If you’ve ever done much Mac troubleshooting, you’ve probably heard about “repair disk permissions” as a solution. Most users don’t deal with permissions at all, so this can be a baffling idea. What are permissions, and why should you repair disk permissions on the Mac?
Why should users repair disk permissions?
macOS is based on Unix, and like Unix, it’s dependent upon permissions. Every file and folder comes with a set of permissions. These permissions indicate which users or applications can interact with that file and how they can interact. Files can have a range of permissions indicating which users can read, write and execute the file, as well as other more nuanced options. While this might seem unnecessary for an individual user’s laptop system, it’s actually a critical part of the operating system’s functionality. Even today permissions are an important part of the macOS infrastructure.
In older versions of macOS apps could change the permissions for files and folders in the home directory pretty easily. As a result, permissions in the home directory could get erroneously changed and corrupted. These incorrect permissions could cause all kinds of strange problems, making applications function incorrectly and spouting all sorts of strange bugs. With incorrect permissions applications and services could be denied access to essential files, causing them to crash or operate unusually. However, on a modern macOS system, home folder permissions are locked, meaning they can’t easily be messed with anymore.
The “Repair Disk Permissions” function was used to return the home folder’s permissions to their expected state. Using this function, the home directory’s contents were checked against the “Bill of Materials” files found in “/var/db/receipts” and “/Library/Receipts.” By analyzing those files the operating system could determine what the home directory’s permissions should be and correct any discrepancies.
How to Repair Disk Permissions
Since home directory permissions are locked in modern versions of macOS, there isn’t a “repair disk permissions” button on macOS anymore. But you can use the “First Aid” tool in Disk Utility to accomplish essentially the same task.
1. Open Disk Utility by typing “Disk Utility” into Spotlight. You can also launch Disk Utility from “/Applications/Utilities/Disk Utility.”
2. Click on your boot volume in the pane on the left. If you didn’t rename the volume, it will be named “Macintosh HD.” On our system we named the volume “Sierra.” Make sure to select the named volume and not the disk itself. The disk will have a more cryptic technical name.
3. Click on the “First Aid” icon in Disk Utility’s toolbar to start the repair process.
4. First, read the confirmation dialog to confirm you’ve selected the correct drive, then click “Run” to start the disk repair process.
5. Read the warning message, then click “Continue.”
6. During the repair process, your computer won’t respond to your input, which is totally normal and expected. The operating system needs to lock you out of the drive to make sure it can correctly analyze the drive’s contents. Even for large drives, it shouldn’t take more than a few minutes.
7. When the process finishes, you can click “Show Details” under the progress bar. This will display a report showing everything the First Aid process accomplished. If the process finds any serious errors, it will inform you of the problem.
Don’t expect miracles from repairing your drive. Repairing your disk permissions might fix some problems with your system, but it’s not a cure-all for problems that aren’t obviously related to permissions. It won’t fix all your problems, dramatically speed up an older Mac or return your machine to “like new” condition. Furthermore, home directory permissions have been locked since El Capitan. This prevents applications from damaging permissions easily. While it’s still possible, it’s dramatically less likely, making “Repair Disk Permissions” an option most Mac users won’t need to use anymore.