Using Disk Utility to repair disk permissions is becoming the catch-all fix for solving system instability. It almost has reached the infamous status of rebuilding the Desktop DB in Mac OS 9. Each time something is installed from a package file a "Bill of Materials" file is created in the /Library/Receipts/ directory. Each of these ".bom" files contains a list of files and/or folders that were installed by that package, along with the proper permissions for each item. According to many Disk Utility overviews the .bom files in /Library/Receipts/ are scanned and compared to the actual permissions of each file on the local file system. In reality, it doesn't appear that this is completely true.
Theory Check
To check this theory, I used two tools, fs_usage to track file system calls & activity when Disk Utility was repairing disk permissions. The binary tool strings was used to search for text strings inside important files.
HintFile
Using fs_usage, I found that Disk Utility accessed the file HintFile.plist. It is located at:
/System/Library/PrivateFrameworks/DiskManagement.framework/Versions/A/Resources/HintFile.plist
This plist file includes permissions for Dock, Widgets, DVD Player, php files,
and libmathCommon.A.dylib in Mac OS X 10.4.5. Most commonly, the message given by the Disk Utility GUI is Using special permissions when the Repair Permissions function is used. This file appears to be used if permissions are accidentally set incorrectly be a system update
DiskManagementTool
Next, the following receipts are accessed by the process DiskManagementTool:
/System/Library/PrivateFrameworks/DiskManagement.framework/Versions/A/Resources/DiskManagementTool
The following receipts were accessed:
/Library/Receipts/BaseSystem.pkg/Contents/Archive.bom
/Library/Receipts/Essentials.pkg/Contents/Archive.bom
/Library/Receipts/AdditionalEssentials.pkg/Contents/Archive.bom
/Library/Receipts/BSD.pkg/Contents/Archive.bom
/Library/Receipts/BSDSDK.pkg/Contents/Archive.bom
/Library/Receipts/X11SDK.pkg/Contents/Archive.bom
/Library/Receipts/DevDocumentation.pkg/Contents/Archive.bom
/Library/Receipts/DevExamples.pkg/Contents/Archive.bom
/Library/Receipts/DevSDK.pkg/Contents/Archive.bom
/Library/Receipts/DeveloperTools.pkg/Contents/Archive.bom
/Library/Receipts/Java.pkg/Contents/Archive.bom
/Library/Receipts/AddressBook.pkg/Contents/Archive.bom
/Library/Receipts/Automator.pkg/Contents/Archive.bom
/Library/Receipts/Mail.pkg/Contents/Archive.bom
/Library/Receipts/MigrationAssistant.pkg/Contents/Archive.bom
/Library/Receipts/OxfordDictionaries.pkg/Contents/Archive.bom
/Library/Receipts/iCal.pkg/Contents/Archive.bom
/Library/Receipts/iChat.pkg/Contents/Archive.bom
/Library/Receipts/iTunes.pkg/Contents/Archive.bom
/Library/Receipts/Safari.pkg/Contents/Archive.bom
/Library/Receipts/AdditionalFonts.pkg/Contents/Archive.bom
/Library/Receipts/BrotherPrinterDrivers.pkg/Contents/Archive.bom
/Library/Receipts/EpsonPrinterDrivers.pkg/Contents/Archive.bom
/Library/Receipts/CanonPrinterDrivers.pkg/Contents/Archive.bom
/Library/Receipts/HewlettPackardPrinterDrivers.pkg/Contents/Archive.bom
/Library/Receipts/LexmarkPrinterDrivers.pkg/Contents/Archive.bom
/Library/Receipts/GimpPrintPrinterDrivers.pkg/Contents/Archive.bom
/Library/Receipts/ElectronicsForImagingPrinterDrivers.pkg/Contents/Archive.bom
/Library/Receipts/RicohPrinterDrivers.pkg/Contents/Archive.bom
/Library/Receipts/XeroxPrinterDrivers.pkg/Contents/Archive.bom
/Library/Receipts/ServerAdminTools.pkg/Contents/Archive.bom
However, this isn't all of the Receipts. As an example, my test system has many receipts which were not accessed for repairing permissions, roughly around 70-80 receipts.
Using the strings command, the following receipts are also included in the DiskManagementTool:
/Library/Receipts/BaseSystem.pkg/Contents/Archive.bom
/Library/Receipts/Essentials.pkg/Contents/Archive.bom
/Library/Receipts/AdditionalEssentials.pkg/Contents/Archive.bom
/Library/Receipts/BSD.pkg/Contents/Archive.bom
/Library/Receipts/BSDSDK.pkg/Contents/Archive.bom
/Library/Receipts/X11User.pkg/Contents/Archive.bom
/Library/Receipts/X11SDK.pkg/Contents/Archive.bom
/Library/Receipts/CommonAccessCard.pkg/Contents/Archive.bom
/Library/Receipts/CommonCriteriaTools.pkg/Contents/Archive.bom
/Library/Receipts/Internal.pkg/Contents/Archive.bom
/Library/Receipts/FatLibraries.pkg/Contents/Archive.bom
/Library/Receipts/DevDocumentation.pkg/Contents/Archive.bom
/Library/Receipts/DevExamples.pkg/Contents/Archive.bom
/Library/Receipts/DevSDK.pkg/Contents/Archive.bom
/Library/Receipts/DeveloperTools.pkg/Contents/Archive.bom
/Library/Receipts/Java.pkg/Contents/Archive.bom
/Library/Receipts/DevInternal.pkg/Contents/Archive.bom
/Library/Receipts/DevFatLibraries.pkg/Contents/Archive.bom
/Library/Receipts/AddressBook.pkg/Contents/Archive.bom
/Library/Receipts/Automator.pkg/Contents/Archive.bom
/Library/Receipts/Mail.pkg/Contents/Archive.bom
/Library/Receipts/MigrationAssistant.pkg/Contents/Archive.bom
/Library/Receipts/OxfordDictionaries.pkg/Contents/Archive.bom
/Library/Receipts/iCal.pkg/Contents/Archive.bom
/Library/Receipts/iChat.pkg/Contents/Archive.bom
/Library/Receipts/iTunes.pkg/Contents/Archive.bom
/Library/Receipts/MicrosoftIE.pkg/Contents/Archive.bom
/Library/Receipts/Safari.pkg/Contents/Archive.bom
/Library/Receipts/AdditionalFonts.pkg/Contents/Archive.bom
/Library/Receipts/AdditionalAsianFonts.pkg/Contents/Archive.bom
/Library/Receipts/BrotherPrinterDrivers.pkg/Contents/Archive.bom
/Library/Receipts/EpsonPrinterDrivers.pkg/Contents/Archive.bom
/Library/Receipts/CanonPrinterDrivers.pkg/Contents/Archive.bom
/Library/Receipts/HewlettPackardPrinterDrivers.pkg/Contents/Archive.bom
/Library/Receipts/LexmarkPrinterDrivers.pkg/Contents/Archive.bom
/Library/Receipts/GimpPrintPrinterDrivers.pkg/Contents/Archive.bom
/Library/Receipts/ElectronicsForImagingPrinterDrivers.pkg/Contents/Archive.bom
/Library/Receipts/RicohPrinterDrivers.pkg/Contents/Archive.bom
/Library/Receipts/XeroxPrinterDrivers.pkg/Contents/Archive.bom
/Library/Receipts/QuickTimeStreamingServer.pkg/Contents/Archive.bom
/Library/Receipts/ApplicationsServer.pkg/Contents/Archive.bom
/Library/Receipts/ServerFatLibraries.pkg/Contents/Archive.bom
/Library/Receipts/ServerInternal.pkg/Contents/Archive.bom
/Library/Receipts/ServerAdminTools.pkg/Contents/Archive.bom
/Library/Receipts/ServerSetup.pkg/Contents/Archive.bom
/Library/Receipts/ServerEssentials.pkg/Contents/Archive.bom
Conclusion
From this evidence, the Disk Utility Repair Permissions function fixes permissions on a very narrowly defined set of receipts. If the total receipt number is counted on an average machine, only between 30 and 40 percent of the Receipts are actually examined in repairing permissions. When closely examined, most of the Receipts are those that were created by the initial install of Mac OS X. In fact, running Repair Permissions could actually create incorrect permissions, restoring permissions that may have been faulty in the initial installation of the operating system.
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