Mysterious truncation of appimage

Logic 2.3.39 stopped working on my Fedora box. It turns out that the appImage file got truncated; the normal length is 140MB and it became just 40MB long. This happened on Oct 23 20:08, and I don’t remember messing with it at that time.

On a hunch, I looked what other files were changed around that time, and I noticed that there is a cache file from the exact same time:
23608711 39380 -rw------- 1 pk pk 40322094 Oct 23 20:08 /home/pk/.config/Logic/Cache/c0fb8f4dc45c8e8e_0
I can’t say for sure whether I was running Logic at that time—it’s possible that I did.

The truncated AppImage file size was 40318070: close but not equal to the Cache file. I assume that the Cache file is app data, and that the size similiarity is just accidental. I did check that the truncated appImage file was identical to the first 40318070 bytes of the correct AppImage file, so it wasn’t like it was overwritten with something—it was really a truncation.

I think that this is unlikely to be a Logic bug, but rather it’s some sort of bad interaction with the OS runtime, but it’d be cool if someone figured out what happened.

NB, the error message is confusing:

Something went wrong trying to read the squashfs image.
Cannot mount AppImage, please check your FUSE setup.
You might still be able to extract the contents of this AppImage
if you run it with the --appimage-extract option.

I don’t see how this can be improved by Logic because it is issued by the runtime before Logic runs—but maybe there’s something to be done to point people to reinstalling the app; it took me several blind alley visits before I realized that the file is damaged and has to be reloaded. The good news is that google search results for this error point to AppImage file corruption, I just couldn’t believe it at first.

Of course the best outcome would be if we figured out how the truncation happened and made sure that it doesn’t ever again.

@przemek.klosowski It looks like the Appimage file got corrupt somehow. How exactly that happened though, that’s a good question… This is the first report we’ve received of this happening. Thanks for providing all the detailed information on the clues you found.

At first glance, I unfortunately don’t think we’ll have much control over the error message that appears. This looks like a FUSE-specific (“Filesystem in Userspace”) error message which corrupted Appimages may show.

I’ll bring this up with the team here to get their thoughts and will let you know if we discover anything relevant.