When booting an Azure VM, this error:
304.863321] —[ end Kernel panic – not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
Solution: remove old linux kernels, your /boot drive is out of space.
-boot to grub and click on “Advanced options”
-Select a previous kernel (should boot fine)
login and enter command
$ df
See if your /boot directory is 100% used
Remove old linux kernels
$ sudo apt-get autoremove
Also, there may be an issue with the storage drivers (that should be built into initramfs) needed for Hyper-V / Azure.
Other Information: https://support.microsoft.com/en-us/help/4091524/how-recovery-azure-linux-vm-from-kernel-related-boot-related-issues