Rsync is a fast and extraordinarily versatile file copying tool.
   It can copy locally, to/from another host over any remote shell,
   or to/from a remote rsync daemon.  It offers a large number of
   options that control every aspect of its behavior and permit very
   flexible specification of the set of files to be copied.  It is
   famous for its delta-transfer algorithm, which reduces the amount
   of data sent over the network by sending only the differences
   between the source files and the existing files in the
   destination.  Rsync is widely used for backups and mirroring and
   as an improved copy command for everyday use.

   Rsync finds files that need to be transferred using a "quick
   check" algorithm (by default) that looks for files that have
   changed in size or in last-modified time.  Any changes in the
   other preserved attributes (as requested by options) are made on
   the destination file directly when the quick check indicates that
   the file's data does not need to be updated.