Clone HDD or flash disks

dd if=/dev/sda of=hdd.img
dd if=hdd.img of=/dev/sda

dd if=/dev/sda1 of=hdd.img
dd if=hdd.img of=/dev/sda1

dd if=/dev/sda1 of=hdd.img
dd if=hdd.img of=/dev/sda1

dd if=/dev/cdrom of=/mnt/cdbackup.iso
dd if=/mnt/cdbackup.iso of=/dev/cdrom

Clone drives over a network:

dd if=/dev/sda | ssh username@host "dd of=/dev/sda"

Dump an image over a network:

dd if=/dev/sda | ssh username@host "dd of=/mnt/hdd.img"

Clone a networked drive onto yours:

ssh username@host "dd if=/dev/sda" | dd of=/dev/sda

Clone a networked image onto yours:

ssh username@host "dd if=/mnt/hdd.img" | dd of=/dev/sda

src
MBR Total Size = 446 + 64 + 2 = 512

• 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

example: 32Gb to 8Gb
Given:

• sdc: 32Gb with sdc1=4Gb, sdc2=4Gb, and 23Gb of free space.
• sdd: 8Gb

Count number of blocks to copy:

8015282176/512 = 15654848

Create image file:

sudo dd if=/dev/sdc of=jr1.img count=15654848

Write image file:

sudo dd if=jr1.img of=/dev/sdd  

First, find out the process id of the dd process by running the following in the new virtual terminal.

$ pgrep -l '^dd$'
8789 dd

To send the USR1 signal to the dd prcoess:

$ kill -USR1  8789
$

Note that as soon as the USR1 signal is detected, dd will print out the current statistics to its STDERR.

$ dd if=/dev/random of=/dev/null bs=1K count=100
0+14 records in
0+14 records out
204 bytes (204 B) copied, 24.92 seconds, 0.0 kB/s