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I have a USB hard drive connected to my Mac. I want it to be readable only by me, and not by the anonymous "guest" user. I right-clicked on the drive in Finder, and set the permissions like this:

Permissions

I also clicked on the gear, and selected "Apply to enclosed items".

But when I log out, and log in as guest, I can still browse the files on the drive. What's going on here? I'm running Sierra 10.12.1.

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Why not just encrypt the drive?

https://www.howtogeek.com/184675/how-to-encrypt-your-macs-system-drive-removable-devices-and-individual-files/amp/

Encrypt Removable Devices

Mac OS X allows you to encrypt an entire drive, like a USB drive or external hard drive. The contents of the drive will be encrypted with a passphrase you choose and no one will be able to access them without that passphrase. It functions like BitLocker To Go on Enterprise editions of Windows, but it’s available to all Mac users.

To encrypt a drive, simply open the Finder and connect the drive to your Mac. Ctrl+click or right-click the drive in the Finder sidebar and select the Encrypt “Drive Name” option.

The disk will be encrypted once you enter your password of choice — be sure to use a secure one! You may have to wait several minutes for the contents of your disk to be encrypted, depending on the size of your drive and its speed.

Don’t lose your password! If you do, you won’t be able to access any files on the encrypted drive.

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  • I did that too, and it helped. I don't understand though why the filesystem permissions are not respected by the system :(
    – Macondo2Seattle
    Commented Mar 7, 2017 at 16:31
  • I think the functionality above within finder is for files on your Mac HD. You can't force the computer not to accept something that's plugged into it. If somebody else wanted to view the drive they could just plug it into their computer. The only way to secure it would be to encrypt the drive directly. Does that make sense?
    – JBallin
    Commented Mar 7, 2017 at 21:23
  • not quite. While I understand that I can't prevent the drive from mounting while logged in as guest, expect that restricting the permissions for the "enclosed items" on that drive should prevent the files on the drive from being read.
    – Macondo2Seattle
    Commented Mar 7, 2017 at 21:27

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