The Repair functions of Disk Utility: what's it all about?
This FAQ provides a brief overview of the Repair Disk and Repair Disk Permissions functions of Disk Utility in Mac® OS X. It is a subset of the more comprehensive information on these topics from our book, Troubleshooting Mac OS X. The following topics are addressed:
Disk Utility, located in the Macintosh HD > Applications > Utilities folder, can perform two types of repairs via the following choices in the First Aid tab:
Repair Disk verifies and, if problems are found, corrects issues with the directory on a disk or volume.
The directory is analogous to a combined address book and road map to where data is stored on a disk or volume. A volume, also known as a partition, is section of a physical hard disk which, from the perspective of the operating system, works like a separate disk. All hard disks have one or more volumes or partitions.
Keep in mind the following key points about Repair Disk:
While Repair Disk can correct a variety of directory problems, it is generally incapable of repairing severe directory corruption. Severe directory corruption can often be repaired by third-party disk utilities, such as Alsoft® DiskWarrior® and Micromat® TechTool® Pro.
Before attempting to use a third-party utility to repair a disk or volume, assure that you have the latest version of the utility that is compatible with the version of Mac OS X you are using.
For additional information about the Repair Disk and Verify Disk functions of Disk Utility, consult Disk Utility Help.
To delve into the technical details of the directory and volume structure of the Mac OS Extended disk format, aka HFS Plus or HFS+, see the Apple® Developer Connection document "Technical Note TN1150: HFS Plus Volume Format."
Repair Disk Permissions verifies and, if problems are found, resets (repairs) the permissions on Apple-originated files and folders (objects), i.e. Mac OS X system-related objects and Apple-provided applications bundled with Mac OS X. This is described in more detail in the AppleCare® Knowledge Base document "About Disk Utility's Repair Disk Permissions feature."
Repair Disk Permissions is only available for volumes on which Mac OS X is installed.
Verification compares the current permissions settings of an Apple-originated object against those specified for that object in its associated installation receipt. If the permissions of an object differ from those specified in its associated receipt, its permissions are reset to the values specified in the receipt. Where receipts are saved depends on the version of Mac OS X you are using:
Never delete files in any of the receipts folders cited above unless specifically instructed to do so by a Mac OS X troubleshoting expert.
It is important to understand that Repair Disk Permissions only verifies and repairs the permissions of Apple-originated objects with Apple-originated receipts. This means that Repair Disk Permissions will not correct permissions problems on:
Repair Disk Permissions often produces messages while it is running. These messages are generally of an informational nature and can usually be ignored. Some of these messages may be repeated every time Repair Disk Permissions is run as the receipt for the object in question is forcing the setting of specific permissions, even if no correction is required. Again, these can also be ignored. Only messages indicating the failure of the Repair Disk Permissions process, or the inability to correct permissions on a specific file or folder, should be of concern.
The AppleCare Knowledge Base document "Troubleshooting permissions issues in Mac OS X" provides some important background information about permissions. You can find additional information about permissions in the educational resources recommended in our "Learning about Mac OS X FAQ".
For additional information about the Verify Disk Permissions and Repair Disk Permissions functions of Disk Utility, consult Disk Utility Help.
Power outages, hard restarts, and system crashes can lead to disk directory corruption, requiring the use Repair Disk to correct such. File System Journaling, introduced in Panther as a default setting for your Mac OS X startup disk, can help minimize the impact of such events on the disk's directory. However, even journaling is not foolproof. For additional details, see our "Data corruption and loss: causes and avoidance" FAQ.
Run Repair Disk:
Repair Disk Permissions
Rogue installers applications that temporarily change, but fail to reset, permissions on System-related files or folders during a software installation are a primary cause of permissions-related problems. Accordingly, you should run Repair Disk Permissions after installing any third-party software that employs its own installer.
In general, given the choice between the Verify or Repair buttons in Disk Utility, select Repair to save time. Verify only checks for problems. If problems are found, you then need to run the corresponding Repair. Repair both verifies and, if problems are found, attempts to perform the required repair. Accordingly, selecting the Repair button is more efficient. Note again that you cannot use Repair Disk to repair your Mac OS X startup disk while your Mac is started up from such: see "The Repair Disk function" section earlier in this FAQ.