partx is a program to tell the kernel about disk partitions. It does not change any data on the media, just the metadata in the kernel.
Most (all?) Linux distributions incorporate this from the [util-linux] project.
(This is included for completeness, and this author is unfamiliar with this program, but it seems likely to be useful mostly if you have whole-disk images in a partition on a larger drive.)
- GPT Partition
- Partitioning guidelines