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 virtualizationlibvirt : 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:
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 : TestMachineMemory : 1 GiBvCPUs : 1OS : Hardware VM on x86_64
Save and exit.
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:
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 TestMachineGraceful reboot virsh reboot TestMachineForced reset virsh reset TestMachineGraceful shutdown virsh shutdown TestMachineForced 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:
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 
