Incompatibility with glib 2.70

[DrMcCoy]

On Gentoo, and possibly other distributions, the AppImage fails to start after upgrading to glib 2.70.

The error is:

cadmus: symbol lookup error: /usr/lib64/libgio-2.0.so: undefined symbol: g_module_open_full

The source of the problem is two-fold:

• glib 2.70 gained another convenience function, g_module_open_full(), which is being used all over the codebase
• the cadmus AppImage only contains some glib libraries. Namely, libgmodule, which is the old version without g_module_open_full(), but not libgio. The system libgio is then used, which expect to find g_module_open_full() => boom

I have no idea what libgio is used for, and if that's needed or pulled in for all installations/distributions. In either case, the proper fix is probably to upgrade glib inside the AppImage and/or put all the glib libs in there. Maybe.

For people with this problem, who don't want to wait for a new cadmus release

There's two ways to work around this: either put the whole of glib (either version) into the AppImage, or alternatively, simple delete libgmodule from the AppImage (i.e. use the system one instead).

To do either of those, you need to extract the AppImage, manipulate its files, and then put the AppImage back together.

You can extract the AppImage by calling it with the --appimage-extract parameter, i.e.:
cadmus.AppImage --appimage-extract

This will create a squashfs-root directory, which you can enter and manipulate. For some reason, though, the cadmus AppImage contains the libraries in duplicate, in two places. In usr/bin/, and in opt/cadmus/. If you want to delete libgmodule-2.0.so.0 or replace all the glib libs, you probably need to do it in both places.

Once you're done, you need to repack it with appimagetool:
appimagetool squashfs-root cadmus.AppImage

With that done, you should have a working cadmus AppImage again.