"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.