Flatpak provides features for application sandboxing and distribution. Applications for the phone will be distributed as flatpaks – packages that can be distributed via repositories. Documentation for the flatpak tool and its flatpak-builder wrapper can be found in the Flatpak documentation.

Installing Flatpak Builder

Versions of these tools provided with modern GNU/Linux distributions should be sufficient. Debian-based distributions provide packages called flatpak and flatpak-builder that can be installed with the following command:

sudo apt -y install flatpak flatpak-builder

The flatpak-builder tool is used to build flatpaks; the flatpak tool is used to install and uninstall flatpaks, manage repositories and keep track of the applications that are available to run.


Building and testing applications locally is straightforward. Cross-compiling applications with Flatpak requires the use of the qemu user mode emulation binaries. On Debian-based platforms these can be installed with the following command:

sudo apt -y install qemu-user-static

This package, or the equivalent on other platforms, is necessary if you want to build applications for the Librem 5 on systems with a processor architecture different to that used by the phone (aarch64).

Installing Runtimes and SDKs for Development

Flatpak uses specific runtimes and SDKs for each target platform. The ones you will use depend on the technologies you will use to write applications for the Librem 5.

When you have installed a suitable runtime and SDK, you can start to develop your application and package it for testing on the phone or in an emulator.