Q&A: Who owns my old backups?

Q Following a system restore on my MacBook, running OS X 10.6.8, I have lost permission to access backups prior to the restore. How can I fix this?

A This most probably occurred because during the restore you have been added as a new user additional to the original user.

Although your user name may be the same, OS X knows users as numbers, typically making the first admin user 501. You may discover that your current numeric ID is 502.

Under the standard permissions set for folders in the Backups.backupdb folder used for storage by Time Machine, this would be seen as a different user, hence lacking permissions to access those backups.

Sometimes you can prevent this from happening during a system restore, but once it has occurred the only reliable way to address it is to change permissions on the affected folders.

If you had a tame Unix wizard to hand, there are some neat command line tricks they could use, but they are not for us lesser mortals: you would do best to manually change these as you need. Although a tedious task, this should not put any of those backups at risk, and over time they will get fixed.

Comments If you have Directory Utility, normally installed in /System/Library/CoreServices/Applications, available, you can browse system-level information including the numeric IDs used internally by OS X for existing users and groups. These are the same numeric IDs used by command line tools such as chown, but hidden from the Finder.

Updated from the original, which was first published in MacUser volume 30 issue 01, 2014.