Using Mac OS X, how do I repair permissions, and what does that do?

Note: This document assumes you are using Mac OS X 10.2 or later.

Mac OS X is based on OPENSTEP technology, which is similar to Unix. As in Unix-based systems, Mac OS X assigns specific access privileges, known as permissions, to each of your programs, folders, and documents, which are associated with a particular owner, a group, or groups. When an error in your permissions settings occurs, it may cause significant problems. For example, your applications may not launch or your system may respond sluggishly. These problems are more likely to occur after you update your operating system or install new software.

To improve your system's performance, use the permissions repair function in OS X's Disk Utility program:

1. To open Disk Utility, from your Applications folder, open your Utilities folder and double-click the Disk Utility icon.
   
   
2. In the column on the left, click your startup disk's icon.
   
   
3. Click the First Aid tab, and then click Repair Disk Permissions. Disk Utility will reset any files and folders with incorrect settings.

Note: If your system's errors are occurring with a third-party application that did not use Apple's installer, a permissions repair may not fix everything. If you follow the steps above, and your application still does not launch, you may need to uninstall or throw away problematic applications and then reinstall them. For more information on removing applications in Mac OS X, see In Mac OS or Mac OS X, what steps should I use to remove an application?

For more information about how permissions work in Mac OS X, see Troubleshooting permissions issues in Mac OS X in Apple's knowledge base.

Also see:

• In Mac OS and Mac OS X, what is the PRAM, and why would I want to zap it?
• On a Mac OS or Mac OS X computer, how do I rebuild the desktop, and why would I want to?
• In Mac OS X, what is First Aid, and when and how should I use it?
• In Mac OS X, how do I quit an application that isn't responding?