Snap

Easily Upgraded, Universal Linux Package

Snaps are containerised software packages that are simple to create and install. They auto-update and are safe to run. And because they bundle their dependencies, they work on all major Linux systems without modification.

Snapcraft is a command line tool used to build snaps. This guide details the recommended steps to get ready to build snaps.The easiest way to package your code as a snap is to use Snapcraft, which supports building from source and from existing packages, integrates into your CI process and handles publishing your snaps to the world.

1. Abstract

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

sudo apt-get install snapcraft

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

• Installation: snap install myapp
• Directly control the delivery of automatic application updates

2. 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 a existing project.

name: dosbox
version: "0.74-svn"
summary: DOSBox
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.

confinement: devmode

apps:
  dosbox:
    command: dosbox

parts:
  dosbox:
    plugin: autotools
    source-type: tar
    source: http://source.dosbox.com/dosboxsvn.tgz
    build-packages:
      - g++
      - make
      - libsdl1.2-dev
      - libpng12-dev
      - libsdl-net1.2-dev
      - libsdl-sound1.2-dev
      - libasound2-dev

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 application.

Before building the part, the dependencies listed as build-package are installed. More information of autotools plugin is given by command snapcraft help autotools.

3.Basic about Snap

Install snap on Ubuntu

Ubuntu includes Snap by default starting with the 16.04LTS release, for the older 14.04LTS release or any flavor, you have to install it form the archive:

sudo apt install snap

Using the snap command

Login with Ubuntu One Account

sudo snap login <youremail>

When you are logged in, find snaps in the snap store, and then you can install it using the snap name.

snap find hello
snap install hello-world
snap list # view details about installed snap

4.Snapcraft

Setup LXD

LXD installation on Ubuntu is quite straightforward:

snap install
sudo lxd init
sudo usermod -g lxd ${USER}
#LXD requires that your user is in the lxd group.

Test a container build

By now should be all set, we can test that everything is setup correctly with a few commands:

mkdir test-snapcraft
cd test-snapcraft
snapcraft init
snapcraft cleanbuild

Build first snap

Snapcraft uses single text file to describe the entire build process for a snap:

vim test-snapcraft/snapcraft.yaml

To get start with a template, you can run snapcraft init, it wll create a new directory snap with a file named snapcraft.yaml , the final file looks like this:

name: hello
version: "2.10"
summary: GNU Hello, the "hello world" snap
description: GNU Hello prints a friendly greeting.
grade: stable
confinement: strict

apps:
  hello:
    command: hello

parts:
  gnu-hello:
    plugin: autotools
    source: http://ftp.gnu.org/gnu/hello/hello-2.10.tar.gz

This is the only file needed in the directory, Snapcraft can use local source code or fetch everything needed to build the snap from remote sources.

Run snapcraft

You can now build a snap out of your snapcraft.yaml by running snapcraft in the project directory:

snapcraft

After this process, the snap is now available in your directory.

$ ls
hello_2.10_amd64.snap  parts  snap  prime 
$ sudo snap install hello_2.10_amd64.snap --dangerous
hello 2.10 installed
$ hello
Hello, World!
$sudo snap remove dosbox