It’s not just you: Flatpak flat-out doesn’t work in the new Ubuntu 25.10 release. The good news? The bug has been confirmed and Canonical’s developers are working on a fix.
While Flatpak itself can be installed using apt, trying to install Flatpaks with Flatpak from the command-line throws a “could not unmount revokefs-fuse filesystem” error, followed by “Child process exited with code 1”.
For those who’ve installed the Ubuntu ‘Questing Quokka’ and wanted to kit it out with their favourite software from Flathub, it’s a frustrating road bump.
Why is Flatpak broken on Ubuntu 25.10?
AppArmor, the tool that enforces Ubuntu’s security policies for apps, is causing the issue.
According to the bug report on Launchpad, the AppArmor profile for fusermount3 lacks the privileges it needs to work properly in Ubuntu 25.10. Fusermount3 is a tool Flatpak relies on to mount and unmount filesystems. Without the right permissions, the installation fails:
Fusermount3 (and umount, which it invokes) needs access to files like /run/mount/utab. AppArmor is currently blocking that access.
No access, no unmount. No unmount, no Flatpak installs.
Worse still, the bug affects everyone running Ubuntu 25.10, whether that’s an upgrade from 25.04 or a spick-and-span fresh install.
There is a workaround
This is a bug and it is being worked on. Although there’s no timeframe for a fix, it is marked as critical, so will be prioritised. I’d recommend waiting for the official fix to rollout as it will resolve things properly, without compromising the security safeguards AppArmor provides.
That said, the bug report does list a workaround. If you’re on Ubuntu 25.10 and you need to be able to install software that is only (easily) available on Flathub, try that out — I won’t copy/paste the fix here as I have not tested it personally.
I don’t recommend you downgrade any packages to earlier versions. It may help resolve the issue but you will need to remember to undo your changes. Older package versions can create conflicts with newer versions that break or prevent updates.
How’d this even happen?
It’d be fair to say Ubuntu 25.10 is the biggest releases in years (my feature overview ran to more than 3000 words). Plenty of time, skill and attention has gone been poured into it. To see this bug overlooked is disappointing, although understandable.
Ubuntu is made of many disparate parts that interact in a myriad of ways. Flatpak is not part of the default Ubuntu install, and it being affected by a change in a component that is part of the default install is not a conspiracy, it’s simply a bug.
I’m sure “Ubuntu sabotages Flatpak” videos are being rendered at full tilt by YouTube raconteurs as I type this, but to be blunt: an accidental snafu like this hardly makes Ubuntu look, much less were it intentional — no-one should disappear down a rabbit hole over this.
As the de-facto Flatpak store, Flathub continues to grow in size, scope and significance. Being unable to benefit from it on the latest Ubuntu is a proper flub – let’s hope that fix comes fast!