aufs-tools 1:4.9+20170918-2 (arm64 binary) in ubuntu focal

 The aufs driver provides a union mount for Linux filesystems. It allows one
 to virtually merge the contents of several directories and/or stack them, so
 that file changes in the aufs union mount end up as changes in only one
 of the source directories.
 .
 This package contains utilities needed to configure aufs containers on-the-fly.