Rsync is a file synchronization utility that transfers files efficiently over local and remote connections using a delta-transfer algorithm.
Rsync solves the problem of transferring large files or file sets across networks by sending only the differences between source and destination files rather than entire files. Its delta-transfer algorithm calculates these differences without requiring both file sets to be present at one location beforehand, making it substantially faster than tools that transfer complete files. The tool works over ssh or rsh for remote transfers and can also operate in daemon mode for public file distribution with optional authentication and access control.
Rsync suits anyone performing backups, restores, or regular file synchronization tasks where bandwidth efficiency matters. It works as a command-line tool with an interface similar to scp but with extensive additional options for controlling transfer behavior. The tool requires no special privileges or setuid installation and works on systems with a functioning ssh or rsh setup, though ssh is recommended for security. Daemon mode makes it suitable for scenarios requiring centralized file distribution or pull-based synchronization. Developers should be aware that building rsync from source requires running a configure script and may need to specify a non-gcc compiler on some systems to enable features like 64-bit file offsets.
The project maintains active communication channels including a mailing list for discussion and announcements, a Discord server for real-time development chat, and a dedicated bug-tracking web page with guidelines for effective issue reporting. Security issues are handled through a separate email address rather than public bug reports. The tool includes comprehensive documentation in the form of manpages and a technical report describing the rsync algorithm.
