Mac OS X - Using Disk Utility to Repair a Disk

This document explains how to use Disk Utility in Mac OS X to repair a disk. Disk Utility is included with OS X and can be used to repair system file permissions and minor errors in a disk's directory structure. It is located in the Utilities folder within the Applications folder on the hard drive. Disk Utility can also be run from a Mac OS X installation disc or recovery partition.

Repair Disk

Disk Utility cannot repair the directory structure of the active startup disk but in Mac OS X 10.4 or newer it can verify the active startup disk. To repair an OS X system disk with Disk Utility, you must startup the computer using the recovery partition. Restart the computer and hold the O key when you hear the startup sound. You can release the key when the boot options appear. Select "recovery" to boot to your recovery partition.

Gray Apple at startup

It is normal for the computer to take longer to startup to a recovery partition. If you are prompted to select a language and you do not see the menu bar at the top of the screen, click the right arrow button to proceed to the next screen.

Select language

The method of opening Disk Utility varies depending on the version of OS X.

Mac OS X 10.2.x through 10.3.x:
Select Open Disk Utility from the Installer menu at the top of the screen.
Installer menu
Mac OS X 10.4.x through 10.6.x:
Choose Disk Utility from the Utilities menu at the top of the screen.
Utilities menu
Mac OS X 10.7.x through 10.9.x:
Choose Disk Utility from the OS X Utilities menu, then click continue.
Utilities menu

The Disk Utility window should look similar to the picture below. Select the name of the hard drive (e.g. Macintosh HD) on the left side of the window and click the First Aid tab if it is not already selected. To check the directory of the disk and attempt repair of any problems found, click the Repair Disk button. If it finds any problems, it will list them. Otherwise, it will say "The volume Macintosh HD appears to be OK."

Note: If no disks are found, it may be an indication of a more serious problem. Call the DoIT Help Desk at 264-HELP (608-264-4357).

Note: If it does find any problems, you should click Repair Disk to scan again. If it finds the same problem(s) during the second scan, it means Disk Utility cannot repair the disk and a more advanced utility is required. Call the DoIT Help Desk at 264-HELP.

Disk Utility - Repair Disk

Repair Disk Permissions

System file permissions can be verified or repaired on the startup disk so it is not necessary to restart to your recovery partition. To check and repair system file permissions, select the name of the hard drive on the left and click the Repair Disk Permissions button.

Disk Utility - Repair Permissions

S.M.A.R.T. Status

Some hard drives are capable of reporting problems before a hardware failure occurs. This is known as Self-Monitoring, Analysis and Reporting Technology or S.M.A.R.T. A hard drive's S.M.A.R.T. status (if available) is only displayed when the the drive (e.g. 57.3 GB IBM IC35L060A...) is selected on the left side of the window.

Select drive model from list

The version of Disk Utility included with Mac OS X 10.4 or newer can display the S.M.A.R.T. status while running from a CD/DVD or the hard drive. The 10.3 version only reports S.M.A.R.T. status while running from the hard drive. The version of Disk Utility in 10.2 does not report S.M.A.R.T. status.

In Mac OS X 10.3 or newer look for the S.M.A.R.T. Status at the bottom of the Disk Utility window. If this line is missing, it means the drive does not support S.M.A.R.T. If the status is Verified, it means the hard drive is probably functioning properly (although there may still be directory issues that S.M.A.R.T. does not check). If the status is Failing, you should backup your data and replace the hard drive.

Device information with S.M.A.R.T. status

Keywords: MacOS OS os X osx Macintosh disk disc utility first aid repair permissions privileges scan hard drive fireball   Doc ID: 3810
Owner: Jeff W.Group: DoIT Help Desk
Created: 2005-07-04 19:00 CDTUpdated: 2014-06-10 12:50 CDT
Sites: DoIT Help Desk, Southern Illinois University Edwardsville