How to create a partition without unmounting?

As you can guess, I am trying to dual boot Ubuntu and Kali. But the thing is that i don't have a spare ubuntu iso(which would allow me to live boot ubuntu and then create a partition using g parted or any other app since my hd remains unmounted). So, it would be very awesome if anyone could provide me a way to create a new partition without unmounting it.. TIA

In order to make a new partition you will have to shrink one and create space for the new one. You can't shrink a mounted partition or unmount a partition of a running system. That's where you need a live ubuntu, either on a CD or simply on a USB-stick.