A hard drive on a Mac follows the permissions guidelines set down by the OS X operating system, such as who can delete or modify a file or program copied to the drive. Change the permissions on an external Mac hard drive in just a few minutes. No software is needed because the permissions functions are built into the OS X operating system, and have been since version 10.3. The procedure is straightforward and takes just a few minutes.
Double-click on the icon of the external hard drive that is on the Mac’s desktop. Click once on a file or folder in the window that appears.
Select “Get Info” from the “File” drop-down menu at the top of the screen.
Click on the icon of the padlock in the lower-right corner of the window that appears. Enter your administration password into the “Password” column of the pop-up window that appears. Click the “OK” button to close the pop-up window.
Click on the arrow that is at the left side of the “Sharing & Permissions” tab near the bottom of the window. Change the drop-down menus below the “Privilege” tab to “Read & Write,” “Read Only” or “No Access.”
Click on the padlock icon again to lock in the changes. Close the window by clicking on the red button at the upper-left corner.