Q&A: ‘Custom access’ to old folders

Q When I got a 2 TB external drive, I used SuperDuper! to transfer files from other drives to it. Since then some folders, even whole volumes, are shown as having ‘custom access’ in the Finder’s Get Info dialog. What does this mean, how did it happen, and how can I fix it?

A Folders in certain key parts of your startup disk, such as Library and System, have permissions that are rigorously controlled, and should be corrected by repairing permissions. Those in your Home folder and on other volumes can be set more freely by users and errant software.

When you view permissions in the Get Info dialog, the Finder explains what they mean for the current user, for example “You can read and write”. When the Finder displays “You have custom access”, it means that the current user has access other than the regular POSIX read and/or write, or the group is broken.

First you must ensure that the volume is formatted using the Mac Extended (HFS+) file system, shown when you inspect it in Disk Utility. This problem can occur when a drive was originally formatted under old versions of OS X such as Tiger, and can then usually be fixed by typing the following commands into Terminal:
sudo chflags -R nouchg /Volumes/MyDisk
sudo chmod -RN /Volumes/MyDisk
sudo chmod 775 /Volumes/MyDisk
for the volume named MyDisk. If you have cloned a drive using SuperDuper! or Carbon Copy Cloner, then this may have mirrored these permissions problems from that older drive, which might have sustained them when upgrading from Tiger.

Alternatively this could be because extended permissions flags are in use, or Access Control Lists (ACLs) have been applied. The latter can be examined and adjusted using TinkerTool System or MacPilot, as detailed here.

Updated from the original, which was first published in MacUser volume 26 issue 25, 2010.