Partitioning ubuntu installed harddrive

Question

I need to create an additional partition on an external harddrive where ubuntu is installed. is there any way i can do this without affecting ubuntu.Its 1Tb and ubuntu and my files only takes 30gb of it. I need an extra partition atleast 400gb. Gparted not allowing me to do that since ubuntu is on the same partition I can connect this external harddrive to another pc but scared if it affects Ubuntu

Answer 1

If you boot a LiveCD or LiveUSB, you can make sure all partitions on the hdd are unmounted and resize to your needs.

Answer 2

Back up your data since repartitioning can result in data loss.

You can't chance an active partition and the partition mounted at / can't be unmounted in a running system. That's why you can't do your intended operation.

Ubuntu provides the so-called "Start Disk Creator" which you can use to put a live system on a USB stick. It needs to be formatted with FAT32.

If you have another computer with a Linux system and GParted on it, you can use it instead, so you don't have to create a live medium. The only important thing is that the partitions aren't mounted.