Incorrect file permissions are one common reason for a Mac computer to run more slowly than normal. When you install an application on your computer, a file called the "Bill of Materials" appears on the Mac. This file acts as a "receipt" that indicates which files are used by the application, and what the user permissions are for each file. Sometimes, these file permissions can change or be lost, which makes it difficult for your computer to run applications. You can use Apple's Disk Utility program to detect these permission errors, and automatically repair them to speed up your system.
Click the "Finder" icon on the Dock. Select "Macintosh HD" on the left side of the window, then click "Applications."
Select "Utilities" and then "Disk Utility." Click the name of your hard drive from the list on the left side. Click the "Show Details" check box.
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Click "Verify Disk Permissions." Wait for the utility to scan your hard drive. Any detected problems appear in the section under "Show Details."
Press "Repair Disk Permissions." Again, wait for your Mac to scan and fix the detected problems. Close the utility window after the repair is complete.