Rsync

zsyncrdiffrdiff-backuprsync algorithmlibrsync
rsync is a utility for efficiently transferring and synchronizing files between a computer and an external hard drive and across networked computers by comparing the modification times and sizes of files.wikipedia
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Andrew Tridgell

Andrew "Tridge" Tridgell
Andrew Tridgell and Paul Mackerras wrote the original rsync, which was first announced on 19 June 1996.
He is the author of and a contributor to the Samba file server, and co-inventor of the rsync algorithm.

Grsync

It has been ported to Windows (via Cygwin, Grsync, or SFU ), FreeBSD, NetBSD, OpenBSD, and macOS.
Grsync is a graphical user interface for rsync.

Delta encoding

deltadelta compressiondeltas
The rsync algorithm is a type of delta encoding, and is used for minimizing network usage.
For example, rsync uses a rolling checksum algorithm based on Mark Adler's adler-32 checksum.

Secure copy

SCP Secure Copy Protocol
Similar to, and, requires the specification of a source and of a destination, of which at least one must be local.
According to OpenSSH developers in April 2019 the scp protocol is outdated, inflexible and not readily fixed; they recommend the use of more modern protocols like sftp and rsync for file transfer.

Rolling hash

rolling checksumBuzhashRabin-Karp rolling hash
The recipient splits its copy of the file into chunks and computes two checksums for each chunk: the MD5 hash, and a weaker but easier to compute 'rolling checksum'. The rolling checksum used in rsync is based on Mark Adler's adler-32 checksum, which is used in zlib, and is itself based on Fletcher's checksum.
Another popular application is the rsync program, which uses a checksum based on Mark Adler's adler-32 as its rolling hash.

Zlib

zlib wrapper
Zlib may be used for additional data compression, and SSH or stunnel can be used for security. The rolling checksum used in rsync is based on Mark Adler's adler-32 checksum, which is used in zlib, and is itself based on Fletcher's checksum.

Cygwin

CygnixCygwin projectWindows/Cygwin
It has been ported to Windows (via Cygwin, Grsync, or SFU ), FreeBSD, NetBSD, OpenBSD, and macOS.

Adler-32

Adler32
The rolling checksum used in rsync is based on Mark Adler's adler-32 checksum, which is used in zlib, and is itself based on Fletcher's checksum.
A "rolling checksum" version of Adler-32 is used in the rsync utility.

Secure Shell

SSHOSSHSSH Client
Zlib may be used for additional data compression, and SSH or stunnel can be used for security.

CwRsync

cwRsync is an implementation of rsync for Windows.

Duplicity (software)

duplicityDéjà Dup
It is used by Dropbox, rdiff-backup, duplicity, and other utilities.
It does this using GnuPG, librsync, tar, and rdiff.

Time Machine (macOS)

Time MachineApple Time MachineApple's Time Machine
A way to mimic the capabilities of Time Machine (macOS) - see also tym.
As a result, tools like rsync cannot be used to replicate a Time Machine volume; replication can only reliably be done by imaging the entire filesystem.

Cp (Unix)

cp cp (copy)
Similar to, and, requires the specification of a source and of a destination, of which at least one must be local.

Casync

According to the creator Lennart Poettering, casync is inspired by rsync and Git, as well as tar.

LuckyBackup

It shares the data differencing and copying tool, rsync, with BackupPC, and several others.

Back in Time (Linux software)

Back In Time
Back In Time uses rsync as backend and has the characteristic feature of using hard links for files which are identical in snapshots at different times, thus using disk space just once for files that remained unchanged.

Patch (Unix)

patchpatches
The delta file can then be applied to file A, turning it into file B (similar to the patch utility).

Remote Differential Compression

RDC is similar in many ways to the older (1996) rsync protocol, but with some useful innovations, in particular the recursive algorithm and cross-file RDC.

File transfer

transfer filestransferring filesfile-transfer
rsync is a utility for efficiently transferring and synchronizing files between a computer and an external hard drive and across networked computers by comparing the modification times and sizes of files.

File synchronization

synchronizationsyncsynchronize
rsync is a utility for efficiently transferring and synchronizing files between a computer and an external hard drive and across networked computers by comparing the modification times and sizes of files.

Computer file

filefilescomputer files
rsync is a utility for efficiently transferring and synchronizing files between a computer and an external hard drive and across networked computers by comparing the modification times and sizes of files.

Computer network

networkcomputer networkingnetworking
rsync is a utility for efficiently transferring and synchronizing files between a computer and an external hard drive and across networked computers by comparing the modification times and sizes of files.