Chapter 12. Updating the cluster to RHCOS 10.x

Prerequisites

• The boot image in your cluster is at least RHCOS 9.x. Note that the boot image on each node remains at RHCOS 9.x after installing or upgrading to RHCOS 10.x. After you configure RHCOS 10.x in your cluster, new nodes boot using RHCOS 9.x initially and automatically upgrade to RHCOS 10.x. For more information, see "Manually updating the boot image".
• Your cluster is updated to OpenShift Container Platform 5.0.
• The nodes in your cluster use hardware compatible with RHCOS 10.x. For example, x86-64-v2 CPUs are not compatible with RHCOS 10.x, and must be replaced with newer CPUs before initiating an update to RHCOS 10.x.

• The nodes in your cluster are configured to use crun as the default container runtime. You cannot update the RHCOS version on nodes that use the runC container runtime, because runC is deprecated in OpenShift Container Platform 5.0. If you attempt to update a machine config pool (MCP) that has runC nodes, the nodes in the pool will degrade and will not update. The MCP status reports the following error:

  apiVersion: machineconfiguration.openshift.io/v1
  kind: MachineConfigPool
  metadata:
    name: worker
  # ...
  status
  # ...
    conditions
    - lastTransitionTime: "2026-09-24T22:42:24Z"
      message: 'Failed to render configuration for pool worker: MachineConfigPool worker
        targets a RHEL 10 OS image where runc is not available. To unblock, migrate
        to crun by removing any ContainerRuntimeConfig that sets defaultRuntime to runc,
        and removing any MachineConfig that sets default_runtime = "runc" in CRI-O configuration
        under /etc/crio/crio.conf.d/'
      reason: ""
      status: "True"
      type: RenderDegraded
    - lastTransitionTime: "2026-09-24T22:42:29Z"
      message: ""
      reason: ""
      status: "True"
      type: Degraded

  You must configure your cluster to use the crun container runtime. For more information, see "Configuring the container runtime".

Verification

• After the nodes have returned to the READY state, check the machine config pool status for the nodes in a machine config pool to view the current RHCOS version by running the following command:

  $ oc get machineconfigpool -n openshift-machine-config-operator <machine_config_pool_name> -o yaml

  Replace <machine_config_pool_name> with the name of a machine config pool.

  Example output

  apiVersion: machineconfiguration.openshift.io/v1
  kind: MachineConfigPool
  metadata:
    name: worker
  # ...
  status
  # ...
    osImageStream:
      name: rhel-10

• Examine the /etc/redhat-release file on a node to see the current RHCOS version on that node by running the following command:

  $ oc debug node/<node_name> -- chroot /host cat /etc/redhat-release

  Replace <node_name> with the name of the node.

  Example output

  Red Hat Enterprise Linux release 10.2 (Coughlan)

• Examine the /etc/os-release file on a node to see the current RHCOS version on that node by running the following command:

  $ oc debug node/<node_name> -- chroot /host cat /etc/os-release

  Replace <node_name> with the name of the node.

  Example output

  NAME="Red Hat Enterprise Linux CoreOS"
  VERSION="10.2.20260824-0 (Coughlan)"
  RELEASE_TYPE=stable
  ID="rhel"
  ID_LIKE="centos fedora"
  VERSION_ID="10.2"
  PLATFORM_ID="platform:el10"
  PRETTY_NAME="Red Hat Enterprise Linux CoreOS 10.2.20260824-0 (Coughlan)"
  # ...