Provisioning Fedora CoreOS on QEMU

This guide shows how to provision new Fedora CoreOS (FCOS) instances on a bare QEMU hypervisor.

Prerequisites

Before provisioning a FCOS instance, you must have an Ignition configuration file containing your customizations. If you do not have one, see Producing an Ignition File.

You also need to have access to an host machine with KVM support. The examples below use the qemu-kvm command-line tool, which must be separately installed beforehand.

If running with SELinux enabled, make sure your OS image and Ignition file are labeled as svirt_home_t, for example by placing them under ~/.local/share/libvirt/images/.

Booting a new VM on QEMU

This section shows how to boot a new VM on QEMU. On this platform, The Ignition file is passed to the VM via the -fw_cfg parameter, which sets the opt/com.coreos/config key in the QEMU firmware configuration device.

You can use -snapshot to make qemu-kvm allocate temporary storage for the VM, or qemu-img create to first create a layered qcow2.

Fetching the QCOW2 image

Fetch the latest image suitable for your target stream (or download and verify it from the web).

STREAM="stable"
coreos-installer download -s "${STREAM}" -p qemu -f qcow2.xz --decompress -C ~/.local/share/libvirt/images/

Setting up a new VM

Launch the new VM using qemu-kvm.

In snaphost mode, all changes that are performed live after boot are discarded once the machine is powered off. If you need to persist your changes, it is recommended to setup a dedicated persistent disk first.

Launching FCOS with QEMU (temporary storage)

qemu-kvm -m 2048 -cpu host -nographic -snapshot \
	-drive if=virtio,file=fedora-coreos-qemu.qcow2 \
	-fw_cfg name=opt/com.coreos/config,file=path/to/example.ign \
	-nic user,model=virtio,hostfwd=tcp::2222-:22

Launching FCOS with QEMU (persistent storage)

qemu-img create -f qcow2 -b fedora-coreos-qemu.qcow2 my-fcos-vm.qcow2
qemu-kvm -m 2048 -cpu host -nographic \
	-drive if=virtio,file=my-fcos-vm.qcow2 \
	-fw_cfg name=opt/com.coreos/config,file=path/to/example.ign \
	-nic user,model=virtio,hostfwd=tcp::2222-:22

Exploring the OS

With QEMU usermode networking, the assigned IP address is not reachable from the host.

The examples above use hostfwd to selectively forward the SSH port on the guest machine to the local host (port 2222).

If you set up an SSH key for the default core user, you can SSH into the VM via the forwarded port:

ssh -p 2222 core@localhost