Software⏱️ 3 min read📅 2026-06-11

How to Fix: Why I am getting error 'Server rejected the 1 private key' error on setting up ssh-slave Docker image

Jenkins SSH slave setup issue with private key error.

Quick Answer: Verify the private key is correctly added to the authorized_keys file and Jenkins credentials, ensuring the correct format and permissions.

📋 Table of Contents

  1. ⚠️ Common Causes
  2. 🚀 How to Resolve This Issue
  3. 💡 Conclusion

The error 'Server rejected the 1 private key' is encountered when setting up an SSH slave Docker image in Jenkins. This issue affects users who are trying to establish a secure connection between their Jenkins master and slave containers.

This error can be frustrating as it prevents the successful launch of the slave container, which is essential for continuous integration and deployment processes.

⚠️ Common Causes

  • The primary reason for this error is that the private key used in the Jenkins credentials is not correctly formatted or does not match the expected format. The private key should be in OpenSSH format (SSH2), which includes a comment line starting with '# ' followed by the public key.
  • Another possible cause could be the incorrect placement of the authorized_keys file, which might lead to the server rejecting the private key.

🚀 How to Resolve This Issue

Format the Private Key Correctly

  1. Step 1: Open a terminal inside the Jenkins master container and run the command `ssh-keygen -t rsa -b 4096` to generate a new RSA key pair.
  2. Step 2: Copy the public key generated by ssh-keygen using the command `cat ~/.ssh/id_rsa.pub` and add it to the authorized_keys file in the ssh-slave container using the command `docker exec -it container_id echo 'id_rsa.pub' >> /root/.ssh/authorized_keys`. Ensure that the permissions are set correctly using `chmod 744 /root/.ssh/authorized_keys`.
  3. Step 3: Verify that the private key is correctly formatted by checking its contents. The file should start with a comment line starting with '# ', followed by the public key.

Check Authorized Keys File Placement

  1. Step 1: Inspect the Dockerfile for the ssh-slave container to ensure that the authorized_keys file is correctly placed. The file should be copied to the /root/.ssh directory and have the correct permissions.
  2. Step 2: Verify that the authorized_keys file is not empty and contains the public key generated by ssh-keygen.

💡 Conclusion

To resolve the 'Server rejected the 1 private key' error, it's essential to correctly format the private key and ensure that the authorized_keys file is placed in the correct location. By following these steps, users should be able to successfully set up their SSH slave Docker image and establish a secure connection between their Jenkins master and slave containers.

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