Snap Build

Snap Build & Publish for the Snap Store

The Snap Store (snapcraft.io) is Canonical's app store for Ubuntu and other Linux distributions that ship snapd. A snap is a self-contained, sandboxed package that bundles your app + all dependencies + a confinement profile.

This skill walks through:

1. Authoring snapcraft.yaml
2. Building the snap locally
3. Registering the name on snapcraft.io
4. Publishing to channels (edge → beta → candidate → stable)
5. Visibility settings (public, private, unlisted)
6. Updates and tracks

When to invoke

• During /app-gtm-release:ship-snap Gates 0-4
• When the user asks: "publish to Snap Store", "snapcraft setup", "snap channels", "Linux desktop distribution via snap", "Ubuntu app store"

Bar 1 — snapcraft.yaml authoring

Snap configuration is a single file at the project root: snap/snapcraft.yaml or ./snapcraft.yaml.

Minimum viable snapcraft.yaml (Flutter desktop example)

name: myapp
base: core24
version: '1.0.0'
summary: Short one-line description
description: |
  Multi-line description.
  Supports Markdown formatting.

grade: stable
confinement: strict

apps:
  myapp:
    command: myapp
    extensions:
      - gnome
    plugs:
      - home
      - network
      - network-bind
      - desktop
      - desktop-legacy
      - wayland
      - x11
      - opengl
      - audio-playback
      - removable-media

parts:
  myapp:
    plugin: flutter
    source: .
    flutter-target: lib/main.dart

Required fields

Confinement modes

For most apps: use strict. Add specific plugs for capabilities you need.

Common plugs (capabilities your app requests)

Plugin choice (under parts)

For non-trivial setups, use nil + override-build shell script:

parts:
  myapp:
    plugin: nil
    source: .
    override-build: |
      cd $CRAFT_PART_SRC
      ./build.sh
      cp -r build/release/* $CRAFT_PART_INSTALL/
    build-packages:
      - make
      - gcc
    stage-packages:
      - libgtk-3-0
      - libssl3

Bar 2 — Local build

Prerequisites

# Ubuntu 24.04 host
sudo snap install snapcraft --classic
sudo snap install lxd
sudo lxd init --auto
sudo usermod -a -G lxd $USER
newgrp lxd

For non-Ubuntu hosts: install multipass instead of LXD. Snapcraft uses Multipass to spin up an Ubuntu VM for the build.

Build command

cd /path/to/your/project
snapcraft

Output: myapp_1.0.0_amd64.snap in the current directory.

Test the snap locally

sudo snap install --dangerous ./myapp_1.0.0_amd64.snap
# --dangerous skips signature verification (snap is unsigned at this stage)

# Run it
myapp

# Inspect interfaces (which plugs are connected)
snap connections myapp

# Connect a plug if needed
sudo snap connect myapp:network

# Uninstall
sudo snap remove myapp

Common build issues

Bar 3 — Snap Store name registration

You need an Ubuntu One account (free): https://snapcraft.io/account

Then register your snap name (claims it for 30 days; you must publish a snap within that window or it returns to the pool):

snapcraft login
snapcraft register myapp

Names are first-come-first-served. Check availability: https://snapcraft.io/store/snap-name-check

Bar 4 — Channels strategy

Snap Store uses a 4-channel risk model. Users subscribe to a channel; updates flow within that channel.

A user installs with snap install myapp (defaults to stable). To install from a different channel:

sudo snap install myapp --channel=beta
sudo snap refresh myapp --channel=stable  # promote later

Branch tracks (parallel release lines)

For long-lived versions:

snapcraft upload --release=2.x/stable myapp_2.5.0_amd64.snap  # 2.x track
snapcraft upload --release=3.x/stable myapp_3.0.0_amd64.snap  # 3.x track

Users on the 2.x track only get 2.x updates. Useful for maintaining LTS versions.

Bar 5 — Publishing flow

First release

snapcraft upload myapp_1.0.0_amd64.snap --release=edge

Wait for review (automated for strict confinement: minutes; manual for classic: 1-2 weeks).

After review passes, the snap is in the edge channel. Test it:

sudo snap install myapp --channel=edge

Promoting through channels

After validating in edge, promote to beta:

snapcraft promote myapp --from-channel=edge --to-channel=beta

Or release a new build directly to beta:

snapcraft upload myapp_1.0.1_amd64.snap --release=beta

Continue: beta → candidate → stable.

Visibility settings (Public, Private, Unlisted)

Snap Store supports three visibility modes:

Set via Snap Store dashboard: https://snapcraft.io/{your-snap}/listing → Visibility.

For private snaps, allow specific Ubuntu One accounts under "Members" tab. They install with:

sudo snap install myapp  # works because Snap Store recognizes their account

Bar 6 — Updates (after first release)

Increment version in snapcraft.yaml:

version: '1.0.1'

Or use git describe to auto-version:

version: git

Build + upload + release:

snapcraft
snapcraft upload --release=edge myapp_1.0.1_amd64.snap

Snapd on user machines auto-refreshes (default: 4x daily, configurable).

Holding refreshes

Users can defer with sudo snap refresh --hold=24h myapp. For mandatory updates (security fixes), publishers can't force, but you can communicate via the snap's metadata or in-app notice.

CI/CD integration

GitHub Actions

- uses: snapcore/action-build@v1
  id: build
- uses: snapcore/action-publish@v1
  with:
    store_login: ${{ secrets.SNAPCRAFT_TOKEN }}
    snap: ${{ steps.build.outputs.snap }}
    release: edge

Generate the token:

snapcraft export-login --snaps myapp --channels edge,beta,candidate,stable -
# Outputs a base64 blob → save as SNAPCRAFT_TOKEN secret in GitHub

GitLab CI / Codemagic / others

Same pattern: install snapcraft → build → upload with token.

Output for /ship-snap Gate 4

Save outcomes to ./go-to-market/snap/notes/gate-4-publish.md:

# Snap Store Publish — {date}

## Registration
- Name: {value}
- Owner: {Ubuntu One account}
- Registered: {date}

## Build
- snapcraft.yaml: {path}
- Output: {filename}
- Size: {MB}
- Confinement: {strict|classic}
- Base: {core22|core24}

## Channels released
- edge: {version|-}
- beta: {version|-}
- candidate: {version|-}
- stable: {version|-}

## Visibility
{public|unlisted|private}

## Snap Store URL
{https://snapcraft.io/myapp}

Resources

• Snapcraft docs — official
• snapcraft.yaml reference — full schema
• Channels & tracks — channel concepts
• Public, private, unlisted snaps — visibility deep dive
• Snapcraft GitHub Action — CI/CD recipe
• Linux app store experience blog — Canonical's perspective