rsync

Andrew Tridgell and Paul Mackerras wrote the original rsync, which was first announced on 19 June 1996.[1] Tridgell discusses the design, implementation, and performance of rsync in chapters 3 through 5 of his Ph.D. thesis in 1999.[12] It is currently maintained by Wayne Davison.[13]

Because of the flexibility, speed, and scriptability of rsync, it has become a standard Linux utility, included in all popular Linux distributions. It has been ported to Windows (via Cygwin, Grsync, or SFU[14]), FreeBSD,[15] NetBSD,[16] OpenBSD,[17] and macOS.

Similar to cp, rcp and scp, rsync requires the specification of a source and of a destination, of which at least one must be local.[18]

Generic syntax:

rsync [OPTION] … SRC … [USER@]HOST:DEST
rsync [OPTION] … [USER@]HOST:SRC [DEST]

where SRC is the file or directory (or a list of multiple files and directories) to copy from, DEST is the file or directory to copy to, and square brackets indicate optional parameters.

rsync can synchronize Unix clients to a central Unix server using rsync/ssh and standard Unix accounts. It can be used in desktop environments, for example to efficiently synchronize files with a backup copy on an external hard drive. A scheduling utility such as cron can carry out tasks such as automated encrypted rsync-based mirroring between multiple hosts and a central server.

A command line to mirror FreeBSD might look like:

$ rsync -avz --delete ftp4.de.FreeBSD.org::FreeBSD/ /pub/FreeBSD/[19]

The Apache HTTP Server supports only rsync for updating mirrors.

$ rsync -avz --delete --safe-links rsync.apache.org::apache-dist /path/to/mirror[20]

The preferred (and simplest) way to mirror the PuTTY website to the current directory is to use rsync.

$ rsync -auH rsync://rsync.chiark.greenend.org.uk/ftp/users/sgtatham/putty-website-mirror/ .[21]

A way to mimic the capabilities of Time Machine (macOS) - see also tym.[22]

$ date=$(date "+%FT%H-%M-%S") # rsync interprets ":" as separator between host and port (i. e. host:port), so we cannot use %T or %H:%M:%S here, so we use %H-%M-%S
$ rsync -aP --link-dest=$HOME/Backups/current /path/to/important_files $HOME/Backups/back-$date
$ ln -nfs $HOME/Backups/back-$date $HOME/Backups/current

Make a full backup of system root directory:[23]

 $ rsync -avAXHS --progress --exclude={"/dev/*","/proc/*","/sys/*","/tmp/*","/run/*","/mnt/*","/media/*","/lost+found"} / /path/to/backup/folder

An rsync process operates by communicating with another rsync process, a sender and a receiver. At startup, an rsync client connects to a peer process. If the transfer is local (that is, between file systems mounted on the same host) the peer can be created with fork, after setting up suitable pipes for the connection. If a remote host is involved, rsync starts a process to handle the connection, typically Secure Shell. Upon connection, a command is issued to start an rsync process on the remote host, which uses the connection thus established. As an alternative, if the remote host runs an rsync daemon, rsync clients can connect by opening a socket on TCP port 873, possibly using a proxy.[24]

Rsync has numerous command line options and configuration files to specify alternative shells, options, commands, possibly with full path, and port numbers. Besides using remote shells, tunnelling can be used to have remote ports appear as local on the server where an rsync daemon runs. Those possibilities allow adjusting security levels to the state of the art, while a naive rsync daemon can be enough for a local network.

The rdiff utility 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). rdiff works well with binary files.

The rdiff-backup script maintains a backup mirror of a file or directory either locally or remotely 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.[28]

The librsync library used by rdiff is an independent implementation of the rsync algorithm. It does not use the rsync network protocol and does not share any code with the rsync application.[29] It is used by Dropbox, rdiff-backup, duplicity, and other utilities.[29]

The acrosync library is an independent, cross-platform implementation of the rsync network protocol.[30] Unlike librsync, it is wire-compatible with rsync (protocol version 29 or 30). It is released under the Reciprocal Public License and used by the commercial rsync software Acrosync.[31]

Duplicity is a variation on rdiff-backup that allows for backups without cooperation from the storage server, as with simple storage services like Amazon S3. It works by generating the hashes for each block in advance, encrypting them, and storing them on the server. It then retrieves them when doing an incremental backup. The rest of the data is also stored encrypted for security purposes.

As of macOS 10.5 and later, there is a special -E or --extended-attributes switch which allows retaining much of the HFS file metadata when syncing between two machines supporting this feature. This is achieved by transmitting the Resource Fork along with the Data Fork.[32]

zsync is an rsync-like tool optimized for many downloads per file version. zsync is used by Linux distributions such as Ubuntu[33] for distributing fast changing beta ISO image files. zsync uses the HTTP protocol and .zsync files with pre-calculated rolling hash to minimize server load yet permit diff transfer for network optimization.

Rclone is an open-source tool inspired by rsync that focuses exclusively on cloud storage system providers. It supports more than 50 different providers and provides an rsync-like interface to backup local data to those providers.[34]

• casync
• Remote Differential Compression
• List of TCP and UDP port numbers

• Official website
• rsync algorithm - 1998-11-09
• rsync Examples (How to use rsync)