Mac OS X: What is Safe Boot, Safe Mode?
Learn more about Safe Boot, a special way to start when troubleshooting.
Safe Mode is the state into which you can start up your Mac by performing a Safe Boot. To perform a Safe Boot, press and hold the Shift key immediately after your Mac starts up. Continue holding down the Shift key until a gray Apple logo appears on the screen.
Starting up into Safe Mode does several things:
- It forces a directory check of the startup volume. You may see a progress bar on the screen during this check, and the computer may take longer than usual to complete its startup.
- It loads only required kernel extensions (some of the items in /System/Library/Extensions).
- Mac OS X v10.5.6 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.
- It disables all fonts other than those in /System/Library/Fonts (Mac OS X v10.4 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 v10.4 or later).
- It disables all startup items and login items (Mac OS X v10.4 or later).
- In Mac OS X v10.3.9 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).
Taken together, these changes can help resolve software or directory issues that may exist on the startup volume.
Some features don't work in Safe Mode
Safe Mode can be useful for troubleshooting. However, certain Mac OS X features do not work in Safe Mode. For example, you can't use DVD Player, capture video in iMovie, use audio input or output devices, or use an internal or external USB modem. The behavior of some devices such as wireless networking may vary depending on computer and Mac OS X version.
Safe Mode in Mac OS X v10.5 or later also disables Quartz Extreme (hardware accelerated graphics). Applications that depend on Quartz Extreme will not open, and the Mac OS X menu bar will appear solid even if "Translucent Menu Bar" is enabled in Desktop & Screen Saver preferences.
Safe Mode in Mac OS X v10.6 or later also disables File Sharing access. This means you will not be able to mount Time Capsule disks or volumes being served by other computers running Mac OS X.