Ubuntu 25.10+ fusermount3 error

[rockschtar]

Describe the bug

Bazaar currently fails to install any Flatpak application on Ubuntu 25.10 (with latest updates). While the system's core Flatpak installation functionality has been fixed and works correctly when installing applications directly via the command line, Bazaar consistently encounters an error during the installation process.

Steps to Reproduce:

1. On Ubuntu 25.10, open the Bazaar application.
2. Attempt to install any Flatpak application
3. The installation fails and the following log output/error message is returned:

Running fusermount wrapper, redirecting to host...
fusermount3: file descriptor 5 is not a socket, can't send fuse fd
Running fusermount wrapper, redirecting to host...
fusermount3: entry for /var/tmp/flatpak-cache-PZQDF3/com.cassidyjames.butler-P1KHF3 not found in /etc/mtab

(bazaar:2): BAZAAR::FLATPAK-CRITICAL **: 11:02:35.617: Transaction failed to complete: Could not unmount revokefs-fuse filesystem at /var/tmp/flatpak-cache-PZQDF3/com.cassidyjames.butler-P1KHF3: Child process exited with code 1

OS

Ubuntu 25.10 Gnome 49

Output of flatpak info io.github.kolunmi.Bazaar. If you are on Bazzite please run rpm -qi bazaar

Bazaar - Discover and install applications

          ID: io.github.kolunmi.Bazaar
         Ref: app/io.github.kolunmi.Bazaar/x86_64/stable
        Arch: x86_64
      Branch: stable
     Version: 0.5.8
     License: GPL-3.0-or-later
      Origin: flathub
  Collection: org.flathub.Stable
Installation: system
   Installed: 14.4 MB
     Runtime: org.gnome.Platform/x86_64/49
         Sdk: org.gnome.Sdk/x86_64/49

      Commit: 8c67ba0a4076c63c7e2e5f66211802ded72cf523b8560d7ccd10589a4574d8b9
      Parent: 2d3135a5408c397e1728c8135d2270342f164d0f7b8fe4f403fd96dbba50298d
     Subject: Merge pull request #49 from kolunmi/0.5.8 (f3eaf0931e17)
        Date: 2025-10-29 08:32:37 +0000

Extra information or context

No response

[tulilirockz]

Looks like a symptom of Ubuntu's uutils thing breaking flatpak, maybe make sure you are fully up to date on Ubuntu 25.10?

[rockschtar]

Looks like a symptom of Ubuntu's uutils thing breaking flatpak, maybe make sure you are fully up to date on Ubuntu 25.10?

Yes, the latest updates are installed. I can install Flatpaks via the CLI, which was initially broken in the Ubuntu 25.10 release. However, installation via Bazaar still doesn't work. I can reproduce this issue on a fresh Ubuntu 25.10 VM with all current updates applied. Maybe again some uutils or apparmor issue?

[tulilirockz]

Could you try installing FUSE2? Just to make sure that's not the problem. You should eventually get a fusermount binary on your CLI

[rockschtar]

Could you try installing FUSE2? Just to make sure that's not the problem. You should eventually get a fusermount binary on your CLI

Same problem with libfuse2 installed.

[martinszeltins]

Guys, I am getting the same error on Ubuntu 25.10

Could not unmount revokefs-fuse filesystem at /var/tmp/flatpak-cache-8NF7E3/ org.gnome.gitlab.ilhooq.Bookup.Locale-W6B7E3: Child process exited with code 1
Could not unmount revokefs-fuse filesystem at /var/tmp/flatpak-cache-8NF7E3/ org.kde.KStyle.Adwaita-KSKJF3: Child process exited with code 1

Screenshot:

[Soupolait]

Same here, and weirdly enough flatpak itself works fine. Installing a flatpak from cli gives no error, and installing one from Gnome Software also works.

[renner0e]

https://bugs.launchpad.net/ubuntu/+source/apparmor/+bug/2130388

• disabling apparmor (I did it with a kernel parameter) makes it work
  please don't do that

• downgrading fuse3 makes it work as well, see
  please don't do that

wget http://archive.ubuntu.com/ubuntu/pool/main/f/fuse3/libfuse3-3_3.14.0-10_amd64.deb
wget http://archive.ubuntu.com/ubuntu/pool/main/f/fuse3/fuse3_3.14.0-10_amd64.deb
sudo dpkg -i --force-downgrade libfuse3-3_3.14.0-10_amd64.deb fuse3_3.14.0-10_amd64.deb
sudo apt-mark hold libfuse3-3 fuse3
sudo rm -rf /var/tmp/flatpak-*

One random person on reddit claims this works:

Edit /etc/apparmor.d/fusermount3 in your favourite text editor, via sudo
Add at line 11 (which should be empty) add: /run/mount/utab.lock rwk,

Save & exit

Reload the fusermount3 rules: sudo apparmor_parser -r /etc/apparmor.d/fusermount3

[Milli189]

is there any updates on this?