CentOS 7 repair MBR and grub

Reproduced

First, repair MBR:

MBR (master boot 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=200

Here the block size as long as less than or equal to 446.

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:

2. Select Enter Rescue mode:

3. Press ENTER to continue:

4. Enter the disk Mount selection mode:

The disks will be mounted to the/mnt/sysimage/

Continue mount the partition in RW mode.

Read only mounts the partition in RO mode.

Skip skips, and in the future, manually mount the disks yourself.

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

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

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

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

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

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

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>

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

Once the repair is complete, you can enter the system and rebuild the configuration file.

Note: CentOS7 because of the use of GRUB2, configuration files and grub have a lot of changes, be sure to remember to backup grub.cfg for recovery.

CentOS 7 repair MBR and grub