Troubleshooting Mac OS X Kernel Panics

One of the scariest things a Mac user can experience is a kernel panic. The Mac stops in its tracks, darkens the display, and gives the message, "You need to restart your computer. Hold down the Power button until it turns off."

If you see the kernel panic message, there's nothing you can do to make it go away except restart your Mac.

Shut Down Your Mac After a Kernel Panic

When you see the restart message, press and hold the Power button until your Mac turns off.

Now it's time to try to figure out what went wrong or at least get your Mac back to working condition. Getting your Mac working again may be as simple as powering it back on. Many kernel panics don't recur, and your Mac operates as you expect.

What Causes a Kernel Panic?

There are several reasons a Mac may have a kernel panic, but most of them are temporary and may not be seen again. These include poorly written applications, plug-ins, add-ons, drivers, and other software components.

You may only see a kernel panic when unusual conditions occur, such as when two or more specific apps are running while most of the memory is in use. Restarting your Mac corrects the problem. Other times, the kernel panic visits from time to time, not on a regular basis, but often enough that you are tired of seeing it.

In those cases, the problem is usually software related, but it can also be failing hardware or a combination of software and hardware problems, such as wrong versions of drivers for a specific piece of hardware, such as a printer.

The most hair-pulling kernel panic is the one that happens every time you try to start up your Mac. In this case, the problem is usually hardware related, but it can also be something as simple as a corrupt system file or driver.

Resolving a Kernel Panic

Because most of the time a kernel panic is transitory, it is tempting to restart your Mac and get back to work. However, if the kernel panic recurs several times, it's time to act.

Restart Using Safe Boot

Start the Mac by holding down the Shift key and pressing the power button. Hold down the Shift key until your Mac starts. This process is called a Safe Boot. During a Safe Boot, the Mac completes a basic check of the startup drive's directory structure. If everything is OK, the operating system loads the bare minimum number of extensions it needs to run. No startup or login items are run, all fonts except those used by the system are disabled, and the dynamic loader cache is dumped.

If your Mac starts up in Safe Boot mode, then the basic underlying hardware of the Mac is functioning, as are most system files. Now try starting your Mac normally. If your Mac restarts without any problems, then a wayward app or driver or some interaction between apps and hardware possibly caused the kernel panic. If the kernel panic doesn't recur in a short time, say a day or two of use, you can consider it a minor inconvenience and get on with using your Mac.

If your Mac won't start up after restarting from Safe Boot mode, then the likely problem is a startup or login item, a corrupt font or font conflict, a hardware issue, a corrupt system file, or a driver/hardware issue.

Kernel Panic Logs

When your Mac restarts after a kernel panic, the panic text is added to the log files that your Mac keeps. Use the Console app located at Applications > Utility to view the crash logs.

1. Launch Console.

   Type "Console" into Spotlight Search to quickly bring up the utility.

2. From the left sidebar, select Diagnostic Reports and then select the most recent crash report to view it. 

   In older macOS versions, you may first need to select Library/Logs to access the Diagnostics Reports folder.

3. Alternatively, to view the diagnostics report directly, navigate to Finder and select Go.

4. Hold down the Option key and then select Library.

5. Select Logs > DiagnosticsReports.

   Check the Crash Reports folder in Console for any recent log entries. Look through the report for a time corresponding to when the kernel panic occurred. It may provide a clue as to what events were taking place immediately before the panic was declared.

Testing Hardware

Isolate your hardware by disconnecting everything but the keyboard and mouse from your Mac. If you're using a non-Apple keyboard that requires a driver to work, temporarily replace the keyboard with the original Apple-supplied keyboard. When everything but the keyboard and mouse is disconnected, restart the Mac. If the Mac starts up, repeat the startup process, reconnecting one piece of external hardware at a time, and restarting after each until you figure out which device is causing the problem. Devices such as wired routers, switches, and printers can all be the source of problems.

If you still can't start your Mac without a kernel panic, it's time to check some basics. Restart your Mac using the OS X installation DVD (on older Macs) or the Recovery HD partition or macOS Recovery on newer Macs, following the instructions for your particular Mac. Once your Mac boots to the installation or recovery screen, use Disk Utility to run a Repair Disk on all drives connected to your Mac, starting with the startup drive. If you run into problems with your hard drive that Repair Disk can't fix, it may be time to replace the drive.

Of course, other hardware problems generate a kernel panic beyond the drive. RAM glitches or even problems with basic components of your Mac, such as the processor or graphics system. Apple Diagnostics online (for Macs introduced after June 2013) and Apple's Hardware Test (for older Macs) can usually find common hardware problems.

Testing Software and Fonts

Disable all startup and login items and then start up again in Safe Boot mode (press the power button and immediately hold down the Shift key). Once your Mac boots, disable startup and login items in the Accounts or Users & Groups system preference pane.

Some applications install system-wide startup items. You can find these items at: /Library/StartupItems on some Macs. Each startup item in this folder is usually located in a subfolder identified by the application's name or some semblance of the application's name. Move all the subfolders to the desktop (you may need to provide an administrator password to move them).

When the startup and login items are disabled, restart your Mac normally. If the Mac starts without any problems, reinstall the startup and login items, one at a time, rebooting after each, until you find the one that's causing the problem.

You can use FontBook to check any fonts you installed with FontBook. Start in Safe Boot mode and then launch FontBook, which is located in the Applications folder. Select multiple fonts and then use the Font Validation option to check for errors and corrupt font files. If you find any problems, use FontBook to disable the fonts.

If You Can't Resolve the Kernel Panic

If nothing you do resolves the kernel panic, it's a good bet the issue is hardware related. It can still be something basic, such as bad RAM or a hard drive that isn't working correctly. Take your Mac to an Apple Store or authorized service center. Making an appointment at an Apple Store is easy, and the diagnosis is free.