Running a QEMU VM

Running a QEMU VM#

This guide walks through running a local QEMU/KVM virtual machine on a Linux host and deploying demo-ops into it. This is the simplest way to try out the platform locally.

Prerequisites#

  • A Linux host with KVM support (/dev/kvm must exist)

  • QEMU installed (qemu-system-x86_64)

  • Bridge networking (br0) configured on the host — VMs appear on the LAN and can receive DHCP addresses

  • Nix installed on the workstation

  • NixOS installer image available

  • Bios firmware for UEFI boot

Prepare UEFI firmware#

nix build nixpkgs#OVMF.fd -o ~/w/ovmf

Prepare NixOS installer#

Make sure to have an installer ISO ready to boot the machine from.

For repeated tests, it may be convenient to build an installer which has your public ssh key already baked in:

See: https://nixos.org/manual/nixos/stable/#sec-building-image

Creating and booting the VM#

1. Create a virtual disk#

qemu-img create -f qcow2 ~/w/disks/demo-dev.qcow2 50G

2. Boot the VM on the bridge#

qemu-system-x86_64 \
  -enable-kvm -m 16G -smp 2 \
  -bios ~/w/ovmf/FV/OVMF.fd \
  -drive file=~/w/demo-dev.qcow2,format=qcow2,if=virtio \
  -cdrom ~/w/nixos-installer/iso/nixos-installer-x86_64-linux.iso \
  -boot d \
  -netdev bridge,id=net0,br=br0 \
  -device virtio-net-pci,netdev=net0 \
  -nographic

The -nographic flag runs the VM headless — the serial console appears in your terminal.

Adjust -m and -smp depending on your needs.

3. Wait until installer boots#

Wait for the installer to boot. Note the DHCP IP address from the console output (or check your router’s lease table).

Note

You may have to select items from the boot menu in case you did already install previously into the machine.

You can tweak things with the -boot option.

4. Verify SSH access#

Verify SSH access from the workstation:

ssh root@<vm-ip> hostname

Deploying demo-ops#

Adjust host configuration#

Adjust the host configuration, e.g. configure IP addresses and put a public SSH key in.

Deploy the machine#

With SSH access confirmed, deploy the demo-ops configuration into the VM:

nix run github:nix-community/nixos-anywhere -- \
  --flake '.#dev' \
  --target-host root@<vm-ip>

After reboot, verify that SSH still works against the deployed system.

Note

If you started with the installer and then deployed a machine into it, the ip address likely has changed to the configured static ip.

QEMU console control#

With -nographic, the VM console is your terminal. Useful shortcuts:

Ctrl-a x

Kill QEMU immediately.

Ctrl-a h

Show all QEMU monitor shortcuts.

poweroff

Run inside the VM for a graceful shutdown.