#coreos #installer #fedora

bin+lib coreos-installer

Installer for Fedora CoreOS and RHEL CoreOS

9 releases (4 breaking)

new 0.5.0 Aug 1, 2020
0.4.0 Jul 24, 2020
0.3.0 Jul 13, 2020
0.1.3 Mar 20, 2020
0.1.0 Nov 8, 2019

#87 in Filesystem

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Build status Container image crates.io

coreos-installer is a program to assist with installing Fedora CoreOS (FCOS) and Red Hat Enterprise Linux CoreOS (RHCOS). It can do the following:

  • Install the operating system to a target disk, optionally customizing it with an Ignition config or first-boot kernel parameters (coreos-installer install)
  • Download and verify an operating system image for various cloud, virtualization, or bare metal platforms (coreos-installer download)
  • List Fedora CoreOS images available for download (coreos-installer list-stream)
  • Embed an Ignition config in a live ISO image to customize the running system that boots from it (coreos-installer iso)

The options available for each subcommand are available via the --help option. This documentation will focus on how to obtain and run coreos-installer.

On Fedora CoreOS or RHEL CoreOS

coreos-installer is included in Fedora CoreOS. Just run coreos-installer from the command line. Fedora CoreOS provides live CD and network boot images you can run from RAM; you can use these to run coreos-installer to install Fedora CoreOS or RHEL CoreOS to disk.

RHEL CoreOS also includes this, but note that versions ≤ 4.4 contain the legacy branch of this software.

Run from a container

You can run coreos-installer from a container. You'll need to bind-mount /dev and /run/udev, as well as a data directory if you want to access files in the host. For example:

sudo podman run --pull=always --privileged --rm \
    -v /dev:/dev -v /run/udev:/run/udev -v .:/data \
    quay.io/coreos/coreos-installer:release \
    install /dev/vdb -s testing -i /data/config.ign

Via a Fedora RPM

coreos-installer is packaged in Fedora:

sudo dnf install coreos-installer

Note in fact you can also do this inside a podman run --privileged type container configured similarly to the above for the "pre-built container" path, not necessarily the host's root filesystem. See also toolbox.

Install with Cargo

You can also install just the coreos-installer binary with Rust's Cargo package manager:

cargo install coreos-installer

Build and install from source tree

To build from the source tree:


To install the binary and systemd units to a target rootfs (e.g. under a coreos-assembler workdir):

make install DESTDIR=/my/dest/dir

Run from a live image using kernel command-line options

If you want a fully automated install, you can configure the Fedora CoreOS live CD or netboot image to run coreos-installer and then reboot the system. You do this by passing coreos.inst.<arg> arguments on the kernel command line.

Kernel command line options for coreos-installer running as a service

  • coreos.inst.install_dev - The block device on the system to install to, such as /dev/sda. Mandatory.
  • coreos.inst.stream - Download and install the current release of Fedora CoreOS from the specified stream. Optional; defaults to installing from local media if run from CoreOS live ISO or PXE media, and to stable on other systems.
  • coreos.inst.image_url - Download and install the specified CoreOS image, overriding coreos.inst.stream. Optional.
  • coreos.inst.ignition_url - The URL of the Ignition config. Optional. If missing, no Ignition config will be embedded, which is probably not what you want.
  • coreos.inst.platform_id - The Ignition platform ID of the platform the CoreOS image is being installed on. Optional; defaults to metal. Normally this should be specified only if installing inside a virtual machine.
  • coreos.inst.save_partlabel - Comma-separated labels of partitions to preserve during the install. Glob-style wildcards are permitted. The specified partitions need not exist. Optional.
  • coreos.inst.save_partindex - Comma-separated indexes of partitions to preserve during the install. Ranges (m-n) are permitted, and either m or n can be omitted. The specified partitions need not exist. Optional.
  • coreos.inst.insecure - Permit the OS image to be unsigned. Optional.
  • coreos.inst.skip_reboot - Don't reboot after installing. Optional.

Installing from ISO

Download a Fedora CoreOS ISO image. The ISO image can install in either legacy boot (BIOS) mode or in UEFI mode. You can boot it in either mode, regardless of what mode the OS will boot from once installed.

Burn the ISO to disk and boot it, or use ISO redirection via a LOM interface. Alternatively you can use a VM like so:

virt-install --name cdrom --ram 4500 --vcpus 2 --disk size=20 --accelerate --cdrom /path/to/fedora-coreos-32.20200715.2.0-live.x86_64.iso --network default

Alternatively you can use qemu directly. Create a disk image to use as install target:

qemu-img create -f qcow2 fcos.qcow2 8G

Now, run the following qemu command:

qemu-system-x86_64 -accel kvm -name fcos -m 4500 -cpu host -smp 2 -netdev user,id=eth0,hostname=coreos -device virtio-net-pci,netdev=eth0 -drive file=/path/to/fcos.qcow2,format=qcow2  -cdrom /path/to/fedora-coreos-32.20200715.2.0-live.x86_64.iso

Once you have reached the boot menu, press <TAB> (isolinux) or e (grub) to edit the kernel command line. Add the parameters to the kernel command line telling it what you want it to do. For example:

  • coreos.inst.install_dev=/dev/sda
  • coreos.inst.ignition_url=http://example.com/config.ign

Now press <ENTER> (isolinux) or <CTRL-x> (grub) to kick off the install.

The install will complete and eventually reboot the machine. After reboot the machine will boot into the installed system and the embedded Ignition config will run on first boot.

Installing from PXE

Download a Fedora CoreOS PXE kernel and initramfs image. The PXE image can install in either legacy boot (BIOS) mode or in UEFI mode. You can boot it in either mode, regardless of what mode the OS will boot from once installed.

Here is an example pxelinux.cfg for booting the installer images with PXELINUX:

DEFAULT pxeboot
LABEL pxeboot
    KERNEL fedora-coreos-32.20200715.2.0-live-kernel-x86_64
    APPEND initrd=fedora-coreos-32.20200715.2.0-live-initramfs.x86_64.img coreos.inst.install_dev=/dev/sda coreos.inst.ignition_url=

If you don't know how to use this information to test a PXE install you can start with something like these instructions for testing out PXE installs via a local VM + libvirt.

Build and test the installer for development

NOTE: The install subcommand writes directly to a block device (disk) and consumes the entire device. The device specified to the installer needs to be available and not currently in use. You cannot target a disk that is currently mounted.

Build coreos-installer and use it to install a Fedora CoreOS testing image to a partitionable loop device:

cargo build
truncate -s 8G image-file
sudo losetup -P /dev/loop0 image-file
sudo target/debug/coreos-installer install /dev/loop0 -s testing


~309K SLoC