Been raked over the coals with this one.
16.04 crashed while running. Could not even get grub to come up. It is not a dual boot system. Only 16.04. Just screen flashing. No command line access with no ability to read log files. No ability to go back to run level 3 (systemctl in ubuntu). Nothing.
At first, I reinstalled grub from an 18.04 trial install. After that I Was able to select "ubuntu recovery" on boot but with no effect. Same flashing of the screen with no command line access.
I'm sure that it is not a physical problem with the disk. A few weeks ago this same thing happened on another drive. I cloned the drive with DDrescue to another drive. Data was ok. The problem followed the new drive, implying that the problem was in the operating system. Somehow, not sure how, I was able to boot the new drive.
Now I am "in" the new drive and the same thing happened.
Loaded 18.04 on top of 16.04 and I can mount 16.04 and see programs, data.
Is there a way back from this? I don't want to have to download 300G on another drive at this point (downloading that much data is expensive).
Thank You Tom