shutdown causes -20, -63, and 1 on 2020 27" iMac

[camner]

After about 2 weeks with the new 2020 27" iMac, I had two kernel panics today.

I ran log show --predicate 'eventMessage contains "Previous shutdown cause"' --last 24h and found shutdown causes of -63, 1, and -20.

I was able to find some info here. Apparently -63 is "unknown" and -20 is caused by the T2 chip initiating a shutdown. I could find no reference to shutdown cause 1.

So:

1. Why would the T2 chip initiate a shutdown?
2. Does anyone know anything about causes 1 and -63?

I had regular spontaneous reboots on my 2015 27" iMac, which is one of the reasons I purchased the 2020 (the other reason being that the machine was 5 years old). On the old machine, the shutdown cause was always -128 ("unknown, but possibly caused by bad memory").

Although the 2015 and 2020 shutdown causes are different, I'm wondering if it could be the software I'm using (I migrated the old system to the new iMac), or perhaps my one peripheral that's always connected (OWC Thunderbay 4 external enclosure).

 

[pldelisle]

Never use migration in these cases. It can be so many things and the problem can switch from one to the other. This is why I deeply dislike migration tools.

Backup manually your data (usually in /Users/<your_username>). Start by reformat the SSD and cleanly reinstall the OS. Install minimum softwares you are required to work.

It will take time but it’s the only way I can think. Such kernel panic should never happen on UNIX-like systems. It’s definitively something bad. There is also a risk it comes from the external bay. I don’t think it requires drivers, but maybe a drive in it enters a power state it’s not supposed to. This can go up to the kernel. Just supposition. Is this SSD or HDDs? If HDDs, what exact model in it?

 

[camner]

Never use migration in these cases. It can be so many things and the problem can switch from one to the other. This is why I deeply dislike migration tools.

Backup manually your data (usually in /Users/<your_username>). Start by reformat the SSD and cleanly reinstall the OS. Install minimum softwares you are required to work.

It will take time but it’s the only way I can think. Such kernel panic should never happen on UNIX-like systems. It’s definitively something bad. There is also a risk it comes from the external bay. I don’t think it requires drivers, but maybe a drive in it enters a power state it’s not supposed to. This can go up to the kernel. Just supposition. Is this SSD or HDDs? If HDDs, what exact model in it?

@pldelisle,

Thanks for your thoughts.

Yeah, when I move to new machine I usually rebuild the system from scratch. I didn't do it in this case because I knew that Big Sur was coming out before too long, and I thought I do the complete system rebuild when I'm ready to upgrade to Big Sur (which won't be before—at least—the first point update).

I have used a variety of drives in the external bay, all HDDs. Mostly various Toshiba and HGST drives. The kernel panics seemed to happen no matter what drives I had in there.

What I was hoping to avoid was to buy a new external enclosure just to troubleshoot this. I need several external drives attached just to keep the things I need available and connected at all times to my Mac. But, I may have to do this in order to fully troubleshoot this annoying issue.

 

[pldelisle]

I’d first suspect the software first. By reinstalling the OS you will eliminate the zero-cost solution.

are the drives in RAID ? Some HDDs doesn’t do well in RAID. That’s why I always use enterprise grade HDDs for RAID (WD Gold for instance). Never had a problem in my NAS with these type of drives. Is SMART available for this enclosure ? If so, anything alarming?

 

[camner]

I’d first suspect the software first. By reinstalling the OS you will eliminate the zero-cost solution.

are the drives in RAID ? Some HDDs doesn’t do well in RAID. That’s why I always use enterprise grade HDDs for RAID (WD Gold for instance). Never had a problem in my NAS with these type of drives. Is SMART available for this enclosure ? If so, anything alarming?

The HDDs are not in RAID. I tried a RAID 0, but the access speeds were so slow that it didn't seem worth while. I'll try the OS reinstall. Thanks.

 

[AZREOSpecialist]

My 27" 2020 iMac had a kernel panic less than an hour after setup. No migration, set up as new. Kernel panic occurred while browsing the web using Safari. Graphics are glitchy w/ 5700XT. Apple needs to issue a patch, these iMacs are having too many problems.

 

[camner]

So, since I first posted, I've had another kernel panic restart, another -20 shutdown cause, which is caused by the T2 security chip "initiating shutdown." More Google searching led to some articles in 2018 about this happening with certain MacBook Pro and iMac Pro models. None of the items I read said anything about a solution.

This is frustrating, to have a new machine subject to spontaneous shutdowns...I'm not sure where to go next for troubleshooting.

 

[PBG4 Dude]

So, since I first posted, I've had another kernel panic restart, another -20 shutdown cause, which is caused by the T2 security chip "initiating shutdown." More Google searching led to some articles in 2018 about this happening with certain MacBook Pro and iMac Pro models. None of the items I read said anything about a solution.

This is frustrating, to have a new machine subject to spontaneous shutdowns...I'm not sure where to go next for troubleshooting.

1-800-MY-APPLE

 

[superpanjy]

My 27" 2020 iMac had a kernel panic less than an hour after setup. No migration, set up as new. Kernel panic occurred while browsing the web using Safari. Graphics are glitchy w/ 5700XT. Apple needs to issue a patch, these iMacs are having too many problems.

I had exact issue. same model. brand new (with 8GB RAM). Kernel panic shut down right after I complete initiall setup. My first iMac after long wait.
upgraded to 128GB OWC ram, same issue.
Changed to 128GB Crucial ram, same issue.

 

[Donnation]

I honestly think it has something to do with third party RAM. I have had 2 Kernel panics since I bought my 2020 iMac with 64GB RAM from Samsung. I opened the RAM door back up and took it out and put it back in and I haven't had the issue since.

 

[PBG4 Dude]

I’ve had zero panics with the 2x32GB Crucial sticks. I’ve only had them installed for about a week though.

 

[superpanjy]

I’ve had zero panics with the 2x32GB Crucial sticks. I’ve only had them installed for about a week though.

same. panic only happens when all 4 slots are used.
jusr curious, was your iMac made in China or Ireland?

 

[PBG4 Dude]

same. panic only happens when all 4 slots are used.
jusr curious, was your iMac made in China or Ireland?

It shipped from China.

 

[Bradleybell1]

I have the same problem on a brand new 2020 iMac. Definitely not memory related.

 

[joecharbo1]

I honestly think it has something to do with third party RAM. I have had 2 Kernel panics since I bought my 2020 iMac with 64GB RAM from Samsung. I opened the RAM door back up and took it out and put it back in and I haven't had the issue since.

I had the same problem with 2x 16g of OWC and 8g of the original apple memory. When i just put the OWC, panic occur. When i put only apple memory, works just fine. I'm triyng some ajustments with the OWC department. I'll come back later if something new happen.