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How To Backup & Restore Master Boot Record (MBR) In Linux
A master boot record (MBR) is a type of boot sector popularized by the IBM Personal Computer. It consists of a sequence of 512 bytes located at the first sector of a data storage device such as a hard disk. MBRs are usually placed on storage devices intended for use with IBM PC-compatible systems.
MBR Total Size
446 + 64 + 2 = 512
Where,
446 bytes – Bootstrap.
64 bytes – Partition table.
2 bytes – Signature.
Backup MBR
Linux or Unix provides “dd” tool to backup any file. Usually, you must be “root” so that you can use it.
Use `dd` linux program to save / recover a disk's MBR
I have an Ubuntu OS installed on my laptop. I want to install Windows 7 as well to another disk partition (I will do it by recovering it from a special partition on my laptop).
After installing Windows, I want to recover my hard drive MBR to be able to load Ubuntu. I have a plan to use linux dd program:
1) (Before installing, perform this command in Linux) dd if=/dev/sda of=/home/user/mbr_backup bs=512 count=1
2) (after installing, load Ubuntu Live CD and launch this) dd if=/home/user/mbr_backup of=/dev/sda bs=512 count=1
3) Load Ubuntu on PC and re-configure the GRUB2 to be able start Windows
I need your advice, I want to be sure I won’t damage the disk (it’s partition table).
Copy Master Boot Record (MBR)
How do I copy MBR from one hard disk to another hard disk under Debian Linux?
To copy MBR simply use the dd command. dd command works under all Linux distros and other UNIX like operating systems too. A master boot record (MBR) is the 512-byte boot sector that is the first sector of a partitioned data storage device of a hard disk.
MBR Total Size
- 446 bytes – Bootstrap.
- 64 bytes – Partition table.
- 2 bytes – Signature.
512 vs 446 Bytes
- Use 446 bytes to overwrite or restore your /dev/XYZ MBR boot code only with the contents of $mbr.backup.file.
- Use 512 bytes to overwrite or restore your /dev/XYZ the full MBR (which contains both boot code and the drive’s partition table) with the contents of $mbr.backup.file.
dd command to copy MBR (identically sized partitions only)
Type dd command as follows:
dd if=/dev/sda of=/dev/sdb bs=512 count=1
Above command will copy 512 bytes (MBR) from sda to sdb disk. This will only work if both discs have identically sized partitions.
dd command for two discs with different size partitions
# dd if=/dev/sda of=/tmp/mbrsda.bak bs=512 count=1
Now to restore the image to any sdb:
# dd if=/tmp/mbrsda.bak of=/dev/sdb bs=446 count=1
The above commands will preserve the partitioning schema.
Linux sfdisk Command Example
Linux sfdisk command can make a backup of the primary and extended partition table as follows. It creates a file that can be read in a text editor, or this file can be used by sfdisk to restore the primary/extended partition table. To back up the partition table /dev/sda, enter:
# sfdisk -d /dev/sda > /tmp/sda.bak
To restore, enter:
# sfdisk /dev/sda < /tmp/sda.bak
The above command will restore extended partitions.
Task: Backup MBR and Extended Partitions Schema
Backup /dev/sda MBR, enter:
# dd if=/dev/sda of=/tmp/backup-sda.mbr bs=512 count=1
Next, backup entries of the extended partitions:
# sfdisk -d /dev/sda > /tmp/backup-sda.sfdisk
Copy /tmp/backup-sda.sfdisk and /tmp/backup-sda.mbr to USB pen or somewhere else safe over the network based nas server.
Task: Restore MBR and Extended Partitions Schema
To restore the MBR and the extended partitions copy backup files from backup media and enter:
# dd if=backup-sda.mbr of=/dev/sda
# sfdisk /dev/sda < backup-sda.sfdisk
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About the Author
If I were to describe myself with one word it would be, creative. I am interested in almost everything which keeps me rather busy. Here you will find some of my technical musings. Securely email me using — PGP: 4CB8 91EB 0C0A A530 3BE9 6D76 B076 96F1 6135 0A1B View all posts by Timothy Conrad