I recently did ubuntu update and then after reboot i got following screen related to kernel panic. The problem for me was that my /boot ran out of space.
Solution:
Restart your machine and go to grub loader
Select "Advanced options for Ubuntu"
Then you will be listed with list of kernels, select one of them and press enter [at least one of them should allow to you boot and login into your ubuntu machine]
Then go to terminal and run:
aptitude search ~ilinux-image
this should list all the kernel images u have in /boot
run
uname -a
to get ur current running kernel
run
sudo apt-get <image name>
for example: sudo apt-get autoremove linux-image-4.4.0-45-generic
to remove the image that you dont need
