Troubleshooting the Kernel

Issues at the kernel stage are indicated by an inability to reach the bright blue screen, as evidence of a failure to load all KEXTs, the core BSD UNIX system, and ultimately the system process. If this is the case, your Mac is stuck at the light gray screen with the dark gray spinning gear icon.

To troubleshoot the kernel:
>Start up the Mac while holding down the Shift key to initiate a Safe Boot. In addition to the Safe Boot procedures covered in the “Troubleshooting the Booter” section ear- lier, this will force the kernel to ignore all third-party KEXTs. If successful, the kernel will start the system ␣␣␣␣␣␣␣ process, which will continue to safe-boot. Completing the kernel startup stage via a Safe Boot indicates the issue may be a third-party KEXT, and you should start up in verbose mode to try to identify the problem KEXT.

>Start up the Mac while holding down Command-V to initiate verbose mode. The Mac will show you the startup process details as a continuous string of text. If the text stops, the startup process has probably also stopped, and you should examine the end of the text for troubleshooting clues. When you find a suspicious item, move it to a quarantine folder and then restart the Mac without Safe Boot, to see if the problem was resolved. This may be easier said than done, as accessing the Mac’s drive to locate and remove the item may not be possible if the Mac is crashing during startup. This is an example of where FireWire target disk mode really shines. As covered in Chapter 4, “File Systems,” you can easily modify the contents of a problematic Mac’s system vol- ume using target disk mode and a second Mac.

N O T E :If your troublesome Mac successfully starts up in Safe Boot mode and you’re trying to find the issue, do not use Safe Boot and verbose mode at the same time. If the startup process succeeds, verbose mode will eventually be replaced by the stan- dard startup interface and you will not have time to identify problematic items.

>If the kernel cannot completely load while safe-booting or you are unable to locate and repair the problematic items, you may need to reinstall Mac OS X on that volume.