How to Fix iMac won’t boot after Migration Assistant During macOS Boot or Installation

How to Fix iMac won’t boot after Migration Assistant During macOS Boot or Installation

Boot failures need a predictable pass through firmware, USB, storage, EFI and verbose logs before reinstalling macOS. Most installer stalls come from firmware settings, an invalid config.plist, wrong SSDTs, bad USB mapping or unsupported storage/controller settings.

Quick Checks

• Backup current state: Save a copy of your working EFI and run a full system backup before changing settings.
• Identify hardware components: Note down your exact CPU, GPU, Wi-Fi card, and motherboard/laptop model.
• Ensure utility alignment: Keep OpenCore, OCLP, and ProperTree updated.

Fix Steps

1. Create a rollback point: Make a Time Machine backup and keep a copy of your last working EFI folder before editing OpenCore, kexts or root patches.
2. Boot verbose: Add -v keepsyms=1 debug=0x100 so the final visible line gives a real clue.
3. Check firmware settings: Disable Secure Boot and Fast Boot, set SATA to AHCI, disable CFG Lock if possible, and use UEFI mode.
4. Validate OpenCore: Update OpenCore, Lilu and core kexts, then run ocvalidate or ProperTree clean snapshot.
5. Recreate the installer: Use a fresh USB installer and try another USB port; older Macs may need a USB 2.0 hub for input during setup.
6. Reset NVRAM: Reset NVRAM from the OpenCore picker before retrying the installer.

Verify It Worked

• Verbose boot moves past the previous stopping line.
• The installer reaches Disk Utility and sees the target disk.
• Keyboard, mouse and USB remain active during recovery.
• OpenCore picker still loads after a cold boot.

Rollback

• Restore the last booting EFI folder.
• Use the officially supported macOS installer to recover the machine.
• Do not erase the internal disk until the installer can boot twice consistently.

Related iATKOS Searches

• OpenCore · OCLP · EFI · kexts · config.plist · macOS troubleshooting

Original Question: "iMac won’t boot after Migration Assistant"

Hi everyone!!! Please help if you have any ideas! Thank you! I have a MacBook Air late 2015 running Monterey and recently I‘ve got a iMac late 2013 running Catalina. I wanted to bring the info from the Air on the iMac. I installed Monterey with OpenCore Patcher, it worked, all good. Tried to move the info from the Air using Migration Assistant and a Time Machine backup. Everything is saved on the disk (as I see when I boot with Catalina) but I can‘t boot in Monterey, it stops loading at one third… Any ideas what should I do? I tried to reinstall but I ended up reinstalling and erasing the data, so I had to do it once again. Any ideas? Tried cmd+r but it showed some apple startup error. What to do next? Thanks submitted by /u/theluckyone75 [link] [comments]