Recently, I had my hands on a problematic macbook pro that often freezes up for unknown reasons, then, just as I disabled its wireless device directly from the terminal as the device isn’t responsive when I tried to turn it on through its graphical interface, it freeze up so I have to hard reset it. When it boots up and after all the services were initialized came another problem, it’s not showing up the login screen anymore and the login window server just keeps on re-spawning. It only displayed a blue screen too with the wheel icon spinning endlessly.

I then restarted the macbook pro then start it on a single-user mode (press command + s on start-up) to find clues for the problem using the commands below.

tail -200 /var/log/system.log | more

Using the above command, I found out that loginWindow service keeps on exiting and throttling while hinting to an authorization file access problem, meaning it’s not able to read the authorization file for some reason. The system.log showed this error when I checked it:

Login Window Started Security Agent
Login Window - Returned from Security Agent
AuthorizationRef returned errAuthorizationDenied. Exiting

To fix this problem, replace the /private/etc/authorization file by the authorization~previous file that is also located on the same folder which is /private/etc. If you have an OS X install disk around then you can mount and copy the authorization file from /Volumes/osx/private/etc/authorization and replace the corrupted file.