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Restoring Old Kernels And Extensions


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If you installed an update and your OS won't boot, here are instructions to restore your kernels and extensions from single user mode if you backed them up:


  • Boot to the boot prompt (tap F8 when machine is starting)
  • Type in -s and hit enter
  • You will boot to a text command prompt
  • Here is the command used to restore kernels:

sudo cp -R /mach_kernel

  • You have to replace with the path of your old kernel, example: /mach_kernel.old
  • Here is the command to restore extensions:

sudo cp -R /System/Library/Extensions/.kext

  • Replace with the path of the extensions you backed up, for example: /System/Library/Extensions.old
  • Replace with the name of the extension you want to replace, for example: AppleSMBIOS
  • Type in 'quit' without quotations to save changes and reboot

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