Repair Disk Permissions
OS X provided Mac users with a new modern operating system with the old foundation of UNIX. One of the benefits of UNIX is it's multi-user capablity. To manage the users of the system, UNIX uses file ownership and permissions. Ownership and permissions is a large subject unto itself, so we will not address the details here. Look for a tutorial in the future or go to osxfaq.com for additional reading.
Occasionally in OS X some key file ownership and permissions get changed for whatever reason by applications and more frequently, program installers. When ownership and permissions get changed, things just don't work as they should. The symptoms might be programs quitting unexpectedly, preferences not being remembered, programs not launching, etc. This is where Repair Disk Permissions utility comes in. This utility, which is part of the Apple Disk Utility program, corrects the ownership and permissions according to Apple specifications. Frequently, this corrects many system and program errors. Repair Disk Permissions is a OS X specific utility and UNIX does not have such issues. Hopefully, this a concern and procedure that will go away in the future.
To repair permissions, open the Disk Utility program found in the Applications>Utility folder on your hard drive root level directory. At the top of the Disk Utility window is a row of tabs. Click on the First Aid tab. On the left is a list of the disk and volumes mounted on your computer system. In the example below, I have two mounted volumes - one named SHHD and another named Media.You will need to click on your boot volume to select it. Only boot volumes can have permissions repaired.
If the buttons labeled "Verify Disk Permissions" and "Repair Disk Permissions" are grayed and not selectable, you have not selected the boot volume or you are not a system administrator. To allow system administrator approval to repair permissions, click on the padlock button on the lower left and enter a system administrators name and password.
Once you have selected a boot volume and have system administrator privileges, you can go ahead and click on the Repair Disk Permissions button. You will see the process begin with messages in the center window and a progress bar below it. This process may take a while so it may be a good time to go for coffee.
Once done, you can quit the Disk Utility program. You do not have to reboot the system for the changes to be effective. It is recommended that you repair your disk permissions after installing new programs or once every month or so of normal usage.