Permission Denied (Publickey) When Accessing EC2: Troubleshooting Guide

Encountering a “Permission denied (publickey)” error when accessing your Amazon EC2 instance can be frustrating. This error typically results from authentication issues causing SSH to fail. Let’s break down the key causes and how to resolve them for both SSH and when using FileZilla to manage files.

Common Causes for “Permission Denied” Error

1. Incorrect Key Pair

Ensure you are using the correct .pem file corresponding to the key pair set up with your EC2 instance. If you’ve lost or didn’t save your original private key, you’ll need to create a new key pair and reconfigure your instance.

2. Usernames for Different AMIs

The username varies depending on the Amazon Machine Image (AMI) you are using. To find the right one:

• Amazon Linux: ec2-user
• Ubuntu: ubuntu
• RHEL: root or ec2-user
• Fedora: fedora or ec2-user
• SUSE Linux: root

If unsure, consult the documentation relevant to your AMI, or try both ec2-user and root.

3. Incorrect Host

Double-check if you are trying to connect to the correct EC2 instance. Verify the instance’s public DNS or IP address from your AWS Management Console.

Additional Troubleshooting

If these steps don’t help, use SSH’s verbose mode to gain additional insights. By adding the -v option to your SSH command (ssh -v -i ...), you’ll receive detailed messages that can pinpoint issues more clearly.

Using FileZilla for File Transfers

To upload or download files to and from your EC2 instance with FileZilla, follow these steps:

1. Set Up FileZilla for SFTP:

   • Open FileZilla and go to File > Site Manager.
   • In the Site Manager, click New Site and select SFTP as the protocol.
   • Enter the public DNS of your EC2 instance in the Host field.

2. Use the Correct Username:

   • Enter the appropriate username for your instance as discussed above.

3. Configure the Key File:

   • FileZilla doesn’t directly accept .pem files. You may need to convert it to a .ppk file using PuTTYgen if you’re using a Windows system.
   • Under Site Manager, go to Key file and select the converted key file.

4. Connect:

   • Click Connect to establish a file transfer session.

Following these guidelines ensures smoother access and troubleshooting for your EC2 instances using SSH and FileZilla. By understanding the environment and correctly configuring your details, you minimize authentication hiccups.