Shipping pre-built binaries makes getting up and running with your application easy, without limiting the number of Linux distributions you support. Snapcraft can ingest these binaries to create snaps that still work on any major Linux distribution.
What problems do snaps solve for pre-built applications?
Distributed binaries rarely include a mechanism to self-update, and in some case require specific versions of system libraries not consistently available in every Linux distribution’s repositories. 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 projects distributing pre-built binaries:
- Bundle all the runtime requirements, including the exact versions of system libraries.
- Simplify installation instructions, regardless of distribution, to
snap install myapp.
- Directly control the delivery of automatic application updates.
- Extremely simple creation of daemons.
By way of an example, let’s take a look at how a snap is created for the geekbench app.
Snaps are defined in a single yaml file placed in the root of your project. The geekbench example shows the entire
snapcraft.yaml for an existing project. We’ll break this down.
name: geekbench4 version: 4.1.0 summary: Cross-Platform Benchmark description: | Geekbench 4 measures your system's power and tells you whether your computer is ready to roar. How strong is your mobile device or desktop computer? How will it perform when push comes to crunch? These are the questions that Geekbench can answer. confinement: devmode parts: geekbench4: plugin: dump source: http://cdn.primatelabs.com/Geekbench-$SNAPCRAFT_PROJECT_VERSION-Linux.tar.gz apps: geekbench4: command: geekbench4
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 with the
description: to declare a multi-line description.
name: geekbench4 version: 4.1.0 summary: Cross-Platform Benchmark description: | Geekbench 4 measures your system's power and tells you whether your computer is ready to roar. How strong is your mobile device or desktop computer? How will it perform when push comes to crunch? These are the questions that Geekbench can answer.
To get started we won’t confine this application. Unconfined applications, specified with
devmode, can only be published 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 just have one: a tarball containing the geekbench binary. In other cases these can point to local or remote zips files, deb files, or tarballs.
In this example we use the
$SNAPCRAFT_PROJECT_VERSION variable derived from the
version: stanza to reference the release tarball.
parts: geekbench4: plugin: dump source: http://cdn.primatelabs.com/Geekbench-$SNAPCRAFT_PROJECT_VERSION-Linux.tar.gz
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
geekbench4.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: geekbench4: command: geekbench4
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 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 --beta --classic snapcraft
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/geekbench4 cd geekbench4 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 geekbench4_*.snap --devmode --dangerous
You can then try running geekbench4.
Removing the snap is simple too:
sudo snap remove geekbench4
Share with your friends
To share your snaps you need to publish them in the snap store. First, create an account on dashboard.snapcraft.io. 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 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.
snapcraft register mysnap
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 store.
snapcraft push --release=edge mysnap_*.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.
This plugin dumps the content from a specified source. In the cases where dumping the content needs some mangling or organizing one would take advantage of the core functionalities available to plugins such as:
Extending and overriding behaviour
You can extend the behaviour of any part in your
snapcraft.yaml with shell commands. These can be run after pulling the source code but before building by using the
prepare keyword. The build process can be overridden entirely using the
build keyword and shell commands. The
install keyword is used to run shell commands after building your code, useful for making post build modifications such as relocating build assets.