To update the boot loader on RHCOS nodes using bootupd, you must either run the bootupctl update command on RHCOS machines manually or provide a machine config with a systemd unit.

Unlike grubby or other boot loader tools, bootupd does not manage kernel space configuration such as passing kernel arguments. To configure kernel arguments, see Adding kernel arguments to nodes.

You can use bootupd to update the boot loader to protect against the BootHole vulnerability.

Updating the boot loader manually

You can manually inspect the status of the system and update the boot loader by using the bootupctl command-line tool.

  1. Inspect the system status:

    # bootupctl status
    Example output for x86_64
    Component EFI
      Installed: grub2-efi-x64-1:2.04-31.el8_4.1.x86_64,shim-x64-15-8.el8_1.x86_64
      Update: At latest version
    Example output for aarch64
    Component EFI
      Installed: grub2-efi-aa64-1:2.02-99.el8_4.1.aarch64,shim-aa64-15.4-2.el8_1.aarch64
      Update: At latest version
  1. OpenShift Container Platform clusters initially installed on version 4.4 and older require an explicit adoption phase.

    If the system status is Adoptable, perform the adoption:

    # bootupctl adopt-and-update
    Example output
    Updated: grub2-efi-x64-1:2.04-31.el8_4.1.x86_64,shim-x64-15-8.el8_1.x86_64
  2. If an update is available, apply the update so that the changes take effect on the next reboot:

    # bootupctl update
    Example output
    Updated: grub2-efi-x64-1:2.04-31.el8_4.1.x86_64,shim-x64-15-8.el8_1.x86_64

Updating the bootloader automatically via a machine config

Another way to automatically update the boot loader with bootupd is to create a systemd service unit that will update the boot loader as needed on every boot. This unit will run the bootupctl update command during the boot process and will be installed on the nodes via a machine config.

This configuration is not enabled by default as unexpected interruptions of the update operation may lead to unbootable nodes. If you enable this configuration, make sure to avoid interrupting nodes during the boot process while the bootloader update is in progress. The boot loader update operation generally completes quickly thus the risk is low.

  1. Create a Butane config file, 99-worker-bootupctl-update.bu, including the contents of the bootupctl-update.service systemd unit.

    See "Creating machine configs with Butane" for information about Butane.

    Example output
    variant: openshift
    version: 4.14.0
      name: 99-worker-chrony (1)
        machineconfiguration.openshift.io/role: worker (1)
      - name: bootupctl-update.service
        enabled: true
        contents: |
          Description=Bootupd automatic update
          ExecStart=/usr/bin/bootupctl update
    1 On control plane nodes, substitute master for worker in both of these locations.
  2. Use Butane to generate a MachineConfig object file, 99-worker-bootupctl-update.yaml, containing the configuration to be delivered to the nodes:

    $ butane 99-worker-bootupctl-update.bu -o 99-worker-bootupctl-update.yaml
  3. Apply the configurations in one of two ways:

    • If the cluster is not running yet, after you generate manifest files, add the MachineConfig object file to the <installation_directory>/openshift directory, and then continue to create the cluster.

    • If the cluster is already running, apply the file:

      $ oc apply -f ./99-worker-bootupctl-update.yaml