Kernel Panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)

Got the error, after update on Ubuntu 18.04:
Kernel Panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)

To solve reboot the server and on the grub menu choose advanced options to choos the old kernel.
Get the Linux kernel exaclty version from grub running:

grep -A100 submenu  /boot/grub/grub.cfg |grep menuentry

Got the entry:

menuentry 'Ubuntu, with Linux 4.15.0-112-generic' --class ubuntu --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-4.15.0-112-generic-advanced-cb314007-7e1b-4b68-bd18-ee3fc9fccf14' {

So the version that failed to boot was 4.15.0-112.
So I recreated the initramfs with the command reflecting the default kernel that is booting:

update-initramfs -u -k 4.15.0-112-generic

And update the grup configuration:

update-grub

After the boot system tarted fine.

Got solution from here.