rsync — Why It Wins

~15 min · rsync, delta-transfer, fundamentals

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The killer feature: delta transfer

rsync compares source and destination at a block level and transfers only what differs. Change a 1 KB string in a 1 GB log file? rsync sends roughly 1 KB plus checksums — not 1 GB. This is the property that makes rsync the universal file-sync tool of the Unix world.

What you get on top of delta

Compression in flight (-z) for slow links.
Resume with --partial when transfers get cut.
Exclude patterns — skip node_modules, .git, etc.
Permissions, timestamps, symlinks, ownership preserved with archive mode (-a).
Dry run (-n) — see exactly what would change without running.
Sync deletion (--delete) — make the destination an exact mirror of the source.
Local or over SSH — same syntax for both.

Code

The classic invocation·bash

# Local-to-local sync
rsync source.txt destination.txt

# The standard daily command
rsync -avz --progress source/ dest/
# -a  archive mode (rlptgoD — preserves everything sane)
# -v  verbose
# -z  compress in transit
# --progress  per-file transfer bars

# Over SSH (same syntax with user@host)
rsync -avz --progress ./project/ office:/home/you_username/project/

External links

Exercise

Find a directory you've scp'd before. Run rsync -avz --progress ./that-dir/ host:/tmp/that-dir-rsync/ — note the time. Run it again with no changes — should finish in seconds (delta transfer found nothing to send). Modify one file in the source, run again — see only that file transfer.