Guide 3: Launching & Connecting to Your Free-Tier Linux Instance

This guide walks you through creating a free, cloud-hosted Linux virtual machine (VM) on Google Cloud Platform and connecting to it via SSH (Secure Shell).

GCP Free Tier VM Rules

Google Cloud provides one free VM instance per account under the Always Free program, provided you match these exact settings:

Part 1: Enabling Compute Engine & Creating the VM

Step 1: Navigate to Compute Engine

1. Open Google Cloud Console.
2. Open the Navigation Menu (the ☰ hamburger menu).
3. Hover over Compute Engine and click VM instances.
4. If prompted to enable the Compute Engine API, click Enable and wait a moment for initialization.

Step 2: Configure VM Instance Details

Click the Create Instance button at the top of the VM instances page. Configure the following fields carefully:

1. Name & Region

• Name: Enter comp141-linux-vm (use lower-case letters, numbers, and hyphens only).
• Region: Choose one of the approved free regions:
  • us-central1 (Iowa) (recommended)
  • us-east1 (South Carolina)
  • us-west1 (Oregon)
• Zone: Any zone (e.g., us-central1-a).

2. Machine Configuration

• Preset: Select General-purpose.
• Series: Select E2.
• Machine type: Select e2-micro (2 vCPU, 1 GB memory).

  You will see an estimated monthly cost on the right side of the screen. As long as you follow the free-tier parameters, your free credits/free tier allowance will cover this cost ($0 out-of-pocket).

3. Boot Disk (CRITICAL STEP)

By default, GCP selects a Balanced Persistent Disk. You must change this to stay in the Free Tier!

1. Under the Boot disk section, click Change.
2. Operating System: Select Debian or Ubuntu.
   • Recommended: Debian GNU/Linux 12 (bookworm) or Ubuntu 24.04 LTS.
3. Boot disk type: Change from “Balanced Persistent Disk” to Standard Persistent Disk.
4. Size (GB): Enter 30.
5. Click Select at the bottom of the pop-up.

4. Firewall & Networking

• Ensure SSH access is allowed (enabled by default on GCP VMs).

5. Create the Instance

Double-check all settings against the table above, then click Create at the bottom of the page. Wait 30–60 seconds for the VM to start (a green checkmark will appear next to comp141-linux-vm).

6. Identify Your VM’s External IP Address

Once the VM finishes launching:

1. You will be on the VM instances page (Compute Engine > VM instances).
2. Look at the table of virtual machines and locate the row for comp141-linux-vm.
3. Find the column labeled External IP (located between Internal IP and Connect).
4. You will see a public IPv4 address (e.g., 34.123.45.67):
   • Hover over the address and click the Copy IP address icon (📋) next to it to copy it to your clipboard.
   • Do not confuse this with the Internal IP (which usually starts with 10.x.x.x and is only accessible within Google Cloud’s private network).
   • Reminder: This address is ephemeral. If you stop and restart your instance, Google will assign a new External IP. Always check this column after starting the VM.

Step 3: Enable Incoming UDP Traceroute in GCP Firewall

By default, Google Cloud’s firewall allows ping (ICMP) and SSH (TCP port 22), but blocks unsolicited incoming UDP traffic. Because standard Unix and macOS traceroute commands probe destinations using UDP ports 33434–33534, traceroute packets sent to your VM’s external IP will time out (* * *) at the final hop unless we open this port range.

To configure your firewall so the VM responds to incoming UDP traceroute requests:

1. In the Google Cloud Console, open the Navigation Menu (☰) in the top-left corner.
2. Navigate to VPC network > Firewall.
3. Click + Create Firewall Rule at the top of the page.
4. Fill in the following details:
   • Name: allow-udp-traceroute
   • Network: default
   • Priority: 1000 (default)
   • Direction of traffic: Ingress
   • Action on match: Allow
   • Targets: Select All instances in the network.
   • Source IPv4 ranges: Enter 0.0.0.0/0.
   • Protocols and ports:
     • Check Specified protocols and ports.
     • Check UDP.
     • Enter port range: 33434-33534.
5. Click Create at the bottom.

[!NOTE] Creating firewall rules in Google Cloud is completely free of charge. Because this rule targets All instances in the network, your comp141-linux-vm will immediately respond to incoming traceroute probes without any additional setup.

Part 2: Connecting to Your VM via In-Browser SSH

For most class exercises, connecting directly through your web browser is the quickest and easiest method—no extra software installation or SSH key configuration is required.

(If you would like to connect from your local terminal or manage instances from the command line using gcloud, see Guide 4: Your VM from the CLI).

Connecting with GCP In-Browser SSH

1. Return to Compute Engine > VM instances in the Google Cloud Console.
2. Find comp141-linux-vm in your list of instances.
3. In the Connect column, click the SSH button.
4. A new browser window will open, automatically establishing an encrypted SSH connection to your Linux terminal.
5. Once loaded, you will see a Linux command prompt similar to:

   username@comp141-linux-vm:~$
   

Part 3: Essential First Linux Commands

Once connected to your shell, verify your system configuration by executing these introductory commands:

1. Check OS Details:

   cat /etc/os-release
   

2. Check System Architecture & Kernel:

   uname -a
   

3. Check Available Disk Space:

   df -h
   

4. Update Package Manager:

   sudo apt update && sudo apt upgrade -y
   

5. Install Essential Tools (e.g., git, curl, nano, tmux, build-essential):

   sudo apt install -y git curl nano tmux build-essential
   

Part 4: Testing Network Connectivity (Ping & Traceroute)

You can verify that your VM and firewall rules are working properly by testing network connectivity from your personal computer’s terminal:

1. Look at your VM on the VM instances page and copy its External IP address.
2. Open a terminal or PowerShell prompt on your personal computer:
   • Test Ping:

     ping <EXTERNAL_IP>
     

     (Press Ctrl+C to stop). The VM should immediately return ICMP replies.

   • Test Traceroute:
     • On macOS or Linux (uses UDP ports 33434–33534):

       traceroute <EXTERNAL_IP>
       

     • On Windows (uses ICMP):

       tracert <EXTERNAL_IP>
       

3. Because we added the allow-udp-traceroute firewall rule, the traceroute will show every network hop all the way to your VM’s external IP at the final hop!

Managing Your VM (Stopping & Starting)

• Stopping your VM: When not working on assignments for extended periods, you can stop the VM to conserve compute resources.
  • In GCP Console, check the box next to comp141-linux-vm and click Stop ⏹ at the top.
  • Alternatively, run sudo shutdown -h now inside the SSH terminal.
• Restarting your VM: Select comp141-linux-vm in GCP Console and click Start / Resume ▶.

  Note on IP Addresses: When you stop and restart a VM, its External IP address may change (ephemeral IP). Use the new External IP or the GCP Browser SSH button to reconnect.

Troubleshooting Checklist