One of my colleagues asked for help the other day with an Ubuntu system that would not boot after an upgrade. It was failing with the error:
Volume group "ubuntu-vg" not found. My first thought was that a hard drive had failed but, booting from a rescue CD, I could see the expected disks. This system was set up with an encrypted partition and LVM, and I found this article very helpful in resolving the problem.
From the rescue CD I was able to mount the root and boot file systems:
cryptsetup open /dev/nvme0n1p3 nvme0n1p3_crypt vgchange -a y mount /dev/mapper/ubuntu—vg-root /mnt mount /dev/nvme0n1p2 /mnt/boot
This was encouraging: the data on disk appeared to be intact. Maybe something had gone wrong creating the initial RAM disk when the kernel was upgraded - I had seen that before when the boot partition ran out of space during an upgrade (there was plenty of space in the boot partition on this system, but a corrupt initrd was still a possibility).
/sys inside the root filesystem, we can chroot into the installed system and re-install the latest kernel:
mount -t proc /proc /mnt/proc mount -t sys /sys /mnt/sys mount —bind /dev /mnt/dev chroot /mnt apt-get update apt-get dist-upgrade apt-get install —reinstall linux-image-4.15.0-136-generic
Now the moment of truth: exit the chroot and try to boot from the SSD. Success! If this hadn’t worked I would have tried booting from an older (previously working) kernel.