Software⏱️ 4 min read📅 2026-06-11

How to Fix: Error message while connecting to EC2 instance via Cygwin

Error connecting to EC2 instance via Cygwin on Windows due to permissions bug.

Quick Answer: Try adding the -m flag to the ssh command, e.g. ssh -i cs184-john-stanford-edu.pem -m ubuntu@ec2-XX-XXX-XXX-XX.us-west-2.compute.amazonaws.com

📋 Table of Contents

  1. 🛑 Root Causes of the Error
  2. 🔧 Proven Troubleshooting Steps
  3. 💡 Conclusion

The error message '/usr/bin/ssh.exe: error while loading shared libraries: cyggssapi-3.dll: cannot open shared object file: No such file or directory' occurs when attempting to connect to an EC2 instance via Cygwin on Windows. This issue affects users who have followed the instructions provided for connecting to their EC2 instances using Cygwin, and is particularly frustrating as it prevents users from accessing their instances.

This error is caused by a permissions bug in Cygwin, which requires additional commands to fix. The problem arises when trying to connect to an EC2 instance via SSH, resulting in the inability to access the instance's files or execute commands.

🛑 Root Causes of the Error

  • The primary cause of this error is the permissions bug in Cygwin, which prevents the program from accessing the shared object file 'cyggssapi-3.dll'. This issue can be resolved by running additional commands to fix the permissions.
  • An alternative cause could be that the '/cygdrive/c' or '/cygdrive/d' directory structure is not being used correctly. However, this should not make a difference as per the instructions provided, and it's likely that the error is related to the Cygwin permissions bug.

🔧 Proven Troubleshooting Steps

Fixing the Cygwin Permissions Bug

  1. Step 1: To fix the permissions bug in Cygwin, run the following command: `chgrp Users cs184-john-stanford-edu.pem` This command changes the group ownership of the .pem file to 'Users', which should resolve the issue.
  2. Step 2: Next, run the following command: `chmod 0400 cs184-john-stanford-edu.pem` This command sets the permissions of the .pem file to 'rw-r--r--', which should allow Cygwin to access the file without any issues.
  3. Step 3: After running these commands, try connecting to your EC2 instance again using the SSH command: `ssh -i cs184-john-stanford-edu.pem /ubuntu@ec2-50-19-140-229.compute-1.amazonaws.com` This should resolve the error and allow you to access your instance.

Alternative Solution

  1. Step 1: As an alternative solution, try modifying the SSH command to include the full DNS name of your EC2 instance: `ssh -i cs184-john-stanford-edu.pem /ubuntu@ec2-50-19-140-229.compute-1.amazonaws.com` This may resolve any issues related to the DNS name not being recognized by Cygwin.
  2. Step 2: However, this alternative solution is unlikely to fix the underlying issue with the Cygwin permissions bug.

💡 Conclusion

To summarize, the error message '/usr/bin/ssh.exe: error while loading shared libraries: cyggssapi-3.dll: cannot open shared object file: No such file or directory' can be resolved by running additional commands to fix the Cygwin permissions bug. By following the steps outlined in this guide, users should be able to access their EC2 instances without any issues.

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