I created a (bootable) backup disk for use in Carbon Copy Cloner and applied Filevault 2 following the CCC instructions. I am using the backup disk to transfer the files to a new computer. The old computer is running Yosemite. The new computer is running High Sierra. I have three users on the old computer, call them A, B and C. A is an administrator, the others are not. User B is the one I use as my main active user for ordinary use. I have successfully done the transfer, so the role of the backup disk is to fill in any gaps or inconsistencies that I may come across. Thus I would still like to be able to read individual files on the backup disk.

Unfortunately, the users on the two computers don't match, which complicates accessing the files.

I set up the new computer with FileVault, for which I had to create a user (administrator). I wanted it to have the same name as the administrator on the old computer; however, when I used migration assistant to transfer the files (from the backup disk, rather than directly from the old computer, which I somehow thought would be safer), it did not integrate the two administrator users, but required me to give a new name to the transferred user A. That was only an inconvenience.

The problem is that when I now try to access the backup disk from the new computer, it misaligns the users in terms of permissions. I will call the administrator that I set up initially on the new computer user A'. I migrated the files for users A and B, which have been set up on the new computer. However, when I access the backup disk,

  • the files in the /Users folder for user A on the backup disk are recognised as being owned by user A' on the new computer,
  • those for user B on the backup as owned by user A on the new computer, and /
  • those for user C on the backup as owned by user B on the new computer.

It looks as though it has somehow seen that there are three users in each case, and lined up the first user with the first set of files, and so on, without comparing the names - presumably it is looking at how the users are indexed internally.

What is the best way to sort this out? I could change the backup disk to Ignore ownership, but I am hesitant to do that, as I might want to be able to boot the old computer from it to check out some issue (as yet unanticipated). Alternatively, I could change the permissions on the /Users/[username] folder for each of the users on the backup disk setting Apply to enclosed items. If Apply to enclosed items works properly, that should solve the problem for accessing the files from the new computer, but it might also confuse the situtation should I ever try to boot from the backup disk.

  • I see that the problem arises from the fact that ownerships are tied to the UID of the user, not the user name. Both computers have users 501, 502 and 503
    – Winter96
    May 15, 2018 at 15:51
  • [completed comment] I see that the problem arises from the fact that ownerships are tied to the UID of the user, not the user name: both computers have users 501, 502 and 503, though not with the same user names. I see also that I could change the UIDs, but from the following comprehensive explanation that sounds like overkill: Change a user's User ID on Mac OS X (10.6 - 10.12) - presumably also works for High Sierra.
    – Winter96
    May 15, 2018 at 15:58


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