Ubuntu Core and its applications run within a within a confined and transaction-based environment. This provides the robustness and security that makes Ubuntu Core ideal for embedded device deployment, but it also requires a different approach from classic Ubuntu systems.
Application management, system configuration and update scheduling in Ubuntu Core is manged by snapd, the snap packaging daemon. Snap features are explained comprehensively in the Snap documentation, while our Ubuntu Core documentation handles the elements of the snap ecosystem that are specifically applicable to Ubuntu Core.
This page of our documentation is a great place to start after you’ve just installed Ubuntu Core and want to learn a few of the basic principles quickly.
Quickstart project
A good place to start is with an IoT web-kiosk. These are autonomous devices that typically display a purpose-built website on a screen. They’re often left unattended for long period, and need to remain secure and up-to-date without requiring human intervention.
To create a web-kiosk in Ubuntu Core, you will need an Ubuntu Core device with a connected display and then run the following commands:
snap install ubuntu-frame
snap install wpe-webkit-mir-kiosk
snap set wpe-webkit-mir-kiosk url=https://ubuntu.com/core
The first command installs ubuntu-frame. This provides the graphical display. The next snap, wpe-webkit-mir-kiosk, installs the web viewer and we use snap set to configure this with the web address we’d like to show.
Interfaces
The installation speed will depend on your network connection and the speed of your device as various interfaces are automatically connected from the snaps to access your system.
You can see which of these are being used with the snap connections command:
Interface Plug Slot Notes
content[graphics-core22] ubuntu-frame:graphics-core22 mesa-core22:graphics-core22 -
content[graphics-core22] wpe-webkit-mir-kiosk:graphics-core22 mesa-core22:graphics-core22 -
hardware-observe ubuntu-frame:hardware-observe :hardware-observe -
network wpe-webkit-mir-kiosk:network :network -
network-bind ubuntu-frame:network-bind :network-bind -
network-bind wpe-webkit-mir-kiosk:network-bind :network-bind -
opengl ubuntu-frame:opengl :opengl -
opengl wpe-webkit-mir-kiosk:opengl :opengl -
wayland wpe-webkit-mir-kiosk:wayland ubuntu-frame:wayland -
Each line in the above output describes how an interface is used to connect an application to a system resource. This is accomplished through a system of plugs and slots which connect a consumer (plug) to a provider (slot). The network interface, for example, connects the system network provider slot (:network) to the application consumer plug (wpe-webkit-mir-kiosk:network) to provide the web view with network access.
The snap connect and snap disconnect commands are used to remove and activate an interface connection. To disable and then re-enable network access to wpe-webkit-mir-kiosk, for instance, you’d type:
snap disconnect wpe-webkit-mir-kiosk:network
snap connect wpe-webkit-mir-kiosk:network
Press the tab key to auto-complete partially typed connections and other snap arguments.
Snap management
To see a summary of system changes, such as interface disconnection and re-connection, plus updates, use the snap changes command:
$ snap changes
ID Status Spawn Ready Summary
7 Done today at 10:35 UTC today at 10:35 UTC Disconnect : from wpe-webkit-mir-kiosk:network
8 Done today at 10:36 UTC today at 10:36 UTC Connect wpe-webkit-mir-kiosk:network to snapd:network
You can list which snaps are installed on your Ubuntu Core system with snap list:
$ snap list
Name Version Rev Tracking Publisher Notes
core22 20240111 1125 latest/stable canonicalâś“ base
mesa-core22 23.0.4 234 latest/stable canonicalâś“ -
pi 22-2 132 22/stable canonicalâś“ gadget
pi-kernel 5.15.0-1050.53 800 22/stable canonicalâś“ kernel
snapd 2.61.2 21185 latest/stable canonicalâś“ snapd
ubuntu-frame 130-mir2.16.3 8588 22/stable canonicalâś“ -
wpe-webkit-mir-kiosk 2.38.5 104 22/stable glancr -
The above shows the standard (and initial) set of snaps in a default Ubuntu Core installation alongside those we installed for the above kiosk.
The default state for an Ubuntu Core image, including which snaps it includes, is defined by its model assertion. You can view the one being used on the current system with the snap known model command, or use snap known serial to show the device serial number:
$ snap known serial
type: serial
authority-id: canonical
brand-id: canonical
model: ubuntu-core-22-pi-arm64
serial: 5764993d-e063-887a-b79c536066ad
[...]
For more details on which snaps are included with Ubuntu Core,see Snaps in Ubuntu Core.
Any snaps you manually install can be removed with the snap remove command:
snap remove wpe-webkit-mir-kiosk
Install a server
Ubuntu Core is also an ideal platform for server applications because it handles both system and application updates automatically.
To transform your device into a NextCloud Server, for instance, install the nextcloud snap:
snap install nextcloud
Open the IP address of your device in a web browser on the same network and you’ll see NextCloud’s Create an admin account prompt.
In common with other server applications, NextCloud runs various services in the background. Snapped services like these can be viewed with the snap services command:
$ snap services
Service Startup Current Notes
nextcloud.apache enabled active -
nextcloud.logrotate enabled inactive timer-activated
nextcloud.mysql enabled active -
nextcloud.nextcloud-cron enabled active -
nextcloud.nextcloud-fixer enabled active -
nextcloud.php-fpm enabled active -
nextcloud.redis-server enabled active -
nextcloud.renew-certs enabled active -
ubuntu-frame.daemon enabled active -
wpe-webkit-mir-kiosk.daemon enabled active -
wpe-webkit-mir-kiosk.restart-watcher enabled active -
The snap stop <service-name>, snap start <service-name> and snap restart <service-name> commands can all be used to start and stop services. If a service offers a reload function, usually to reload a configuration file without requiring a full restart, this can be added to restart with the --reload argument.
Similarly, services can be stopped from starting automatically, and re-enabled, with the snap disable <service-name> and snap enable <service-name> commands respectively.
For more information on services, take a look at Services and daemons.
Next steps
The snap command includes comprehensive help output. To see this, type snap help followed by the command. The output will often include additional arguments that can be useful. Autocompletion can also help when tying snap commands, both to complete a command itself, and also to complete the names of snaps or interfaces. Type snap followed by a space and then the tab key to see the list of all possible commands, for instance.
For more information on how to work with snaps, including how to make data snapshots, how to install specific revisions, see the Snap Documentation .