C/C++ applications

Snapcraft builds on top of tools like autotools, make, and cmake to create snaps for people to install on Linux.

Why are snaps good for C/C++ projects?

Snapcraft bundles necessary libraries required by the application, and can configure the environment for confinement of applications for end user peace of mind. Developers can ensure their application is delivered pre-packaged with libraries which will not be replaced or superseded by a distribution vendor.

Here are some snap advantages that will benefit many C/C++ projects:

  • 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 version of whatever is required, along with all of your app’s dependencies, be they binaries 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.

Build a snap in 20 minutes

Typically this guide will take around 20 minutes and will result in a working C++ application in a snap. Once complete, you’ll understand how to package C/C++ applications as snaps and deliver them to millions of Linux users. After making the snap available in the store, you’ll get access to installation metrics and tools to directly manage the delivery of updates to 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 by a single YAML file placed either in the root folder of your project (old style), or in a top-level snap/ directory (new style). The following example shows the entire snapcraft.yaml file for an existing project, DOSBox. Don’t worry, we’ll break this down.

DOSBox Snap

Snaps are defined in a single yaml file placed in the root of your project. The DOSBox example shows the entire snapcraft.yaml for an existing project. We’ll break this down.

snapcraft.yaml for DOSBox 
name: dosbox
version: "0.74-svn"
summary: DOS emulator
description: |
  DOSBox is a x86 emulator with Tandy/Hercules/
  CGA/EGA/VGA/SVGA graphics sound and DOS. It's
  been designed to run old DOS games under
  platforms that don't support it.

base: core18
confinement: devmode

parts:
  dosbox:
    plugin: autotools
    source-type: tar
    source: http://source.dosbox.com/dosboxsvn.tgz
    build-packages:
      - g++
      - make
      - libsdl1.2-dev
      - libpng-dev
      - libsdl-net1.2-dev
      - libsdl-sound1.2-dev
      - libasound2-dev
    stage-packages:
      - freeglut3
      - libsdl-sound1.2
      - libsdl-net1.2
      - libxcursor1
      - libxi6
      - libxinerama1
      - libxrandr2
      - libxrender1
      - libopenal1
      - libsndio6.1
      - libspeex1
      - libvorbisfile3
      - libwayland-client0
      - libwayland-cursor0
      - libwayland-egl1-mesa
      - libxkbcommon0
      - libglu1-mesa
      - libasound2
      - libasyncns0
      - libbsd0
      - libcaca0
      - libdbus-1-3
      - libflac8
      - libgcc1
      - libgcrypt20
      - libgl1
      - libglvnd0
      - libglx0
      - libgpg-error0
      - liblz4-1
      - liblzma5
      - libncursesw5
      - libogg0
      - libpng16-16
      - libpulse0
      - libsdl1.2debian
      - libslang2
      - libsndfile1
      - libstdc++6
      - libsystemd0
      - libtinfo5
      - libvorbis0a
      - libvorbisenc2
      - libwrap0
      - libx11-6
      - libxau6
      - libxcb1
      - libxdmcp6
      - libxext6
      - zlib1g

apps:
  dosbox:
    command: dosbox
    environment:
      "LD_LIBRARY_PATH": "$SNAP/usr/lib/$SNAPCRAFT_ARCH_TRIPLET/pulseaudio"
      "DISABLE_WAYLAND": "1"

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: dosbox
version: "0.74-svn"
summary: DOS emulator
description: |
  DOSBox is a x86 emulator with Tandy/Hercules/
  CGA/EGA/VGA/SVGA graphics sound and DOS. It's
  been designed to run old DOS games under
  platforms that don't support it.

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 the pipe symbol ‘|’ 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 one of the supported standard bases 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

Parts

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 one: the DOSBox source release tarball. In other cases these can point to local directories, remote git repositories or other revision control systems.

Before building the part, the dependencies listed as build-packages are installed. The autotools plugin uses the standard tools, configure and make to build the part.

parts:
  dosbox:
    plugin: autotools
    source-type: tar
    source: http://source.dosbox.com/dosboxsvn.tgz
    build-packages:
      - g++
      - make
      - libsdl1.2-dev
      - libpng-dev
      - libsdl-net1.2-dev
      - libsdl-sound1.2-dev
      - libasound2-dev

There’s also a large stage-packages section.

    stage-packages:
      - freeglut3
      - libsdl-sound1.2
      - libsdl-net1.2
[...]
      - libxext6
      - zlib1g

These are the packages required by DOSBox to run, and mirror the same packages required by the binary on a standard distribution installation.

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

Apps

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; that is, if the installed snap application has the name dosbox.dosbox, you can run it as merely dosbox. If the names differ, then apps must be prefixed with the snap name (dosbox.somethingelse, 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:
  dosbox:
    command: bin/dosbox
    environment:
      "LD_LIBRARY_PATH": "$SNAP/usr/lib/$SNAPCRAFT_ARCH_TRIPLET/pulseaudio"
      "DISABLE_WAYLAND": "1"

You can see we also make two adjustments to the run time environment for DOSBox, the first to work around a PulseAudio issue and the second to disable Wayland. These kinds of requirements are usually figured out through trial and error after an initial build.

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 can download the example repository with the following command:

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

After you’ve created the snapcraft.yaml file, 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 dosbox_0.74-svn_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 dosbox_*.snap --devmode --dangerous

You can then try it out:

$ dosbox

Screenshot_20190613_152721

Removing the snap is simple too:

$  sudo snap remove dosbox

You can clean up the build environment with the following command:

$ 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 mysnap

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 upload --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.

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

Last updated 1 year, 3 months ago.

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