Help! Migrating from 2020 iMac to M4 Studio cause iMac do not boot any more...

[JohnArtist]

So I just upgraded from a 2020 iMac to a M4 Studio. I used Migration Assistant and things loaded up just fine on my new Mac. I used to transfer System settings, etc., and not documents because the old iMac had a 4TB and the Studio has 1 TB and External SSDs.

I copied all my Documents over manually without issue.

There problem is that I realized that iMovie saves it’s Library outside the documents folder (and into the Movies folder) which I did not back-up to my external back-up drives.

Plugging my old iMac in, I tried booting up, but it goes about halfway (progress bar), hangs for 2 minutes or so, and restarts automatically. This will go on forever if I let it.


** A number of people have described this exact scenario (including this happening after MA) online but I found no definitive solutions.***


So, I tried Target Disk Mode. I connected my 2020 iMac in TDM to both my new Mac Studio and my old 2018 Mac mini with the proper cable (USB-C connector with Thunderbolt).

Both systems SEE the TDM Mac in Disk Utility, but won’t mount them so I can copy the documents I need. I even turned off Security on the 2020 iMac in Recovery mode, but it still doesn’t work. On the Studio, it asks for a password to access the TDM iMac (yay!) but never gets any further (won’t show mounted on desktop), but shows in Disk Utility partially grayed out.

ANY thoughts? ON getting access to the TDM drive?? I tried mounting using terminal commands, etc. No dice.

In Recovery Mode on the 2020 iMac, Disk Utility scans the drive and reports zero errors.


I have one more option, and that is to reinstall ONLY the Mac OS on the 2020 iMac (without full erase), but I do NOT want to do this if I can mount the TDM drive first. I don’t want to risk messing up the drive and then having to FULLY erase it.

 

[Bigwaff]

Plugging my old iMac in, I tried booting up, but it goes about halfway (progress bar), hangs for 2 minutes or so, and restarts automatically. This will go on forever if I let it.

Have you tried booting in Safe Mode?

Start up your Mac in safe mode

Starting up your Mac in safe mode may help you diagnose problems with your Mac.

support.apple.com

 

[JohnArtist]

Have you tried booting in Safe Mode?

Start up your Mac in safe mode

Starting up your Mac in safe mode may help you diagnose problems with your Mac.

support.apple.com

Yes. I tried Safe Mode (same boot issue -- hangs then restarts); reset NVRAM, reset SMC. None of these worked.

Recovery Mode scans the SSD as fine. But hooking up to another Mac can't access the drives. It won't mount.

I turned off the T2 security on the TDM Mac. The Studio asks for a admin password when connecting but it never shows up on the desktop. My 2018 Mac mini doesn't ask for PW but shows the TDM Mac grayed out in Disk Utility and won't mount.

 

[Mr_Brightside_@]

What about reinstalling the OS from recovery?

 

[Bigwaff]

Try booting iMac in verbose mode. Perhaps the logging statements shown will provide some detail.

 

[Fishrrman]

OP:

Can you boot to INTERNET recovery?
(this is NOT THE SAME as "the recovery partition")

How to boot to Internet Recovery:
1. Power down, all the way off
2. Hold down the Command-Option-R keys (all at once and don't let go!)
3. Reach around and press and release the power on button
4. DON'T LET GO of those keys!
5a. If you are connected to the net via ethernet, you can let go when you see the spinning globe.
5b. If you are connected via wifi, let go of the keys when you're asked for your wifi password (ethernet is better if available)
6. The internet utilities take a while to load, be patient.

At this point, I might consider trying to re-install the complete OS (not even sure if that's your problem).

Finally, I'd like to offer some advice that won't help you fix the iMac right now.
But... if you had taken it earlier, might have saved you a LOT of trouble.

That advice is:
Start using either CarbonCopyCloner or SuperDuper to create a "cloned backup" of your internal drive onto an external drive.
If you had a full clone backup, ALL of your "stuff" from the internal drive would be on it, and you wouldn't be fumbling around trying to get it now.

My opinion only
Others will disagree
Some will disagree vehemently.