I used dd
to copy an Ubuntu 18.04 installation from a 64GB partition on drive X to a 128GB partition on drive Y. See the below images for the problem; I am still limited to 64GB despite having a 128GB partition.
From "Disks" (shows partition size)
Baobab (aka Disk Usage Analyzer)
EDIT: Answer is below. I used resize2fs
to grow the filesystem.