Linux as a Virtualization Guest VIrtual Machines

In this guide, you’ll learn how to manage virtual machines (VMs) on Linux using QEMU-KVM and Libvirt’s virsh CLI. By the end, you will be able to install dependencies, define VM domains via XML, control VM lifecycle, adjust resources, and clean up definitions—all from the command line. This workflow is fundamental for self-hosted virtualization and supports major cloud platforms like AWS, DigitalOcean, and Google Cloud. Example: A single Linux server with 64 CPU cores and 1 TiB RAM can host dozens of isolated VMs, each with its own dedicated vCPU and memory allocation.

1. Installing Dependencies

Install QEMU, KVM, and Libvirt tools:

sudo dnf install -y qemu-kvm libvirt

qemu-kvm: Hardware-accelerated virtualization
libvirt: API and utilities for managing VMs

You may also need to start and enable the libvirtd service:

sudo systemctl enable --now libvirtd

2. Defining a Virtual Machine Domain

Libvirt uses XML to describe VM configurations (called domains). Create a file named testmachine.xml:

vim testmachine.xml

Paste this minimal configuration:

<domain type="kvm">
  <name>TestMachine</name>
  <memory unit="GiB">1</memory>
  <vcpu>1</vcpu>
  <os>
    <type arch="x86_64">hvm</type>
  </os>
</domain>

This sets:

Name: TestMachine
Memory: 1 GiB
vCPUs: 1
OS: Hardware VM on x86_64

Save and exit.

3. Defining and Listing Domains

virsh define testmachine.xml

Expected output:

Domain 'TestMachine' defined from testmachine.xml

List all domains, including inactive:

virsh list --all

Sample:

Id	Name	State
-	TestMachine	shut off

Omit --all to list only running domains.

4. VM Lifecycle Management

Use the following commands to control the VM. See the quick reference table below.

Action	Command
Start	`virsh start TestMachine`
Graceful reboot	`virsh reboot TestMachine`
Forced reset	`virsh reset TestMachine`
Graceful shutdown	`virsh shutdown TestMachine`
Forced power-off	`virsh destroy TestMachine`

# Example: Start the VM
virsh start TestMachine

# Verify running VMs
virsh list

reset simulates pressing the reset button.
destroy cuts power immediately—like unplugging the VM.

5. Deleting a Domain

Remove the domain definition only:

virsh undefine TestMachine

--remove-all-storage will also delete associated disk images:

virsh undefine TestMachine --remove-all-storage

6. Autostart Configuration

Enable the VM to start on host boot:

virsh autostart TestMachine

Disable autostart:

virsh autostart --disable TestMachine

7. Inspecting VM Details

Retrieve detailed VM information:

virsh dominfo TestMachine

Sample output:

Id:             -
Name:           TestMachine
UUID:           01a57937-3fbb-4191-9cec-a73383456fa8
OS Type:        hvm
State:          shut off
CPU(s):         1
Max memory:     1048576 KiB
Used memory:    1048576 KiB
Persistent:     yes
Autostart:      disable

8. Modifying VM Resources

Adjusting vCPUs

Increase maximum vCPUs:

virsh setvcpus TestMachine 2 --config --maximum

Set vCPUs for next boot:

virsh setvcpus TestMachine 2 --config

Adjusting Memory

Set maximum memory:

virsh setmaxmem TestMachine 2048M --config

Verify changes:

virsh dominfo TestMachine

9. Starting and Verifying Changes

Start the VM with updated resources:

virsh start TestMachine

Confirm the running state:

virsh dominfo TestMachine

Expected fields:

State:        running
CPU(s):       2
Max memory:   2097152 KiB
Used memory:  2097152 KiB

Quick Reference: Common `virsh` Commands

Command	Description
virsh define <file>.xml	Define a new VM domain
virsh start <domain>	Start a VM
virsh shutdown <domain>	Graceful shutdown
virsh destroy <domain>	Forced power off
virsh reboot <domain>	Reboot VM
virsh reset <domain>	Forced reset
virsh list [—all]	List VMs (active/inactive)
virsh undefine <domain> [—remove-all-storage]	Remove VM definition
virsh autostart <domain> [—disable]	Enable/disable autostart
virsh dominfo <domain>	Show domain information
virsh setvcpus <domain> <count> [—config] [—maximum]	Adjust vCPUs
virsh setmaxmem <domain> <size> [—config]	Adjust max memory

References

Watch Video

Linux as a Virtualization Guest Tools and Images

Linux as a Virtualization Guest Containers

Introduction

System Architecture

Linux Installation and Package Management

GNU and Unix Commands

Devices, Linux Filesystems, Filesystem Hierarchy Standard

Conclusion and Mock Exam

Linux as a Virtualization Guest VIrtual Machines

1. Installing Dependencies

2. Defining a Virtual Machine Domain

3. Defining and Listing Domains

4. VM Lifecycle Management

5. Deleting a Domain

6. Autostart Configuration

7. Inspecting VM Details

8. Modifying VM Resources

Adjusting vCPUs

Adjusting Memory

9. Starting and Verifying Changes

Quick Reference: Common `virsh` Commands

References

Watch Video

​1. Installing Dependencies

​2. Defining a Virtual Machine Domain

​3. Defining and Listing Domains

​4. VM Lifecycle Management

​5. Deleting a Domain

​6. Autostart Configuration

​7. Inspecting VM Details

​8. Modifying VM Resources

​Adjusting vCPUs

​Adjusting Memory

​9. Starting and Verifying Changes

​Quick Reference: Common virsh Commands

​References

Watch Video

1. Installing Dependencies

2. Defining a Virtual Machine Domain

3. Defining and Listing Domains

4. VM Lifecycle Management

5. Deleting a Domain

6. Autostart Configuration

7. Inspecting VM Details

8. Modifying VM Resources

Adjusting vCPUs

Adjusting Memory

9. Starting and Verifying Changes

Quick Reference: Common `virsh` Commands

References