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iMac 2019 27” - Use Caution with 15.6.1 Update

B

bsbeamer

macrumors 601
Original poster
Sep 19, 2012
4,321
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A simple point update took 7+ hours to install, didn’t even work properly and ruined this machine to the point where I needed to erase the internal (non-removable) SSD and start over with a new macOS install from bootable USB flash drive. Simple reinstall OS would not work. Recovery reinstall would not fix. No FirstAid fix would help. NVRAM reset didn’t help. Literally stuck in a boot loop that kept kicking out into recovery.

Luckily was finally able to boot into safe mode and clone the system drive to a SATA SSD via USB cable, so hopefully can use that to import from later today.

Whatever you do, MAKE SURE YOU HAVE A BOOTABLE CLONE BEFORE UPDATING. SATA SSD or NVME SSD is recommended. Multiple issues with standard portable external HDDs that get reformatted APFS by system for clone. (Use Carbon Copy Cloner.)

This machine is one of the last without T2 and believe something broke the APFS boot during update. Updates have been a pain throughout macOS 15 with several restarts required, but this is the worst it has been. This was stuck like it was trying to update firmware. Reminded me of MacPro5,1 updates with new AMD GPU.

This machine is EOL’d soon. Probably last iMac I ever buy TBH.
 
bsbeamer said:
A simple point update took 7+ hours to install, didn’t even work properly and ruined this machine to the point where I needed to erase the internal (non-removable) SSD and start over with a new macOS install from bootable USB flash drive. Simple reinstall OS would not work. Recovery reinstall would not fix. No FirstAid fix would help. NVRAM reset didn’t help. Literally stuck in a boot loop that kept kicking out into recovery.

Luckily was finally able to boot into safe mode and clone the system drive to a SATA SSD via USB cable, so hopefully can use that to import from later today.

Whatever you do, MAKE SURE YOU HAVE A BOOTABLE CLONE BEFORE UPDATING. SATA SSD or NVME SSD is recommended. Multiple issues with standard portable external HDDs that get reformatted APFS by system for clone. (Use Carbon Copy Cloner.)

This machine is one of the last without T2 and believe something broke the APFS boot during update. Updates have been a pain throughout macOS 15 with several restarts required, but this is the worst it has been. This was stuck like it was trying to update firmware. Reminded me of MacPro5,1 updates with new AMD GPU.

This machine is EOL’d soon. Probably last iMac I ever buy TBH.
Click to expand...
Similar condition my MacBook Pro 13inch M1 ended up in.
When I got to the Mac this am it was in the recovery partition.
Reboots just looped . . the white bar getting to just start moving then reboots.
I have Time Machine backups so I elected to attempt recovery. This requires a clean install of OSX then using migration assistant. The worry is that that display is showing 8 hours and 52 minutes to re-install the operating system . . . this does not bode well for the SSD I fear.

Auto updates are now OFF on my other MacBook.
 
jimm1 said:
Similar condition my MacBook Pro 13inch M1 ended up in.
When I got to the Mac this am it was in the recovery partition.
Reboots just looped . . the white bar getting to just start moving then reboots.
I have Time Machine backups so I elected to attempt recovery. This requires a clean install of OSX then using migration assistant. The worry is that that display is showing 8 hours and 52 minutes to re-install the operating system . . . this does not bode well for the SSD I fear.

Auto updates are now OFF on my other MacBook.
Click to expand...
Time Machine, while it has benefits, really sucks in this migration assistant situation. Working from an SSD clone is a lot faster, easier and more reliable. Was about 1.5 hours from reinstall and import with migration assistant for about 650-700GB of data. Almost everything works as it did previously. Almost all “log in” software licenses needed to be sorted out, however.

Cannot recommend an SSD clone of system enough. Old ones I cycle through every 2 weeks are HDDs and would have taken 8-12 hours at minimum.
 
bsbeamer said:
Time Machine, while it has benefits, really sucks in this migration assistant situation. Working from an SSD clone is a lot faster, easier and more reliable. Was about 1.5 hours from reinstall and import with migration assistant for about 650-700GB of data. Almost everything works as it did previously. Almost all “log in” software licenses needed to be sorted out, however.

Cannot recommend an SSD clone of system enough. Old ones I cycle through every 2 weeks are HDDs and would have taken 8-12 hours at minimum.
Click to expand...
I used to run CCC for backups onto SSD. But a) got too complicated with the newer OSX changes and b) the data qty was getting too big for the 500GB SSD (1TB disk in the MacBook Pro)

Anyway . . . so after approx 4 hours and so many reboots - never seen so many - password entry 6 times then another reboot . . the system came up with all my user data seemingly intact. I did not have to use migration assistant to recover. Something seriously amiss in 15.6.1 . .

Time to invest in a few backup SSD's . . .

Auto update will be turned off on the MacBook Pro now . . . typing this on my M1 Air - my travel beast.
 
You just do a basic backup to external using CCC then run the installer and point it to that drive. It will boot into that drive with everything intact. I always leave the installer in my apps folder.
 
bsbeamer said:
This machine is one of the last without T2 and believe something broke the APFS boot during update. Updates have been a pain throughout macOS 15 with several restarts required, but this is the worst it has been. This was stuck like it was trying to update firmware.
Click to expand...
My experience with a 2019 iMac has been the opposite - macOS 15 updates have been quicker than before and, in every case, painless. I am sorry to say but I suspect there is a problem with your iMac or macOS.

Does your iMac have a Fusion Drive? If so, you might do better booting from an external Thunderbolt drive.
 
gilby101 said:
My experience with a 2019 iMac has been the opposite - macOS 15 updates have been quicker than before and, in every case, painless. I am sorry to say but I suspect there is a problem with your iMac or macOS.

Does your iMac have a Fusion Drive? If so, you might do better booting from an external Thunderbolt drive.
Click to expand...
No fusion drive. Single 1TB SSD direct from Apple. No SMART reported issues. No issues on any drive monitoring. Other forums report it is an issue with lack of T2 for this machine, likely the last Intel Mac without T2 that is still (currently) supported.
 
I agree with gilby101. I have had no difficulty on my 2019 iMac with OSX updates at all Sonoma or Sequoia. OSX damaging APFS during update sounds most unlikely.
Is everything smooth now you have reformatted and which OSX have you installed and are using?
 
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