My 2020 iMac doesn't like to boot...

[VivienM]

So, I've had this mid-2020 iMac for a little over 18 months.

A few months ago, I accidentally cut its power off (oops, didn't realize that it wasn't on a UPS and I stepped on a power cable) and it wouldn't boot back up. Kernel panics on boot.

Usually, after some fiddling (e.g. booting into diagnostics then rebooting), it will eventually manage to boot. And when it does it gives a weird message about a kernel extension being disabled (doesn't say which one). Once it does, it's perfectly stable. But... it now seems that every reboot, e.g. the final one in the 13.6 install sequence today, triggers boot loop kernel panics.

It passes Apple diagnostics just fine, and boots just fine with the shift key held down. Disk first aid gave all partitions a clean bill of health.

The log-type data talks about timeouts with remoted which doesn't seem to mean much.

I had a Satechi USB-C thingy plugged in but I've now unplugged it and no change. No other devices plugged in.

Any thoughts/advice/etc? Usually, I've just let it be once I somehow manage to get it booted, but it seems like the next reboot will trigger boot loop craziness again and I'm starting to run out of patience with this...

 

[VivienM]

Just to add to this, I managed to get it booted in safe mode just now and open a web browser, this is what it is reporting and wanting to send to Apple:

panic(cpu 2 caller 0xffffff8015b95941): userspace watchdog timeout: no successful checkins from remoted
remoted returned not alive with context : is_alive_func returned unhealthy : device not connected (code: 0x2
service: logd, total successful checkins in 184 seconds: 19, last successful checkin: 0 seconds ago
service: remoted, no successful checkins in 184 seconds
service: opendirectoryd, total successful checkins in 184 seconds: 18, last successful checkin: 0 seconds ago
service: configd, total successful checkins in 184 seconds: 1, last successful checkin: 0 seconds ago

Panicked task 0xffffff95745bb9d8: 4 threads: pid 115: watchdogd
Backtrace (CPU 2), panicked thread: 0xffffff87151cbb30, Frame : Return Address
0xffffffd0a257b5b0 : 0xffffff801287205d
0xffffffd0a257b600 : 0xffffff80129c6144
0xffffffd0a257b640 : 0xffffff80129b5c57
0xffffffd0a257b690 : 0xffffff8012812951
0xffffffd0a257b6b0 : 0xffffff801287233d
0xffffffd0a257b7a0 : 0xffffff80128719e7
0xffffffd0a257b800 : 0xffffff8012fdb3f3
0xffffffd0a257b8f0 : 0xffffff8015b95941
0xffffffd0a257b900 : 0xffffff8015b955dc
0xffffffd0a257b920 : 0xffffff8015b946b9
0xffffffd0a257ba50 : 0xffffff8012f526de
0xffffffd0a257bbb0 : 0xffffff80129728e9
0xffffffd0a257bcc0 : 0xffffff801284c51a
0xffffffd0a257bd60 : 0xffffff8012863282
0xffffffd0a257bdd0 : 0xffffff8012863907
0xffffffd0a257bef0 : 0xffffff801299b513
0xffffffd0a257bfa0 : 0xffffff8012812db6
Kernel Extensions in backtrace:
com.apple.driver.watchdog(1.0)[BD08CE2D-77F5-358C-8F0D-A570540A0BE7]@0xffffff8015b93000->0xffffff8015b95fff

Process name corresponding to current thread (0xffffff87151cbb30): watchdogd

Mac OS version:
22G120

Kernel version:
Darwin Kernel Version 22.6.0: Fri Sep 15 13:39:52 PDT 2023; root:xnu-8796.141.3.700.8~1/RELEASE_X86_64
Kernel UUID: F75FC53F-FC1A-3AB6-8980-EF66A83DD51D
roots installed: 0
KernelCache slide: 0x0000000012400000
KernelCache base: 0xffffff8012600000
Kernel slide: 0x00000000124dc000
Kernel text base: 0xffffff80126dc000
__HIB text base: 0xffffff8012500000
System model name: iMac20,1 (Mac-CFF7D910A743CAAF)
System shutdown begun: NO
Hibernation exit count: 0

System uptime in nanoseconds: 184008424311
Last Sleep: absolute base_tsc base_nano
Uptime : 0x0000002ad7c1bdd0
Sleep : 0x0000000000000000 0x0000000000000000 0x0000000000000000
Wake : 0x0000000000000000 0x0000000cd56394d0 0x0000000000000000
Compressor Info: 0% of compressed pages limit (OK) and 0% of segments limit (OK) with 0 swapfiles and OK swap space
Zone info:
Zone map: 0xffffff80a1757000 - 0xffffffa0a1757000
. PGZ : 0xffffff80a1757000 - 0xffffff80b1758000
. VM : 0xffffff80b1758000 - 0xffffff857bdbe000
. RO : 0xffffff857bdbe000 - 0xffffff8714a8a000
. GEN0 : 0xffffff8714a8a000 - 0xffffff8bdf0f0000
. GEN1 : 0xffffff8bdf0f0000 - 0xffffff90a9756000
. GEN2 : 0xffffff90a9756000 - 0xffffff9573dbc000
. GEN3 : 0xffffff9573dbc000 - 0xffffff9a3e423000
. DATA : 0xffffff9a3e423000 - 0xffffffa0a1757000
Metadata: 0xfffffff9efe2e000 - 0xfffffffa0fe2e000
Bitmaps : 0xfffffffa0fe2e000 - 0xfffffffa1fe2e000
Extra : 0 - 0

last started kext at 182274432328: >!AHIDKeyboard 231 (addr 0xffffff8013c77000, size 20480)
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[VivienM]

Well, this was "fun" with the T2, but I managed to get this thing to boot memtest86+ (hey, it is just a near-generic x86 box...). Let's see if it thinks my RAM is bad...

 

[Nermal]

Does booting into diagnostics/recovery always work? It sounds like more of a software issue than a hardware one (thankfully - I own one of these machines and I'm not ready for random hardware failure yet!)

 

[VivienM]

Does booting into diagnostics/recovery always work? It sounds like more of a software issue than a hardware one (thankfully - I own one of these machines and I'm not ready for random hardware failure yet!)

Seems to, yes...

I'm hopingish for a software issue too, although I am not really in a mood to reinstall an OS. I feel like across both my Windows machines and Macs, I haven't had one get screwed up to the point of needing a reinstall in ~15 years...

I suspect, though maybe not, that the software issue could be fixed without a reinstall if I could just find some clue about what's unhappy. But part of me is just hoping I can get it to boot once and leave it like this until Sonoma and... hope that Sonoma fixes this somehow. Yeah right.

 

[rpmurray]

Have you tried booting with Verbose mode turned on? Maybe see if it trips up at a certain point during boot that can provide a clue.

To boot up your Mac in verbose mode:​

° Power down your Mac.

° Restart it and down the Command and V keys.

° Continue holding the keys until you see white text on the screen.

 

[VivienM]

Have you tried booting with Verbose mode turned on? Maybe see if it trips up at a certain point during boot that can provide a clue.

Tried that earlier. Lots of things scroll by really quickly in text mode, then it goes into GUI mode with a big Apple logo, then presumably around 180 seconds later, it gets unhappy, drops back to text mode without saying anything obvious and then immediately reboots.

One thing I didn't try is something that helped the first time around... or seemed to, at least... deleting some kind of file related to Photos. Let me try and google that...

 

[VivienM]

Here's what I think is actually going on: something is causing the boot to stall. If that thing takes less than 180 seconds to continue, the machine boots fine and it's all good. If that thing takes more than 180 seconds, watchdog kernel panics the machine.

The last two boots, it's booted fine, but it stays stuck at a particular place in the apple logo slidey thing for a very, very long time.

So then, I guess that leaves the obvious question... what is it actually waiting for?

 

[PBG4 Dude]

Sounds like an executable/daemon got corrupted, which would necessitate an OS reinstall.

 

[Nermal]

Doesn't the "signed system volume" (or whatever it's called) prevent that sort of corruption? My understanding was that you'd get a "damaged system" error if any of the files contained errors.

It therefore shouldn't be necessary to reinstall the OS either. An "erase all content and settings" may be a solution (albeit a blunt instrument) to get rid of whatever's causing the issue, but I don't believe that it's necessary to manually reinstall the entire OS on modern Macs.

 

[VivienM]

It therefore shouldn't be necessary to reinstall the OS either. An "erase all content and settings" may be a solution (albeit a blunt instrument) to get rid of whatever's causing the issue, but I don't believe that it's necessary to manually reinstall the entire OS on modern Macs.

My current plan, given it is running right now, is to install Sonoma on Monday and hope for the best and that it unsticks whatever is stuck...

If it is still broken after that, then I guess it is clean install time.

 

[HDFan]

As an interim measure you could install etrecheck which might give you some insights.

 

[VivienM]

Well, this seems encouraging... installed Sonoma and so far it booted just fine into Sonoma...

(meanwhile my M1 Max MBP is being more Sonoma-hostile...)

 

[theorist9]

I'm hopingish for a software issue too, although I am not really in a mood to reinstall an OS.

I don't believe that it's necessary to manually reinstall the entire OS on modern Macs.

Just for future reference, in case people run into intractable software issues in the future and come across this thread:

I'm wondering if you folks are confusing "reinstalling the OS" (which is an easy automated process that involves essentially the same steps updating to a new OS, and can be very effective at fixing difficult software issues), with doing a "clean install" (which is indeed a laborious PITA).

I.e.:
Clean Install (hard): (1) Erase Disk; (2) Reinstall MacOS; (3) Spend weekend doing fresh installs of all your applications, restoring all the custom configuration settings for each.

Reinstall OS (easy): (1) Late in the evening, go into the appropriate recovery mode*; (2) Follow on-screen directions to reinstall OS; (3) Go to bed--it will be done by morning.

I've done had to do the latter (reinstall OS) a few times on my 2019 iMac running Monterey. I ran into issues that normal approaches couldn't solve, and reinstaling the OS fixed them. Since the OS is on a separate signed volume, doing this doesn't touch your apps or user accounts.

[*There are three options: Install the OS that came with your Mac; install the last OS that was on your Mac; and install the latest OS available for your Mac. On Intel Macs, these can be accessed by pressing different key combos during the reboot]

 

[HDFan]

(3) Spend weekend doing fresh installs of all your applications, restoring all the custom configuration settings for each.

Certainly the best way, but you could also restore the applications from backup/migration assistant. Many will work fine.

 

[theorist9]

Certainly the best way, but you could also restore the applications from backup/migration assistant. Many will work fine.

Yes, and that's what I actually did myself when I moved from my 2014 MBP to my 2019 iMac. But in my post I was talking about two different ways to restore the OS, so Migration Assistant isn't relevant here, since Migration Assistant allows you to migrate everything except the OS.