Introduction to Flatpak (original) (raw)

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Flatpak is a framework for distributing desktop applications across various Linux distributions. It was created by developers with a long history of working on the Linux desktop and is run as an independent open source project.

Terminology🔗

• Flatpak: a system for building, distributing, and running sandboxed desktop applications on Linux.
• Flatpak application: an application installed via the flatpak command or through a graphical interface, such as GNOME Software or KDE Discover.
• Runtime: also called platform, an integrated environment providing basic utilities needed for a Flatpak application to work.
• BaseApp: an integrated set of additional libraries and frameworks, such as Electron, for Flatpak applications that need more than just the basic runtime.
• Flatpak bundle: a single-file export format containing a Flatpak application or runtime.

Target audience🔗

Flatpak can be used by all kinds of desktop applications and aims to be as agnostic as possible in terms of how applications are built. There are no requirements regarding which programming languages, build tools, toolkits or frameworks can be used.

While Flatpak only runs on Linux, it can be used by applications that target other operating systems as well as those that are Linux-specific. Applications can be open source or proprietary (although some distribution services, likeFlathub, can have restrictions in this respect).

Flatpak’s only technical requirements are that applications follow a small number of Freedesktop standards to enable desktop integration (see Requirements & Conventions).

Issues with the current packaging model🔗

It is important to understand the problems with the current model of packaging applications to understand the existence of Flatpak:

• Fragmentation and duplicated work: each Linux distribution has their own package managers and package formats that are incompatible with each other. This leads to a lot of fragmentation and duplicated work since the same application needs to be packaged multiple times for various distributions. Furthermore, developers either need to learn the format of every distribution or support only a few. This makes the Linux desktop a difficult platform for software vendors to target.
• Limited to apps that are packaged: not every application is packaged for every Linux distribution. If an application isn’t packaged for a specific distribution, users are left with limited and unreliable options, often technical in nature.
• Limited to distributions that have the apps: users are limited to only the distributions that have all the necessary applications for their workflow.
• Hard to innovate in OS space: distribution maintainers spend a huge amount of time and effort in packaging rather than focusing on improving their distributions.
• Old and outdated packages: LTS distributions often have very old versions of applications packaged. This complicates bug reproducibility or leads to support requests for bugs that have been fixed upstream in newer versions.

Flatpak addresses these issues by enabling developers to distribute applications from one source and target the entire Linux desktop.

Reasons to use Flatpak🔗

Flatpak offers major advantages over most system package managers:

• Universality: Flatpak allows applications to be installed and run on virtually any Linux distribution, including non-GNU distributions, systemd-free distributions, immutable distributions and various architectures without requiring the developer to have access to the relevant hardware.
• Space for innovation: Flatpak allows distribution maintainers to focus on innovating their distribution without being burdened by packaging concerns.
• Stability: breakages in Flatpak applications do not affect the system since they run in isolated environments.
• Rootless install: Flatpak does not require elevated privileges to install applications or runtimes.
• Sandboxed applications: one of Flatpak’s main goals is to increase the security of desktop systems. This is achieved by isolating applications from one another and limiting their access to the host environment.

Flatpak also offers advantages over other universal approaches to Linux application distribution:

• Decentralized by design: Flatpak offers decentralized hosting and distribution, allowing developers or downstreams to host their own applications and application repositories.
• Desktop integration: Flatpak offers native integration with many Linux desktop environments, allowing users to easily browse, install, run, and manage Flatpak applications.
• Space efficiency: Flatpak saves storage by deduplicating libraries and other files used by multiple applications.
• Delta updates: only updated data is downloaded during updates, saving network bandwidth.

Other benefits for developers include:

• Forward-compatibility: the same Flatpak application can run on different versions of a distribution, including unreleased versions, without needing any changes.
• Bundling: this allows application developers to ship almost any dependency or library as part of their applications, giving them complete control over their applications.
• Consistent application environments: Flatpak provides a consistent and identical application runtime environment across devices and distributions. This makes bug identification and testing easier.
• Branches: this allows application developers to distribute multiple branches of an application (e.g. stable, beta, etc.) while retaining the same name.
• Maintained platforms: Flatpak runtimes contain a collection of common dependencies for the applications to use, easing application development and maintenance.

In general, Flatpak is best suited for desktop applications. While command-line applications also work, Flatpak may not be suitable in some cases:

• The application needs to elevate privileges using su, sudo, pkexec, etc. Flatpak cannot run SUID binaries inside the sandbox.
• The application requires access to /proc on the host or unfiltered access to processes. This is not allowed as Flatpak has a private proc.
• The application uses a syscall blocklisted by Flatpak’s seccomp filter. For example, Flatpak won’t allow spawning sub-namespaces in the sandbox.
• Kernel modules or drivers are non-application packages and won’t work as a Flatpak.

In general, if the sandbox prohibits an application’s core functionality or becomes too inconvenient or obtrusive, Flatpak may not be the most suitable packaging choice.

Flatpak also won’t export udev rules or systemd services from the sandbox to the host and requires manual configuration after installing the Flatpak package.

Information about Flatpak’s internals can be found in Under the Hood.