Unionfs is a stackable unification file system, which can appear to
merge the contents of several directories (branches), while keeping
their physical content separate.  Unionfs is useful for unified source
tree management, merged contents of split CD-ROM, merged separate
software package directories, data grids, and more.  Unionfs allows
any mix of read-only and read-write branches, as well as insertion and
deletion of branches anywhere in the fan-out.  To maintain Unix
semantics, Unionfs handles elimination of duplicates, partial-error
conditions, and more.  This release also includes additional
preliminary features that were specifically designed for security
applications, such as snapshotting and sandboxing.

unionctl is used to control a unionfs file system.
uniondbg  runs  unionfs  debugging ioctls.

• Anton Farygin

• unionfs_utils