Rsync

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 lqquick checkrq 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.

General

rsync copies files either to or from a remote host, or locally on the current host (it does not support copying files between two remote hosts).

There are two different ways for rsync to contact a remote system: using a remote-shell program as the transport (such as ssh or rsh) or contacting an rsync daemon directly via TCP. The remote-shell transport is used whenever the source or destination path contains a single colon (:) separator after a host specification. Contacting an rsync daemon directly happens when the source or destination path contains a double colon (::) separator after a host specification, OR when an rsync:// URL is specified (see also the lqUSING RSYNC-DAEMON FEATURES VIA A REMOTE-SHELL CONNECTIONrq section for an exception to this latter rule).

As a special case, if a single source arg is specified without a destination, the files are listed in an output format similar to lqls -lrq.

As expected, if neither the source or destination path specify a remote host, the copy occurs locally (see also the --list-only option).

rsync refers to the local side as the lqclientrq and the remote side as the lqserverrq. Don't confuse lqserverrq with an rsync daemon -- a daemon is always a server, but a server can be either a daemon or a remote-shell spawned process.