LVMの容量減らす

# check verify disk.
sudo e2fsck -f /dev/mapper/brokenwebapps-root
# resize fs.
sudo resize2fs /dev/mapper/brokenwebapps-root 20G # to 20G
# resize lvm.
sudo lvm lvreduce -L20G /dev/mapper/brokenwebapps-root                                                                                                                            fw.cpp:L711-上流判断
  WARNING: Reducing active logical volume to 20.00 GiB.
  THIS MAY DESTROY YOUR DATA (filesystem etc.)
Do you really want to reduce brokenwebapps/root? [y/n]: y
  Size of logical volume brokenwebapps/root changed from <63.38 GiB (16224 extents) to 20.00 GiB (5120 extents).
  Logical volume brokenwebapps/root successfully resized.