IMAC flash Drive Reinstall

Follow this step-by-step guide to perform a clean installation of macOS on your iMac using your provided OpenCore Legacy Patcher flash drive.

Part 1: Erasing Your Old Drive

Note: Do not insert your flash drive just yet. We need to prepare your iMac's internal storage first.
  1. Turn on your iMac and immediately press and hold Ctrl + Shift + R (Note: On standard Apple keyboards, the Internet Recovery shortcut is usually Command + Option + R). Keep holding until you see an Apple logo or a spinning globe.
  2. Once it finishes loading, connect to your Wi-Fi network if prompted. If there is no prompt, proceed to the next step.
  3. When the macOS Recovery screen appears, choose Disk Utility from the four available options.
  4. In the upper-left corner of the Disk Utility window, click the View button (it looks like a small drop-down tab) and select Show All Devices.
  5. In the left sidebar, click on the very top option in your storage list. This is your physical internal SSD.
  6. Click the Erase button at the top of the window and enter the following settings:
    • Name: Macintosh HD (or any name you prefer)
    • Format: APFS
    • Scheme: GUID Partition Map
  7. Click Erase and wait for the formatting process to complete.
  8. Once finished, click Done. Click the Apple logo in the top-left corner of the screen and select Shut Down.

Part 2: Booting from the Flash Drive

  1. Now, insert the provided flash drive into a USB port on your iMac.
  2. Turn on the iMac and immediately press and hold the Option key (use the Alt key if you are using a generic Windows keyboard).
  3. Keep holding the key until the boot options menu appears on your screen.
  4. Select the EFI Boot option. Wait a moment, and the four recovery options from earlier will appear again.

Part 3: Installing macOS

  1. From the recovery menu, choose Install macOS Tahoe / Sequoia / Sonoma (the name will match the version on your drive) and click Continue.
  2. When the installer window appears, click Continue again and agree to the Terms & Conditions.
  3. Select the internal drive you just erased (e.g., "Macintosh HD") and click Continue. This is where macOS will be installed.
  4. Allow the installation to run. This typically takes up to an hour, depending on your exact Mac model. The screen may go black or restart a few times—this is normal.
  5. After the installation finishes, follow the standard on-screen prompts to set up your user account, Wi-Fi, and preferences. Once you reach the desktop Home Screen, move to the final part below.

Part 4: Finalizing OpenCore Configuration

Important: A pop-up message might automatically appear asking if you’d like to install OpenCore to disk. Click Cancel on this prompt. We will do this manually to ensure the correct settings are applied.
  1. Open your Applications folder and launch the OpenCore-Patcher app manually.
  2. Click on Settings within the app, and uncheck the box next to "Show OpenCore Boot Picker".
  3. Return to the OpenCore app's home screen and click Build and Install OpenCore.
  4. Once it finishes building, click Install to disk.
  5. You will be asked where to install it. Choose your internal formatted drive (do not choose the USB flash drive, which is usually highlighted in blue).
  6. On the next screen, click the blue-highlighted partition option that has the letters EFI in it.
  7. The app will finish installing and give you an option to Ignore or Reboot. You must click Reboot for the updates to take effect.
  8. As soon as the iMac reboots, you can safely remove the flash drive.

Great job! Your freshly installed macOS is now fully set up and ready to roll. Enjoy your upgraded Mac experience!

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