Repairing disk permissions is a troubleshooting activity commonly associated with the Mac OS X operating system. The efficacy of repairing permissions to troubleshoot application errors has been debated.
The BSD layer in Mac OS X (and Darwin) is responsible for file-system security, including the management of the Unix (POSIX) permissions model. Applications depend on the correct assignment and interpretation of permissions in order to function properly.
Repairing permissions involves checking the permissions of a set of files and folders on a volume with Mac OS X installed against a list of correct POSIX permissions and correcting any discrepancies. The list of correct permissions is compiled by consulting the various bill-of-materials (.bom) files. Typically, these files are stored within reduced-size Installer package (.pkg) files in the Receipts folder in the local Library folder (/Library/Receipts) on the volume being checked. Whenever a user installs software that uses the Mac OS X Installer package format, a bill-of-materials file is created which can be consulted for future permission repair.
Files whose permissions have been incorrectly altered by an administrator, an administrator operating with root privileges, or a poorly designed installer package (installed with similar privileges) can cause a wide array of problems ranging from application errors to the inability to boot Mac OS X. Repairing permissions can become necessary, but has become increasingly less so for versions of Mac OS X after Panther (10.3).
A permissions repair can be performed using Disk Utility (/Applications/Utilities/Disk Utility.app) by selecting a Mac OS X startup volume and clicking the Repair Disk Permissions button in the First Aid section. A verification procedure, which will only check permissions, but not perform repairs, is also available. Both operations can be performed by using the diskutil command-line utility, which can be executed via local Terminal or remotely via SSH or the Send UNIX Command in Apple Remote Desktop:
diskutil repairPermissions /Volumes/<disk name>
- Gruber, John. "Seriously, ‘Repair Permissions’ Is Voodoo". Daring Fireball. John Gruber. Retrieved March 13, 2009.
- "Security Overview: Permissions". Developer. Apple Inc. Retrieved April 4, 2007.[dead link]
- "About Disk Utility's Repair Disk Permissions feature". Knowledge Base. Apple Inc. Retrieved April 4, 2007.
- Darwin and Mac OS X System Manager's Manual –