As I detailed recently, Apple has started to recommend that users repair permissions again in Sierra. Now it is only on your Home folder, but could potentially fix quite a wide range of problems, some of which are common.

I have followed Apple’s instructions on this iMac17,1 running Sierra 10.12.5, and I am not sure that it was a good move. I hadn’t been suffering from any of the problems listed, but if the procedure works when you have problems, it should do no harm when things are working normally.

The diskutil resetUserPermissions command

I am always a little worried when running undocumented commands, as you don’t really know what they are doing, or why they are undocumented. In this case, the command ran fine, but on my huge Home folder took well over a minute to complete. It assured me that it all went fine, and I saw no error code, but it is very hard to know whether it did anything useful.

So far everything seems to be working just as it did before. However the first Time Machine backup after repairing permissions was very large and took well over an hour to complete. That suggests that permissions were altered on a large number of files and folders.

A better package: RepairHomePermissions

The Apple support note recommends users enter an undocumented command into Terminal. If that returns a specific error code, users are recommended to enter another command, then repeat the first. That is not a good way ahead for the great majority of users, many of whom simply will not use Terminal even under supervision.

I have therefore wrapped the procedure up into a little app, which guides the user through the Finder preliminaries, then runs the first command. If that returns an error of the type quoted by Apple, it then runs the second command, and tries the first again after that.

The app to do this is RepairHomePermissions, available from Downloads above.

If you feel able to test it, I would be very grateful, but caution that (whilst I believe that it should be totally harmless) this does use an undocumented command and is still in test.

After my run-in with diskutil resetUserPermissions on my main Mac, I have tried RepairHomePermissions out on my MacBook Air, which has a relatively tiny Home folder and doesn’t back up. It completed correctly in the twinkling of an eye, without error. I hope that is the case for you too.

If you are using Time Machine backups, be prepared for that large and long backup after you have repaired permissions, and be ready to restore from backup or correct permissions afterwards if the procedure breaks anything. I cannot see that it should, but…