Rsync is a free software utility for Unix- and Linux-like systems that copies files and directories from one host to another.
Rsync is considered to be a lightweight application because file transfers are incremental -- after the initial full transfer, only bits in files that have been changed are transferred. Rsynch is often used to provide offsite backups by syncing data to a remote machine outside a firewall. It is also used for mirroring Web sites.
Rsync is available on most Linux distributions by default. It can be used to update whole directory trees and file systems and can preserve soft links, hard links, file ownership, permissions, devices and times. Rsync requires no special privileges to install and can use remote shell (RSH), secure shell (SSH) or direct sockets as the transport.
See also: FTP, remote data backup, differential backup, incremental backup, delta differencing, cloud backup