In OS X Mountain Lion, I have an external encrypted HD (Mac OS, journaled and encrypted) and I want to have it only accessible for one user (or a group).

Is this possible or do I have to unmount the drive every time I close or change my session?

  • Why don't you just encrypt it using a passphrase that only the single user knows?
    – Ramhound
    Jan 3, 2013 at 15:04
  • 1
    @Ramhound that is my problem, If I switch the session to another one with the unit already mounted the encryption password is not required again, so if I enter my session, enter the password and I switch to another one the disk is accesible. I set permissions to that disk only for my user and group as suggested and problem solved.
    – emenegro
    Jan 4, 2013 at 9:45

2 Answers 2


In general, for any kind of filesystem, you can simply use file system permissions to influence who can access the files and who cannot. Simply change the permissions of the root folder of your filesystem accordingly.


Right click a Volume, uncheck 'Ignore ownership on this volume' (unlock fist).

For files created before (with 'Ignore ownership on this volume' checked). Its owner will be A under user A, and B under user B.

You need to set the file permission again to make it take effect for existing files.

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