What do I do in Safe Mode?
Start up an unruly Mac and perform automated fixes
If your Mac struggles to start up on occasion, Safe Mode can help fix it. Sometimes this is caused by an app that automatically launches and crashes the system. Other possible causes include insufficient memory, faulty extensions or a corrupt document or web page that was open when you last shut down.
Use Safe Mode to free your Mac of whatever’s holding it back. In this mode, your Mac loads the operating system and only required kernel extensions, and it checks over the startup disk for errors and attempts to fix any it finds. The font cache, kernel cache and other system caches are deleted in case they are the cause of your problem.
Other items, including userinstalled fonts, Startup Items and Login Items, are prevented from opening automatically. While this may sound unintuitive – since you want to use those apps and sites manually once you’ve reached the desktop – using Safe Mode helps free your Mac of operational clutter. If you can’t recreate your problem while in this mode, restart your Mac as normal to see whether the issue returns.
Start in Safe Mode
To start in Safe Mode, restart your Mac, hold ß when you hear the startup chime, and release it when you see the Apple logo. MacBooks must first be plugged into a power source. You’ll need to log in to your user account even if your Mac normally does so automatically. If you use FileVault, you may need to log in twice after restarting with the ß key pressed.
Not everything you usually do on your Mac will work in Safe Mode. You won’t be able to play DVDs or capture video in apps like iMovie. Some input, output or other devices may be unavailable too. This is a temporary, thing however.
Although Safe Mode loads fewer things, it may take longer than usual for your Mac to finish starting up. This is because of the checks and attempts at error resolution it undertakes. These safety checks are broadly similar to the repairs performed by Disk Utility in OS X. Your Mac may restart if it finds an issue while checking your startup disk for errors. If your Mac restarts or shuts down repeatedly, you should book it in for a repair.
Once Safe Mode has completed its checks, simply restart your Mac to return to its normal state. Future restarts should be faster than before. If your Mac is still having problems or you get error messages when starting as normal, you may need to disable items that are set to load at startup.
To do this, go to System Preferences > Users & Groups, click your account name then Login Items. Note all the items that are listed. Next, select all the items in the list and click the – button. Restart your Mac. If your problem is gone, add items back to the list one at a time, restarting after each one. If the problem recurs, it’s likely that the last item you added is the cause. Remove it and restart again as confirmation. Downloading a new version of that app or extension may help. If not, you’ll need to do without it – also, try contacting its developer for support.
NVRAM and SMC are low-level fixes that you should only try after you’ve exhausted all other self-help troubleshooting. After tinkering in Safe Mode and restarting, you can confirm OS X has started as normal by opening System Information and selecting Software.