CentOS7 Repairing MBR and Grub

CENTOS7 Repairing MBR and Grub

First, repair MBR:

MBR (masterboot record main boot recording):

the hard disk's 0 cylinders, 0 heads, and 1 sectors are referred to as the primary boot sector . Where 446Byte is bootloader,64byte for partition table, and the remaining 2Byte is magic number.

Backup MBR:

#dd IF=/DEV/SDA Of=/root/mbr.bak count=1 bs=512

Destroy Bootloader:

#dd If=/dev/zero OF=/DEV/SDA count=1 bs=512

Repair method:

1. Mount disk repair with other systems.

The repair method is similar to the disc repair and is also used with the Grub2-install command.

2. Repair with the installation CD.

1. Mount the disc and select Troubleshooting on the disc Boot interface:

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2. Select Enter Rescue mode:

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3. Press ENTER to continue:

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4. Enter the disk Mount selection mode:

                  disk will be mounted to/mnt/sysimage/under

1. 1. 1. 1. continue mount the partition in RW mode.

         2. read only mounts partitions in RO mode.

         3. skip Skip and manually mount the disk in the future.

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5. Select continue, wait a moment, prompt has been mounted complete.

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6. Enter the rescue mode command line at this point:

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7. Rebuild the bootloader using the Grub2-install command:

#grub2-install ROOT-DIRECTORY=/MNT/SYSIMAGE/DEV/SDA

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show no errors, use sync to write to the hard drive, reboot restart the system.

8. No error after reboot, GRUB is running normally:

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At this point, the MBR repair is complete.

Second, repair grub

Grub configuration file is missing:

Boot will be directly into the grub interface, displayed as Grub>

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The repair steps are as follows:

Grub>insmod XFS

Grub>set root= (hd0,1)

Grub>linux16/vmlinuz-xxxxx Root=/dev/mapper/centos-root

Grub>initrd16/initramfs-.xxxxx.img

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CentOS7 Repairing MBR and Grub