How to: Slim fails with a 'no permission to read from' error
This problem shouldn't happen anymore because the exported artifacts are saved in a tar file and the master app doesn't need to access the files directly anymore.

If you run older versions of Slim you can get around this problem by running Slim from a root shell. That way it will have access to all exported files.

Slim copies the relevant image artifacts trying to preserve their permissions. If the permissions are too restrictive the master app might not have sufficient privilege to access these files when it's building the new minified image.