Title

“Creating and Customizing Virtual Machines with NUMA Awareness on Modern Linux (Fedora/Ubuntu 2025)”

Introduction

Virtualization has evolved significantly, and tools like libvirt, virt-manager, and QEMU/KVM now allow fine-grained control over CPU topology, NUMA nodes, and memory allocation. In this guide, we’ll create a fully functional VM using both GUI and CLI methods, compatible with Fedora 42 and Ubuntu 24.04 LTS. We’ll also explore how to assign NUMA nodes, distribute vCPUs and memory, and customize devices and networks.

1. Install Dependencies

Fedora

sudo dnf install -y @virtualization libvirt virt-install virt-manager qemu-kvm
sudo systemctl enable --now libvirtd

Ubuntu

sudo apt update
sudo apt install -y qemu-kvm libvirt-daemon-system libvirt-clients virt-manager bridge-utils
sudo systemctl enable --now libvirtd

Check KVM support:

egrep -c '(vmx|svm)' /proc/cpuinfo

2. Create a Storage Pool and Network

Create a storage pool

sudo mkdir -p /var/lib/libvirt/images
sudo virsh pool-define-as default dir - - - - "/var/lib/libvirt/images"
sudo virsh pool-autostart default
sudo virsh pool-start default

Verify default NAT network

sudo virsh net-list --all

If missing:

sudo virsh net-define /usr/share/libvirt/networks/default.xml
sudo virsh net-autostart default
sudo virsh net-start default

3. Create a Virtual Machine (Basic)

Example for Fedora 42:

virt-install \
  --name testvm \
  --vcpus 8 \
  --memory 8192 \
  --disk path=/var/lib/libvirt/images/testvm.qcow2,size=40 \
  --os-variant fedora-42 \
  --cdrom ~/Downloads/Fedora-Workstation-Live-x86_64-42-1.6.iso \
  --network network=default \
  --graphics spice

4. NUMA-Aware CPU and Memory Configuration

NUMA configuration is not exposed by default in virt-manager, but you can define it manually in the domain XML.

Edit the VM definition:

sudo virsh edit testvm

Add NUMA topology inside <cpu> and <memoryBacking> sections:

<cpu mode='host-passthrough'>
  <numa>
    <cell id='0' cpus='0-3' memory='4096' unit='MiB'/>
    <cell id='1' cpus='4-7' memory='4096' unit='MiB'/>
  </numa>
</cpu>

<memoryBacking>
  <source type='memfd'/>
  <access mode='shared'/>
  <allocation mode='immediate'/>
</memoryBacking>

This setup:

  • Creates 2 NUMA nodes
  • Assigns 4 vCPUs and 4 GB RAM per node
  • Uses memfd for shared memory performance

Restart the VM:

sudo virsh destroy testvm
sudo virsh start testvm

Validate:

sudo virsh vcpuinfo testvm
sudo virsh dommemstat testvm

5. Advanced Customization Examples

Pin vCPUs to Physical Cores

sudo virsh vcpupin testvm 0 0
sudo virsh vcpupin testvm 1 1
sudo virsh vcpupin testvm 2 2
sudo virsh vcpupin testvm 3 3

Use Hugepages for Better Performance

Add to VM XML:

<memoryBacking>
  <hugepages>
    <page size='1' unit='GiB'/>
  </hugepages>
</memoryBacking>

Enable hugepages on host:

sudo sysctl -w vm.nr_hugepages=8

6. Manage the VM

# Start / stop / autostart
sudo virsh start testvm
sudo virsh shutdown testvm
sudo virsh autostart testvm

# Connect to console
sudo virsh console testvm

Or use virt-manager GUI.

7. Optional: Bridge Networking

To connect your VM to the external LAN:

Fedora example

sudo nmcli connection add type bridge ifname br0 con-name br0
sudo nmcli connection add type ethernet ifname enp1s0 master br0

Then modify VM XML:

<interface type='bridge'>
  <source bridge='br0'/>
  <model type='virtio'/>
</interface>

8. Clone or Template VMs

sudo virt-clone --original testvm --name devvm --auto-clone

9. Delete VM

sudo virsh destroy testvm
sudo virsh undefine testvm --remove-all-storage