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 be used to Verify and Repair disk permissions. 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 above, as this is done routinely on the start up disk. You can use first aid to do this manually for external hard drives. 

 

Repairing Disk Permissions with First Aid on OS X El Capitan and above

Follow these steps in OS X El Capitan or above:

1. Open Disk Utility, which is in the Utilities folder within your applications folder. 
2. Select the Hard Drive you would like to check from the list of volumes.
3. Click the 'First Aid' button
4. When prompted if you would like to run First Aid, click run. (Note: If after doing this a second dialog box appears saying "First Aid needs to temporarily lock the boot volume" Click Continue
5. Once this is completed, click Done If you would like more info about the state of your before first aid was run, click Show Details. 

 

Repairing Disk Permissions on OS X Yosemite and Earlier

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.