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Thanks to Canonical's push to get Snaps adopted by everyone, they've created a tool called Snapcraft which makes building a Snap relatively easy. Having said that, there are a few gotchas that Raoul encountered while trying to build a Snap on Debian.

Installing Snap

First we'll need Snap. Install snapd on either Ubuntu or Debian:

 $ sudo apt install snapd

Getting Snapcraft

If you're running Ubuntu 16.04 and up, Snapcraft is already part of your distro. If you're running another operating system you can use their Docker image to run Snapcraft on an Ubuntu 16.04 base.

We recommend using Docker anyway, as it provides a clean build environment without extra dependencies that one might have installed but forgotten about.

First, install Docker. Once Docker is installed, make sure the service is running:

 $ sudo service docker status

Make sure you followed the instructions on the Docker site to add your user to the group so that you don't have to use sudo with Docker. Lastly you'll want to pull the Snapcraft Docker image down:

 $ docker pull snapcore/snapcraft

Building the Snap

Now that you have the Snapcraft image, you'll need the snapcraft.yaml file. Raoul currently has this file in a separate repository for automated building on Launchpad in future. Let's grab it:

 $ bzr branch lp:~raoul-snyman/openlp/snapcraft

Now you should just be able to build the snap from there.

WARNING: There are some gotchas with building snaps using the Docker image. Use the command below rather than the command found on the Snapcraft site as it will get around these issues.
 $ docker run -v $PWD:$PWD -w $PWD snapcore/snapcraft bash -c "apt update && apt upgrade -y && snapcraft clean && snapcraft"

This build can easily take up to 20 minutes to complete (longer if you're on a slower machine), so go get yourself a cup of coffee while you wait for it to finish.

Once the build is done, you should have a file that is named something like openlp_2.4.5_amd64.snap in the same directory as the snapcraft.yaml file.

Installing the Snap

Obviously once you're done building, you want to install the snap. Installing locally unsigned snaps is supported via the --dangerous command line argument. Yep, it can be dangerous!

 $ sudo snap install openlp_2.4.5_amd64.snap --dangerous

That should take all of a few seconds to install, quite an anticlimax after the lengthy build! Now, let's test it out by running:

 $ /snap/bin/openlp

And if all went well you should see OpenLP!