btrfs
- Measure real btrfs disk use without sudo
Get the real on-disk size of a btrfs path, after compression and reflinked copies, by running the host's compsize in a rootful Docker container.
- 12.4 GB of duplicates, 3.4 GB on disk
On compressed btrfs, du and a duplicate finder overstated what deleting would free, and a permission error hid 15.8 GB. compsize, without sudo, told the truth.