Recently I noticed that despite upgrading kernel on my OVH VPS it's still using old version. After some research I discovered that OVH base image(Debian 8, VPS 2016 SSD 1) uses extlinux to manage master boot record. While I was used to self updating GRUB configuration, extlinux didn't point to new kernel automatically after upgrade. I found it's configuration in /boot/extlinux/extlinux.conf:
default linux
timeout 1
label linux
kernel boot/vmlinuz-3.16.0-4-amd64
append initrd=boot/initrd.img-3.16.0-4-amd64 root=/dev/vda1 console=tty0
console=ttyS0,115200 ro quiet
changed paths to initial RAM disk and Linux image:
default linux
timeout 1
label linux
kernel ../vmlinuz-4.9.0-8-amd64
append initrd=../initrd.img-4.9.0-8-amd64 root=/dev/vda1 console=tty0
console=ttyS0,115200 ro quiet
and updated extlinux with:
$ extlinux --install /boot/extlinux
After reboot extlinux loaded fresh kernel.