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An OCI base image of Fedora CoreOS with batteries included

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uCore

build-ucore

What is this?

You should be familiar with Fedora CoreOS, as this is an OCI image of CoreOS with "batteries included". More specifically, it's an opinionated, custom CoreOS image, built daily with some commonly used tools added in. The idea is to make a lightweight server image including most used services or the building blocks to host them.

WARNING: This image has not been heavily tested, though the underlying components have. Please take a look at the included modifications and help test if this project interests you.

Images & Features

fedora-coreos

NOTE: formerly named fedora-coreos-zfs, that version of the image did not offer the nvidia option. Please update with rpm-ostree rebase.

A generic Fedora CoreOS image image with choice of add-on kernel modules:

NOTE: currently, zincati fails to start on systems with OCI based deployments (like uCore). Upstream efforts are active to correct this.

ucore

Suitable for running containerized workloads on either baremetal or virtual machines, this image tries to stay lightweight but functional for multiple use cases, including that of a storage server (NAS).

Note: per cockpit instructions the cockpit-ws RPM is not installed, rather it is provided as a pre-defined systemd service which runs a podman container.

ucore-hci

Hyper-Coverged Infrastructure(HCI) refers to storage and virtualization in one place... So this image primarily adds the virtualization stack.

  • Starts with ucore to give you everything above, plus:
  • Adds the following:
    • cockpit-machines: Cockpit GUI for managing virtual machines
    • libvirt-client: virsh command-line utility for managing virtual machines
    • libvirt-daemon-kvm: libvirt KVM hypervisor management
    • virt-install: command-line utility for installing virtual machines

Note: Fedora now uses DefaultTimeoutStop=45s for systemd services which could cause libvirtd to quit before shutting down slow VMs. Consider adding TimeoutStopSec=120s as an override for libvirtd.service if needed.

Tips and Tricks

Immutability and Podman

These images are immutable and you probably shouldn't install packages like in a mutable "normal" distribution.

Fedora CoreOS expects the user to run services using podman. moby-engine, the free Docker implementation, is installed for those who desire docker instead of podman.

Default Services

To maintain this image's suitability as a minimal container host, most add-on services are not auto-enabled.

To activate pre-installed services (cockpit, docker, tailscaled, etc):

sudo systemctl enable --now SERVICENAME.service

Note: libvirtd is enabled by default, but only starts when triggerd by it's socket (eg, using virsh or other clients).

Docker/Moby and Podman

NOTE: CoreOS cautions against running podman and docker containers at the same time. Thus, docker.socket is disabled by default to prevent accidental activation of the docker daemon, given podman is the default.

Podman and FirewallD

Podman and firewalld can sometimes conflict such that a firewall-cmd --reload removes firewall rules generated by podman.

A service is included to mitigate this by monitoring for firewall reload events on dbus and then reloading podman networks. If needed, enable like so: systemctl enable --now podman-firewalld-reload.service

Distrobox

Users may use distrobox to run images of mutable distributions where applications can be installed with traditional package managers. This may be useful for installing interactive utilities such has htop, nmap, etc. As stated above, however, services should run as containers.

CoreOS and ostree Docs

It's a good idea to become familar with the Fedora CoreOS Documentation as well as the CoreOS rpm-ostree docs. Note especially, this image is only possible due to ostree native containers.

Sanoid/Syncoid

sanoid/syncoid is a great tool for manual and automated snapshot/transfer of ZFS datasets. However, there is not a current stable RPM, rather they provide instructions on installing via git.

ucore has pre-install all the (lightweight) required dependencies (perl-Config-IniFiles perl-Data-Dumper perl-Capture-Tiny perl-Getopt-Long lzop mbuffer mhash pv), such that a user wishing to use sanoid/syncoid only need install the "sbin" files and create configuration/systemd units for it.

NVIDIA

If you installed an image with -nvidia in the tag, the nvidia kernel module, basic CUDA libraries, and the nvidia-container-toolkit are all are pre-installed.

Note, this does NOT add desktop graphics services to your images, but it DOES enable your compatible nvidia GPU to be used for nvdec, nvenc, CUDA, etc. Since this is CoreOS and it's primarily intended for container workloads the nvidia container toolkit should be well understood.

Note the included driver is the latest nvidia driver as bundled by negativo17. This package was chosen over rpmfusion's due to it's granular packages which allow us to install just the minimal nvidia-driver-cuda packages.

Other NVIDIA Drivers

If you need an older (or different) driver, consider looking at the container-toolkit-fcos driver. It provides pre-bundled container images with nvidia drivers for FCOS, allowing auto-build/loading of the nvidia driver IN podman, at boot, via a systemd service.

If going this path, you likely won't want to use the ucore -nvidia image, but would use the suggested systemd service. The nvidia container toolkit will still be required but can by layered easily.

ZFS

If you installed an image with -zfs in the tag (or fedora-coreos-zfs), the ZFS kernel module and tools are pre-installed, but like other services, ZFS is not pre-configured to load on default.

Load it with the command modprobe zfs and use zfs and zpool commands as desired.

Per the OpenZFS Fedora documentation:

By default ZFS kernel modules are loaded upon detecting a pool. To always load the modules at boot:

echo zfs > /etc/modules-load.d/zfs.conf

ZFS and immutable root filesystem

The default mountpoint for any newly created zpool tank is /tank. This is a problem in CoreOS as the root filesystem (/) is immutable, which means a directory cannot be created as a mountpoint for the zpool. An example of the problem looks like this:

# zpool create tank /dev/sdb
cannot mount '/tank': failed to create mountpoint: Operation not permitted

To avoid this problem, always create new zpools with a specified mountpoint:

# zpool create -m /var/tank tank /dev/sdb

If you do forget to specify the mountpoint, or you need to change the mountpoint on an existing zpool:

# zfs set mountpoint=/var/tank tank

SecureBoot

For those wishing to use the nvidia image with a pre-build kmod AND run SecureBoot, the kmod will not be loaded by the kernel until the public signing key has been imported as a MOK (Machine-Owner Key).

Do so like this:

sudo mokutil --import /etc/pki/akmods/certs/akmods-ublue.der

The utility will prompt for a password. The password will be used to verify this key is the one you meant to import, after rebooting and entering the UEFI MOK import utility.

How to Install

Prerequsites

This image is not currently available for direct install. The user must follow the CoreOS installation guide. There are varying methods of installation for bare metal, cloud providers, and virtualization platforms.

All CoreOS installation methods require the user to produce an Ignition file. This Ignition file should, at mimimum, set a password and SSH key for the default user (default username is core).

Install and Manually Rebase

You can rebase any Fedora CoreOS x86_64 installation to uCore. Installing CoreOS itself can be done through a number of provisioning methods.

To rebase an Fedora CoreOS machine to the latest uCore (stable):

  1. Execute the rpm-ostree rebase command (below) with desired IMAGE and TAG.
  2. Reboot, as instructed.
  3. After rebooting, you should pin the working deployment which allows you to rollback if required.
sudo rpm-ostree rebase ostree-unverified-registry:ghcr.io/ublue-os/IMAGE:TAG

Tag Matrix

IMAGE TAG
fedora-coreos - stable stable-nvidia, stable-zfs,stable-nvidia-zfs
fedora-coreos - testing testing-nvidia, testing-zfs, testing-nvidia-zfs
ucore - stable stable, stable-nvidia, stable-zfs,stable-nvidia-zfs
ucore - testing testing, testing-nvidia, testing-zfs, testing-nvidia-zfs
ucore-hci - stable stable, stable-nvidia, stable-zfs,stable-nvidia-zfs
ucore-hci - testing testing, testing-nvidia, testing-zfs, testing-nvidia-zfs

Install with Auto-Rebase

Your path to a running uCore can be shortend by using examples/ucore-autorebase.butane as the starting point for your CoreOS ignition file.

  1. As usual, you'll need to follow the docs to setup a password. Substitute your password hash for YOUR_GOOD_PASSWORD_HASH_HERE in the ucore-autorebase.butane file, and add your ssh pub key while you are at it.
  2. Generate an ignition file from your new ucore-autorebase.butane using the butane utility.
  3. Now install CoreOS for hypervisor, cloud provider or bare-metal. Your ignition file should work for any platform, auto-rebasing to the ucore:stable (or other IMAGE:TAG combo), rebooting and leaving your install ready to use.

Verification

These images are signed with sigstore's cosign. You can verify the signature by downloading the cosign.pub key from this repo and running the following command:

cosign verify --key cosign.pub ghcr.io/ublue-os/ucore

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An OCI base image of Fedora CoreOS with batteries included

License:Apache License 2.0

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