rsync copies files — but only the differences. On a repeat run it sends just the changed blocks, which turns a multi-gigabyte backup into a few megabytes over the wire. That single property made rsync the backbone of two decades of backups, mirrors, and deploys.
The daily form #
$ rsync -av projects/ backup/projects/-a is archive mode — recursion plus permissions, times, symlinks, the lot. -v narrates. Note the trailing slash on the source: projects/ copies the contents; projects copies the directory itself. The slash rule is the number-one rsync surprise, and it is the same ambiguity as cp — here it is load-bearing.
The flags that matter #
| Flag | Effect |
|---|---|
-a | Archive: recurse and preserve attributes |
-v / -vv | Verbose / more verbose |
-n | Dry run — show what would happen |
--delete | Remove destination files missing from source |
-z | Compress during transfer |
--exclude= | Skip patterns |
-P | Progress plus resumable partial files |
Dry-run before any real sync is the habit; --delete is the flag that makes it non-negotiable, because delete makes the sync two-directional in consequence if not in intent.
Real patterns #
A nightly backup with exclusions, over ssh:
$ rsync -avP --delete --exclude=".cache" --exclude="node_modules" ~/projects/ backup@server:/backups/laptop/A deploy: build locally, ship only the delta, then flip a symlink:
$ rsync -av --delete dist/ server:/srv/app/releases/v1.5/
$ ssh server 'ln -sfn /srv/app/releases/v1.5 /srv/app/current'Restore is the same command with source and destination swapped — backups you have never restored are hopes, not backups.
For encrypted, deduplicated backups beyond mirroring, see restic and friends; for imaging whole disks, dd. The terminal notes series continues.