flatpak-builder

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name: flatpak-builder description: Complete guide for packaging Linux applications as Flatpaks for distribution on Flathub. Use this skill whenever the user mentions: "flatpak", "flathub", "packaging for linux", "creating a flatpak", "flatpak manifest", "flatpak sandbox", "desktop file", "metainfo", "appstream", "flatpak-builder", "linux app distribution", "app icon linux", ".desktop file", "publish to flathub", or any time they want to make their app installable via flatpak. ALWAYS trigger on any flatpak/flathub packaging question, even if they just say "how do I make my app a flatpak" or "I want to publish my app on Linux". Covers manifests, runtimes, MetaInfo/AppStream XML, desktop files, icons at all sizes, sandbox permissions, build systems (cmake, meson, simple), Flathub submission, linting, GitHub Actions CI, and verification.

Flatpak Builder Skill

This skill covers everything needed to package an application as a Flatpak and publish it to Flathub — from the first manifest to a live store listing.

Quick Reference — Required Files

Every Flathub submission needs these files:

File	Location (in build)	Purpose
$APP_ID.yaml (or .json)	repo root	Flatpak manifest
$APP_ID.metainfo.xml	/app/share/metainfo/	AppStream metadata
$APP_ID.desktop	/app/share/applications/	Desktop entry
Icons (multiple sizes)	/app/share/icons/hicolor/<size>/apps/	App icons

→ For manifest deep-dive, see references/manifest.md → For MetaInfo/AppStream XML, see references/metainfo.md → For icons and desktop files, see references/icons-and-desktop.md → For Flathub submission process, see references/submission.md

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Step 1: Choose Your Application ID

The ID follows reverse-DNS format: {tld}.{vendor}.{product}

# Own a domain?
com.example.MyApp

# GitHub/GitLab hosted (REQUIRED format for code hosting)
io.github.yourusername.yourrepo
io.gitlab.yourusername.yourrepo
page.codeberg.yourusername.yourrepo

Rules:

• 3-5 components, max 255 chars
• Characters: [A-Z][a-z][0-9]_ only (dash - allowed only in last component)
• Do NOT end in .app, .desktop, .linux
• Must exactly match the ID in your MetaInfo file
• ID determines verification method — choose carefully, renaming requires resubmission

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Step 2: Choose a Runtime

Runtime	SDK	Use for
org.freedesktop.Platform//24.08	org.freedesktop.Sdk//24.08	Base/minimal apps
org.gnome.Platform//48	org.gnome.Sdk//48	GTK4/GNOME apps
org.kde.Platform//6.9	org.kde.Sdk//6.9	Qt6/KDE apps

• Freedesktop: new major version every August, 2-year support
• GNOME: synced with GNOME releases (~6 month cycle)
• KDE: synced with Qt releases
• Never use EOL runtimes — submissions will be rejected

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Step 3: Write the Manifest

See references/manifest.md for complete examples for each build system.

Minimal YAML manifest skeleton:

id: io.github.yourusername.yourapp
runtime: org.freedesktop.Platform
runtime-version: '24.08'
sdk: org.freedesktop.Sdk
command: your-app-binary

finish-args:
  - --share=ipc
  - --socket=fallback-x11
  - --socket=wayland
  - --device=dri

modules:
  - name: your-app
    buildsystem: cmake-ninja   # or: meson, simple, autotools
    sources:
      - type: git
        url: https://github.com/yourusername/yourapp.git
        tag: v1.0.0
        commit: abc123...

Key manifest rules:

• NO network access during build — all sources must be declared upfront
• No pre-compiled binaries
• All dependencies must be listed as modules or sourced from runtime/shared modules
• Minimize finish-args — only request what the app actually needs

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Step 4: Icons (Critical!)

Icons must be installed at the correct paths. Missing or wrong sizes = linter failure.

Required sizes for Flathub:

/app/share/icons/hicolor/16x16/apps/$APP_ID.png
/app/share/icons/hicolor/32x32/apps/$APP_ID.png
/app/share/icons/hicolor/48x48/apps/$APP_ID.png
/app/share/icons/hicolor/64x64/apps/$APP_ID.png
/app/share/icons/hicolor/128x128/apps/$APP_ID.png
/app/share/icons/hicolor/256x256/apps/$APP_ID.png
/app/share/icons/hicolor/512x512/apps/$APP_ID.png
/app/share/icons/hicolor/scalable/apps/$APP_ID.svg  ← SVG preferred

Install icons in your manifest:

- name: your-app
  buildsystem: simple
  build-commands:
    - install -Dm644 icons/512x512.png /app/share/icons/hicolor/512x512/apps/io.github.you.yourapp.png
    - install -Dm644 icons/256x256.png /app/share/icons/hicolor/256x256/apps/io.github.you.yourapp.png
    - install -Dm644 icons/scalable.svg /app/share/icons/hicolor/scalable/apps/io.github.you.yourapp.svg

See references/icons-and-desktop.md for full guidance including taskbar appearance.

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Step 5: Desktop File

[Desktop Entry]
Name=My App
Comment=Short description of what it does
Exec=myapp
Icon=io.github.yourusername.yourapp
Type=Application
Categories=Utility;
StartupNotify=true
StartupWMClass=myapp

Install to /app/share/applications/io.github.yourusername.yourapp.desktop

The filename must match your App ID exactly.

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Step 6: MetaInfo XML

See references/metainfo.md for the complete required XML structure.

Minimum required tags: id, name, summary, description, metadata_license, project_license, developer, launchable, screenshots, releases, content_rating

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Step 7: Build and Test Locally

# Install the builder
flatpak install -y flathub org.flatpak.Builder
flatpak remote-add --if-not-exists --user flathub https://dl.flathub.org/repo/flathub.flatpakrepo

# Build and install
flatpak run --command=flathub-build org.flatpak.Builder --install io.github.you.yourapp.yaml

# Run your app
flatpak run io.github.you.yourapp

# Lint the manifest
flatpak run --command=flatpak-builder-lint org.flatpak.Builder manifest io.github.you.yourapp.yaml

# Lint the repo
flatpak run --command=flatpak-builder-lint org.flatpak.Builder repo repo

Fix all linter errors before submitting. Both errors AND warnings are fatal.

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Step 8: Submit to Flathub

See references/submission.md for the complete PR workflow.

TL;DR:

1. Fork flathub/flathub on GitHub (uncheck "master branch only")
2. Clone with --branch=new-pr
3. Create a new branch, add your files, push
4. Open PR against the new-pr base branch (NOT master)
5. Title: "Add io.github.you.yourapp"

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Common Linter Failures

Error	Fix
Missing MetaInfo	Create $APP_ID.metainfo.xml
Wrong icon path	Name must exactly match $APP_ID, not just app name
Missing content_rating	Add <content_rating type="oars-1.1" />
EOL runtime	Update to current runtime version
Network in build	Remove network calls, pre-vendor all deps
Desktop file mismatch	Filename must be $APP_ID.desktop
Missing release tag	Add at least one <release> entry
Icon too small	Provide at least 128x128, ideally up to 512x512

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Sandbox Permissions Cheatsheet

Only request what you need. Prefer XDG portals over static permissions.

finish-args:
  # Display
  - --socket=wayland           # Wayland (preferred)
  - --socket=fallback-x11      # X11 fallback
  - --share=ipc                # Needed for X11 shared memory
  - --device=dri               # GPU access (for OpenGL/Vulkan)

  # Filesystem
  - --filesystem=home          # Full home dir (avoid if possible!)
  - --filesystem=xdg-documents # XDG documents folder
  - --filesystem=xdg-pictures  # XDG pictures
  - --filesystem=host:ro       # Read-only host FS (very permissive)

  # Audio
  - --socket=pulseaudio        # PulseAudio / PipeWire

  # Network
  - --share=network            # Internet access

  # D-Bus
  - --talk-name=org.freedesktop.Notifications  # Notifications
  - --own-name=com.example.MyApp              # Own a bus name

Use portals instead of --filesystem=home wherever possible.