SSH Trouble shooting

1️⃣ Connection Timeout

• Symptom: SSH hangs and times out.

• Cause: Almost always a security group / firewall issue.

• Fix:

  • Allow inbound traffic on port 22 in the security group.

  • Confirm that security group is actually attached to your instance.

2️⃣ Still Timing Out (Security Group Is Correct)

• Symptom: Same timeout, even after fixing the security group.

• Cause: A corporate or personal firewall is blocking the connection.

• Fix: Use EC2 Instance Connect instead (covered next lecture).

3️⃣ Windows: "ssh: command not found"

• Symptom: Windows doesn't recognize the ssh command.

• Cause: No SSH client installed on your system.

• Fix:

  • Use PuTTY to connect.

  • Still stuck? Fall back to EC2 Instance Connect.

4️⃣ Connection Refused

• Symptom: Instance is reachable, but connection gets rejected.

• Cause: SSH service isn't running on the instance.

• Fix:

  1. Restart the instance.

  2. If that fails, terminate it and launch a new one.

  3. Make sure it's Amazon Linux 2.

5️⃣ Permission Denied (publickey,gssapi-keyex,gssapi-with-mic)

• Symptom: Access denied when trying to SSH in.

• Cause: Wrong (or missing) key, or wrong username.

• Fix:

  • Double-check you're using the correct key pair for that instance.

  • Use username ec2-user — e.g. ec2-user@<public-ip>.

  • In PuTTY, set the username field to ec2-user.

6️⃣ Nothing Works

• Symptom: Every method has failed.

• Fix:

  • Don't panic.

  • Use EC2 Instance Connect.

  • Confirm the instance is Amazon Linux 2 so it matches the tutorial.

7️⃣ "It Worked Yesterday, Not Today"

• Symptom: SSH suddenly stops working after previously connecting fine.

• Cause: The instance's public IP changed after a stop/start.

• Fix: Update your SSH command or PuTTY config with the new IP.