OpenSource For You

Snappy Ubuntu Core for Embedded and IoT Devices

Ubuntu Core is a minimalist­ic version of Ubuntu. It is lightweigh­t and is designed for use with embedded systems and IoT devices. Snaps are universal Linux packages, which are faster to install, easier to create, and safe to run and work on multiple distr


The biggest challenge in delivering Linux applicatio­ns is dependency resolution. As distributi­ons update underlying libraries frequently, it is not always possible to offer applicatio­n binaries as offline archives. One can’t think of downgradin­g an applicatio­n if underlying packages are upgraded, which are in turn required by some more applicatio­ns. Also, it’s not possible to keep multiple versions of the same library in view of different applicatio­ns. Ubuntu Core has a solution for all this complexity, whereby a single device can host multiple isolated applicatio­ns with their own dependenci­es.

Ubuntu ‘snaps’ are universal packages supported on many Linux distributi­ons and on various devices. Any Linux applicatio­n can be bundled as a snap, which can be easily deployed across the distributi­ons and across devices with isolated environmen­ts. This ensures secure execution and better transactio­nal management with flexible upgradable or downgradab­le support.

Snaps are based on Ubuntu Core, which is a minimal rendition of Ubuntu, specifical­ly designed for embedded and IoT devices. The core image consists of the kernel, a minimal set of drivers and a basic file system in the form of a core snap with basic functional­ity. You can’t update the core by adding packages unlike other typical Linux distributi­ons. Each snap is bundled with its own dependenci­es for the functional­ity not provided by the core. It supports transactio­nal updates of the snaps, which can be upgraded or downgraded easily without affecting other snaps. Also, snaps can be remotely upgraded.

The snap format file system

When Ubuntu Core is installed, the OS snap gets installed initially. This snap is packed with rootfs, providing basic features like network services, standard libraries and daemon management. It is the platform for subsequent snaps offering applicatio­n logic. This enables universal packaging as all snaps run on the basis of the OS snap provided by the core, eliminatin­g any dependenci­es with the host environmen­t.

Each snap comes with an isolated file system in squashfs format, which gets mounted in a sub-directory under /snap. For example, when foo snap is installed, its file system is mounted under /snap/foo/xx, where xx represents a revision of the snap. There can be multiple

revisions of file systems under /snap/foo but /snap/ foo/current always points to the desired version as per the recent upgrade or downgrade. Each user-accessible applicatio­n of the snap is linked under /snap/bin, with the <snap-name>.<app-name> convention, e.g., /snap/ bin/foo.test for an applicatio­n named test under the snap foo. The meta data of the snap is available in the form of meta/snap.yaml under the mounted file system.

Use cases

As the underlying stack is read only and each snap has a self-contained file system, Ubuntu Core is the perfect choice for industrial solutions for which security is a critical concern. Here are some cases of Ubuntu Core powered solutions:

IoT gateways for industrial solutions, like the Dell Edge gateway

DeviceHive IoT toolkit

Cloud based servers like NextCloud

Digital signage

Robots and drones

Some popular snaps

Here are some popular applicatio­ns available from the snap store:

Atom, a text editor

NextCloud, a cloud based server for data storage VLC, a multi-media player

Docker, a container manager

Cassandra, a scalable NoSQL database

Blender, a 3D creation suite

Stellarium, a planetariu­m software

Rocket.Chat, a Web chat server

The Telegram desktop client

Jenkins, a leading automation server for building, testing and deployment­s

OpenHAB, a home automation middleware software Mosquitto, a MQTT broker

Clients for AWS, like Azure cloud solutions


Ubuntu Core comes with a snap manager, snapd, which is present by default in Ubuntu Xenial (16.04 LTS) onwards; for older versions of Ubuntu and other distributi­ons you can install the snap manager as follows:

apt-get install snapd

If you are planning to build custom snaps, install snapcraft also, as follows:

apt-get install snapcraft

Replace apt-get with any other package manager like yum, dnf, zypper, pacman, poky, etc, for non-Debian based distributi­ons.

Ubuntu Core is available for dedicated installati­on for various embedded targets like Raspberry Pi Models 2 and 3, Compute Module 3, Intel Joulie, Dragon Board, Intel NUC kit, Samsung Artik, etc. Also, Ubuntu Core can be installed through KVM on any desktop as a virtual machine, for which you can download the core image for the AMD 64 architectu­re, extract the archive and run the following command:

qemu-sytem-x86_64 -smp 2 -m 1500 -netdev user, id=mynet0, hostfwd=tcp::8022-:22,hostfwd=tcp::8090-:80 -device virtionetp­ci,netdev=mynet0 drive file=ubuntucore­16amd64. img,format=raw

Now log in to the core using ssh as follows: ssh username@localhost -p 8022

Working with snaps

Let’s try working with snaps in CLI mode, assuming osfy as the snap’s name.

To search for available snaps based on the osfy keyword, use the following command:

snap find osfy

To install a specific snap from the store, use the command given below:

snap install osfy

Observe the file hierarchy in /snap/osfy/current. Run the applicatio­n associated with snap by using

the following command: osfy.test #from /snap/bin

For listing of installed snaps, use the command given below:

snap list

To check the informatio­n about a particular installed snap, use the following command:

snap info osfy The following command updates all installed snaps: \sudo snap refresh

The following command updates a particular installed snap:

sudo snap refresh osfy

To roll back a snap to a previous version, use the command given below:

sudo snap revert osfy The next command uninstalls a specific snap: sudo snap remove osfy

The following command removes symlinks of the apps in /snap/bin and stops the associated services:

sudo snap disable osfy

To start the snap services and make symlinks for the apps available in /snap/bin, use the following command:

sudo snap enable osfy

To list the environmen­t variables associated with a snap, use the command given below:

sudo snap run osfy.env

Classic snap

Since the core is read-only and not meant for developmen­t purposes, you can install ‘classic snap’ to enter in classic mode on devices deployed with solely Ubuntu Core. Normal package management with apt-get is allowed in classic mode. But avoid this classic snap if secure deployment is the prime concern. sudo snap install --devmode classic sudo classic

Now, in the prompt enabled by classic mode, you can try any developer commands such as those shown below:

sudo apt-get update sudo apt-get install vim gcc snapcraft


Interfaces allow snaps to exchange services with each other. A snap provides the service in the form of slot and another snap can consume it in the form of plug. Some important interfaces are network, network-bind, camera, bluetoothc­ontrol, firewallco­ntrol, logobserve, etc. To list out all possible interfaces and consumer snaps plugged into each of them, use the following command:

snap interfaces

To list interfaces plugged by a particular snap, the following command should be used:

snap interfaces osfy

In the absence of a plugs entry in the apps section of the manifest file, we need to connect the interfaces manually. For example, if a foo snap is providing a bar interface slot and osfy snap wants to plug into it, run the following command:

snap connect osfy:bar foo:bar

Building custom snaps

You can package any Linux applicatio­n as a snap. For this, create an empty directory and run the following command to create the basic skeleton of metadata in the name of snapcraft.yaml:

snapcraft init

Now edit the parts, apps sections of snapcraft.yaml as per the tutorial in­nap. And, finally, run the snapcraft command to build the snap by retrieving all required sources, building each part, and staging and priming the outcome of all parts in stage, prime directorie­s. Finally, the contents of the prime sub-directory will be bundled

 ??  ??
 ??  ?? Figure 1: The snap execution environmen­t
Figure 1: The snap execution environmen­t
 ??  ?? Figure 2: Snap interfaces
Figure 2: Snap interfaces

Newspapers in English

Newspapers from India