Can I not share external hard drives through my Macbook's standard file sharing system? I'm trying to share an external hard drive through lan file sharing (SMB). The sharing works for folders and file in my Macbook. I have set up a “Sharing” account that I give access to the files I want to share. 

The problem is that the “plus” button to add a user with access to that folder is greyed out when I select the hard drives, so I cannot add my file sharing account. And the users that already have access cannot be edited, they're also greyed out, as is the minus button. Basically I cannot edit anything. 

I have also tried using my administrator account since that one is already added to the folder's users with access list, but I cannot make SMB work with that account. 

The hard drives are in ExFat and Fat32 formats. I know I can share them through my WiFi router, but I need to share them through my Macbook.

I tried adding my Sharing account to the Permissions box on the Get Info dialogue, but PathFinder didn't let me save the changes (it didn't give me a reason), and Finder just says that “You can read and write” but doesn't show me any other options to add, subtract, edit or see other users with access. 

I don't know if this is a sharing issue, a permissions issue or both.

So, is sharing an external hard drive possible? If so, what am I missing?
To add to @nohillside answer you can share a FAT32 formatted drive but not set  permissions as the filesystem doesn't support it.



If you want to control access to files on the USB by permissions then format it using a filesystem that supports it (such as HFS) and changes will be avaliable in File Sharing.