Provisioning Fedora CoreOS on libvirt

This guide shows how to provision new Fedora CoreOS (FCOS) instances on a libvirt platform, using the QEMU hypervisor.

Prerequisites

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

Fedora CoreOS has a default core user that can be used to explore the OS. If you want to use it, finalize its configuration by providing e.g. an SSH key.

You also need to have access to a host machine with libvirt. The examples below use the virt-install command-line tool, which must be separately installed beforehand.

If running on a host with SELinux enabled (use the sestatus command to check SELinux status), make sure your OS image and Ignition file are labeled as svirt_home_t. You can do this by placing them under ~/.local/share/libvirt/images/ or running chcon -t svirt_home_t /path/to/file.

Launching a VM instance

  1. Fetch the latest image suitable for the qemu platform using coreos-installer (or download and verify it from the web). You can use coreos-installer as a container, or on Fedora install it from the repos.

    STREAM="stable"
# as an installed binary:
coreos-installer download -s $STREAM -p qemu -f qcow2.xz --decompress -C ~/.local/share/libvirt/images/
# or as a container:
podman run --pull=always --rm -v "${HOME}/.local/share/libvirt/images/:/data" -w /data \
    quay.io/coreos/coreos-installer:release download -s $STREAM -p qemu -f qcow2.xz --decompress

  2. Launch a new machine via virt-install, using the Ignition file with your customizations.

    IGNITION_CONFIG="/path/to/example.ign"
IMAGE="/path/to/image.qcow2"
VM_NAME="fcos-test-01"
VCPUS="2"
RAM_MB="2048"
STREAM="stable"
DISK_GB="10"
# For x86 / aarch64,
IGNITION_DEVICE_ARG=(--qemu-commandline="-fw_cfg name=opt/com.coreos/config,file=${IGNITION_CONFIG}")

# For s390x / ppc64le,
IGNITION_DEVICE_ARG=(--disk path="${IGNITION_CONFIG}",format=raw,readonly=on,serial=ignition,startup_policy=optional)

# Setup the correct SELinux label to allow access to the config
chcon --verbose --type svirt_home_t ${IGNITION_CONFIG}

virt-install --connect="qemu:///system" --name="${VM_NAME}" --vcpus="${VCPUS}" --memory="${RAM_MB}" \
        --os-variant="fedora-coreos-$STREAM" --import --graphics=none \
        --disk="size=${DISK_GB},backing_store=${IMAGE}" \
        --network bridge=virbr0 "${IGNITION_DEVICE_ARG[@]}"
virt-install requires both the OS image and Ignition file to be specified as absolute paths.
Depending on your version of virt-install, you may not be able to use --os-variant=fedora-coreos-* and will get an error. In this case, you should pick an older Fedora variant (--os-variant=fedora31 for example). You can find the variants that are supported by you current version of virt-install with osinfo-query os | grep '^\s*fedora'.
DISK_GB should be at least as big as the default size of the image. For Fedora CoreOS, this is currently 10 GB.
Make sure that your user has access to /dev/kvm. The default is to allow access for everyone, but on some distributions you may need to add yourself to the kvm group.
You can escape out of the serial console by pressing CTRL + ].

If you set up an SSH key for the default core user, you can SSH into the VM and explore the OS:

ssh core@<ip address>

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