Ubuntu – Stuck on boot, on ‘loading initial ramdisk’ or dropped to busybox

I made the mistake of assuming all the background was part of the problem, when the problem was just that grub2 couldn't find the system:

Kernel panic - not syncing: VFS: Unable to mount root fs...

I imagine the cause is that I forgot to run "sudo update-grub2" after running "sudo update-initramfs."

The solution turned out to be to boot to a Live CD, mount and chroot to the hard drive, and re-run update-initramfs and update-grub2, as detailed here.

Two complications I encountered were:

1. "fdisk -l" doesn't work on GPT volumes; you have to use "gdisk -l" instead.
2. I have /boot and / on different volumes, and / is encrypted.

So I needed to modify the mount sequence as follows:

sudo cryptsetup luksOpen /dev/sdaX sdaX_crypt
sudo mount /dev/mapper/sdaX_crypt /mnt
sudo mount /dev/sdaY /mnt/boot
sudo mount --bind /dev /mnt/dev
sudo mount --bind /dev/pts /mnt/dev/pts
sudo mount --bind /proc /mnt/proc
sudo mount --bind /sys /mnt/sys
sudo chroot /mnt

So I am back into my system, though I still don't have a cursor. But that is another problem.

Ok, figured it out.

The UUID of sdb3_crypt (where / and swap are located) somehow wasn't right in /etc/crypttab. I verified this by comparing the UUIDs listed in /etc/crypttab with those listed in /dev/disk/by-uuid/. No idea how that got wrong, but I must have fat fingered it somewhere along the way.

I corrected /etc/crypttab with the correct UUID of /dev/sdb3, then updated the initramfs ($update-initramfs -c -k 4.4.0-24-generic). Reboot and now it works ok.