I've just installed the linux kernel 4.4 on Ubuntu server 16.04, which initially was 14.04 running kernel version 2.6 (but was then upgraded to 16.04 and of course when you do this, the kernel isn't changed). I ran update-grub after installing the new kernel and rebooted the server. It boots ok (thankfully) …

Ubuntu VPS Hosting via Ubuntu server not booting upgraded kernel.