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Chapter 12. Updating the boot loader on RHCOS nodes using bootupd

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.

Note

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

12.1. Updating the boot loader manually
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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

12.2. Updating the bootloader automatically via a machine config
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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.

Note

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.

    Note

    The Butane version you specify in the config file should match the OpenShift Container Platform version and always ends in 0. For example, 4.13.0. See "Creating machine configs with Butane" for information about Butane.

    Example output

    variant: openshift
version: 4.13.0
metadata:
  name: 99-worker-chrony
    1 
    
  labels:
    machineconfiguration.openshift.io/role: worker
    2 
    
systemd:
  units:
  - name: bootupctl-update.service
    enabled: true
    contents: |
      [Unit]
      Description=Bootupd automatic update

      [Service]
      ExecStart=/usr/bin/bootupctl update
      RemainAfterExit=yes

      [Install]
      WantedBy=multi-user.target

    1 2
    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
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