I had the error mentioned in the title. I thought my SSD had died.
Thanks to Kernel Panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0) I was able to boot into the system again.
This happened after an apt update && apt upgrade, which installed a new kernel, possibly also some other things.
Going back to GNU/Linux 4.4.0-70-generic from GNU/Linux 4.4.0-71-generic allowed me to boot into the system.
Made a full backup.
I did a sudo apt-get purge linux-image-4.4.0-71-generic in order to remove what I believed to be a faulty Kernel.
My system has been acting up lately and I believe I have a faulty memory module. This may have messed things up, but I am not certain of this.
When I did a ls in GRUB after pressing the c-Key, the SSD was not listed, but only a HDD entry is in there. I added an HDD about 3 weeks ago, in order to backup the important stuff onto it. It used to be a two-partition HDD, both initially NTFS, but I reformatted one of them to ext3 I believe, in order to be able to use the file permissions.
The entry in GRUB for ls is a single line of (hd0) (hd0,msdos5) (hd0,msdos1)
I was expecting a sda entry for the ssd, as I've read in https://ubuntuforums.org/showthread.php?t=1751574
After purging the latest Kernel, when doing an apt update I was told that there was a linux-image-4.4.0-66-generic Kernel which I could apt autoremove. I did that, as I knew that I have the working .70-Kernel, that is ok. I was expecting GRUB to get rebuilt to a point where the hd0 would get removed, since I removed (unplugged from the SATA port) it prior to performing the apt autoremove.
I also did a sudo update-grub and sudo update-grub2, none of these seem to remove the hd0 entry.
What could have caused my problem on the .77-Kernel? I would like to apt upgrade it again, for the system to install it again, but it won't appear. Maybe because I used the --purge option, I don't know.
Could it be the posssibly faulty memory module which messed up the kernel, or could GRUB have been upgraded together with the last Kernel upgrade, and somehow made a wrong assumption about the hd0, possibly telling the Kernel to use that one as the root fs?
What would be my next step of trying to figure out what is going on here?
Oh, before rebooting I had a problem with a Docker container, it wouldn't restart, which was actually the reason for me to do a sudo poweroff. I have the Linux shutdown-sequence on video.
