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CONTRIBUTING.md

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Flatpak uses a traditional autoconf-style build mechanism. The exact steps required depend on your distribution. Below are some steps that should work on Debian and Fedora, based on the configure options used to build those distributions' packages, These options will install into /usr, which will overwrite your distribution-provided system copy of Flatpak. You should only do this if you understand the risks of it to the stability of your system, and you probably want to do it in a VM or on a development machine that's expected to break sometimes!

On Debian

git clone https://github.com/flatpak/flatpak
cd flatpak
sudo apt build-dep flatpak
NOCONFIGURE=1 ./autogen.sh
./configure --prefix=/usr --sysconfdir=/etc --localstatedir=/var --libdir=\${prefix}/lib/x86_64-linux-gnu --runstatedir=/run --disable-auto-sideloading --disable-selinux-module --enable-gdm-env-file --enable-installed-tests --with-dbus-config-dir=/usr/share/dbus-1/system.d --with-privileged-group=sudo --with-run-media-dir=/media --with-system-bubblewrap=bwrap --with-system-dbus-proxy=xdg-dbus-proxy --with-systemdsystemunitdir=/lib/systemd/system --with-system-helper-user=_flatpak --enable-docbook-docs --enable-documentation --disable-gtk-doc
make -j$(nproc)
make check -j$(nproc)
sudo make install

On Fedora

git clone https://github.com/flatpak/flatpak
cd flatpak
sudo dnf builddep flatpak
sudo dnf install gettext-devel socat
NOCONFIGURE=1 ./autogen.sh
./configure --prefix=/usr --sysconfdir=/etc --libdir=/usr/lib64 --localstatedir=/var --enable-docbook-docs --enable-installed-tests --enable-selinux-module --with-system-bubblewrap --with-system-dbus-proxy
make -j$(nproc)
make check -j$(nproc)
sudo make install

How to run a specified set of tests

Sometimes you don't want to run the whole test suite but just one you're working on. This can be accomplished with a command like:

make check TESTS='tests/test-alias@system.wrap tests/test-alias@user.wrap'

More info

Dependencies you will need include: autoconf, automake, libtool, bison, gettext, gtk-doc, gobject-introspection, libcap, libarchive, libxml2, libsoup, gpgme, polkit, libXau, ostree, json-glib, appstream, libseccomp (or their devel packages).

Most configure arguments are documented in ./configure --help. However, there are some options that are a bit more complicated.

Flatpak relies on a project called Bubblewrap for the low-level sandboxing. By default, an in-tree copy of this is built (distributed in the tarball or using git submodules in the git tree). This will build a helper called flatpak-bwrap. If your system has a recent enough version of Bubblewrap already, you can use --with-system-bubblewrap to use that instead.

Bubblewrap can run in two modes, either using unprivileged user namespaces or setuid mode. This requires that the kernel supports this, which some distributions disable. For instance, Debian and Arch (linux kernel v4.14.5 or later), support user namespaces with the kernel.unprivileged_userns_clone sysctl enabled.

If unprivileged user namespaces are not available, then Bubblewrap must be built as setuid root. This is believed to be safe, as it is designed to do this. Any build of Bubblewrap supports both unprivileged and setuid mode, you just need to set the setuid bit for it to change mode.

However, this does complicate the installation a bit. If you pass --with-priv-mode=setuid to configure (of Flatpak or Bubblewrap) then make install will try to set the setuid bit. However that means you have to run make install as root. Alternatively, you can pass --enable-sudo to configure and it will call sudo when setting the setuid bit. Alternatively you can enable setuid completely outside of the installation, which is common for example when packaging Bubblewrap in a .deb or .rpm.

There are some complications when building Flatpak to a different prefix than the system-installed version. First of all, the newly built Flatpak will look for system-installed flatpaks in $PREFIX/var/lib/flatpak, which will not match existing installations. You can use --with-system-install-dir=/var/lib/flatpak to make both installations use the same location.

Secondly, Flatpak ships with a root-privileged PolicyKit helper for system-wide installation, called flatpak-system-helper. It is D-Bus activated (on the system bus) and if you install in a non-standard location it is likely that D-Bus will not find it and PolicyKit integration will not work. However, if the system installation is synchronized, you can often use the system installed helper instead— at least if the two versions are close enough.

This repository

The Flatpak project consists of multiple pieces, and it can be a bit challenging to find your way around at first. Here is a quick intro to each of the important subdirectories:

  • app: the commandline client. Each command has a flatpak-builtins- source file
  • common: contains the library, libflatpak. It also contains various pieces of code that are shared between the library, the client and the services. Non-public code can be recognized by having a -private.h header file.
  • completion: commandline auto completion support
  • data: D-Bus interface definition files and GVariant schemas
  • doc: The sources for the documentation, both man pages and library documentation
  • icon-validator: A small utility that is used to validate icons
  • oci-authenticator: service used for authenticating the user for installing from oci remotes (e.g. for paid apps)
  • po: translations
  • portal: The Flatpak portal service, which lets sandboxed apps request the creation of new sandboxes
  • revokefs: A FUSE filesystem that is used to transfer files downloaded by the user to the system-helper without copying
  • session-helper: The flatpak-session-helper service, which provides various helpers for the sandbox setup at runtime
  • tests: The testsuite
  • subprojects/bubblewrap: Flatpak's unprivileged sandboxing tool which is developed separately and exists here as a submodule
  • subprojects/libglnx: a small utility library for projects that use GLib on Linux, as a submodule
  • subprojects/dbus-proxy: a filtering proxy for D-Bus connections, as a submodule
  • subprojects/variant-schema-compiler: a tool for generating code to efficiently access data encoded using GVariant, as a submodule
  • system-helper: The flatpak-system-helper service, which runs as root on the system bus and allows non-root users to modify system installations