Complete toolkit for rsync 3.4.1, the fast file-copying tool using delta-transfer algorithm. Use when backing up files, mirroring directories, syncing data across hosts via SSH or rsync daemon, implementing incremental backups, configuring rsyncd.conf daemons, or managing filter rules.
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name
rsync-3-4-1
description
Complete toolkit for rsync 3.4.1, the fast file-copying tool using delta-transfer algorithm. Use when backing up files, mirroring directories, syncing data across hosts via SSH or rsync daemon, implementing incremental backups, configuring rsyncd.conf daemons, or managing filter rules.
Rsync is a fast and extraordinarily versatile file-copying tool. It can copy locally, to/from another host over any remote shell (typically SSH), or to/from a remote rsync daemon. 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, mirroring, and as an improved copy command for everyday use.
Rsync finds files that need to be transferred using a "quick check" algorithm (by default) that looks for files that have changed in size or in last-modified time. Any changes in other preserved attributes are made on the destination file directly when the quick check indicates that the file's data does not need to be updated.
Key features include:
Delta-transfer algorithm for efficient network usage
Support for copying links, devices, owners, groups, and permissions
Exclude and exclude-from options similar to GNU tar
CVS exclude mode for ignoring common build artifacts
Transparent remote shell support (SSH, rsh)
No super-user privileges required
Pipelining of file transfers to minimize latency
Anonymous or authenticated rsync daemons for mirroring
Incremental recursion for large file trees (reduced memory usage)
Batch mode for applying the same updates to many identical systems
Compression during transfer with configurable algorithms
ACL and extended attribute preservation
When to Use
Backing up files locally or across hosts
Mirroring directories (keeping source and destination in sync)
Syncing data over SSH between servers
Implementing incremental rotating backups with --link-dest or --backup-dir
Creating batch update files for bulk deployment to multiple identical systems
Setting up rsync daemons for anonymous or authenticated file distribution
Managing complex include/exclude filter rules for selective transfers
Moving files (using --remove-source-files)
Performing dry runs to preview what changes rsync would make
Core Concepts
Transfer Modes
Rsync operates in three modes:
Local copy — both source and destination are on the same machine:
rsync -av /src/dir/ /dest/dir/
Remote shell (pull) — pulling files from a remote host via SSH:
rsync -av user@remote:/src/dir/ /local/dest/
Remote shell (push) — pushing files to a remote host via SSH:
rsync -av /local/src/ user@remote:/dest/dir/
Rsync daemon (pull) — connecting directly to an rsync daemon:
A trailing slash on the source changes behavior significantly:
rsync -av /src/foo /dest — copies the directory foo into /dest, creating /dest/foo
rsync -av /src/foo/ /dest — copies the contents of foo into /dest
Both set the attributes of the containing directory on the destination
For daemon connections, no trailing slash is needed to copy module contents:
rsync -av host::module /dest
Archive Mode (-a)
The -a (archive) flag is shorthand for -rlptgoD:
-r — recurse into directories
-l — copy symlinks as symlinks
-p — preserve permissions
-t — preserve modification times
-g — preserve group
-o — preserve owner (requires root on receiver)
-D — preserve devices and specials
Note: -a does not include -A (ACLs), -X (xattrs), -U (atimes), -N (crtimes), or -H (hard links). Add these explicitly when needed: rsync -aAXHN.
Delta-Transfer Algorithm
By default, rsync sends only the changed portions of files. This is controlled by the quick check algorithm, which compares file size and modification time. If both match, the file is skipped entirely. If they differ, rsync computes checksums on data blocks to identify exactly which portions need transferring.
Use --whole-file (-W) to disable delta-transfer and send files whole (faster for local copies or high-bandwidth connections where disk I/O is the bottleneck).
Quick Check vs. Checksum
Quick check (default): compares size and modification time — fast
Checksum (-c): computes full-file checksums — thorough but slow, uses lots of disk I/O
Always use -t (preserve times) or -a (archive mode) in your initial copy, otherwise rsync cannot effectively skip unchanged files on subsequent runs.
Command-Line Options: Complete reference of all rsync options including transfer rules, delete modes, compression, and checksum algorithms → Command-Line Options
Filter Rules and Pattern Matching: Include/exclude patterns, merge files, per-directory filters, modifiers, anchoring, and interaction with deletions → Filter Rules
