SSH Passwordless Login Failure: Troubleshooting Key-based Authentication

SSH Passwordless Login Failure: Troubleshooting Key-based Authentication

In this article, we will discuss the common issues and solutions related to SSH key-based authentication when attempting passwordless login to remote servers. We will cover the key concepts, subtopics, and provide detailed steps to help you resolve any issues you might encounter.

Prerequisites

Before we dive into the topic, ensure that you have the following prerequisites in place:

• An SSH client installed on your local machine
• SSH server installed on the remote server
• Generated SSH key on your local machine

Generating SSH Key

If you haven't generated an SSH key yet, you can do so by running the following command in your terminal:

 
 ssh-keygen -t rsa -b 4096 -C "[email protected]"
 
 

This command will generate a new RSA key with a length of 4096 bits and associate your email address with the key. Press Enter when prompted to enter a file in which to save the key.

Copying SSH Key to Remote Server

To copy the SSH key to the remote server, you can use the ssh-copy-id command:

 
 ssh-copy-id user@remote_server_ip
 
 

Replace "user" with your username on the remote server and "remote_server_ip" with the IP address or domain name of the remote server.

Issue: SSH Key Not Found on Remote Server

If you encounter the error message "Permission denied (publickey,keyboard-interactive), please try again.", it means that the SSH server does not have your public key in its authorized_keys file. To resolve this issue:

1. Check the remote server's ~/.ssh/authorized_keys file to ensure that your public key is present.
2. If your public key is not present, you will need to copy it to the remote server manually.

Issue: SSH Key Format Incorrect

If you encounter the error message "Could not read key '/Users/your_username/.ssh/id_rsa.pub': No such file or directory.", it means that the SSH key file format is incorrect. To resolve this issue:

1. Regenerate your SSH key using the ssh-keygen command.
2. Copy the new public key to the remote server using the ssh-copy-id command.

Summary

In this article, we discussed the common issues and solutions related to SSH key-based authentication when attempting passwordless login to remote servers. We covered the key concepts, subtopics, and provided detailed steps to help you resolve any issues you might encounter. For further reading, we recommend the following resources:

• SSH Key Generation
• How to Set Up SSH Keys on DigitalOcean