iMac stuck in bootup/shutdown cycle

[fpdiver]

I have an iMac (Model details: iMac, Late 2011 model, 27 inch, 4 Gb RAM, Intel 3.4GHz i7) which has recently started shutting down midway through its boot up process (when the Apple Logo is displayed). It continues in that cycle until I turn it off.

When run in Verbose mode, I get the following message:

pid exited (signal 0, exit 1)panic(cpu 2 caller 0xffffff80093cicde) Launchd died\nState at last exception:\n\n~@/SourceCache/xnu/xnu-2782.20.48/bsd/kern/kern_exit.c:363

Debugger called: <panic>

I have tried the following:

• Cmd - R: (recovery mode) - the iMac doesn’t respond to this and remains in its boot up/shut down cycle
• Shift: (safe mode) - behaves the same as for recovery mode.
• I used the Option key to load boot menu - it won’t boot from recovery partition and won’t boot from a bootable installer for Sierra on a USB disk (shuts down again).
• I used Alt+Option - won’t boot from Internet (tried both WiFi and Ethernet)
• I have reset the NVRAM
• I have run memtest86 and the memory checks out ok
• I ran fsck -fy from single user mode and that checks out OK (but trying to boot after running it gives the same behaviour).
• I have booted it in Target Disk mode attached to a Mac Book Pro and used Disk Utilities to scan the disk which checked out ok.

Can anyone suggest any other options I can try or help me diagnose the problem? Or is my only hope a genius bar?

I thought it would be possible to install a new OS on the disk via Target Disk mode but I that doesn’t seem to be the case. I’m not precious about any of the files on the disk (and could get them off anyway if needed using Target Disk mode) so if solutions involve formatting the hard drive then that is no problem.

Any help greatly appreciated!

 

[honestone]

From your description of what is happening via Target Disk Mode, cannot understand why you can't do a clean, "virgin" installation of the Mac OS you are using (by the way, what is that?). What you should be able to do is to use Disk Utility on the Mac Book Pro to Erase and Format (and if necessary, Partition) the internal drive on your iMac. Then, as long as you have the "appropriate" Mac OS installation file on the MacBook Pro, you should be able to launch it on the MacBook Pro, and perform the installation onto your iMac's internal drive.

When you do the Erase, you might want to make a few passes in doing that.

Now, if for example you want the latest version of Sierra, OS 10.12.3, while on the MacBook Pro, go to the App Store, selected "Featured", and on the right of the subsequent screen, you'll see "macOS Sierra". When you download it, a file entitled "Install macOS Sierra" will appear in the Applications on the MacBook Pro. Make a copy of it somewhere else on the MacBook Pro. Then, launch it from the Applications folder, and proceed with the installation. When that completes, make another copy of the "Install macOS Sierra" somewhere on the iMac's hard drive. Boot up your iMac, and as long as everything is good, you'll go through the setup process on the iMac.

 

[Spawn_Dooley]

Can anyone suggest any other options I can try or help me diagnose the problem? Or is my only hope a genius bar?

If you see the full panic report, look for the last loaded kext, that will likely be the troublemaker. The dialogue will go something like:

System uptime in nanoseconds: 32537827373433 last loaded kext.....

 

[fpdiver]

Thanks both for your replies.

@honestone - I thought I would be able to install a clean version of the OS on the disk via target disk mode but the reading around I did suggested otherwise. If I understand correctly you are suggesting this is possible, with the following steps:
1. Boot iMac in target disk mode connected to the Mac Book Pro
2. Use Disk Utilities on the Mac Book Pro to Erase, Format and Partition (as necessary) the iMac's hard drive
3. Using a downloaded OS installer, install my desired version of Mac OS on to the iMac's hard drive (can you point the installers at an external disk?)
4. Once complete, place the installer on the iMac hard drive
5. Restart the iMac and complete the installation

Whats the purpose of dropping the installer onto the iMac? Is that just so its available when computer restart?

@Spawn_Dooley - no changes (applications or peripherals) were made to the computer in the few weeks before the crash first occurred, this really came out of the blue. I'll try and capture the kext.

 

[honestone]

Yes, those are the correct steps, but you forgot one important thing that I previously stated: For step #3, after you download the version of the Mac OS you want from the App Store, first make a copy of it in another location on your MacBook Pro. (Here are those steps repeated: When you download it, a file entitled "Install macOS Sierra" will appear in the Applications on the MacBook Pro. Make a copy of it somewhere else on the MacBook Pro. Then, launch it from the Applications folder, and proceed with the installation.). The reason for this is that after you launch that file from the Applications folder on the MacBook Pro and complete the installation onto your iMac (and yes you can point the installation to an external device), that file will go away. So, with that copy initially made, once the installation completes onto the iMac, copy that copy on the MacBook Pro to a location on your iMac. Once you have it on your iMac, you'll have just in case you need it, without having to visit the App store and download it again.

One other thing is that you never stated what Mac OS you are/were using on the iMac, and what OS you have on the MacBook Pro.

 

[fpdiver]

@Spawn_Dooley - I don't see any text in the panic report that mentions the last loaded kext. Other than the text I put in my original post it seems to just dump a load of Hex and some info on the system model.

I've also tried the D and Cmd-D options to run Apple Diagnostics but neither seem to be recognised (the iMac continues with is boot up/shut down behaviour).