rsync - incremental file transfer program for Unix systems

rsync is a file transfer program for Unix systems. rsync uses the rsync algorithm which provides a very fast method for bringing remote files into sync. It does this by sending just the differences in the files across the link, without requiring that both sets of files are present at one of the ends of the link beforehand. It can update whole directory trees and filesystems. It can use rsh, ssh or direct sockets as the transport.