Debugging

This section includes documentation on how to debug Flatpak apps.

Running debugging tools

Because Flatpak runs each application inside a sandbox, debugging tools can’t be used in the usual way, and must instead be run from inside the sandbox. To get a shell inside an application’s sandbox, it can be run with the --command option:

$ flatpak run --command=sh --devel <application-id>

This creates a sandbox for the application with the given ID and, instead of running the application, runs a shell inside the sandbox. From the shell prompt, it is then possible to run the application. This can also be done using any debugging tools that you want to use. For example, to run the application with gdb:

$ gdb /app/bin/<application-binary>

This works because the --devel option tells Flatpak to use the SDK as the runtime, which includes debugging tools like gdb. The --devel option also adjusts the sandbox setup to enable debugging.

Nota

The Freedesktop SDK (on which many others are based), includes a range of debugging tools, such as gdb, strace, nm, dbus-send, dconf, and many others.

gdb is much more useful when it has access to debug information for the application and the runtime it is using. Flatpak splits this information off into debug extensions, which you should install before debugging an application:

$ flatpak install <runtime-id>.Debug

When the --devel option is used, Flatpak will automatically use any matching debug extensions that it finds.

It is also possible to get a shell inside an application sandbox without having to install it. This is done using flatpak-builder’s --run option:

$ flatpak-builder --run <build-dir> <manifest> sh

This sets up a sandbox that is populated with the build results found in the build directory, and runs a shell inside it.

Creating a .Debug extension

Like many other packaging systems, Flatpak separates bulky debug information from regular content and ships it separately, in what is called a .Debug extension.

When an application is built, flatpak-builder automatically creates a .Debug extension. This can be disabled with the no-debuginfo option.

Overriding sandbox permissions

It is sometimes useful to have extra permissions in a sandbox when debugging. This can be achieved using the various sandbox options that are accepted by the run command. For example:

$ flatpak run --devel --command=sh --system-talk-name=org.freedesktop.login1 <application-id>

This command runs a shell in the sandbox for the given application, granting it system bus access to the bus name owned by logind.