How to enlarge a fixed VDI file with linux inside?

Question

linux

Actually, there is a virtual machine on debian, with 10 GB of memory.
There was a need to expand the place to 100 GB.
VBoxManage modifyhd file.vdi --resize 100000
gave an error

VBoxManage.exe: error: Resize hard disk operation for this format is not implemented yet!

Google claims that the problem is in the fixed disk and recommends " Clone VDI tool "
I ran VDI through it with the following settings:

At the same time, the new disk began to weigh as much as it was written on.

Loaded, executed df, but the OS does not see an increase in disk size.
(you can not count the numbers, 10GB of space is available on the screenshot)
CHADNT?

Answer 1

df outputs the size of the file system, which has nothing to do with the size of the physical or virtual disk.
Now the guest should have a physical disk of 100 available, but you haven't told the system how to use that extra capacity. Resize partitions, resize the file system. Just like moving a physical machine to another larger physical disk.