:doc:`first-build` has already provided a quick demonstration of how applications get built with Flatpak. This page provides an additional general overview of what's involved.
flatpak-builder is the primary tool for building Flatpak applications. It allows you to take the source files for an application and build it into a Flatpak application. It also allows multiple other dependencies to be built at the same time, which get bundled into the build.
The input to
flatpak-builder is a manifest file. This specifies the parameters for the application that will be built, such as its name and which runtime it will depend on. The manifest also lists all the modules that are to be built as part of the build process. A source for each module can be specified, including links to file archives or version control repositories. One of the modules (usually the last one) is the application code itself.
The basic format used to invoke
$ flatpak-builder <build-dir> <manifest>
<build-dir> is the path to the directory that the application will be built into, and
<manifest> is the path to a manifest file. The contents of
<build-dir> can be useful for testing and debugging purposes, but is generally treated as an artifact of the build process.
flatpak-builder is run:
- The build directory is created, if it doesn't already exist
- The source code for each module is downloaded and verified
- The source code for each module is built and installed
- The build is finished, by setting sandbox permissions
- The build result is exported to a repository (which will be created if it doesn't exist already)
The application can then be installed from the repository and run.
Software Development Kits (SDKs)
Instead of being built using the host environment, Flatpak applications are built inside a separate environment, called an SDK.
SDKs are like the regular runtime that applications run in. The difference is that SDKs also include all the development resources and tools that are required to build an application, such as build and packaging tools, header files, compilers and debuggers.
Each runtime has an accompanying SDK. For example, there is both a GNOME 3.26 runtime and a GNOME 3.26 SDK. Applications that use the runtime are built with the matching SDK.
Like runtimes, SDKs will sometimes be automatically installed for you, but if you do need to manually install them, they are installed in the same way as applications and runtimes, such as:
$ flatpak install flathub org.gnome.Sdk//3.26