Repairing disk permissions in OS X (Yosemite and earlier)

Permissions are file settings that affect the ability to read, write, or execute (open or run) the file. If a file's permissions are no longer set correctly, software that uses the file (such as Serato DJ) might not work correctly. You can see a file or folder's permissions in the Sharing & Permissions section of its Get Info window.

In OS X Yosemite and earlier, Disk Utility can repair file permissions on a startup disk. Beginning with OS X El Capitan, system file permissions are automatically protected. It's no longer necessary to verify or repair permissions with Disk Utility on OS X El Capitan and later (although you can still do it using Terminal if required).

Repairing Disk Permissions on OS X Yosemite and Earlier

Follow these steps in OS X Yosemite or earlier:
  1. Open Disk Utility, which is in the Utilities folder of your Applications folder.
  2. Select the startup disk from the list of volumes.
  3. Click the First Aid tab.
  4. To check for incorrect permissions, click Verify Disk Permissions.
  5. Once the verification is finished, click Repair Disk Permissions to repair the incorrect permissions.

Reset your computer's PRAM

After verifying and repairing any incorrect permissions you have on your drive it's a good idea to reset your computers PRAM.
Follow the steps here to reset your computer's PRAM on OS X.
Note: Resetting PRAM may change some system settings and preferences. Use System Preferences to restore your settings.