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backup

Data

backup

ssh root@remoteIP "dd if=/dev/mmcblk0p1" | gzip -1 - | dd of=boot.img.gz

reading and transfer at remote machine to reduce the CPU pressure and make the whole processs finish in a short time.

restore

For the restore process, it's better to do it locally

gzip -dc path/to/boot.img.gz | sudo dd of=/dev/mmcblk0p1

MBR & partation table (Schema)

Backing up the MBR

The MBR is stored in the the first 512 bytes of the disk. It consist of 3 parts: The first 446 bytes contain the boot loader. The next 64 bytes contain the partition table (4 entries of 16 bytes each, one entry for each primary partition). The last 2 bytes contain an identifier To save the MBR into the file "mbr.img": dd if=/dev/hda of=/mnt/sda1/mbr.img bs=512 count=1

To restore (be careful: this could destroy your existing partition table and with it access to all data on the disk): dd if=/mnt/sda1/mbr.img of=/dev/hda

If you only want to restore the boot loader, but not the primary partition table entries, just restore the first 446 bytes of the MBR:

dd if=/mnt/sda1/mbr.img of=/dev/hda bs=446 count=1

To restore only the partition table, one must use

dd if=/mnt/sda1/mbr.img of=/dev/hda bs=1 skip=446 count=64

You can also get the MBR from a full dd disk image. dd if=/path/to/disk.img of=/mnt/sda1/mbr.img bs=512 count=1

backup the partation table of a disk

sfdisk -d /dev/mmcblk0  > table.bak

restore a partition table file to a disk

sfdisk /dev/mmcblk0 <  table.bak

show schema: sfdisk -l /dev/mmcblk0

partition table of /dev/mmcblk0
  │unit: sectors

  │/dev/mmcblk0p1 : start=     2048, size=   196608, Id= e, bootable
  │/dev/mmcblk0p2 : start=   198656, size=  7016448, Id=83
  │/dev/mmcblk0p3 : start=        0, size=        0, Id= 0
  │/dev/mmcblk0p4 : start=        0, size=        0, Id= 0