What does Repair Disk Permissions do?
Every file, folder and program on your hard drive has associated permissions that specify which users can read, write, or run that file. For example, you can set up your computer so that your cat can’t delete your dog’s files. These complex permissions can become confused or corrupt, and even administrators can be prevented from opening programs. When your system was first installed, and every time you install an application or an update, the installer leaves a receipt on your system. This receipt (in /Library/Receipts) lists what files were installed, where, and what the permissions were supposed to be. (The receipt files are optimized for computer use, and aren’t easy for users to read.) The Repair Disk Permissions function reads all these receipts, and attempts to reset the files on your disk to match their state at installation. This can be quite useful.
