Rsync

rsync is a command line tool which synchronizes files and directories from one location to another while minimizing data transfer using delta encoding when appropriate. An important feature of rsync not found in most similar programs/protocols is that the mirroring takes place with only one transmission in each direction.

rsync can copy or display directory contents and copy files, optionally using compression and recursion.

rsync has the default TCP port of 873.

Usage

Examples

Let's say you wish to rsync your home directory (e.g. /home/bob) with a backup directory/disk (e.g. /backup). The following command will accomplish this:

rsync -avz --delete /home/bob/ /backup/

where a means archive, v mean do it verbosely, z mean compress the data, and delete means to delete the backup file if the original file (i.e. in /home/bob) has been deleted since the last rsync.

The same can be done where the backup disk is on a remote machine via ssh. See here for more information.

Variations

rdiff and rdiff-backup

There also exists a utility called rdiff, which uses the rsync algorithm to generate delta files with the difference from file A to file B (like the utility diff, but in a different delta format). The delta file can then be applied to file A, turning it into file B (similar to the patch utility).

Unlike diff, the process of creating a delta file has two steps: first a signature file is created from file A, and then this (relatively small) signature and file B is used to create the delta file. Also unlike diff, rdiff works well with binary files.

Using rdiff, a utility called rdiff-backup has been created, capable of maintaining a backup mirror of a file or directory over the network, on another server. rdiff-backup stores incremental rdiff deltas with the backup, with which it is possible to recreate any backup point.

External links

• Wikipedia article on rsync
• rsync homepage
• A useful tutorial
• rsync algorithm
• Xdelta – alternative implementation of file differencing and delta encoding
• Unison, allows bidirectional synchronisation