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What Does The Repair Function Of Disk Utility Do?
When the Apple installer is used to install software, the installation package (.pkg file) leaves a receipt, which is a smaller package containing information about all the installed files, including their permission information.
The Repair functions of Mac's Disk Utility examines and performs permission repairing of folders and files those have their permissions corrupted, and changes them to match with the original/best settings.
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What Causes Permissions To Change?
Some people claim that permissions change on their own. This is false because there is always something or someone that causes permissions to change. Permissions can be changed in many ways, for example:
System crashes, power interruptions or heavy folder activity can cause disk corruption and thus increase the risk for permissions to change.
Bad backup utilities:
If the backup utility you use does not fully support permissions or itself has no appropriate rights to write system level files, restoring files may result in permissions related problems.
Bad installers can alter permissions on files or directories and this is often the main cause of permissions problem.
Some software temporarily change file permissions but then don’t reset them later.
There are even more ways for permissions to be changed than these. If your Mac ever behaves abnormally, you should consider permissions problem as a possible cause for this.
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Why Is It Necessary To Repair Permissions?
If permissions on specific files are not set correctly, you can face problems when Mac OS attempts to access them. For example, you may experience trouble printing documents, launching applications, logging into your account, etc. Similarly, if a third party or Apple application requires access to a folder or file and their permissions are not set correctly, the application might not run properly. In such a situation, the Repair Disk Permissions feature of Disk Utility can repair such problems.
Many system files have permissions set for certain applications or users, so that these files can’t be accessed by others. But if these permissions somehow get altered so that accessing these files is no longer denied, repairing permissions can fix this issue.
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Should I Repair Permissions As Routine Maintenance?
An incorrect permission neither leads to another incorrect permission nor does it cause data loss in most circumstances. It is also true that permissions problems occur much less in the latest versions of Mac operating systems; Mac OS X 10.3 and later. However, we know the principle “Prevention is better than cure"; we should avoid any inconvenience by making preparations for it beforehand. In the case of permissions, it is always good to check for incorrect permissions on a regular basis so that any future, unexpected problem can be avoided. Apple too recommends that permissions should be repaired as early as possible lest noticeable symptoms start to occur.
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How Do I Repair Permission ?
The Disk Utility program in Mac OS X comes with the Repair Disk feature. It lets you repair corrupted/altered permissions on files and folders. To use the Disk Utility, launch it from the Utilities Folder, select the disk you want to check (usually the startup disk), click on the First Aid tab then click on the Repair Disk Permissions button at the bottom of the screen.