Skip to content
uCORE

Menu

Choosing an image

uCore ships as three container images. Each adds another layer of capability on top of the one before it, so you can start small and move up without reinstalling.

The three images

All three are built on Fedora CoreOS and delivered from the same registry. Pick the smallest one that covers what the machine needs.

IMAGE ADDS LAYER
ucore-minimal Container host: Podman on Fedora CoreOS. 01
ucore Storage and NAS tools: ZFS, Samba, NFS. 02
ucore-hci Virtualization: KVM and libvirt. 03

ucore-minimal

A lightweight bare-metal or VM host for containerized workloads. It includes Cockpit services, firewalld, QEMU and VMware guest agents, Docker buildx and Compose, podman-compose, Tailscale, WireGuard tools, tmux, selected Realtek 2.5G USB Ethernet udev rules, ZFS and pv. It provides the uBlue signing key used for Secure Boot support of signed drivers.

The Cockpit web service runs as a predefined Podman container; the cockpit-ws RPM is not installed. Zincati automatic update and reboot is disabled. Staged updates are provided through rpm-ostreed.

ucore

Builds on ucore-minimal for storage and NAS use. It adds Cockpit storage tools, Distrobox, duperemove, full wireless firmware, mergerfs, NFS server utilities, Performance Co-Pilot, rclone, Samba, SnapRAID, usbutils, Cockpit ZFS Manager, and Sanoid/Syncoid dependencies.

ucore-hci

Builds on ucore with Cockpit Machines, libvirt client and KVM daemon, and virt-install. Fedora’s default service stop timeout can end libvirtd before slow VMs have shut down; consider a TimeoutStopSec=120s override for libvirtd.service if needed.

Release streams

Every image is published on three streams: lts, stable, and testing. stable is the right choice for most machines. testing receives changes first. The lts stream uses the stable base with a longterm kernel.

Tags

A full image reference combines an image name with a tag. The tag names the stream and any driver variant.

STREAM ONLYSTREAM+NVIDIASTREAM+NVIDIA LTS
ltslts-nvidialts-nvidia-lts
stablestable-nvidiastable-nvidia-lts
testingtesting-nvidiatesting-nvidia-lts

The same tags apply to ucore-minimal, ucore, and ucore-hci. The multi-architecture image manifest selects x86_64 or aarch64 automatically; the Fedora CoreOS installation media must still match the target machine’s architecture.

referenceExample image reference
ghcr.io/ublue-os/ucore:stable

Switching images

Moving between existing uCore images is a rebase. The new image is staged alongside the current one and takes effect on the next reboot.

shellSwitch an rpm-ostree-managed uCore system
sudo rpm-ostree rebase \    ostree-image-signed:docker://ghcr.io/ublue-os/ucore:stable

After the image is staged, reboot. If it does not suit the machine, the previous deployment is still there. Roll back with rpm-ostree rollback and reboot. For Fedora CoreOS transitions, bootc-managed systems, or more detail, see Existing systems and rebasing.

Source: uCore image features and tag matrix. Checked September 18, 2026.