tell the kernel about the existence of a partition
addpart device partition start length
addpart tells the Linux kernel about the existence of the specified partition. The command is a simple wrapper around the "add partition" ioctl.
This command doesn't manipulate partitions on a block device.
device The disk device.
partition The partition number.
start The beginning of the partition (in 512-byte sectors).
length The length of the partition (in 512-byte sectors).
The addpart command is part of the util-linux package and is available from https://www.kernel.org/pub/linux/utils/util-linux/.