aumvdown --version (return code: 0)
aufs-util for aufs4.9 20170918
aumvdown --help (return code: 0)
usage: aumvdown [options] file ...
move-down the specified file (an opposite action of copy-up)
from the highest branch where the file exist to the next
lower writable branch.
options:
-b | --lower-branch-id brid
-B | --upper-branch-id brid
-i | --interactive
-k | --keep-upper
-o | --overwrite-lower
-r | --allow-ro-lower
-R | --allow-ro-upper
-v | --verbose
-V | --version
aufs-util for aufs4.9 20170918