If you upgrade the Photon OS Linux kernel with tdnf upgrade linux, you must modify the /boot/grub.cfg file to reflect the correct kernel version so that it works with AWS and GCE images. For example, if you install Photon OS 1.0 with kernel 4.4.8 and then upgrade the Linux kernel to 4.4.26, you must edit the /boot/grub2/grub.cfg file to replace the line containing linux /boot/vmlinuz-4.4.8 with linux /boot/vmlinuz-4.4.26. On Photon OS 3.0, reboot to load the new kernel. No grub modification needed.