Snapcraft supports using the CMake build system, familiar to MOOS developers, to create snaps for people to install on Linux.
What problems do snaps solve for 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. That means not only is the initial distribution difficult, but getting updates is an exercise left to the reader. With snapcraft it’s just one command to produce a bundle that works anywhere and can be automatically updated.
Here are some snap advantages that will benefit many MOOS projects:
- Bundle all the runtime requirements, including the exact version of MOOS/MOOS-IvP, system libraries, etc.
- Simplify installation instructions, regardless of distribution, to
snap install mymoosapp.
- Directly control the delivery of application updates.
- Extremely simple creation of daemons.
Note: We strongly recommend using an Ubuntu 16.04 host, VM or container for this guide. While it is possible to use newer releases of Ubuntu, or other Linux distributions, this may result in incorrect libraries being pulled into the build.
Let’s take a look at the ping pong MOOS example application, and show how simple it is to snap.
Snaps are defined in a single yaml file placed in the root of your project. Here is the entire
snapcraft.yaml for this project. Let’s break it down.
name: moos-ping version: 0.1 summary: MOOS Ping Example description: | The MOOS ping example requires the MOOSDB as well as the ping/pong application. grade: devel confinement: devmode parts: moos: source: https://github.com/themoos/core-moos/archive/10.0.2.a-release.tar.gz plugin: cmake configflags: - -DCMAKE_INSTALL_PREFIX=/ moos-examples: source: https://github.com/themoos/examples-docs-moos.git source-subdir: docs/examples/AppExamples source-depth: 1 plugin: cmake after: [moos] artifacts: - bin/ex1010 apps: MOOSDB: command: MOOSDB ex1010: command: ex1010
snapcraft.yaml 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. The
summary: can not exceed 79 characters. You can use a pipe in the
description: key to declare a multi-line description.
name: moos-ping version: 0.1 summary: MOOS Ping Example description: | The MOOS ping example requires the MOOSDB as well as the ping/pong application.
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.
Parts define how to build your app. Parts can be anything: programs, libraries, or other assets needed to create and run your application. In this case we have two: MOOS itself, and the examples. Parts can point to local directories, remote git repositories, or tarballs.
Since MOOS is its own part, we can make sure the version of MOOS exactly corresponds to the version our application requires, and it’ll get bundled into the snap just like the rest of the application.
Note that, since MOOS provides headers and libraries required to build the examples, we specify that the examples should build
after: [moos]. Snapcraft will then ensure the MOOS part is built before building the examples.
Note also that the examples do not provide suitable install rules. As a result, instead of relying on
make install to do the right thing, we specify the exact
artifacts we want from the part, and the cmake plugin copies them over instead of running
Finally, note that the
examples-docs-moos repository contains rather large PDFs. As such, pulling its entire history can take some time, so we use
source-depth: 1 to specify that we only want the latest commit, not the entire history.
parts: moos: source: https://github.com/themoos/core-moos/archive/10.0.2.a-release.tar.gz plugin: cmake configflags: - -DCMAKE_INSTALL_PREFIX=/ moos-examples: source: https://github.com/themoos/examples-docs-moos.git source-subdir: docs/examples/AppExamples source-depth: 1 plugin: cmake after: [moos] artifacts: - bin/ex1010
Apps are the commands and services exposed to end users. 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
moos-ping.command-name, for example). This is to avoid conflicting with apps defined by other installed snaps.
If you don’t want your command prefixed you can request an alias for it on the Snapcraft forum. These are set up automatically when your snap is installed from the Snap Store.
apps: MOOSDB: command: MOOSDB ex1010: command: ex1010
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.
Building the snap
You’ll first need to install snap support, and then install the snapcraft tool:
sudo snap install snapcraft --classic
If you have just installed snap support, start a new shell so your
PATH is updated to include
/snap/bin. You can then build this example yourself:
git clone https://github.com/snapcraft-docs/moos-ping cd moos-ping snapcraft
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 moos-ping_*.snap --devmode --dangerous
You can then try it out by running the MOOSDB in one shell (this could also be made a daemon):
Run the example in “pong” mode in another shell:
And finally, run the example in “ping” mode in yet another shell:
Removing the snap is simple too:
sudo snap remove moos-ping
Share with your friends
To share your snaps you need to publish them in the Snap Store. First, create an account on the dashboard. Here you can customize 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:
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
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.
Here are all the CMake plugin-specific keywords:
- artifacts: (list) Link/copy the given files from the make output to the snap installation directory. If specified, the 'make install' step will be skipped. - make-parameters: (list of strings) Pass the given parameters to the make command. - make-install-var: (string; default: DESTDIR) Use this variable to redirect the installation into the snap. - configflags: (list of strings) configure flags to pass to the build using the common cmake semantics.
You can view them locally by running:
snapcraft help cmake