Apple’s Disk Utility is installed automatically with every Mac OS X installation. You’ll find it in this folder:
(your hard disk) > Applications > Utilities > Disk Utility
While Disk Utility is most commonly used to initialize, format, and partition disks, it also verifies and repairs the integrity of disks and disk permissions.
When your Mac behaves strangely, Disk Utility can often help resolve the problem.
Disk permissions are used to control who can access each file and folder on your Mac. Some files and folders should only be accessible by Mac OS X itself, some to individual programs, some to the current user (you), and, if there are multiple user accounts on your Mac, some to each of the other user accounts. Other files should be accessible to everyone. Incorrect disk permissions, particularly on the startup disk, can cause strange behavior. Disk Utility can often resolve the problem.
1. Double-click the disk utility icon to open Disk Utility.
2. Click on the name of your startup disk in the column at the left side of the window. Then click the Repair Disk Permissions button. When the repair is complete quit Disk Utility…you’re done.