AWS EC2: Fixing SSH Terminal Issues When Instance Runs

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If you’re having trouble connecting to your EC2 instance via SSH, don’t worry—there are some common issues that can be easily fixed. Here’s a simple guide to help you troubleshoot and solve the problem.

First, check your network settings. Even if your security group allows SSH on port 22, the problem might be with your subnet’s Network Access Control List (NACL). NACLs are like filters for your network traffic, and they need to allow inbound traffic on port 22 and outbound traffic on the temporary ports (1024-65535). If these rules aren’t set correctly, your connection could be blocked.

Next, look at your route tables. Confirm that your subnet has a route pointing to an Internet Gateway (0.0.0.0/0 → igw-xxxxx), especially if you’re trying to connect from outside your network. Without this, your instance won’t be reachable from the internet.

It’s also important to verify that the SSH service is running on your instance. Sometimes the SSH daemon may not be active or might not start properly during setup. If you can connect through other methods like EC2 Instance Connect or Systems Manager, you can check and restart the SSH service from there.

Another common issue involves the username. If you’re using an Ubuntu AMI, “ubuntu” is correct. However, for Amazon Linux, the default username is “ec2-user,” and for Debian, it’s “admin.” Make sure you’re using the right username for your specific operating system.

Check if your instance has a public IP address assigned, especially if it’s in a private subnet. Instances in private subnets without proper NAT or internet gateway setup won’t be accessible from the outside.

Finally, don’t forget about the security inside the operating system. Firewalls like iptables or firewalld could be blocking SSH connections. Review the internal firewall rules to ensure they allow traffic on port 22.

To troubleshoot effectively, try connecting using EC2 Instance Connect or Systems Manager Session Manager. These options let you access your instance even if SSH isn’t working initially. Also, review the VPC Flow Logs to see if traffic is being rejected, and check the system logs or instance screenshots from the AWS console to spot any boot errors or misconfigurations.

Since your instance is passing all the status checks, it’s running properly. The issue is likely with the network setup. Double-check your subnet’s routing, security group, NACL rules, and your local network’s restrictions. Once you address these areas, your SSH connection should work smoothly.