---
name: "rsyncd"
section: "5"
platform: "macos"
package: "rsync"
version: "184"
release: "macOS 26.5"
platforms: ["macos"]
url: "https://new.carta.tech/rsyncd"
---

# rsyncd(5)

rsyncd wire protocol

## NAME

**rsyncd** – rsyncd wire protocol

## DESCRIPTION

The **rsyncd** protocol described in this relates to the BSD-licensed [openrsync(1)](/openrsync/1.md), a re-implementation of the GPL-licensed reference utility [rsync(1)](/rsync/1.md). It is compatible with version 27 of the reference.

The **rsyncd** protocol is an envelope protocol for [rsync(5)](/rsync/5.md) between a client and an rsync://-capable server. It provides a means to exchange capabilities information prior to file transfer.

In this document, "client" refers to the [openrsync(1)](/openrsync/1.md) utility making the request. It follows that "server" refers to the daemon servicing the request.

A connection between a client and server consists of host, a module, and zero or more paths.

```
openrsync rsync://host/module/path1 rsync://host/path2... dest
```

At this time, operating in sender mode (with the rsync:// host receiving information) is not described in this document.

### Data types

These are the same as in [rsync(5)](/rsync/5.md). A newline is always a standalone \\n.

### Client process

After initialising a connection, the client and server exchange the following information, in order. This portion of the process is *not* multiplexed.

1. client sends requested module followed by newline

2. server responds with preamble followed by standalone newline

The requested module must have non-zero length. The preamble consists in a sequence of lines. Each line either contains free-form text sent by the server as a "motd" (message of the day) or a command:

```
@RSYNCD: command\n
```

The only supported command is the server protocol specification:

```
@RSYNCD: xx[.yy]\n
```

The optional component is the submodule, which may be discarded. The version may only be specified once. Both the motd and commands end in the special termination command:

```
@RSYNCD: OK\n
```

Following that, the client must send the command-line arguments that would otherwise be used to start a [openrsync(1)](/openrsync/1.md) server. Each argument must be specified on its own line, e.g.,

```
--server\n--sender\n-r\n-t\n.\npath1\npath2
```

This must be followed by a standalone newline.

If the server does not understand or accept any of the command-line arguments, it will exit at this point.

Following this, the client must read the integer-length session checksum seed. Multiplexing is subsequently enabled.

The sequence that follows is stipulated in [rsync(5)](/rsync/5.md) following the handshake.

## SEE ALSO

[openrsync(1)](/openrsync/1.md), [rsync(5)](/rsync/5.md)