Kindly refer below for more on "dd" command.
dd - Disk Dump
How to use dd command ?
1. Create an empty file of 650MB size.
#dd if=/dev/zero of="empty_file" bs=1024k count=650
2. To Create ISO from CD OR DVD
#dd if=/dev/cdrom of=file.iso
3. Create an exact image of this floppy-disk by issuing the command
#dd if=/dev/fd0 of=floppy.img
4. Create backup of HDD or partition
#dd if=/dev/sdb of=backup.dd
5. Creating backup of one hardisk in to second HDD.
#dd if=/dev/sda of=/dev/sdb
6. How to take backup of only MBR and MBR + Partition Table;
#dd if=/dev/sda of=mbr.bak bs=1 count=446 (Backup only MBR)
#dd if=/dev/sda of=mbr_part.bak bs=1 count=512 (Backup MBR + Partition Table)
To restore,
#dd if=mbr.bak of=/dev/sda bs=1 count=446 (Restore only MBR)
#dd if=mbr_part.bak of=/dev/sda bs=1 count=512 (Backup only MBR)
7. To wipe the hard disk completely,
#dd if=/dev/zero of=/dev/sda
