How to back up Master Boot Record (MBR) in Linux

Backing up the Master Boot Record (MBR) before changing partitions, installing another operating system, or experimenting with boot loaders preserves a known-good boot path. A small backup image created in advance can be restored quickly if the primary disk stops booting after modifications, avoiding longer recovery work.

On Linux systems that use BIOS-style partitioning, the MBR occupies the first 512 bytes of a disk and contains the initial boot loader code, the primary partition table, and a signature. The dd utility reads and writes raw blocks from devices such as /dev/sda and can copy this 512-byte region into a regular file without altering its structure, which is ideal for saving and restoring the MBR.

Running dd with elevated privileges against the wrong device or in the wrong direction can destroy data, so disk names must be checked carefully before proceeding. Keeping the backup on separate storage such as a USB drive or network share protects it from disk failures, and including the disk name and date in the file name helps track which backup belongs to which system.

1. Open a terminal with access to sudo on the Linux system.

   $ whoami
   root

2. List available disks to identify the device that holds the MBR to be backed up.

   $ lsblk
   NAME      MAJ:MIN RM   SIZE RO TYPE MOUNTPOINTS
   loop0       7:0    0     1G  0 loop /mnt/data
   loop1       7:1    0   512M  0 loop 
   loop2       7:2    0    64M  0 loop 
   loop7       7:7    0    64M  0 loop 
   `-loop7p1 259:0    0    31M  0 part 
   ##### snipped #####
   vda       254:0    0   1.8T  0 disk 
   `-vda1    254:1    0   1.8T  0 part /etc/hosts
                                       /etc/hostname
                                       /etc/resolv.conf
   vdb       254:16   0 606.5M  1 disk

3. Note the full device name of the target disk such as /dev/sda or /dev/nvme0n1 instead of a partition entry.

   Using a partition like /dev/sda1 instead of the whole disk omits the MBR region and produces an unusable backup for boot recovery.

4. Back up the first 512 bytes from the selected disk into a regular file using dd.

   $ sudo dd if=/dev/loop2 of=/root/sg-work/disk-lab/mbr-lab.bin bs=512 count=1
   1+0 records in
   1+0 records out
   512 bytes copied, 0.000135583 s, 3.8 MB/s

   Reversing the if and of parameters or pointing either one at the wrong device can overwrite the MBR or another disk region, which may prevent the system from booting.

5. Check the backup file size to confirm that exactly 512 bytes were written.

   $ ls -l /root/sg-work/disk-lab/mbr-lab.bin
   -rw-r--r-- 1 root root 512 Dec 22 08:02 /root/sg-work/disk-lab/mbr-lab.bin

   A size of 512 bytes indicates that the full MBR sector, including partition table and signature, has been saved.

6. Inspect the backup contents for recognizable strings such as the boot loader name.

   $ strings /root/sg-work/disk-lab/mbr-lab.bin
   GRUB

   Strings like GRUB suggest that the boot loader code was captured correctly when using the GRUB boot loader.

7. Copy the backup file to external storage such as a USB drive or network share.

   $ cp /root/sg-work/disk-lab/mbr-lab.bin /media/usb-backups/

   Storing backups on a separate device protects them from failures or accidental overwrites on the main disk.

8. Record the source disk, backup file name, and storage location in notes or documentation for future reference.