"Failed to register AppImage in system via libappimge"

[TheNightRider12]

Pre-submit checks

• I checked for similar issues beforehand, but could not find any, not even closed ones. I could not add my bug report to any existing issue.
• I am going to take the time to to fill in all the required details. I know that the bug report will be dismissed otherwise.

Describe the bug

I am trying to install the app image from here https://github.com/martinrotter/rssguard/releases
specifically https://github.com/martinrotter/rssguard/releases/download/devbuild5/rssguard-devbuild5-90ef2a498-qt6-linux64.AppImage
and when I open the AppImage I then click "Integrate and Run" and then I get the error " failed to register AppImage in system via libappimge".

Expected behavior

I expected to be able to install the AppImage successfully.

Steps to reproduce the issue

1. Go to https://github.com/martinrotter/rssguard/releases
2. Download: rssguard-devbuild5-90ef2a498-qt6-linux64.AppImage
3. Click on the AppImage once downloaded
4. Click "Integrate and run"
5. See if you are successful or not
   6

Screenshots

Distribution and desktop environment

Ubuntu 24.04.3 LTS
Kernel: 6.14.0-33
64Bit Desktop

Installed AppImageLauncher version

v3.0.0-beta-3
96cb937
Release v3.0.0-beta-3

List of AppImages you tried (ideally with URL)

RssGuard (not working) https://github.com/martinrotter/rssguard/releases/download/devbuild5/rssguard-devbuild5-90ef2a498-qt6-linux64.AppImage
YouTube Music (working) https://github.com/pear-devs/pear-desktop/releases/download/v3.11.0/YouTube-Music-3.11.0.AppImage

Additional context

N/A

[TheAssassin]

Apparently, this AppImage uses a nonstandard runtime. It claims to be compatible with type 2, but tools like appimagelint cannot easily analyze it therefore. It does not seem to use squashfs.

Edit: "Run once" works as expected.

Edit 2: libappimage also fails to integrate this because it is not a squashfs image. This is therefore a libappimage bug.

[TheNightRider12]

Interesting. I can see if an earlier build works. There is a 4.x branch of the app but it will be deprecated eventually. When I get a chance I can try the 4.x release AppImage. Maybe the developer changed something in the 5.x builds.

[TheAssassin]

So this AppImage is using uruntime, a third-party runtime. Internally, it is using DwarFS, which libappimage has no support for. This explains why AppImageLauncher cannot work with it.

A quick fix is for this AppImage to switch back to squashfs which uruntime claims to support as well.

[JohnHillsCodeProjects]

A quick fix is for this AppImage to switch back to squashfs which uruntime claims to support as well.

I'm new to Linux, so can you please explain how I can fix this with squashfs. Like how do I use mksquashfs, where do I do it, etc?

[rogerw-gh]

Latest RaspberryPi imager does not integrate on Debian Linux, running the AppImage from the CLI, not through the gui shows this error Squashfs image uses (null) compression, this version supports only xz, zlib.
Since October 2025 there are numerous reports of AppImages failing to integrate, e.g. https://forum.cursor.com/t/recent-appimages-are-not-working-squashfs-image-uses-null-compression-this-version-supports-only-xz-zlib-ubuntu-22/69811 and https://forum.bambulab.com/t/cannot-open-or-install-bambu-studio-02-02-1-60-under-ubuntu-24-04/193146 and openscad/openscad#5736.

I use OpenSCAD so I know this is borked, I have compiled from source to resolve this..
It appears the AppImage build tool has broken AppImageLauncher.

Building raspberry-pi-imager from source results in:

Deploying Qt dependencies using /opt/Qt/6.9.3/gcc_64...
Squashfs image uses (null) compression, this version supports only xz, zlib.
ERROR: appimage_shall_not_be_integrated : sqfs_open_image error: /home/rogerw/devel/rpiimager/rpi-imager/appimage-tools/linuxdeploy-x86_64.AppImage
AppImageLauncher error: appimage_shall_not_be_integrated() failed (returned -1)
Squashfs image uses (null) compression, this version supports only xz, zlib.
ERROR: appimage_is_terminal_app : sqfs_open_image error: /home/rogerw/devel/rpiimager/rpi-imager/appimage-tools/linuxdeploy-x86_64.AppImage
AppImageLauncher error: appimage_is_terminal_app() failed (returned -1)
Squashfs image uses (null) compression, this version supports only xz, zlib.
ERROR: appimage_register_in_system : sqfs_open_image error: /home/rogerw/Applications/linuxdeploy-x86_64_ff442e851db38b0947d29a4111d1d927.AppImage

[gokulcoder7]

A quick fix is for this AppImage to switch back to squashfs which uruntime claims to support as well.

I'm new to Linux, so can you please explain how I can fix this with squashfs. Like how do I use mksquashfs, where do I do it, etc?

+1