Let's say we have a Mac configured with three user accounts:


When Alice logs into her account, she connects a USB drive that contains files she needs to work with. Bob logs in at the same time and realizes he can access her USB drive through Finder. He has full permission to view and edit her files.

How can Alice mount her USB drive in a way that only she has access to it?


  • Mac OS X 10.10.5
  • USB drive (FAT32)


  • What format is the USB in HFS, FAT32, ExFAT? You can find that out by Get Info (Cmd+I).
    – user14492
    Sep 18, 2015 at 18:05
  • @user14492 the USB drive is formatted as FAT32
    – fire_water
    Sep 18, 2015 at 18:09
  • Aww. FAT32 doesn't support permission. I was thinking you only give alice the permission to read/write to the whole drive, then other's won't be able to access it.
    – user14492
    Sep 18, 2015 at 18:10

1 Answer 1


If you format the drive as HFS+ (essentially Mac formatted) you can set permissions on it (which any admin user can change of course). If it is anything else (PC formats: FAT, exFAT, etc.) you can't set permissions

Probably the best thing would be to put an encrypted DMG on the thumb drive. Anyone could get to the DMG but only the person with the correct credentials could open it.


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