< Guidelines and HOWTOs
Revision as of 13:21, 6 March 2018 by Jgrulich (talk | contribs) (Add some useful information how to debug portals)

Guidelines and HOWTOs/Flatpak

Flatpak is a solution for creating sandboxed software builds for GNU/Linux systems. You can find more information here.


At the moment we are building nightlies of most of our applications. It has the master version of the applications, so expect some unstable development quirks. On the bright side, if you find one, you get to tell the developers so they can fix it!

Here's how to install an application from the terminal:

flatpak remote-add --if-not-exists flathub https://flathub.org/repo/flathub.flatpakrepo
flatpak remote-add --if-not-exists kdeapps --from https://distribute.kde.org/kdeapps.flatpakrepo
flatpak install kdeapps org.kde.okular

Or just open the flatpakrepo files with Discover or your otherwise favorite software center:

Qt and KF5 Runtime

We provide a runtime with Qt and all KDE Frameworks 5 (except for the 4th tier) to make sure it's easily adaptable for any KDE Application and possibly most Qt-based applications as well.

This runtime can be added by following these instructions:

flatpak install flathub org.kde.Platform//5.9
flatpak install flathub org.kde.Sdk//5.9
All flatpak commands (such as remote-add and install) accept a --user option to install things at the user level, without being prompted for the sudo password every time.

Compile your application

Now you get to compile your favorite application. If you want to see how it's done, you can see some of the ones that have already been built. You can find it here.

To compile an applications, you should create a json file similar to the ones in the previous link. Then you'd just need to trigger the build and get it into a repository. For testing, I recommend just creating a local one (to publish an rsync will be required).

mkdir app repo
flatpak-builder --ccache --repo=repo --subject="Build of AWESOMEAPP `date`" app org.kde.AWESOMEAPP.json

This will do everything required and create a repository in ./repo. To test the application we add the repository (called remotes), we install the application and then we run it:

flatpak remote-add awesomeapp repo --no-gpg-verify
flatpak install awesomeapp org.kde.AWESOMEAPP
flatpak run org.kde.AWESOMEAPP

Now you will see that some things don't work and you'll have the privilege to start fixing things!


In the following repositories you'll find the code in charge of packaging the runtime (Qt 5 and KF5) and then several (but not all, yet) KDE Applications.

Flatpak portals

Portals are high-level session bus APIs that provide selective access to resources to sandboxed applications. The implicit expectation of portals is that the user will always be involved in granting or rejecting a portal request, thus most portal APIs will lead to user interaction in the form of dialogs.

Since such dialogs must fit into the user experience of the desktop shell, the portal APIs are implemented by a generic frontend called xdg-desktop-portal which calls out to desktop-specific implementations that provide the actual UI. The bus name through which the portal APIs are available is org.freedesktop.portal.Desktop, with the object path /org/freedesktop/portal/desktop implementing the various portal interfaces.

You can find more information about flatpak portals here.

KDE implementation of portals

KDE backend for flatpak portals is called xdg-desktop-portal-kde and is now part of Plasma releases (starting with Plasma 5.10). Currently it supports most of the portals. If you want to test KDE flatpak portals, you can use this simple test app.

Debugging portals

To get some debug information, you first kill both xdg-desktop-portal and xdg-desktop-portal-kde running instances. Then first start xdg-desktop-portal-kde with:

QT_LOGGING_RULES='xdg-desktop*.debug=true' /usr/libexec/xdg-desktop-portal-kde

then in another terminal session start xdg-desktop-portal with:

G_MESSAGES_DEBUG=all /usr/libexec/xdg-desktop-portal

You can use above mentioned testing application to test various portals. You should then see debug output from xdp-kde similar to:

xdg-desktop-portal-kde: Desktop portal registered successfuly
xdg-desktop-portal-kde-file-chooser: OpenFile called with parameters:
xdg-desktop-portal-kde-file-chooser:     handle:  "/org/freedesktop/portal/desktop/request/1_255/t"
xdg-desktop-portal-kde-file-chooser:     parent_window:  "x11:1"
xdg-desktop-portal-kde-file-chooser:     title:  "Flatpak test - open dialog"
xdg-desktop-portal-kde-file-chooser:     options:  QMap(("accept_label", QVariant(QString, "Open (portal)"))("filters", QVariant(QDBusArgument, ))("modal", QVariant(bool, true))("multiple", QVariant(bool, true)))

You can see which portal has been called, whether it has been called or when you check output from xdg-desktop-portal then you should see message in case of portal error (usually related to DBus). You can also monitor dbus messages using dbus-monitor, which indicates whether portals get involved at all as everything goes through DBus.

Styles and integration with other desktops

We are aware that not everyone is using KDE/Qt applications in Plasma desktop. For this flatpak comes with extensions, where you specify a directory (with themes, icons) where third-party is allowed to install additional stuff as an addition to what we have in our runtimes. At this moment we have added support for Gnome in form of adwaita icons and adwaita-qt style. All you need to is install following extensions using commands below:

flatpak install kdeapps org.freedesktop.Platform.Icontheme.Adwaita
flatpak install kdeapps org.kde.KStyle.Adwaita
flatpak install kdeapps org.kde.PlatformTheme.QGnomePlatform

This page was last edited on 6 September 2020, at 10:23. Content is available under Creative Commons License SA 4.0 unless otherwise noted.