进入Linux Live CD并chroot到本地硬盘

sudo su
mount /dev/sda4 /mnt  #系统根分区对应的sdaX
mount /dev/sda2 /mnt/boot/efi  #EFI 分区
mount -t proc proc /mnt/proc
mount -t sysfs sys /mnt/sys
mount -o bind /dev /mnt/dev
mount -t devpts pts /mnt/pts

chroot /mnt

执行Grub2安装命令

grub2-install --directory=/usr/lib64/grub/x86_64-efi --target=x86_64-efi --efi-directory=/boot/efi --boot-directory=/boot/efi --bootloader-id=ubuntu --removable sda2

重启

update-grub2

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