External drives

File ownership on external drives

Every file on your Mac belongs to a user account, but macOS usually ignores ownership on external drives. That's why moved files show you as their owner, and why Storage Studio's moves don't keep ownership — while they do keep permissions, dates and the rest.

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On your Mac's built-in disk, every file has an owner — the user account it belongs to — and permissions that say what the owner and everyone else may do with it. External drives work a little differently, and that affects what a move can keep.

macOS ignores ownership on most external drives

When you connect an external drive, macOS usually treats it as a drive you might plug into any Mac. On such a drive, the account numbers that record ownership on one Mac would mean nothing on another, so macOS sets the drive to ignore ownership. You can see this in Finder: select the drive, choose Get Info, and look for the Ignore ownership on this volume checkbox under Sharing & Permissions.

With ownership ignored:

  • every file on the drive appears to belong to whoever is using the Mac at the time;
  • setting a file's owner on the drive has no lasting effect.

On an APFS or Mac OS Extended drive, the files' permissions — read, write and run — are still stored.

What this means for your moves

Storage Studio's folder moves keep each file's permissions, dates, Finder tags and much more — see What a move keeps. They don't keep ownership, for two reasons:

  1. On a drive that ignores ownership, there's nothing to keep it in.
  2. Storage Studio moves your files as you, not as an administrator, so it can't make a file belong to a different account.
What happens to a file's owner on a trip to the drive and back

For almost everyone this changes nothing you'd notice. The folders you move are your own, and when they come back to your Mac they belong to you, just as before.

When you might notice

  • On a shared Mac. If you move a folder that belongs to another person's account, it comes back belonging to you. Move only your own folders, or have each person move their own.
  • Apps installed for the whole Mac. Some apps belong to the system account rather than to a person. The Apps window doesn't offer to move those — see Why some apps can't be moved.

See also: File ownership, What to know about exFAT drives, Drive formats.

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