AWS EC2 Ubuntu实例SSH连接超时问题求助（macOS High Sierra）

Hey there! Let's walk through fixing this SSH timeout issue—this is one of the most common hurdles for first-time EC2 users, so we'll get it sorted out.

Here are the key steps to check, in order of how likely they are to be the problem:

1. Verify Your Security Group Inbound Rules #

This is the #1 culprit for SSH timeouts. EC2 instances block all inbound traffic by default unless explicitly allowed:

• Go to the AWS EC2 Console, find your smpapp instance, and click on its associated Security Group (under the "Security" tab).
• Click "Edit inbound rules" and make sure there's a rule for SSH (TCP) on port 22.
• For the "Source" field, either select "My IP" (AWS will auto-fill your current public IP) or use 0.0.0.0/0 temporarily (only for testing—switch back to your IP once it works for security).
• Save the rules and wait 30 seconds, then try SSH again.

2. Double-Check Your SSH Command Format #

It's easy to mix up the username or IP address. For Ubuntu EC2 instances, the default username is ubuntu (not root or your local macOS username). Your command should look exactly like this:

ssh -i smpapp.pem ubuntu@[your-instance-public-ip]

Make sure you're replacing [your-instance-public-ip] with the actual public IP of your instance (you can find this in the EC2 Console's instance details).

3. Confirm Instance Status and Public IP #

• Ensure your instance is in the running state (check the EC2 Console). If it was stopped and restarted, the public IP might have changed (unless you assigned an Elastic IP). Double-check the IP in your SSH command matches the current one.

4. Test Network Connectivity #

From your macOS terminal, run these commands to diagnose where the connection is failing:

• Test if you can reach the instance: ping [your-instance-public-ip] (if this times out, it's a network/security issue, not SSH itself).
• Test if port 22 is open: telnet [your-instance-public-ip] 22 (you should see a message like SSH-2.0-OpenSSH_8.2p1 Ubuntu-4ubuntu0.9 if the port is open).

5. Check Network ACLs (If Security Group Looks Good) #

Network ACLs are another layer of firewall for your subnet. If your security group is correct but you still can't connect:

• Go to the EC2 Console, navigate to your instance's subnet, then click on the associated Network ACL.
• Ensure inbound rules allow TCP port 22 from your IP (or 0.0.0.0/0 for testing), and outbound rules allow all traffic (or at least TCP port 22 responses).

6. Rule Out Local macOS Network Issues #

• If you're using a VPN or proxy, try disconnecting it—sometimes these block SSH traffic to external instances.
• Check macOS's built-in firewall: Go to System Preferences > Security & Privacy > Firewall, and make sure it's not blocking outgoing SSH connections. You can temporarily turn it off to test.

Start with steps 1 and 2 first—those fix 90% of SSH timeout issues for new EC2 users. Let me know if any of these steps resolve your problem!

内容的提问来源于stack exchange，提问作者Christopher Costello