Using Safe Boot Mode in Mac OS X

Booting into safe mode in Mac OS X is just a matter of holding down the shift key during system start, it’s helpful for troubleshooting a problematic Mac and does a number of things:

* Disables all startup & login items
* Loads only essential kernel extensions
* Disables all third party fonts
* Deletes font caches
* Forces a directory check (like Disk Repair)
* Removes a dynamic loader cache which can cause problems after a System Update
* Disables Quartz Extreme accelerated graphics

Basically if a Mac functions fine in Safe Mode but things are going wrong during a normal boot, something is obviously going wrong in the startup process, and safe mode helps you to narrow down the cause. It’s not something I’ve had to use often, but there’s been at least two occasions where machines were hanging upon loading the Finder and a funky 3rd party login item was to blame. If you ever get a blank blue screen after System Update, booting into Safe Mode will often resolve this by deleting the caches.

You can read more about Mac OS X’s Safe Boot Mode at Apple’s Knowledge Base