-gnome-without-the-apps">
   <title>GNOME without the apps</title>

   <para>
    If you’d like to only use the GNOME desktop and not the apps, you can disable them with:
   </para>

<programlisting>
<xref linkend="opt-services.gnome.core-utilities.enable"/> = false;
</programlisting>

   <para>
    and none of them will be installed.
   </para>

   <para>
    If you’d only like to omit a subset of the core utilities, you can use <xref linkend="opt-environment.gnome.excludePackages"/>.
    Note that this mechanism can only exclude core utilities, games and core developer tools.
   </para>
  </section>

  <section xml:id="sec-gnome-disabling-services">
   <title>Disabling GNOME services</title>

   <para>
    It is also possible to disable many of the <link xlink:href="https://github.com/NixOS/nixpkgs/blob/b8ec4fd2a4edc4e30d02ba7b1a2cc1358f3db1d5/nixos/modules/services/x11/desktop-managers/gnome.nix#L329-L348">core services</link>. For example, if you do not need indexing files, you can disable Tracker with:
   </para>

<programlisting>
<xref linkend="opt-services.gnome.tracker-miners.enable"/> = false;
<xref linkend="opt-services.gnome.tracker.enable"/> = false;
</programlisting>

   <para>
    Note, however, that doing so is not supported and might break some applications. Notably, GNOME Music cannot work without Tracker.
   </para>
  </section>

  <section xml:id="sec-gnome-games">
   <title>GNOME games</title>

   <para>
    You can install all of the GNOME games with:
   </para>

<programlisting>
<xref linkend="opt-services.gnome.games.enable"/> = true;
</programlisting>
  </section>

  <section xml:id="sec-gnome-core-developer-tools">
   <title>GNOME core developer tools</title>

   <para>
    You can install GNOME core developer tools with:
   </para>

<programlisting>
<xref linkend="opt-services.gnome.core-developer-tools.enable"/> = true;
</programlisting>
  </section>
 </section>

 <section xml:id="sec-gnome-enable-flashback">
  <title>Enabling GNOME Flashback</title>

  <para>
   GNOME Flashback provides a desktop environment based on the classic GNOME 2 architecture. You can enable the default GNOME Flashback session, which uses the Metacity window manager, with:
  </para>

<programlisting>
<xref linkend="opt-services.xserver.desktopManager.gnome.flashback.enableMetacity"/> = true;
</programlisting>

  <para>
   It is also possible to create custom sessions that replace Metacity with a different window manager using <xref linkend="opt-services.xserver.desktopManager.gnome.flashback.customSessions"/>.
  </para>

  <para>
   The following example uses <literal>xmonad</literal> window manager:
  </para>

<programlisting>
<xref linkend="opt-services.xserver.desktopManager.gnome.flashback.customSessions"/> = [
  {
    wmName = "xmonad";
    wmLabel = "XMonad";
    wmCommand = "${pkgs.haskellPackages.xmonad}/bin/xmonad";
  }
];
</programlisting>

 </section>
 <section xml:id="sec-gnome-gdm">
  <title>GDM</title>

  <para>
   If you want to use GNOME Wayland session on Nvidia hardware, you need to enable:
  </para>

<programlisting>
<xref linkend="opt-services.xserver.displayManager.gdm.nvidiaWayland"/> = true;
</programlisting>

  <para>
   as the default configuration will forbid this.
  </para>
 </section>

 <section xml:id="sec-gnome-icons-and-gtk-themes">
  <title>Icons and GTK Themes</title>

  <para>
   Icon themes and GTK themes don’t require any special option to install in NixOS.
  </para>

  <para>
   You can add them to <xref linkend="opt-environment.systemPackages"/> and switch to them with GNOME Tweaks.
   If you’d like to do this manually in dconf, change the values of the following keys:
  </para>

<programlisting>
/org/gnome/desktop/interface/gtk-theme
/org/gnome/desktop/interface/icon-theme
</programlisting>

  <para>
   in <literal>dconf-editor</literal>
  </para>
 </section>

 <section xml:id="sec-gnome-shell-extensions">
  <title>Shell Extensions</title>

  <para>
   Most Shell extensions are packaged under the <literal>gnomeExtensions</literal> attribute.
   Some packages that include Shell extensions, like <literal>gnome.gpaste</literal>, don’t have their extension decoupled under this attribute.
  </para>

  <para>
   You can install them like any other package:
  </para>

<programlisting>
<xref linkend="opt-environment.systemPackages"/> = [
  gnomeExtensions.dash-to-dock
  gnomeExtensions.gsconnect
  gnomeExtensions.mpris-indicator-button
];
</programlisting>

  <para>
   Unfortunately, we lack a way for these to be managed in a completely declarative way.
   So you have to enable them manually with an Extensions application.
   It is possible to use a <link xlink:href="#sec-gnome-gsettings-overrides">GSettings override</link> for this on <literal>org.gnome.shell.enabled-extensions</literal>, but that will only influence the default value.
  </para>
 </section>

 <section xml:id="sec-gnome-gsettings-overrides">
  <title>GSettings Overrides</title>

  <para>
   Majority of software building on the GNOME platform use GLib’s <link xlink:href="https://developer.gnome.org/gio/unstable/GSettings.html">GSettings</link> system to manage runtime configuration. For our purposes, the system consists of XML schemas describing the individual configuration options, stored in the package, and a settings backend, where the values of the settings are stored. On NixOS, like on most Linux distributions, dconf database is used as the backend.
  </para>

  <para>
   <link xlink:href="https://developer.gnome.org/gio/unstable/GSettings.html#id-1.4.19.2.9.25">GSettings vendor overrides</link> can be used to adjust the default values for settings of the GNOME desktop and apps by replacing the default values specified in the XML schemas. Using overrides will allow you to pre-seed user settings before you even start the session.
  </para>

  <warning>
   <para>
    Overrides really only change the default values for GSettings keys so if you or an application changes the setting value, the value set by the override will be ignored. Until <link xlink:href="https://github.com/NixOS/nixpkgs/issues/54150">NixOS’s dconf module implements changing values</link>, you will either need to keep that in mind and clear the setting from the backend using <literal>dconf reset</literal> command when that happens, or use the <link xlink:href="https://nix-community.github.io/home-manager/options.html#opt-dconf.settings">module from home-manager</link>.
   </para>
  </warning>

  <para>
   You can override the default GSettings values using the <xref linkend="opt-services.xserver.desktopManager.gnome.extraGSettingsOverrides"/> option.
  </para>

  <para>
   Take note that whatever packages you want to override GSettings for, you need to add them to
   <xref linkend="opt-services.xserver.desktopManager.gnome.extraGSettingsOverridePackages"/>.
  </para>

  <para>
   You can use <literal>dconf-editor</literal> tool to explore which GSettings you can set.
  </para>

  <section xml:id="sec-gnome-gsettings-overrides-example">
   <title>Example</title>

<programlisting>
services.xserver.desktopManager.gnome = {
  <link xlink:href="#opt-services.xserver.desktopManager.gnome.extraGSettingsOverrides">extraGSettingsOverrides</link> = ''
    # Change default background
    [org.gnome.desktop.background]
    picture-uri='file://${pkgs.nixos-artwork.wallpapers.mosaic-blue.gnomeFilePath}'

    # Favorite apps in gnome-shell
    [org.gnome.shell]
    favorite-apps=['org.gnome.Photos.desktop', 'org.gnome.Nautilus.desktop']
  '';

  <link xlink:href="#opt-services.xserver.desktopManager.gnome.extraGSettingsOverridePackages">extraGSettingsOverridePackages</link> = [
    pkgs.gsettings-desktop-schemas # for org.gnome.desktop
    pkgs.gnome.gnome-shell # for org.gnome.shell
  ];
};
</programlisting>
  </section>
 </section>

 <section xml:id="sec-gnome-faq">
  <title>Frequently Asked Questions</title>

  <section xml:id="sec-gnome-faq-can-i-use-lightdm-with-gnome">
   <title>Can I use LightDM with GNOME?</title>

   <para>
    Yes you can, and any other display-manager in NixOS.
   </para>

   <para>
    However, it doesn’t work correctly for the Wayland session of GNOME Shell yet, and
    won’t be able to lock your screen.
   </para>

   <para>
    See <link xlink:href="https://github.com/NixOS/nixpkgs/issues/56342">this issue.</link>
   </para>
  </section>

  <section xml:id="sec-gnome-faq-nixos-rebuild-switch-kills-session">
   <title>Why does <literal>nixos-rebuild switch</literal> sometimes kill my session?</title>

   <para>
    This is a known <link xlink:href="https://github.com/NixOS/nixpkgs/issues/44344">issue</link> without any workarounds.
    If you are doing a fairly large upgrade, it is probably safer to use <literal>nixos-rebuild boot</literal>.
   </para>
  </section>
 </section>
</chapter>
