Software⏱️ 3 min read📅 2026-06-19

How to Fix: Cygwin rsync protocol error

Cygwin rsync protocol error fix for 64bit windows and linux.

Quick Answer: Check the SSH version compatibility between Windows and Linux, and ensure that the SSH key authentication is properly configured.

📋 Table of Contents

  1. 🔍 Why This Happens
  2. 🔧 Proven Troubleshooting Steps
  3. ✨ Wrapping Up

The Cygwin rsync protocol error occurs when attempting to transfer files between a 64-bit Windows machine and a 64-bit Linux machine using rsync with SSH. This issue is frustrating because it prevents users from efficiently transferring large files between the two platforms.

In this guide, we will walk you through the root causes of the Cygwin rsync protocol error and provide steps to resolve the issue.

🔍 Why This Happens

  • The primary cause of the Cygwin rsync protocol error is related to the SSH connection. When using rsync with SSH, the connection is established, but the authentication process fails due to a mismatch in the SSH key formats or incorrect permissions on the remote machine. Additionally, another possible cause is related to the rsync version compatibility issue between the Windows and Linux machines.
  • Another alternative cause could be related to the firewall settings on either the Windows or Linux machine blocking the incoming SSH connection.

🔧 Proven Troubleshooting Steps

Resolving SSH Key Format Mismatch

  1. Step 1: Step 1: Check the SSH key format on both machines. Ensure that the public key is in the correct format (OpenSSH) and not in a different format such as PuTTY.
  2. Step 2: Step 2: Verify the permissions on the remote machine's authorized_keys file to ensure it allows incoming connections from the Windows machine.
  3. Step 3: Step 3: Update the SSH configuration files on both machines to match the expected format. This may involve updating the /etc/ssh/sshd_config file on the Linux machine and the C:\.ssh/config file on the Windows machine.

Resolving Firewall Configuration

  1. Step 1: Step 1: Check the firewall settings on both machines to ensure that incoming SSH connections are allowed. On Windows, this can be done by opening the Windows Defender Firewall with Advanced Security and configuring the rules to allow incoming connections on port 22.
  2. Step 2: Step 2: Verify that the rsync command is correctly formatted and includes the correct options (e.g., -i, -z) to ensure a secure connection.

✨ Wrapping Up

To resolve the Cygwin rsync protocol error, it is essential to identify and address the root cause of the issue. By following these steps, you should be able to resolve the SSH key format mismatch or firewall configuration issues that are causing the error. If you continue to experience problems, consider seeking further assistance from a qualified IT professional.

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