A confined desktop "kiosk" experience

Mir
1

Sometimes, even on the “desktop” you want to run a single application without access to anything else. And that is possible with a combination of Mir and snaps.

Here’s a recipe for building this.

Ingredients

mir-kiosk-desktop

This is a “stage-snap” that contains a simple, “kiosk” display server designed for running a single fullscreen application. It also provides the boilerplate for launching a single application and for registering with the display manager.

The resulting snap needs registering with the desktop manager by running:

/snap/NAME_OF_SNAP/current/desktop/setup

And also connecting the login-session-control and ‘hardware-observe’ interfaces:

snap connect NAME_OF_SNAP:login-session-control
snap connect NAME_OF_SNAP:hardware-observe

There are certain elements that needed to be included in the final snap:

parts:
  mir-kiosk-desktop:
    plugin: nil
    stage-snaps: [mir-kiosk-desktop]
    override-build: |
      snapcraftctl build
      sed s/\$\{SNAPCRAFT_PROJECT_NAME}/${SNAPCRAFT_PROJECT_NAME}/g --in-place $SNAPCRAFT_PART_INSTALL/desktop/setup
      sed s/\$\{SNAPCRAFT_PROJECT_NAME}/${SNAPCRAFT_PROJECT_NAME}/g --in-place $SNAPCRAFT_PART_INSTALL/desktop/mir-kiosk-desktop.desktop

layout:
  /usr/share/X11:
    bind: $SNAP/usr/share/X11
  /usr/bin/xkbcomp:
    symlink: $SNAP/usr/bin/xkbcomp
  /usr/share/icons:
    bind: $SNAP/usr/share/icons
  /usr/share/fonts:
    bind: $SNAP/usr/share/fonts
  /etc/fonts:
    bind: $SNAP/etc/fonts

plugs:
  opengl:         # For Mir
  wayland:        # For Mir
  network-bind:   # For Mir (to serve X11)
  login-session-control: # To start a desktop session
  hardware-observe: # To start a desktop session

An example application

The other thing you need to include in your snap is an application. I’ve created an example (mir-kiosk-desktop-example) using Kodi.

For this you need to install snapcraft, check out and build the project:

snap install snapcraft
git clone https://github.com/MirServer/mir-kiosk-desktop-example.git
cd mir-kiosk-desktop-example
snapcraft
snap install --dangerous *.snap

Then you need to register with the display manager and connect the interfaces you want:

/snap/mir-kiosk-desktop-example/current/desktop/setup
/snap/mir-kiosk-desktop-example/current/connect-interfaces

After this you can log out, select “mir-kiosk-desktop-example” instead of “Ubuntu” (or “Ubuntu on Wayland”, or whatever) from the greeter menu and login to a confined desktop session running Kodi.

When you exit from Kodi you’ll be logged out of the desktop session and you’ll be back at the greeter.

Your application

Obviously, you may want to use a different application and for that you’ll have to work on the snap packaging for that application. We’re not quite at the stage yet when you can simply configure an application installed locally on your system. It has to be part of the “kiosk-desktop” snap.

To give some clues there’s a second worked example (Zoom) in the git repository. So go back the the mir-kiosk-desktop-example build directory and type:

git checkout zoom
snapcraft
snap install --dangerous *.snap
/snap/mir-kiosk-desktop-example/current/desktop/setup
/snap/mir-kiosk-desktop-example/current/connect-interfaces

Now you can do the same things, except with Zoom.

Testing

It is convenient to test snaps like this without logging out and logging in. To make that easier you can run the snap in a “Mir-on-X” window provided by mir-kiosk:

snap install mir-kiosk
WAYLAND_DISPLAY=wayland-99 mir-kiosk

And from a second terminal:

WAYLAND_DISPLAY=wayland-99 mir-kiosk-desktop-example
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