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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.

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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

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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.

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3. Defining and Listing Domains

Register the domain with Libvirt: 
virsh define testmachine.xml
Expected output: 
Domain 'TestMachine' defined from testmachine.xml
List all domains, including inactive: 
virsh list --all
Sample:
IdNameState
-TestMachineshut off
Omit --all to list only running domains.

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4. VM Lifecycle Management

Use the following commands to control the VM. See the quick reference table below.
ActionCommand
Startvirsh start TestMachine
Graceful rebootvirsh reboot TestMachine
Forced resetvirsh reset TestMachine
Graceful shutdownvirsh shutdown TestMachine
Forced power-offvirsh 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.

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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

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6. Autostart Configuration

Enable the VM to start on host boot: 
virsh autostart TestMachine
Disable autostart: 
virsh autostart --disable TestMachine

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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

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8. Modifying VM Resources

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Adjusting vCPUs

Increase maximum vCPUs: 
virsh setvcpus TestMachine 2 --config --maximum
Set vCPUs for next boot: 
virsh setvcpus TestMachine 2 --config

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Adjusting Memory

Set maximum memory: 
virsh setmaxmem TestMachine 2048M --config
Verify changes: 
virsh dominfo TestMachine

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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

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Quick Reference: Common virsh Commands

CommandDescription
virsh define <file>.xmlDefine 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

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References

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