What you’ll learn

In this tutorial we will create a snap of a HTML5/Electron application to act as the graphical user interface for an IoT or kiosk device. For the introduction to this tutorial series and the Mir display server, please visit here.

This tutorial assumes you are familiar with the material in Make an X11-based Kiosk Snap.

What you’ll need

• An Ubuntu desktop running any current release of Ubuntu or an Ubuntu Virtual Machine on another OS.
• A ‘Target Device’ from one of the following:
  • A device running Ubuntu Core 18.
    This guide shows you how to set up a supported device. If there’s no supported image that fits your needs you can create your own core image.
  • Using a VM You don’t have to have a physical “Target Device”, you can follow the tutorial with Ubuntu Core in a VM. Install the ubuntu-core-vm snap: sudo snap install --beta ubuntu-core-vm --devmode For the first run, create a VM running the latest Core image: sudo ubuntu-core-vm init From then on, you can spin it up with: sudo ubuntu-core-vm You should see a new window with Ubuntu Core running inside. Setting up Ubuntu Core on this VM is the same as for any other device or VM. See, for example, https://developer.ubuntu.com/core/get-started/kvm.
  • Using Ubuntu Classic You don’t have to use Ubuntu Core, you can use also a “Target Device” with Ubuntu Classic. Read this guide to understand how to run kiosk snaps on your desktop, as the particular details won’t be repeated here.

We use Wayland as the primary display interface. We will use Mir to manage the display and support connections from Wayland clients and Snapd will confine the applications and enable Wayland protocol interactions through Mir, securely.

Currently Electron does not have Wayland support, so we will use a tiny intermediary X11 server called Xwayland.

Click here for more information on this architecture.

Due to the myriad of Electron app packaging systems, this tutorial will assume you already have a snap of your Electron app for Ubuntu Classic. Details on achieving this are available here:

https://docs.snapcraft.io/build-snaps/electron

This guide will start with a working hello-world snap for Electron, that functions solely on Ubuntu Classic. Take this YAML as a starting point:

name: electron-hello-world-kiosk
version: '0.1'
summary: Hello World Electron app
description: |
  Simple Hello World Electron app as an example
base: core18
confinement: strict
grade: devel

apps:
  electron-hello-world-kiosk:
    command: desktop-launch "$SNAP/electron-helloworld/electron-quick-start" "--no-sandbox"

plugs:
  browser-support:
  network:
  network-bind:
  opengl:
  pulseaudio:
  x11:

parts:
  electron-helloworld:
    plugin: nodejs
    source: https://github.com/electron/electron-quick-start.git
    after: [desktop-gtk3]
    override-build: |
        case $SNAPCRAFT_ARCH_TRIPLET in
          "i386-linux-gnu") ARCH="ia32";;
          "x86_64-linux-gnu") ARCH="x64";;
          "arm-linux-gnueabihf") ARCH="armv7l";;
          "aarch64-linux-gnu") ARCH="arm64";;
          *) echo "ERROR: electron does not support the '$SNAPCRAFT_ARCH_TRIPLET' architecture" && exit 1;;
        esac
        npm install electron-packager &&
        ./node_modules/.bin/electron-packager . --overwrite --platform=linux --arch=$ARCH --output=release-build --prune=true
        cp -v -R ./electron-quick-start-linux-$ARCH $SNAPCRAFT_PART_INSTALL/electron-helloworld
    stage-packages:
    - libasound2
    - libgconf-2-4
    - libnss3
    - libx11-xcb1
    - libxss1
    - libxtst6

    build-packages:
    - nodejs
    - npm
    - unzip

  # Adapted from snapcraft-desktop-helpers https://github.com/ubuntu/snapcraft-desktop-helpers/blob/master/snapcraft.yaml#L183
  desktop-gtk3:
    source: https://github.com/ubuntu/snapcraft-desktop-helpers.git
    source-subdir: gtk
    plugin: make
    make-parameters: ["FLAVOR=gtk3"]
    build-packages:
      - build-essential
      - libgtk-3-dev
    stage-packages:
      - libxkbcommon0  # XKB_CONFIG_ROOT
      - ttf-ubuntu-font-family
      - dmz-cursor-theme
      - light-themes
      - adwaita-icon-theme
      - gnome-themes-standard
      - shared-mime-info
      - libgtk-3-0
      - libgdk-pixbuf2.0-0
      - libglib2.0-bin
      - libgtk-3-bin
      - unity-gtk3-module
      - libappindicator3-1
      - locales-all
      - xdg-user-dirs
      - ibus-gtk3
      - libibus-1.0-5    

Some points about this YAML

• snapcraft-desktop-helpers is used to ease environment setup for electron. We need to copy/paste the relevant YAML right now.
• npm is the packaging tool being used
• It uses “electron-packager” to build the electron app.
• the"override-build" scriptlet is used to run commands to install electron-packager, build the package and install the final binary into a suitable location in the snap.
• the stage-packages are those we find necessary for the final binary to function. You may need to add more depending on the complexity of your application.
• it supports i386, amd64, armhf and arm64.

Build and test

Build the snap with:

snapcraft

and on your desktop, install and run:

sudo snap install --dangerous ./electron-hello-world-kiosk_0.1_amd64.snap
snap run electron-hello-world-kiosk

This should pop up a window with “Hello World” printed.

Once the snap is running on your Ubuntu desktop, we need to perform a few alterations to have it function as a kiosk app snap. We will follow the xwayland-kiosk-helper documentation:

1. add xwayland-kiosk-helper to the parts list
2. to the app command:, add xwayland-kiosk-launch after the desktop-launch
3. add a daemon command: which adds daemon: simpleandrestart-condition: always
4. set the XWAYLAND_FULLSCREEN_WINDOW_HINT environment variable to window_role="browser-window"
5. change x11 plug to wayland.

Finally we want this snap to start on boot and be restarted if it fails, so make it a daemon.

The final YAML file will look like this:

name: electron-hello-world-kiosk
version: '0.1'
summary: Hello World Electron app for a Kiosk
description: |
  Simple Hello World Electron app as an example of a HTML5 Kiosk
base: core18
confinement: strict
grade: devel

apps:
  electron-hello-world-kiosk:
    command: desktop-launch xwayland-kiosk-launch "$SNAP/electron-helloworld/electron-quick-start" "--no-sandbox"

  daemon:
    daemon: simple
    restart-condition: always
    command: desktop-launch xwayland-kiosk-launch "$SNAP/electron-helloworld/electron-quick-start" "--no-sandbox"

environment:
  XWAYLAND_FULLSCREEN_WINDOW_HINT: window_role="browser-window"

plugs:
  browser-support:
  network:
  network-bind:
  opengl:
  pulseaudio:
  wayland:

parts:
  electron-helloworld:
    plugin: nodejs
    source: https://github.com/electron/electron-quick-start.git
    after: [desktop-gtk3, xwayland-kiosk-helper]
    override-build: |
        case $SNAPCRAFT_ARCH_TRIPLET in
          "i386-linux-gnu") ARCH="ia32";;
          "x86_64-linux-gnu") ARCH="x64";;
          "arm-linux-gnueabihf") ARCH="armv7l";;
          "aarch64-linux-gnu") ARCH="arm64";;
          *) echo "ERROR: electron does not support the '$SNAPCRAFT_ARCH_TRIPLET' architecture" && exit 1;;
        esac
        npm install electron-packager &&
        ./node_modules/.bin/electron-packager . --overwrite --platform=linux --arch=$ARCH --output=release-build --prune=true
        cp -v -R ./electron-quick-start-linux-$ARCH $SNAPCRAFT_PART_INSTALL/electron-helloworld
    stage-packages:
    - libasound2
    - libgconf-2-4
    - libnss3
    - libx11-xcb1
    - libxss1
    - libxtst6
    build-packages:
    - nodejs
    - npm
    - unzip

  # Adapted from snapcraft-desktop-helpers https://github.com/ubuntu/snapcraft-desktop-helpers/blob/master/snapcraft.yaml#L183
  desktop-gtk3:
    source: https://github.com/ubuntu/snapcraft-desktop-helpers.git
    source-subdir: gtk
    plugin: make
    make-parameters: ["FLAVOR=gtk3"]
    build-packages:
      - build-essential
      - libgtk-3-dev
    stage-packages:
      - libxkbcommon0  # XKB_CONFIG_ROOT
      - ttf-ubuntu-font-family
      - dmz-cursor-theme
      - light-themes
      - adwaita-icon-theme
      - gnome-themes-standard
      - shared-mime-info
      - libgtk-3-0
      - libgdk-pixbuf2.0-0
      - libglib2.0-bin
      - libgtk-3-bin
      - unity-gtk3-module
      - libappindicator3-1
      - locales-all
      - xdg-user-dirs
      - ibus-gtk3
      - libibus-1.0-5

  xwayland-kiosk-helper:
    plugin: cmake
    source: https://github.com/MirServer/xwayland-kiosk-helper.git
    build-packages: [ build-essential ]
    stage-packages: [ xwayland, i3, libegl1-mesa, libgl1-mesa-glx ]

Build as usual with

snapcraft

(for building for other architectures, follow this guide)

Once you have a snap of your electron-based app, push it to your device:

scp electron-hello-world-kiosk_0.1_amd64.snap <user>@<ip-address>:~

using your device’s SSH username & IP address details.

We now have the .snap file on the device in its home directory. We need to install the snap. In your ssh session to your device:

snap install --dangerous ./electron-hello-world-kiosk_0.1_arm64.snap 

On your device, you should see the “Hello world” screen you saw earlier.

Your device is now a kiosk! Rebooting will restart mir-kiosk and electron-hello-world-kiosk automatically.

Congratulations, you have created your first graphical kiosk snap using Electron for Ubuntu Core.

If you have a kiosk or digital signage product and need help deploying an Electron app, talk to us!