1. Run ‘Repair System Permissions‘ in Disk Utility.
Repairing system level permissions won’t solve the kext cache problem, but you’ll want to make sure they are all in order first. There is no need to repair ACL permissions for this procedure.
2. Open Terminal.app
Copy and paste the following:
sudo chown root:admin /
Hit ‘return’ and type in your admin password. This step ensures that the admin user has ownership permissions for everything on the startup disk.
3. Fix the kext cache permissions
Paste the following code into Terminal.app, hitting ‘return’ again and supplying the password if requested (if you do this shortly after step 2 you may not be asked for the password again):
sudo touch /System/Library/Extensions
4. Clear Console log and restart
The next two steps aren’t strictly necessary, but are good practice. Open Console.app, click ‘All Messages’ in the sidebar and hit the ‘Clear Display’ button in the Tool bar. Now, restart your mac.
5. Check for the problem
See if the procedure was successful by opening Console.app again, choosing ‘All messages’ in the sidebar and typing
in the filter/search bar over on the right. If you carried out the procedure above correctly, it shouldn’t return any ‘can’t create kext cache / user isn’t root’ messages since the restart time.
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