Check type 2 AppImages

[probonopd]

https://github.com/AppImage/AppImageSpec/blob/master/draft.md#type-2-image-format

Experimental implementation:
https://github.com/probonopd/appimagetool

The advantage of this is that there is no fixed offset for the filesystem image, which means that it is not so tightly size-restricted.

[orivej]

Thanks for referring me to the spec!

It's neat how you solved the loss of application icons in squashfs images and automated chmod +x with appimaged.

Why did you keep chdir($mnt/usr) in the spec and in AppRun? What applications benefit from this?

[probonopd]

Some applications and libraries hardcode paths in /usr. This is why for these, we binary patch the absolute path /usr to the relative path ././ which works if we cd to $APPDIR/usr before executing the app, and if the app does not call chrdir().

There are more elegant ways around this, but so far none of them seems to work 100% yet. Contributions in this area are highly welcome.