The cpdup utility makes an exact mirror copy of the source in the
destination, creating and deleting files and directories as necessary.
UTimes, hardlinks, softlinks, devices, permissions, and flags are
mirrored. By default, cpdup asks for confirmation if any file or
directory needs to be removed from the destination and does not copy
files which it believes to have already been synchronized (by
observing that the source and destination file’s size and mtimes
match). cpdup does not cross mount points in either the source or the
destination. As a safety measure, cpdup refuses to replace a
destination directory with a file.