MOOS applications

Linux install instructions for MOOS applications often get complicated.

System dependencies, which differ from distribution to distribution, must be separately installed. There’s no standard packaging in MOOS: typically one builds both MOOS (or MOOS-IvP) and the MOOS application from source.

All this that means not only is the initial distribution difficult, but getting updates is an exercise left to the reader.

With snapcraft, it’s one command to produce a bundle that works anywhere and can be automatically updated.

What problems do snaps solve for MOOS applications?

  • Snaps are easy to discover and install
    Millions of users can browse and install snaps graphically in the Snap Store or from the command-line.
  • Snaps install and run the same across Linux
    They bundle the exact versions of the tools you need, including MOOS/MOOD-IvP, along with all of your app’s dependencies, be they modules or system libraries.
  • Snaps automatically update to the latest version
    Four times a day, users’ systems will check for new versions and upgrade in the background.
  • Upgrades are not disruptive
    Because upgrades are not in-place, users can keep your app open as it’s upgraded in the background.
  • Upgrades are safe
    If your app fails to upgrade, users automatically roll back to the previous revision with data preserved.

Build a snap in 20 minutes

Ready to get started? By the end of this guide, you’ll understand how to make a snap of your app that can be published in the Snap Store, showcasing it to millions of Linux users.

:information_source: For a brief overview of the snap creation process, including how to install snapcraft and how it’s used, see Snapcraft overview. For a more comprehensive breakdown of the steps involved, take a look at Creating a snap.

Getting started

Snaps are defined in a single YAML file placed in the root folder of your project. The following shows the entire snapcraft.yaml file for an example MOODDB project. Don’t worry, we’ll break this down.

name: test-moos
version: '0.1'
summary: MOOS Example
description: |
  This example includes MOOSDB, the main communication mechanism for all MOOS
  apps.

base: core18
confinement: devmode

parts:
  test-moos:
    source: https://github.com/themoos/core-moos/archive/v10.4.0.tar.gz
    plugin: cmake
    build-packages: [g++]

apps:
  test-moos:
    command: bin/MOOSDB

Metadata

The snapcraft.yaml file starts with a small amount of human-readable metadata, which usually can be lifted from the GitHub description or project README.md. This data is used in the presentation of your app in the Snap Store.

name: test-moos
version: '0.1'
summary: MOOS Example
description: |
  This example includes MOOSDB, the main communication mechanism for all MOOS
  apps.

The name must be unique in the Snap Store. Valid snap names consist of lower-case alphanumeric characters and hyphens. They cannot be all numbers and they also cannot start or end with a hyphen.

By specifying git for the version, the current git tag or commit will be used as the version string. Versions carry no semantic meaning in snaps.

The summary can not exceed 79 characters. You can use a chevron ‘>’ in the description key to declare a multi-line description.

Base

The base keyword defines a special kind of snap that provides a run-time environment with a minimal set of libraries that are common to most applications. They’re transparent to users, but they need to be considered, and specified, when building a snap.

base: core18

core18 is the current standard base for snap building and is based on Ubuntu 18.04 LTS.

Security model

To get started we won’t confine this application. Unconfined applications, specified with devmode, can only be released to the hidden “edge” channel where you and other developers can install them.

confinement: devmode

Confinement

To get started we won’t confine this application. Unconfined applications, specified with devmode, can only be released to the hidden “edge” channel where you and other developers can install them.

confinement: devmode

Parts

Parts define how to build your app. Parts can be anything: programs, libraries, or other assets needed to create and run your application. Parts can point to local directories, remote git repositories, or tarballs.

Snapcraft supports using the CMake build system, familiar to MOOS developers, to create snaps for people to install on Linux, which is used to build this part:

parts:
  test-moos:
    source: https://github.com/themoos/core-moos/archive/v10.4.0.tar.gz
    plugin: cmake
    build-packages: [g++]

For more details on CMake-specific metadata, see The CMake plugin.

Apps

Apps are the commands and services exposed to end users. If your Apps are the commands you want to expose to users and any background services your application provides. Each key under apps is the command name that should be made available on users’ systems.

The command specifies the path to the binary to be run. This is resolved relative to the root of your snap contents and automatically searches in the usr/sbin, usr/bin, sbin, and bin sub directories of your snap.

apps:
  test-moos:
    command: bin/MOOSDB

If your command name matches the snap name, users will be able run the command directly. If the names differ, then apps are prefixed with the snap name (test-xsv.command-name, for example). This is to avoid conflicting with apps defined by other installed snaps.

If your application is intended to run as a service you simply add the line daemon: simple after the command keyword. This will automatically keep the service running on install, update and reboot.

You can request an alias on the Snapcraft forum if your command name and snap name do not match but you don’t want your command prefixed. These aliases are set up automatically when your snap is installed from the Snap Store.

Building the snap

You can download the example repository with the following command:

$ git clone https://github.com/snapcraft-docs/moos

After you’ve created the snapcraft.yaml, you can build the snap by simply executing the snapcraft command in the project directory:

$ snapcraft
Using 'snapcraft.yaml': Project assets will be searched for from the 'snap' directory.
Launching a VM.
[...]
Snapped test-moos_0.1_amd64.snap

The resulting snap can be installed locally. This requires the --dangerous flag because the snap is not signed by the Snap Store. The --devmode flag acknowledges that you are installing an unconfined application:

$ sudo snap install test-moos_*.snap --devmode --dangerous

You can then try it out:

$ test-moos -h

Removing the snap is simple too:

$ sudo snap remove test-moos

You can also clean up the build environment, although this will slow down the next initial build:

$ snapcraft clean

By default, when you make a change to snapcraft.yaml, snapcraft only builds the parts that have changed. Cleaning a build, however, forces your snap to be rebuilt in a clean environment and will take longer.

Publishing your snap

To share your snaps you need to publish them in the Snap Store. First, create an account on the dashboard. Here you can customise how your snaps are presented, review your uploads and control publishing.

You’ll need to choose a unique “developer namespace” as part of the account creation process. This name will be visible by users and associated with your published snaps.

Make sure the snapcraft command is authenticated using the email address attached to your Snap Store account:

$ snapcraft login

Reserve a name for your snap

You can publish your own version of a snap, provided you do so under a name you have rights to. You can register a name on dashboard.snapcraft.io, or by running the following command:

$ snapcraft register mymoossnap

Be sure to update the name: in your snapcraft.yaml to match this registered name, then run snapcraft again.

Upload your snap

Use snapcraft to push the snap to the Snap Store.

$ snapcraft push --release=edge mymoossnap_*.snap

If you’re happy with the result, you can commit the snapcraft.yaml to your GitHub repo and turn on automatic builds so any further commits automatically get released to edge, without requiring you to manually build locally.

Congratulations! You’ve just built and published your first Go snap. For a more in-depth overview of the snap building process, see Creating a snap.

Last updated 5 months ago. Help improve this document in the forum.