docker/cli · error

copying between containers is not supported

Error message

copying between containers is not supported

What it means

In runCopy, the CLI parses both arguments for a CONTAINER:PATH form and sets direction bits fromContainer/toContainer. When both source and destination name a container (direction == acrossContainers), it returns this error because the Docker API has no endpoint to copy directly between two containers — the CLI only supports container↔local-filesystem transfers.

Source

Thrown at cli/command/container/cp.go:243

	}

	var direction copyDirection
	if srcContainer != "" {
		direction |= fromContainer
		copyConfig.container = srcContainer
	}
	if destContainer != "" {
		direction |= toContainer
		copyConfig.container = destContainer
	}

	switch direction {
	case fromContainer:
		return copyFromContainer(ctx, dockerCli, copyConfig)
	case toContainer:
		return copyToContainer(ctx, dockerCli, copyConfig)
	case acrossContainers:
		return errors.New("copying between containers is not supported")
	default:
		return errors.New("must specify at least one container source")
	}
}

func resolveLocalPath(localPath string) (absPath string, _ error) {
	absPath, err := filepath.Abs(localPath)
	if err != nil {
		return "", err
	}
	return archive.PreserveTrailingDotOrSeparator(absPath, localPath), nil
}

func copyFromContainer(ctx context.Context, dockerCLI command.Cli, copyConfig cpConfig) (err error) {
	dstPath := copyConfig.destPath
	srcPath := copyConfig.sourcePath

	if dstPath != "-" {

View on GitHub (pinned to e9452d6e78)

Solutions

1. Copy in two steps through the host: `docker cp containerA:/path ./tmp && docker cp ./tmp containerB:/path`.
2. Stream via tar to avoid a temp dir: `docker exec containerA tar -C /path -cf - . | docker exec -i containerB tar -C /path -xf -`.
3. Share data via a named volume mounted into both containers instead of copying.

Example fix

# before
docker cp appA:/data appB:/data
# after
docker cp appA:/data ./data
docker cp ./data appB:/data

When it happens

Trigger: `docker cp containerA:/path containerB:/path` — both positional args contain a colon-prefixed container reference, setting both direction flags.

Common situations: Users assuming docker cp works like scp between two remote endpoints; migration scripts trying to move data between containers directly; paths on the local filesystem that contain a colon being misparsed as container references.

Related errors

• destination can not be empty
• must specify at least one container source
• content size not available for stdin
• got a device
• got an irregular file

AI-assisted analysis of docker/cli@e9452d6e78 (2026-08-01). Data as JSON: /data/errors/b243466156935b68.json. Report an issue: GitHub.