Most of the time I encounter boot issue in ubuntu and tend to loose data because of it. This is very time consuming and a hindrance to the work. There is a nifty technique to get over ‘ERROR vfs unable to mount root fs on unknown-block’ by reinstalling GRUB boot-loader.
To reinstall, you need a live CD or download and write a bootable USB drive for the same version of ubuntu. Once booted in to the OS, open a terminal and install boot-repair.
sudo add-apt-repository ppa:yannubuntu/boot-repair sudo apt-get update sudo apt-get install -y boot-repair && boot-repair
Open boot-repair by typing boot-repair in terminal.
According to majority of posts, you can get over the issue by trying ‘Recommended repair’ and reboot the machine. I tried it and it did not work for me. So I navigated to Advanced options->GRUB options->Reset GRUB to its most recent version
Even though upgrading GRUB installs newest version of GRUB irrespective of the current version of OS(ubuntu 17.10). After reboot, the system booted to the existing ubuntu 16.04.3 installation.