I have a retina MacBook Pro, and I am currently running macOS via USB from an external drive. I would like a way to prevent programs that I install on the external drive from writing files to the actual internal drive. To do this, I thought of unmounting the internal drive, in order to prevent files from being written to it, but in Disk Utility it seems as though it's not possible to "unmount" the internal drive. Is there any way I can unmount it, or even make sure that no program installations (via pkg files) have access to the internal drive?

  • 1
    What about using diskutil from Terminal, e.g: sudo diskutil unmountDisk disk0 – user3439894 Feb 3 '17 at 16:00
  • Wow, how simple! And I didn't find anything after much searching. It was disk1 for me, though. Would there be any risk of damage if I unmounted the disk? I'm scared of causing problems, because I almost feel like this was left out of Disk Utility's GUI for a reason... – user223178 Feb 3 '17 at 17:03

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