I have three Macs at the house and have the same user account setup on each of them. The users on two of the machines were initially set up using migration assistant to transfer user accounts.

When accessing the Advanced Options menu under System Preferences > Accounts > > Advanced Options, I notice that the UUIDs on each machine are different. The User ID and Group values are identical.

Question: should the user UUID (different than UID) be set to the same on each of the computers? Any disadvantage if they are not? Does OS X use the uid (e.g. 501) to determine if the users on two different machines are the "same"?

  • 1
    My guess: If migration assistant assigns a new UUID when you migrate a user to a new machine, I don't think you should mess with that. And regarding your final question: I don't know if OS X ever does determine that two users on two different machines are the same. It would be scary if any file sharing protocol ever made that decision based on uid, for example. Jun 19, 2011 at 15:34
  • @Harald NFS does work exactly that way by default. File ownership is determined by UID. There are options to change that, like mapping root to nobody. This works fine when users are centrally managed and don't have admin access to their machines, or are trusted at some level.
    – KeithB
    Jun 19, 2011 at 19:25
  • @KeithB: Sure, but NFS is sort of an oddity in the MacOS world. Which doesn't stop me from using it at home (my fileserver runs FreeBSD). Point taken, though. Jun 20, 2011 at 7:54

1 Answer 1


UUID means universally unique identifier. It sounds like the identifiers for the three accounts are unique. In other words, the system works.


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