The fdisk output confirms it. Your root partition is only 256 GB, and it’s full. That sounds more like an issue with how your OS was set up, rather than something actually being wrong.
You should be able to extend the root partition in place since the remainder of the free space is contiguous following it. You can find various guides online for different methods to do this. I’m not going to vouch for a particular one without knowing more about your system.
Now, if I could offer a little bit of advice. I don’t know how deep you are into using this system yet, but I would have installed it with LVM. Although it does add some steps to something like a partition resize, it also opens up a lot of options for how to approach this kind of situation, some of which are much safer than what you’re about to have to do. Definitely take a snapshot before resizing.
Another thing to consider. You may want a separate virtual disk to house NC’s data folder. If your database is on the root partition, and that partition is unable to write due to filling up, it can lead to problems with the database, not to mention other various parts of the OS.
I don t know exactly, i once made a snap in VM, today I first had to consolidate this snap. Than deleted all Snapshots. In the VMware interface the disk provisioning now shows a disk size of 59Tb. Before I could not change that disk size. fdisk -l /dev/sda now shows
Device Start End Sectors Size Type
/dev/sda1 2048 4095 2048 1M BIOS boot
/dev/sda2 4096 536868863 536864768 256G Linux filesystem
=== START OF INFORMATION SECTION ===
Vendor: VMware
Product: Virtual disk
Revision: 1.0
User Capacity: 64,424,509,440,000 bytes [64.4 TB]
Logical block size: 512 bytes
LU is fully provisioned
Device type: disk
Local Time is: Sat Apr 18 12:33:11 2020 UTC
SMART support is: Unavailable - device lacks SMART capability.