Author: Olivier Fourdan

GNOME Kiosk, the lightweight, specialized compositor continues to evolve In GNOME 50 by adding new configuration options and improving accessibility.

Window configuration

User configuration file monitoring

The user configuration file gets reloaded when it changes on disk, so that it is not necessary to restart the session.

New placement options

New configuration options to constrain windows to monitors or regions on screen have been added:

• lock-on-monitor: lock a window to a monitor.
• lock-on-monitor-area: lock to an area relative to a monitor.
• lock-on-area: lock to an absolute area.

These options are intended to replicate the legacy „Zaphod“ mode from X11, where windows could be tied to a specific monitor. It even goes further than that, as it allows to lock windows on a specific area on screen.

The window/monitor association also remains true when a monitor is disconnected. Take for example a setup where each monitor, on a multiple monitors configuration, shows different timetables. If one of the monitors is disconnected (for whatever reason), the timetable showing on that monitor should not be moved to another remaining monitor. The lock-on-monitor option prevents that.

Initial map behavior was tightened

Clients can resize or change their state  before the window is mapped, so size, position, and fullscreen as set from the configuration could be skipped. Kiosk now makes sure to apply configured size, position, and fullscreen on first map when the initial configuration was not applied reliably.

Auto-fullscreen heuristics were adjusted

• Only normal windows are considered when checking whether another window already covers the monitor (avoids false positives from e.g. xwaylandvideobridge).
• The current window is excluded when scanning “other” fullscreen sized windows (fixes Firefox restoring monitor-sized geometry).
• Maximized or fullscreen windows are no longer treated as non-resizable so toggling fullscreen still works when the client had already maximized.

Compositor behavior and command-line options

New command line options have been added:

• --no-cursor: hides the pointer.
• --force-animations: forces animations to be enabled.
• --enable-vt-switch: restores VT switching with the keyboard.

The --no-cursor option can be used to hide the pointer cursor entirely for setups where user input does not involve a pointing device (it is similar to the -nocursor option in Xorg).

Animations can now be disabled using the desktop settings, and will also be automatically disabled when the backend reports no hardware-accelerated rendering for performance purpose. The option --force-animations can be used to forcibly enable animations in that case, similar to GNOME Shell.

The native keybindings, which include VT switching keyboard shortcuts are now disabled by default for kiosk hardening. Applications that rely on the user being able to switch to another console VT on Linux, such as e.g Anaconda, will need to explicit re-enable VT switching using --enable-vt-switch in their session.

These options need to be passed from the command line starting gnome-kiosk, which would imply updating the systemd definitions files, or better, create a custom one (taking example on the the ones provided with the GNOME Kiosk sessions).

Accessibility

Accessibility panel

An example of an accessibility panel is now included, to control the platform accessibility settings with a GUI. It is a simple Python application using GTK4.

(The gsettings options are also documented in the CONFIG.md file.)

Screen magnifier

Desktop magnification is now implemented, using the same settings as the rest of the GNOME desktop (namely screen-magnifier-enabled, mag-factor, see the CONFIG.md file for details).

It can can be enabled from the accessibility panel or from the keyboard shortcuts through the gnome-settings-daemon’s “mediakeys” plugin.

Accessibility settings

The default systemd session units now start the gnome-settings-daemon accessibility plugin so that Orca (the screen reader) can be enabled through the dedicated keyboard shortcut.

Notifications

• A new, optional notification daemon implements org.freedesktop.Notifications and org.gtk.Notifications using GTK 4 and libadwaita.
• A small utility to send notifications via org.gtk.Notifications is also provided.

Input sources

GNOME Kiosk was ported to the new Mutter’s keymap API which allows remote desktop servers to mirror the keyboard layout used on the client side.

Session files and systemd

• • X-GDM-SessionRegister is now set to false in kiosk sessions as GNOME Kiosk does not register the session itself (unlike GNOME Shell). That fixes a hang when terminating the session.
  • Script session: systemd is no longer instructed to restart the session when the script exits, so that users can logout of the script session when the script terminates.

GNOME Kiosk is a separate Wayland compositor built on the same core components as GNOME Shell, such as Mutter.

While it does not provide a desktop UI, it is intended for kiosk and appliance use cases.

Originally designed to run a single application in fullscreen mode, recent development has expanded its scope toward more versatile window management and system integration.

Recent Releases Overview

47

• Support for Shell introspection API (in --unsafe-mode).

48

• Initial support for configurable windows via window-config.ini.
• Added Shell Screenshot D-Bus API.

49

• Extended window configuration: set-on-monitor, set-window-type, window tags.
• Added support for remote sessions (Systemd).
• Fixes for GrabAccelerators, media keys, and compositor shortcut inhibition.

Window Configuration and Tagged Clients

One of the recent main areas of development has been window configuration.

• In GNOME 48, Kiosk gained initial support for configuring windows via a static configuration file (window-config.ini).
• In GNOME 49, this functionality was extended with additional options:
  • set-on-monitor: place windows on a specific monitor.
  • set-window-type: assign specific roles to windows (e.g. desktop, dock, splash).
  • Matching based on Window tags: allow selection of windows based on toplevel tags, a new feature in Wayland protocols 1.43.

Additionally, with the new (in mutter from GNOME 49) gnome-service-client utility, toplevel windows tags can be assigned to clients at launch, making it possible to configure their behavior in Kiosk without modification to the client.

Example: configuring a tagged client in Kiosk

GNOME Kiosk searches for the window configuration file window-config.ini in the following locations:

• The base directory for user-specific application configuration usually $HOME/.config/gnome-kiosk/window-config.ini
• The system-wide list of directories for application data $XDG_DATA_DIRS This list usually includes:
  • /var/lib/flatpak/exports/share/gnome-kiosk/window-config.ini
  • /usr/local/share/gnome-kiosk/window-config.ini
  • /usr/share/gnome-kiosk/window-config.ini

Therefore, for a user configuration, edit $HOME/.config/gnome-kiosk/window-config.ini to read:

[all]
set-fullscreen=false
set-above=false

[desktop]
match-tag=desktop
set-window-type=desktop
set-fullscreen=true

With this configuration, GNOME Kiosk will treat any surface with the toplevel tag desktop as a „desktop“ type of window.

launching a tagged client

gnome-service-client -t desktop weston-simple-shm

This command starts the weston-simple-shm client and associates the tag desktop with its surface.

The end result is the weston-simple-shm window running as a background window placed at the bottom of the windows stack.

This combination makes it possible to build structured kiosk environments with different Wayland client used as docks or desktop windows for implementing root menus.

Accessibility and Input

Several improvements have been made to input handling and accessibility:

• Fixes for GrabAccelerators support.
• Support for media keys in Systemd sessions.
• Ability to inhibit compositor shortcuts.
• Compatibility with screen reader usage.

Remote Sessions

As of GNOME 49, Kiosk supports remote sessions when run under Systemd. This allows kiosk sessions to be used not only on local displays but also in remote session contexts.

D-Bus APIs

Although GNOME Kiosk is a separate compositor, it implements selected D-Bus APIs also available in GNOME Shell for compatibility purposes. These include:

• Screenshot API (added in 48).
• Shell introspection when started with --unsafe-mode (added in 47).

This makes it possible to use existing GNOME testing and automation frameworks such as Ponytail and Dogtail with kiosk sessions.

These APIs allow automation scripts to inspect and interact with the user interface, enabling the creation of automated tests and demonstrations for kiosk application (using tools like GNOME ponytail and dogtail).

GNOME Kiosk is the Wayland compositor used with the Wayland enabled version of Anaconda, the installer for Fedora (and Red Hat Enterprise Linux as well). The support for introspection and screenshots is used by anabot, the framework for automated testing of the installer.

Development Direction

Future development of GNOME Kiosk is expected to continue along the following lines:

• Configuration refinement: further improving flexibility of the window configuration system.
• Accessibility: ensuring kiosk sessions benefit from GNOME’s accessibility technologies.

The goal remains to provide a focused, reliable compositor for kiosk and appliance deployments, without implementing the full desktop UI features of GNOME Shell.