Repair permissions in OS X
When a Mac is having problems saving files, opening files, or hanging on a procedure, it sometimes is the case that the process/user doesn't have permission to do what it wants to the file.
Repair Permissions is the appellation for the automatic repair of permissions that is a feature of Disk Utility, as well as other utilities in OS X. Here I'll list some special repair permission tricks.
In OS 10.5 and up, files have an access control list (ACL), besides the standard UNIX permissions. This list can get corrupted, and can be repaired by Disk Utility as part of Repair Disk, but it doesn't handle user folders. For that, you need one of a couple different utilities, depending on what version of OS X you're running.
Lion repair ACLs
- Restart Lion, and before you hear the chime, hold down the Command and R keys. This key combo tells any computer with Lion up to start from the recovery partition, from which you can do repairs, use Terminal, or install OS X.
- You’ll be at the Repair Utilities screen. Click the Utilities item in the Menu Bar, then click Terminal.
- In the Terminal window, type resetpassword and hit Return.
- The password reset utility window launches, but you’re not going to reset the password. Instead, click on icon for your Mac’s hard drive at the top. From the dropdown below it, select the user account where you’re having issues.
- At the bottom of the window, you’ll see an area labeled Reset Home Directory Permissions and ACLs. Click the Reset button there.
The reset process takes just a couple of minutes. When it’s done, exit the programs you’ve opened and restart your Mac.
Leopard and Snow Leopard repair ACLs
See Apple's guide: http://support.apple.com/kb/TS1334
Apple's earlier guide explains what permissions are and what repairing them does: http://support.apple.com/kb/HT2963
