Host Platform Support (Platform support)













Best effort support

AppImage has a number of significant issues building images for GUI apps. It is incompatible with the use of binary wheels, and the use of an older Linux base image for compatibility purposes is incompatible with using modern GUI frameworks. Even when a GUI toolkit can be installed, the AppImage packaging process frequently introduces bugs related to DBus integration or libraries like WebKit2 that use subprocesses.

Briefcase provides an AppImage backend for historical reasons, but we strongly discourage the use of AppImages for distribution. We maintain unit test coverage for the AppImage backend, but we do not build AppImages as part of our release process. We will accept bug reports related to AppImage support, and we will merge PRs that address AppImage support, but the core team does not consider addressing AppImage bugs a priority.

If you need to distribute a Linux app, System packages or Flatpaks are much more reliable options.

AppImage provides a way for developers to provide “native” binaries for Linux users. It allow packaging applications for any common Linux based operating system, including Ubuntu, Debian, Fedora, and more. AppImages contain all the dependencies that cannot be assumed to be part of each target system, and will run on most Linux distributions without further modifications. Briefcase uses Linuxdeploy to build the AppImage in the correct format.

Packaging binaries for Linux is complicated, because of the inconsistent library versions present on each distribution. An AppImage can be executed on any Linux distribution with a version of libc greater than or equal the version of the distribution where the AppImage was created.

To ensure that an application is built in an environment that is as compatible as possible, Briefcase builds AppImages inside Docker. The Docker base image used by Briefcase can be configured to any manylinux base using the manylinux application configuration option; if manylinux isn’t specified, it falls back to an Ubuntu 18.04 base image. While it is possible to build AppImages without Docker, it is highly recommended that you do not, as the resulting AppImages will not be as portable as they could otherwise be.


AppImage works by attempting to autodetect all the libraries that an application requires, copying those libraries into a distribution, and manipulating them to reflect their new locations. This approach can work well… but it is also prone to major problems. Python apps (which load their dependencies dynamically) are particularly prone to exposing those flaws.

Briefcase makes a best-effort attempt to use the AppImage tools to build a binary, but sometimes, the problem lies with AppImage itself. If you have problems with AppImage binaries, you should first check whether the problem is a limitation with AppImage.

Icon format

AppImages use .png format icons. An application must provide icons in the following sizes:

  • 16px

  • 32px

  • 64px

  • 128px

  • 256px

  • 512px

AppImages do not support splash screens or installer images.

Additional options

The following options can be provided at the command line when producing AppImages.


Use native execution, rather than using Docker to start a container.


A configuration argument to be passed to the Docker build command for the app image. For example, to provide an additional build argument to the Dockerfile, specify --Xdocker-build=--build-arg=ARG=value. See the Docker build documentation for details on the full list of options that can be provided.

You may specify multiple --Xdocker-build arguments; each one specifies a single argument to pass to Docker, in the order they are specified.

Application configuration

The following options can be added to the<appname>.linux.appimage section of your pyproject.toml file.


The manylinux tag to use as a base image when building the AppImage. Should be one of:

  • manylinux1

  • manylinux2010

  • manylinux2014

  • manylinux2_24

  • manylinux2_28

New projects will default to manylinux2014. If an application doesn’t specify a manylinux value, ubuntu:18.04 will be used as the base image.


The specific tag of the manylinux image to use. Defaults to latest.


A list of operating system packages that must be installed for the AppImage build to succeed. If a Docker build is requested, this list will be passed to the Docker context when building the container for the app build. By default, entries should be Ubuntu 18.04 apt package requirements. For example:

system_requires = ['libgirepository1.0-dev', 'libcairo2-dev']

would make the GTK GI and Cairo operating system libraries available to your app.

If you see errors during briefcase build of the form:

Could not find dependency:

but the app works under briefcase dev, the problem may be an incomplete system_requires definition. The briefcase build process generates a new environment that is completely isolated from your development environment, so if your app has any operating system dependencies, they must be listed in your system_requires definition.


A list of linuxdeploy plugins that you wish to be included when building the AppImage. This is needed for applications that depend on libraries that have dependencies that cannot be automatically discovered by Linuxdeploy. GTK and Qt both have complex runtime resource requirements that can be difficult for Linuxdeploy to identify automatically.

The linuxdeploy_plugins declaration is a list of strings. Briefcase can take plugin definitions in three formats:

  1. The name of a plugin known by Briefcase. One of gtk or qt.

  2. A URL where a plugin can be downloaded

  3. A path to a local plugin file

If your plugin requires an environment variable for configuration, that environment variable can be provided as a prefix to the plugin declaration, similar to how environment variables can be defined for a shell command.

For example, the gtk plugin requires the DEPLOY_GTK_VERSION environment variable. To set this variable with the Briefcase-managed GTK Linuxdeploy plugin, you would define:

linuxdeploy_plugins = ["DEPLOY_GTK_VERSION=3 gtk"]

Or, if you were using a plugin stored as a local file:

linuxdeploy_plugins = ["DEPLOY_GTK_VERSION=3 path/to/plugins/"]


Any additional Docker instructions that are required to configure the container used to build your Python app. For example, any dependencies that cannot be configured with apt-get could be installed. dockerfile_extra_content is string literal that will be added verbatim to the end of the project Dockerfile.

Any Dockerfile instructions added by dockerfile_extra_content will be executed as the brutus user, rather than the root user. If you need to perform container setup operations as root, switch the container’s user to root, perform whatever operations are required, then switch back to the brutus user - e.g.:

dockerfile_extra_content = """
RUN <first command run as brutus>

USER root
RUN <second command run as root>

USER brutus

Platform quirks

Use caution with --update-support

Care should be taken when using the --update-support option to the update, build or run commands. Support packages in Linux AppImages are overlaid with app content, so it isn’t possible to remove all old support files before installing new ones.

Briefcase will unpack the new support package without cleaning up existing support package content. This should work; however, ensure a reproducible release artefacts, it is advisable to perform a clean app build before release.

Apps using WebKit2 are not supported

WebKit2, the library that provides web widget support, can’t currently be deployed with AppImage. WebKit2 uses subprocesses to manage network and rendering requests, but the way it packages and launches these subprocesses isn’t currently compatible with AppImage.

In addition, many of the commonly used manylinux base images predate the release of WebKit2. As a result, system packages providing WebKit2 are not available on these base images. manylinux_2_28 is the earliest supported manylinux image that provides WebKit2 support.

Runtime issues with AppImages

Packaging on Linux is a difficult problem - especially when it comes to binary libraries. The following are some common problems you may see, and ways that they can be mitigated.

Failure to load libpango-1.0-so.0

Older Linux distributions (e.g., Ubuntu 18.04) may not be compatible with AppImages of Toga apps produced by Briefcase, complaining about problems with and an undefined symbols (fribidi_get_par_embedding_levels_ex is a common missing symbol to be reported). This is caused because the version of fribidi provided by these distributions. Unfortunately, there’s no way to fix this limitation.

Undefined symbol and Namespace not available errors

If you get the error:

ValueError: Namespace Something not available


ImportError: /usr/lib/ undefined symbol: some_symbol

it is likely that one or more of the libraries you are using in your app requires a Linuxdeploy plugin. GUI libraries, or libraries that do dynamic module loading are particularly prone to this problem.

ELF load command address/offset not properly aligned

Briefcase uses a tool named Linuxdeploy to build AppImages. Linuxdeploy processes all the libraries used by an app so that they can be relocated into the final packaged binary. Building a manylinux binary wheel involves a tool named auditwheel that performs a very similar process. Unfortunately, processing a binary with Linuxdeploy after it has been processed by auditwheel can result in a binary library that cannot be loaded at runtime.

This is particularly common when a module installed as a binary wheel has a dependency on external libraries. For example, Pillow is a Python library that contains a binary submodule; that submodule uses libpng, libtiff, and other system libraries for image manipulation. If you install Pillow from a manylinux wheel, you may see an error similar to the following at runtime:

Traceback (most recent call last):
File "/tmp/.mount_TestbewwDi98/usr/app/testbed/", line 54, in main
File "/tmp/.mount_TestbewwDi98/usr/app/testbed/", line 94, in test_pillow
   from PIL import Image
File "/tmp/.mount_TestbewwDi98/usr/app_packages/PIL/", line 132, in <module>
   from . import _imaging as core
ImportError: ELF load command address/offset not properly aligned

This indicates that one of the libraries that has been included in the AppImage has become corrupted as a result of double processing.

The solution is to ask Briefcase to install the affected library from source. This can be done by adding a "--no-binary" entry to the requires declaration for your app. For example, if your app includes Pillow as a requirement:

requires = ["pillow==9.1.0"]

You can force Briefcase to install Pillow from source by adding:

requires = [
    "--no-binary", "pillow",

Since the library will be installed from source, you also need to add any system requirements that are needed to compile the binary library. For example, Pillow requires the development libraries for the various image formats that it uses:

system_requires = [
    ... other system requirements ...

If you are missing a system requirement, the call to briefcase build will fail with an error:

error: subprocess-exited-with-error

× pip subprocess to install build dependencies did not run successfully.
│ exit code: 1
╰─> See above for output.

note: This error originates from a subprocess, and is likely not a problem with pip.
>>> Return code: 1

Unable to install requirements. This may be because one of your
requirements is invalid, or because pip was unable to connect
to the PyPI server.

You must add a separate --no-binary option for every binary library you want to install from source. For example, if your app also includes the cryptography library, and you want to install that library from source, you would add:

requires = [
    "--no-binary", "pillow",
    "--no-binary", "cryptography",

If you want to force all packages to be installed from source, you can add a single :all declaration:

requires = [
    "--no-binary", ":all:",

The --no-binary declaration doesn’t need to be added to the same requires declaration that defines the requirement. For example, if you have a library that is used on all platforms, the declaration will probably be in the top-level requires, not the platform-specific requires. If you add --no-binary in the top-level requires, the use of a binary wheel would be prevented on all platforms. To avoid this, you can add the requirement in the top-level requires, but add the --no-binary declaration to the Linux-specific requirements:

formal_name = "Hello World"
requires = [

requires = [
    "--no-binary", "pillow"