Safe Mode (to Safe Boot) OS X

To start up into Safe Mode (to Safe Boot), do this:

  1. Be sure the computer is shut down.
  2. Press the power button.
  3. Immediately after you hear the startup tone, hold the Shift key. The Shift key should be held as soon as possible after the startup tone but not before.
  4. Release the Shift key when you see the gray Apple icon and the progress indicator (looks like a spinning gear).

During startup in Mac OS X 10.4 or later, you will see “Safe Boot” on the login window, which appears even if you normally log in automatically.

During startup in Mac OS X 10.2 through 10.3.9, you will see “Safe Boot” on the Mac OS X startup screen.

To leave Safe Mode in any version of Mac OS X, restart the computer normally, without holding any keys during startup.

Starting up into Safe Mode does several things:

  • It forces a directory check of the startup volume.
  • It loads only required kernel extensions (some of the items in /System/Library/Extensions).
  • In Mac OS X 10.3.9 or earlier, Safe Mode runs only Apple-installed startup items (such items may be installed either in /Library/StartupItems or in /System/Library/StartupItems; these are different than user-selected account login items).
  • It disables all fonts other than those in /System/Library/Fonts (Mac OS X 10.4 or later).
  • It moves to the Trash all font caches normally stored in /Library/Caches/com.apple.ATS/(uid)/ , where (uid) is a user ID number such as 501 (Mac OS X 10.4 or later).
  • It disables all startup items and login items (Mac OS X 10.4 or later).
  • Mac OS X 10.5.6 or later: A Safe Boot deletes the dynamic loader shared cache at (/var/db/dyld/). A cache with issues may cause a blue screen on startup, particularly after a Software Update. Restarting normally recreates this cache.

Taken together, these changes can help resolve software or directory issues that may exist on the startup volume.

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2 Responses to Safe Mode (to Safe Boot) OS X

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