How to rescue system while boot grub lost

Symptoms

System boot fails and entering rescue mode.

Solution

Boot with ISO, enter rescue mode and create grub.cfg file.

chroot /mnt/sysroot
mount /dev/cdrom /mnt
rpm -ivh /mnt/Packages/kernel-core-*.rpm --force
grub2-mkconfig >/boot/grub2/grub.cfg
reboot