Two, grub menu resume
preparations: Analog fault grub menu
grub menu configuration file is deleted again after restarting the server will be shown below, which can not start properly. 
After the server restart, after a few steps with the same MBR sector recovery operations until entering the emergency mode command.
1, the guide rescue mode, the mirroring system load
command: CHROOT / mnt / sysimage / 
2, to re-establish the partition sda load
command: the install-grub2 / dev / sda 
. 3, rebuild grub profile menu
command: grub2-mkconfig -o / boot /grub2/grub.cfg 
4, after exiting the bash mode to restart the server to verify whether the normal boot
exit
reboot
