Richard Chamberlain

Posted on Apr 5, 2025

Running Linux in QEMU: How to Build a VM from an ISO

#linux #virtualization #sysadmin #devops

Running Linux in QEMU for Testing on IBM PowerPC (or x86)

I recently had the chance to work on an IBM Power 6 system running Linux—a first for me. While I’ve spent years working with x86 and ARM systems, PowerPC architecture was uncharted territory until now.

The need came up during a project involving a critical application where we had to validate compatibility with Power architecture. Rather than using the actual hardware (and tying it up), I fired up a QEMU virtual machine on my MacBook Pro M3 to simulate the environment.

Surprisingly, it worked beautifully: fast to build, simple to configure, and perfect for quick app validation.

💡 Pro Tip: This tutorial uses qemu-system-x86_64 for demo purposes, but the same steps apply for PowerPC—just swap in qemu-system-ppc.
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📚 Table of Contents

Introduction
🔍 Why Build a Custom QCOW2 Image?
🛠 Step 1: Create a Blank QCOW2 Disk
🚀 Step 2: Boot the Ubuntu ISO with Your QCOW2 Disk
- Breakdown of the Command
🔁 Step 3: Reboot into the Installed System
🧠 Final Thoughts
🔗 Resources

If you're a developer or systems engineer looking to test Linux on different architectures or just need a portable virtual machine for experimentation, this guide will walk you through creating a QEMU VM from an ISO file and a blank QCOW2 disk.

🔍 Why Build a Custom QCOW2 Image?

Sure, many Linux distributions offer prebuilt QCOW2 cloud images, but sometimes you need more control.

For instance:

You’re installing a specialized stack like ROS 2 on Ubuntu.
You want to simulate a different CPU architecture.
You're building a portable development lab on your laptop.

Whatever the case, starting from an ISO gives you a flexible and consistent VM environment.

🛠 Step 1: Create a Blank QCOW2 Disk

Start by creating a 40GB disk in QCOW2 format:

qemu-img create -f qcow2 ubuntu-ros2.qcow2 40G

Why QCOW2?

QCOW2 is a smart choice for virtualization:

Supports snapshots
Saves disk space through compression
Lightweight and portable

🚀 Step 2: Boot the Ubuntu ISO with Your QCOW2 Disk

Now, boot your ISO using QEMU and attach the new disk. This command launches a VM with:

4 GB RAM
2 vCPUs
Boot from ISO
Port forwarding from host port 2222 to VM SSH port 22

qemu-system-x86_64 \
  -m 4G \
  -smp 2 \
  -boot d \
  -cdrom ubuntu-22.04.iso \
  -drive file=ubuntu-ros2.qcow2,format=qcow2 \
  -netdev user,id=net0,hostfwd=tcp::2222-:22 \
  -device e1000,netdev=net0 \
  -display default,show-cursor=on

Breakdown of the Command

Flag	Purpose
`-m 4G`	Allocates 4GB of memory
`-smp 2`	Uses 2 CPU cores
`-boot d`	Boots from CD-ROM (ISO)
`-cdrom`	Path to your Ubuntu ISO
`-drive`	Your blank QCOW2 disk
`-netdev` / `-device`	Sets up networking + SSH forwarding
`-display`	Shows the VM window with a visible cursor

Once the Ubuntu installer boots, walk through the installation and select your new disk.

🔁 Step 3: Reboot into the Installed System

After the install is complete, power down the VM. Now restart it, this time booting from the QCOW2 disk directly:

qemu-system-x86_64 \
  -m 4G \
  -smp 2 \
  -drive file=ubuntu-ros2.qcow2,format=qcow2 \
  -netdev user,id=net0,hostfwd=tcp::2222-:22 \
  -device e1000,netdev=net0 \
  -display default,show-cursor=on

🔒 Security Tip: If you're planning to SSH into the VM, set up your public SSH key and secure your user account.

🧠 Final Thoughts

Whether you're testing for PowerPC compatibility, building custom environments for embedded systems, or just geeking out with virtualization, QEMU is an incredibly versatile tool.

It gives you a high degree of flexibility:

No need for dedicated servers
Easily simulate alternate architectures
Keep your workflows portable and reproducible

With just a few commands, you’ve set up a clean, isolated Linux environment that’s ready for development, debugging, or deployment testing.

🔗 Resources

Have questions about Linux or virtualization? Drop a comment or reach out—always happy to chat!

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