OS X: What is Safe Boot, Safe Mode?
Learn more about Safe Mode, a special way to start when troubleshooting.
What is "Safe Mode"?
Safe Mode is a way to start up your Mac that performs certain checks and prevents certain software from automatically loading or opening.
Starting up in Safe Mode does several things:
- It forces a check of the startup volume, just like the First Aid feature of Disk Utility. You may see a progress bar on the screen during this check, and the computer takes longer than usual to complete its startup.
- It loads only required kernel extensions.
- It disables all fonts installed by the user.
- It moves font caches to the Trash that are 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 in Mac OS X v10.4 or later.
- In Mac OS X v10.3.9 or earlier, Safe Mode opens only Apple-installed startup items (such items may be installed either in /Library/StartupItems or in /System/Library/StartupItems). These items are different from user-selected account login items.
Taken together, these changes can help resolve or isolate certain issues that exist on the startup volume.
Starting up in Safe Mode
To start up into Safe Mode (to Safe Boot), follow these steps.
- Be sure your Mac is shut down.
- Press the power button.
- 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 the tone.
- Release the Shift key when you see the gray Apple logo and the progress indicator (looks like a spinning gear).
After the logo appears, you should see a progress bar during startup. This indicates that your computer is performing a directory check as part of Safe Mode.
To leave Safe Mode, restart your computer without holding any keys during startup.
Starting in Safe Mode without a keyboard
If you don't have a keyboard available to start in Safe Mode but you already have remote access to the computer, you can configure the computer to startup in Safe Mode using the command line.
- Access the command line by either opening Terminal remotely, or by logging into the computer using SSH.
- Execute the following command in Terminal or on the command line:
sudo nvram boot-args="-x"
(If you want to start in Verbose mode as well, use sudo nvram boot-args="-x -v" instead )
- After using Safe Boot, to return to a normal startup, execute this command in Terminal or the command line:
sudo nvram boot-args=""
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 do not open in Safe Mode, 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 can't mount Time Capsule disks or volumes being served by other computers running Mac OS X in Safe Mode.