Packaging Apps To Run on Any Linux Device

It's a Snap!

Finding Nemo

Figure 3 shows a search using the keyword host. This is a command that you'll be using frequently with snap if you're pulling in other people's snaps. Instead of search , as in Docker, the Snap Store uses find to look for useful snaps.

Figure 3: Searching for a snap with the word "host" in the Name or Summary.

To install one of the newly found packages, just use the install command (Figure 4). Opting sensibly for the second package from the top, because it's from Canonical, I use the command:

Figure 4: Installing a snap made by Canonical.
$ snap install wifi-ap

In the console, you can see the snap output as it installs successfully.

Shopping Lists

Another command you'll need frequently is the list command, which shows your installed snaps. Figure 5 shows two locally installed snaps: core and wifi-ap, both created by Canonical.

Figure 5: Running a list command displays local snap information.

A quick glance at what the docs have to say about a Hello World! snap can be found on the Usage page [11]. I remember when I first saw this, I was surprised to see the output without any prepended command on the host's command prompt (i.e., no snap command). I just typed hello after installing the snap:

$ hello
Hello, world!

The output denotes success.

Remember the wifi-ap snap? This command has a lot of juicy information, which you can see by entering the info command (Listing 2). The description section should be self-explanatory; just below that, a URL points you to the snap's source code [12]. Also note the options listed under the commands section, which lists the possible parameters you can send to the snap.

Listing 2

Getting wifi-ap Snap Information

root@chris:~# snap info wifi-ap
name:      wifi-ap
summary:   "WiFi Access Point based on hostapd"
publisher: canonical
contact:   snappy-canonical-storeaccount@canonical.com
description: |
  This snap is implementing a WiFi access point based on hostapd and allows
  easily to share a internet connection or just create a network others can
  easily connect to.
  Please find the source of this snap at:
    https://code.launchpad.net/~snappy-hwe-team/snappy-hwe-snaps/+git/wifi-ap
commands:
  - wifi-ap.config
  - wifi-ap.setup-wizard
  - wifi-ap.status
tracking:    stable
installed:   15 (146) 31MB -
refreshed:   2017-05-05 16:20:19 +0000 UTC
channels:
  stable:    15     (146) 31MB -
  candidate: 15     (146) 31MB -
  beta:      16     (186) 31MB -
  edge:      17-dev (194) 31MB -

If you follow the source link to the Ubuntu Launchpad site, navigate to the Get this repository section, and then run the git clone command with the -b (branch) switch (Listing 3), you can download the latest source. If you then enter the wifi-ap directory, you can see, among all the small files, the all-important snapcraft.yaml file.

Listing 3

Getting the Latest wifi-ap Source Code

root@chris:~# git clone -b master https://git.launchpad.net/~snappy-hwe-team/snappy-hwe-snaps/+git/wifi-ap
Cloning into 'wifi-ap'...
remote: Counting objects: 2220, done.
remote: Compressing objects: 100% (1903/1903), done.
remote: Total 2220 (delta 882), reused 955 (delta 182)
Receiving objects: 100% (2220/2220), 2.71 MiB | 0 bytes/s, done.
Resolving deltas: 100% (882/882), done.
Checking connectivity... done.

Snap, Crackle, and Pop

Now I'll look at how you can create your own very basic snap. In this example, you just want to perform a super-simple echo command of whatever input (STDIN) is typed. To develop your own snaps, you need to install the snapcraft package:

$ apt install snapcraft

After a little more than 8MB of files are installed, you can start creating a snap with an init command (Figure 6), which pulls in a template.

Because I've already run hello and wifi-ap, those snaps are in the snap/ directory, along with the snapcraft.yaml file:

root@chris:~# ls snap/
core  hello  snapcraft.yaml  wifi-ap

Listing 4 shows the intuitive and easy-to-follow template file.

Listing 4

A snapcraft.yaml Template File

name: my-snap-name # you probably want to 'snapcraft register <name>'
version: '0.1' # just for humans, typically '1.2+git' or '1.3.2'
summary: Single-line elevator pitch for your amazing snap # 79 char long summary
description: |
  This is my-snap's description. You have a paragraph or two to tell the
  most important story about your snap. Keep it under 100 words though,
  we live in tweetspace and your description wants to look good in the snap
  store.
grade: devel # must be 'stable' to release into candidate/stable channels
confinement: devmode # use 'strict' once you have the right plugs and slots
parts:
  my-part:
    # See 'snapcraft plugins'
    plugin: nil

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