Repairing disk permissions is a troubleshooting activity commonly associated with the OS X (formerly Mac OS X) operating system by Apple Inc. The efficacy of repairing permissions to troubleshoot application errors has been debated.
The BSD layer in 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 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 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 OS X. Repairing permissions can become necessary, but has become increasingly less so for versions of the OS after Panther (10.3).
In OS X El Capitan, Apple introduced a security feature called System Integrity Protection. With it enabled, root privileges are no longer able to change system files and folders, including their permissions. Permissions repairs are instead performed automatically upon system installs and updates. To that end, Disk Utility as well as the corresponding diskutil command-line operation lost the ability to repair permissions.
In systems prior to OS X El Capitan, a permissions repair can be performed by selecting an OS X startup volume and clicking the Repair Disk Permissions button in the First Aid section of Disk Utility. A verification procedure, which will only check permissions, 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>. In OS X El Capitan, the command-line utility
pkgutil can verify and repair permissions of installed packages, but cannot modify permissions of files and folders protected by System Integrity Protection.
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