Safe Boot mode forces a directory check of your hard drive. This is identical to using Disk Utility’s Repair Disk or the fsck command in the terminal.
- It loads only the required kernel extensions (some of the items are located in /System/Library/Extensions)
- The cache of kernel extensions used to speed startup during normal use is ignored. (The cache file is located in /System/Library/Extensions.kextcache)
- Safe Boot only runs the Apple installed startup items (these items are in the /Library/Startup Items and /System/Library/Startup items – and these are DIFFERENT than the login items).
- Safe Boot can work around issues caused by your software or directory damage on the startup volume.
This is how you Start Up in Safe Mode:
Be sure the computer is turned off. Now press the power button. Just after you hear the startup tone, press and hold the down the shift key. Now release the shift key when you see the start up screen with the gray background with the Apple logo. During the startup, you will see “Safe Boot” on the Mac OS X startup screen.
To leave the Mac OS X Safe Mode just restart you Mac normally, without holding any keys during the startup period.