Shift Booting: Safety First
This is the second post in a short series about what you can do with key combinations during startup. But this won’t be a just long list of every key combination available, we’ll also cover why and how to use them. See the first article to learn about Option Booting.
Shift Booting
Booting your Mac while holding down the Shift Key (until the Spinning Gear appears) performs a Safe Boot, which if it is successful (more an that later), will result in your Mac running in Safe Mode. If you used Mac OS 7, 8, or 9, you probably recall holding down the Shift Key to disable extensions. A Safe Boot performs a similar function in Mac OS X.
What Safe Boot Does
- Disables all non-system fonts
- Clears all font caches
- Disables all Startup and Login Items
- Loads only required Kernel Extensions
- Runs a directory check on the boot drive
- Boots to the Login Window, even if the computer is normally set to Automatic login
While in Safe Mode
- Networking and Internet will probably not work
- Many hardware functions will be disabled
- Many input and output devices will not work
Why Use Safe Boot and Safe Mode
Safe Boot and Safe Mode and very useful when troubleshooting a misbehaving Mac. There are many circumstances where a Safe Boot would be helpful.
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Troubleshooting Startup
Performing a Safe Boot will check many of the fundamental issues that can cause your Mac to get stuck somewhere along the startup process. If your Mac won’t startup, you can power it down and boot up holding down shift. If your Mac makes it through startup, then you probably have a software problem and the next step would likely be an Archive and Install of Mac OS X. If your Mac was having startup problems and shuts down during Safe Boot, you are probably having Hard Drive issues and should get expert help ASAP because your data is in jeopardy.
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Troubleshooting Login
For most users, it will be very difficult to differentiate between a startup issue and a login issue, but fortunately, a Safe Boot can test and eliminate some of the causes of both. If you restart or login to your computer and can see your desktop picture or dock, but can’t get any farther, a Safe Boot may fix the issue. Once you’ve successfully booted to Safe Mode, trying restarting. If you still can’t get full access to your account, your Mac probably needs some TLC from a Tech.
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Troubleshooting Font Problems
Font problems can be very tricky to recognize and diagnose because the symptoms usually do present as directly font-related. If fonts are displaying oddly in your applications or documents, and programs like the Adobe Creative Suite and Microsoft Office are crashing, try a Safe Boot and then test the applications and documents you were having trouble with. If they work, it may have been either bad font or bad font cache. If they continue to work after restarting again normally, you lucked out. If they fail, you have a long road ahead of you hunting down the culprit font.
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Troubleshooting Kernel Panics
Statistically, most Kernel Panics are hardware-related but attempting a Safe Boot is a quick and easy step that can save downtime in the rare occasion that one is not. It is particularly relevant with Kernel Panics that occur during startup. If you can’t reproduce your Kernel Panics while booted to Safe Mode, you should investigate possible software causes.
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Troubleshooting Crashes
This is a broad category, but if you have a number of third-party preference panes installed, or applications that run background processes (monitoring applications, backup applications, etc.) and are experiencing crashes, a Safe Boot can be helpful in diagnosing conflicts between these applications.
There are a lot more uses for Safe Booting and Safe Mode, but this is enough to get started. As with Option Booting, this is not a tool for everyday use, but a good arrow to have in your quiver when you need it. Next week, we’ll talk about about a less involved boot option: your mouse button.