EFI grub centos 7

grub2-mkconfig -o /boot/efi/EFI/centos/grub.cfg
yum reinstall grub2-efi grub2-efi-modules  shim

https://community.centminmod.com/threads/grub-help.12867/page-3

without EFI

grub2-mkconfig –o /boot/grub2/grub.cfg