I am currently stuck at the login screen, unable to login--each attempt just takes me back to the login screen.
This started with trying to update to OS X Mojave (from High Sierra), due to the constant message popping up urging me to upgrade. So, I finally decided to do so.
During the update, I got a kernel panic that was stuck in an infinite loop due to
install error -69854.
So, I decided to try to reinstall Mojave booting to disk utility, but after 30 minutes of install, I got the same error.
Then, I reinstalled OS X Yosemite via disk utility (original OS version that came with the iMac). That seemed to go fine until I tried to log in. At the login screen, I typed in my password correctly, and it looked like it was starting to log me in, then the screen went black and immediately went back to the login screen.
I booted in safe mode and got the same behavior--looked like it was logging in, but then went black and back to login screen.
*Note that I tried an incorrect password as well, just to ensure I was typing it correctly. When typing an incorrect password, it stays on the login screen. So I know it's not the password.
repair permissions in Disk Utility, which completed successfully.
Then I tried doing a
repair disk, but that failed with "unable to unmount volume for repair."
I rebooted again and tried to login again, but same issue.
I reset NVRAM, just in case, but same issue.
I rebooted in safe mode, but same issue.
I'm on an iMac that is a late 2013 model. No issues prior to trying to upgrade to OS X Mojave.
Any other thoughts/steps?
I'm currently creating a bootable Mojave disk to see if I have any better luck, but I'm not optimistic.