Rsync is a fast and versatile file synchronization tool that allows to copy and sync files locally and from rsync service or any device that supports remote shell (Rsync does not support synchronization between remote devices). Rsync offers a large number of options that control every aspect of its behaviour and permit very flexible specification of the set of files to be copied.
Rsync implements a very efficient transfer algorithm based on deltas which reduces the amount of data sent over the network due it sends only the differences between the source and the destination file.
Rsync is widely used for backups and mirroring.
Rsync finds the files that need to be transferred using a quick check algorithm (by default), looking for files that have changed in size or in last modified date.