Apple has offered a secure boot option (sometimes called Safe Mode) since Jaguar (OS X 10.2.x). Safe Boot can be a key troubleshooting step when you’re having problems with your Mac. These could be issues with your Mac starting up, or problems you run into while using your Mac, like having apps not start or Apps that seem to cause your Mac to freeze, crash, or shut down.
Secure Boot works by allowing your Mac to start up with the minimum number of extensions, preferences, and system fonts it needs to run. By minimizing the boot process to only those components that are required, Safe Boot can help you troubleshoot by isolating problems.
Safe Boot can get your Mac back up and running when you’re having problems caused by corrupted apps or data, software installation issues, damaged fonts, or preference files. In all cases, the problem you may experience is a Mac that won’t boot up completely and freezes at some point on the way to the desktop, or a Mac that boots up successfully, but then freezes or crashes when you perform specific tasks. or you use specific applications.
Safe boot and safe mode
You may have heard of these two terms. Technically, they’re not interchangeable, although most people won’t care which term you use. But to make things clear, Safe Boot is the process of forcing your Mac to boot using minimal system resources. Safe mode is the mode your Mac operates in after it has completed a safe boot.
What happens during a secure boot?
During the boot process, a Safe Boot will do the following:
- Do a directory check of the boot drive.
- Load only the bare minimum of kernel extensions that OS X needs to run.
- Disable all fonts that are not in /System/Library/Fonts. These are the fonts supplied by Apple; all third party fonts will be disabled.
- Move all font caches to trash.
- Disable all startup or login items.
- Delete the dynamic loader cache (OS X 10.5.6 or later). This can fix issues that cause the blue screen to freeze on system startup.
Some features will not be available
Once the safe boot is complete and you are at the desktop of your Mac, you will be operating in safe mode. Not all OS X features work in this special mode. Specifically, the following capabilities will be limited or will not work at all.
- The DVD player does not work.
- iMovie will not be able to capture video.
- Devices connected to the audio input or output will not work.
- Internal or external modems do not work.
- AirPort cards may not work. This depends on the version of the card and the version of the operating system used.
- Quartz Extreme does not work. Applications that use Quartz Extreme features, such as translucent windows, may not work properly.
- Network file sharing will be disabled in OS X 10.6 and later.
How to start a safe boot and run it in safe mode
To safely boot your Mac with a wired keyboard , do the following:
- Shut down your Mac.
- Hold down the Shift key.
- Turn on your Mac.
- Release the Shift key when you see the login window or desktop.
To safely boot your Mac with a Bluetooth keyboard , do the following:
- Shut down your Mac.
- Turn on your Mac.
- When you hear the Mac startup sound, hold down the Shift key.
- Release the Shift key when you see the login window or desktop.
With your Mac running in Safe Mode, you can fix the problem you’re having by, for example, removing an app that’s causing problems, deleting a startup or login item that’s causing problems, or starting Disk First Aid and repairing permissions.
You can also use Safe Mode to start a reinstall of the current version of Mac OS using a combo update. Combo updates will update system files that may be corrupt or missing while leaving all your user data intact.
Additionally, you can use the Secure Boot process as a simple Mac maintenance procedure, deleting many of the cache files used by the system, preventing them from becoming too large and slowing down some processes.