How & Why to Repair Disk Permissions in OS X with Disk Utility http://revealedtech.com/tips-solution/how-why-to-repair-disk-permissions-in-os-x-with-disk-utility/

Repairing Disk Permissions is a simple procedure that Mac users can run with the Disk Utility app or through the command line, and, as the name suggests, it repairs the permissions of various files on the target drive. Repairing permissions can be helpful when troubleshooting some fairly specific issues, or after installing or uninstalling a set of Mac applications that may have erroneously modified permissions somewhere on a drive. This is a largely misunderstood process, so we’re going to shine some light on it, and if you’re unfamiliar, how to resolve permissions issues with the repair procedure.

We’ll discuss why you may want to repair permissions in a moment, but aside from resolving some specific permission related issues with files or folders in OS X, whether user attributed or caused by modifying of removing software, the permission repair function is greatly misattributed and is rarely the panacea of troubleshooting remedies that you may see ascribed to it, though that doesn’t suggest that you should not incorporate it into part of an occasional maintenance routine for a Mac. Do keep in mind that when you’re updating OS X, the repair permissions procedure is kicked off on it’s own.

First, let’s learn how to both repair and verify disk permissions (the latter of which really isn’t necessary), and then let’s learn a bit more about the process itself and why it would even be necessary.

Repairing Disk Permissions with Disk Utility in OS X

This will repair any discrepancies in permissions found with various files and folders on the target disk connected to the Mac. You can do this with a boot volume or external drive, or both, it doesn’t matter which.

1. Open the Disk Utility application in OS X (located in /Applications/Utilities/)


2. Select the disk from the left side menu to repair permissions for


3. Go to the “First Aid” tab and click the “Repair Disk Permissions” button and let the process run from start to finish – this may take a while depending on the size and speed of the hard drive

You will likely see multiple messages stating that various files and directories have been “Repaired” after finding differing permissions, which will look something like this:

Permissions differ on “Applications/.DS_Store”; should be -rw-rw-r– ; they are -rw-r–r–

Repaired “Applications/.DS_Store”

Group differs on “Library/Printers/PPDs/Contents/Resources”; should be 80; group is 0.

Repaired “Library/Printers/PPDs”

When finished, you will see a “Permissions repair complete” message appear in the Disk Utility console. If you have multiple hard drives or volumes attached to the Mac, you may as well run the process again on the other drive while you’re in here.

Verifying Disk Permissions on a Mac with Disk Utility

The verification process can usually be skipped, all it does is check to see if there are any improper permissions issues that can be resolved with the repair function. Nonetheless, it can be good practice to run the verify procedure anyway, but since in the repair process things will be verified anyway, we’ll cover it second:

1. If you haven’t already, open the Disk Utility app, found in the /Applications/Utilities/ folder (or accessible through Spotlight by hitting Command+Spacebar)


2. Select the disk in question that you wish to verify permissions for


3. Under the “First Aid” tab, click the “Verify Disk Permissions” button and let the process run

Nearly all Mac users who run verify (or repair) will discover that some permissions are off, usually with obscure files in the temporary or Library folders, thus don’t be alarmed if you see things pop up with messages like:

“Group differs on “Library/Printers/PPDs/Contents/Resources”; should be 80; group is 0.”

“Permissions differ on “Applications/.DS_Store”; should be -rw-rw-r– ; they are -rw-r–r– “

If you do see any differing permissions, go ahead and run the Repair function next. Or you can jump straight to repair without verifying, there is no harm in doing so.

Why Repair Disk Permissions on a Mac?

Permissions for some files and folders will inevitably change, whether because a user modified the permissions of a file or folder that they shouldn’t have, or because of the installation or removal of an application or utility. Taking the latter example, sometimes installing and uninstalling an application can result in some files with specific permissions being changed from, say, only being writable by the active user to being universally writable (or not writable at all), or vice versa, thus leading to some permissions errors when that file is being accessed in the future. In most cases, these inconsistencies with specific file permissions won’t impact applications, performance, or anything else notable on the Mac, but in some relatively rare circumstances they can cause trouble, leading to either erroneous behavior in OS X. In an extreme example of a problem generated by improper permissions, the completely broken display of system fonts showing up as wild characters rather than the text you’d expect to see can be result of the system fonts folder having improper permissions and being attributed to the wrong user or group.

Because differing permissions on files or folders, either with or without consequences, is nearly guaranteed to happen over time when using a Mac and installing and uninstalling a variety of applications, repairing permissions is worthwhile on an occasional basis. Feel free to add it to the list of maintenance to perform on some semi-regular basis for a Mac, just don’t expect it to perform any miracles or speed up your Mac, that’s just not how it works.

And yes, the permissions repair process is identical in all versions of OS X with the Disk Utility app, regardless of whether the Mac is running Yosemite, Mavericks, Mountain Lion, Tiger, Leopard, or whatever else. Similarly, the process works whether you’re booted normally, in single user mode, or from a repair drive.

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How & Why to Repair Disk Permissions in OS X with Disk Utility