MBR repair

 First, create a partition put the backup file, the backup point MBR sector

partprobe  /dev/sdb

mkfs.ext4 /dev/sdb1

Create a mount point mkdir / backup

Mount mount / dev / sdb1 / backup

Backup dd if = / dev / sda of = / backup / sda.mbr.bak bs = 512 count = 1

Remove MBR sector dd if = / dev / zero of = / dev / sda bs = 512 count = 1

Reboot reboot

Enter emergency mode

Create a new mount point mkdir / aa

Mount mount / dev / sdb1 / aa

Recovery dd if = / aa / sda.mbr.bak of = / dev / sda

Exit exit exit