Bad plan trying to use DropBox:
https://manual.calibre-ebook.com/faq...rked-drive-nas
Quote:
Do not put your calibre library on a networked drive.
A filesystem is a complex beast. Most network filesystems lack various filesystem features that calibre uses. Some don’t support file locking, some don’t support hardlinking, some are just flaky. Additionally, calibre is a single user application, if you accidentally run two copies of calibre on the same networked library, bad things will happen. Finally, different OSes impose different limitations on filesystems, so if you share your networked drive across OSes, once again, bad things will happen.