How to Troubleshoot Update Failures from Ventura to Sonoma on Late 2015 Retina 5K iMacs

How to Troubleshoot Update Failures from Ventura to Sonoma on Late 2015 Retina 5K iMacs

Upgrading a Late 2015 Retina 5K iMac (iMac17,1) from macOS Ventura to macOS Sonoma using OCLP can sometimes fail mid-installation. Users report that they see the boot options and start the upgrade to 'Macintosh HD', but returning to the computer reveals a generic install error or boot stall. This happens because the OpenCore configuration on the internal EFI partition was not updated to match Sonoma's requirements before the update was run. This guide explains how to repair and complete the Sonoma installation.

1. Prerequisites

• Hardware configuration: Late 2015 Retina 5K 27-inch iMac (Intel Core i7, 32GB RAM, AMD Radeon R9 GPU).
• Required tools: OpenCore Legacy Patcher app, a 16GB USB drive, and access to a working macOS desktop (either local or on another Mac).
• Warning: Ensure all data is backed up before running major upgrades on unsupported hardware.

2. Compatibility Snapshot

• iMac17,1 support: Fully compatible with macOS Sonoma via OCLP. Requires legacy graphics patches to restore hardware acceleration for the AMD Radeon R9 M390/M395 GPU.
• APFS Compatibility: Sonoma requires updated APFS filesystem drivers, which are injected during the OCLP compilation process.

3. Installation Preparation

1. Rebuild OCLP USB: If your system is stuck, download the latest OCLP app on another Mac.
2. Flash Patcher: Run the app, select 'Create macOS Installer', download the Sonoma installer, and flash it to the USB drive. Build and write OpenCore settings to the USB.

4. EFI and config.plist Review

1. Boot via USB: Insert the OCLP USB into the back of your iMac. Hold Option/Alt on boot and select the yellow **EFI Boot** icon on the USB drive.
2. Run Installer: From the OpenCore picker, select 'Install macOS Sonoma' to launch the installer app. This ensures the correct, updated boot patches are loaded into RAM.

5. Post-Installation

1. Write to Internal: Once the Sonoma installation completes and you boot into the desktop, open the OCLP app.
2. Build on Internal: Select 'Build and Install OpenCore' and write it to the iMac's internal SSD/Fusion Drive EFI. This allows you to boot without the USB drive.
3. Root Patches: Run 'Post-Install Root Patch' to restore full graphics acceleration for the Radeon R9 GPU.

6. Troubleshooting

Reported Issue: Installer Fails with Macintosh HD Write Error

1. Stale Patcher Files: If the installer reports a write failure, it means legacy graphics patches from Ventura are blocking the upgrade. Boot into Recovery Mode, use Disk Utility to run First Aid on your system partition, and reboot using the updated OCLP USB.
2. Fusion Drive Lag: iMacs with Fusion Drives can take longer to convert directory indexes during the update. Do not force shut down the machine unless the loading bar is frozen for over 2 hours.

Common Hackintosh Checks

• Ensure you have at least 45GB of free space on your drive before starting the upgrade.

7. Dual Boot and Advanced Configuration

• Secondary Boot Options: If you dual-boot Windows, ensure OpenCore is set as the primary boot target in your system BIOS settings.

8. Verification, Maintenance and Rollback

• Verify: Confirm your version displays macOS Sonoma 14.x and check that graphics transparent elements are rendering correctly.

9. References and Glossary

• References: Dortania OCLP Sonoma upgrade instructions.
• Glossary: iMac17,1 (Apple model identifier for Late 2015 27-inch iMac), Fusion Drive (Apple's hybrid HDD/SSD setup), Patcher (OCLP application).

Downloads and Essential Files

• Download OpenCore Legacy Patcher GUI (Official Release)