Use the following command to copy the partition table from sda to sdb.
sfdisk -d /dev/sda | sfdisk -f /dev/sdb
sfdisk -d dumps the partition table on to stdout. This is being piped to sfdisk /dev/sdb with the –force to write it on /dev/sdb.
You can use dd to copy the Master Boot Record (MBR) from one device to another (or to a file). For example, copying the MBR from sda to sdb would be done with
dd if=/dev/sda of=/dev/sdb bs=512 count=1
The flags are
if, input file (either device or ordinary file)
of, output file (either device or ordinary file)
bs, block size in bytes
count, number of blocks to copy.
The MBR contains the partition table for the four primary partitions, so this solution alone will not copy the definition for the extended partitions.