4.3. Configuring the container runtime

You can configure the container runtime used with new workloads on your nodes, based on which runtime you or your organization prefers. You can use either crun, which is considered a faster and more lightweight runtime, or runc, which is more widely used than crun.

For information on crun and runc, see "About the container engine and container runtime".

Starting in OpenShift Container Platform 4.18, crun is the default container runtime for new installations. You can change between the runtimes by using a ContainerRuntimeConfig object, as described in the following procedure. Changing the container runtime affects new workloads only. Existing workloads continue to use their existing container runtime.

If you updated your cluster from OpenShift Container Platform 4.17, the runc container runtime remains unchanged as the default. During the upgrade, two MachineConfig objects, one for the control plane nodes and one for the worker nodes, were created to override the new default runtime. You can migrate the container runtime to crun, on a schedule of your choosing, by removing either or both of the MachineConfig objects.

Procedure

If your cluster is updated from OpenShift Container Platform 4.17, you can use the crun container runtime by deleting the following MachineConfig objects:
- Migrate your worker nodes to crun by running the following command:
  $ oc delete machineconfig 00-override-worker-generated-crio-default-container-runtime
- Migrate your control plane nodes to crun by running the following command:
  $ oc delete machineconfig 00-override-master-generated-crio-default-container-runtime
For any OpenShift Container Platform 4.18 or greater cluster, you can configure crun or runc as the container runtime for specific nodes by creating a container runtime configuration:
1. Create a YAML file for the ContainerRuntimeConfig CR:
  apiVersion: machineconfiguration.openshift.io/v1 kind: ContainerRuntimeConfig metadata: name: configure-runc spec: machineConfigPoolSelector: matchLabels: pools.operator.machineconfiguration.openshift.io/worker: '' containerRuntimeConfig: defaultRuntime: "runc"
  where:
  - spec.machineConfigPoolSelector.matchLabels:: Specifies a label for the machine config pool that you want you want to modify.
  - spec.containerRuntimeConfig.defaultRuntime:: Specifies the container runtime to use with new workloads on the nodes in the specified machine config pool, either crun or runc.
2. Create the ContainerRuntimeConfig CR:
  $ oc create -f <file_name>.yaml

Verification

After the nodes return to a ready state, open an oc debug session to a node by running the following command:
```
$ oc debug node/<node_name>
```
Set /host as the root directory within the debug shell by running the following command:
```
sh-5.1# chroot /host
```
Check the container runtime by using the following command:
```
sh-5.1# crio status config | grep default_runtime
```
Example output
```
INFO[2026-01-27 23:09:18.413462914Z] Starting CRI-O, version: 1.30.14-6.rhaos4.17.gitfa27f6f.el9, git: unknown(clean)
    default_runtime = "runc"
```
The default_runtime parameter specifies the container runtime that OpenShift Container Platform uses for new workloads on this node, either crun or runc, depending on what you have configured.

4.3. Configuring the container runtime

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