Tuesday, February 1, 2022

Should You Ever Repair Permissions?

Howard Oakley:

One of the less-recognised benefits of SIP was that it effectively prevented this from happening, although improvements in system installers undoubtedly played their part as well. The signed and sealed System volume in Big Sur and Monterey is an even better guarantee that everything on that volume must now be in perfect condition.


El Capitan provided a short break from repairing permissions. Once Sierra had been released, Apple quietly posted a support note (long since removed, and not archived) recommending a new procedure, which could fix a long list of problems[…]


In March 2020, Apple changed the procedure again, to running a new tool repairHomePermissions in Recovery mode, then reinstalling macOS. By June 2020, Apple had removed its support note, silently erasing all trace of these procedures.


The problems that Apple originally attributed to damaged permissions on preference files often arose without any mishandling on the part of the user, nor by apps. The only explanation which fits the facts is that those problems were attributable to bugs in cfprefsd which became prominent in Sierra, and lingered for a couple of years.

I continue to get lots of customer support requests due to messed up file permissions, ownership, and ACLs. Many of these seem to be caused by incorrect manual migrations or restorations from backup. I’m not sure whether these could have been fixed using the Repair Home app, as I had forgotten it existed.


Update (2022-11-30): Howard Oakley:

The big mystery is the repairHomePermissions tool. While this is present in Ventura, it has no man page, no usage information, and proves to be a launcher for an app that doesn’t even exist outside Recovery mode. Neither can I find an Apple Support article that mentions it any more.

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Same for me, I get sporadic cases where data or preferences are not being saved, and I suspect they fall in to two classes. One is, as you note, incorrect manual migrations or restorations from backup. The other I suspect is corrupted preference files. It’s plausible that these are also caused by broken migrations or restorations, but I suspect there are cases where the permission API can correct the preference files.

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