rsync Flag Explainer
Paste any rsync command and get a per-flag breakdown of what it does.
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rsync -avzP --delete --exclude=node_modules /src/ user@host:/dst/
command flag path value
Source
/src/
Destination
user@host:/dst/
This command contains destructive flags: --delete
Always test with --dry-run (-n) first. A wrong source or trailing slash can wipe files on the destination.
6 known
| Flag | Long Form | Meaning |
|---|---|---|
-a | --archive | Archive mode — equivalent to -rlptgoD. Recursively copies files while preserving symlinks, permissions, modification times, group, owner, and device/special files. |
-v | --verbose | Verbose output. Use -vv or -vvv for increasing detail. Shows files as they are transferred. |
-z | --compress | Compress file data during transfer. Useful over slow networks; usually unnecessary on fast LANs or when files are already compressed. |
-P | Shortcut for --partial --progress. Keeps partially transferred files on interrupt and shows a per-file progress bar. | |
--deleteRisky | Delete files on the destination that no longer exist on the source. Makes the destination an exact mirror — files removed from the source are erased on the destination. | |
--exclude | Exclude files matching the given pattern (e.g. --exclude=node_modules or --exclude='*.log'). Can be specified multiple times. |
What does the rsync command do?
rsync ("remote sync") is a Unix utility that efficiently transfers and synchronizes files between two locations — locally, between two machines, or to and from a remote server over SSH. Its claim to fame is the delta-transfer algorithm: rsync only sends the parts of a file that have changed, which makes incremental backups and large-tree mirroring dramatically faster than tools like scp or cp. The catch is that rsync's behavior is controlled almost entirely by its flags, and a single missing or misplaced flag can mean copying the wrong files, blowing away the wrong directory, or silently dropping permissions.
Most Common rsync Flag Combinations
Most real-world rsync commands you will see in scripts, tutorials, and Stack Overflow answers fall into a handful of patterns:
| Combination | What it does |
|---|---|
| -a | Archive — recursive + preserve everything (perms, times, owner, group, symlinks, devices). |
| -av | Archive with verbose output. Most common starting point. |
| -avz | Archive, verbose, compress in transit. Standard for SSH transfers over the internet. |
| -avzP | Adds --partial --progress for resumable transfers with a progress bar. |
| -avh | Archive, verbose, human-readable file sizes. |
| -avn | Archive verbose dry-run — see what would happen without doing it. |
| -av --delete | Mirror mode — destination becomes an exact copy of source, including deletions. |
Risky rsync Flags to Watch For
These flags can permanently delete data. Always pair them with --dry-run (-n) the first time you run a command:
| Flag | Risk |
|---|---|
| --delete | Erases anything on the destination that isn't in the source. A wrong source path can empty an entire directory. |
| --delete-excluded | Also deletes files that match your --exclude patterns from the destination. |
| --remove-source-files | Deletes files from the source after a successful transfer — turns rsync into a move. |
| --inplace | Overwrites files in-place rather than via a temp file. If the transfer fails partway, the destination file is left corrupted. |
Frequently Asked Questions
What are rsync flags?
Flags (also called options or switches) are the letters and words after the rsync command that change its behavior — for example -a tells rsync to use archive mode and --delete tells it to remove destination files that aren't in the source. rsync supports both short flags (a single dash and one letter, like -v) and long flags (two dashes and a word, like --verbose). Short flags can be combined: -avz is the same as -a -v -z. Most rsync commands you'll encounter are mostly flags — they control recursion, what to preserve, what to delete, what to compress, and how to talk to the remote host.
What does -avz mean in rsync?
-avz is the most common rsync flag combination, especially for transfers over SSH. It expands to three separate flags: -a (archive mode — recursive copy that preserves permissions, modification times, owners, groups, symlinks, and devices), -v (verbose — print each file as it's transferred), and -z (compress data during transit, useful over slower networks). You'll often see it written as -avzP, which adds --partial --progress so transfers are resumable and show a live progress bar.
What is the difference between rsync --include and --exclude?
--exclude tells rsync to skip files matching a pattern; --include tells it to keep files that would otherwise be excluded. Order matters: rsync evaluates rules top to bottom and uses the first match wins. To copy only .txt files from a directory, the trick is --include='*.txt' --include='*/' --exclude='*' — include the files you want, include directories so rsync can recurse into them, then exclude everything else. Putting --exclude='*' before your --include rules will silently match everything first and skip your target files.
Should I use the -z (--compress) flag with rsync?
Use -z when transferring over a slow or metered network (typically over the internet via SSH) and the files you're sending are compressible — text, source code, logs. Skip -z on a fast LAN or local disk-to-disk copies; the CPU overhead of compression actually slows the transfer down because the network isn't the bottleneck. Skip it for already-compressed content too (videos, JPEGs, .zip, .gz, Docker images) — you'll just burn CPU rewriting incompressible bytes. A modern alternative is --compress-choice=zstd for better speed-vs-ratio on rsync 3.2+.
Why does the trailing slash matter in rsync?
A trailing slash on the source path changes what rsync copies. rsync /src/ /dst/ copies the contents of /src into /dst — you end up with /dst/file1, /dst/file2. rsync /src /dst/ (no trailing slash on source) copies the directory itself into /dst — you end up with /dst/src/file1, /dst/src/file2. The trailing slash on the destination is cosmetic and doesn't change behavior. This is the single most common rsync footgun, especially when combined with --delete: a misplaced slash can dump files in the wrong place or wipe an entire directory.
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