This is an old revision of the document!
First you resize the VM disk offline on Proxmox Boot the VM and enter it:
sudo su
# fdisk -l /dev/sda
# parted /dev/sda
Answer: Fix
resize part 3 100%
quit
# pvresize /dev/sda3 # lvresize –extents +100%FREE –resizefs /dev/mapper/ubuntu–vg-ubuntu–lv
Take a breath, it's done. I should read up on LVM management.