Chapter 11. 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. 11.1. 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. 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 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 If an update is available, apply the update so that the changes take effect on the 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 11.2. 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. 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. Create a Butane config file, 99-worker-bootupctl-update.bu , including the contents of the bootupctl-update.service systemd unit. Note See "Creating machine configs with Butane" for information about Butane. Example output variant: openshift version: 4.12.0 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. Use Butane to generate a MachineConfig object file, 99-worker-bootupctl-update.yaml , containing the configuration to be delivered to the nodes: USD butane 99-worker-bootupctl-update.bu -o 99-worker-bootupctl-update.yaml 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: USD oc apply -f ./99-worker-bootupctl-update.yaml

Commands:
# bootupctl status
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
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
# bootupctl adopt-and-update
Updated: grub2-efi-x64-1:2.04-31.el8_4.1.x86_64,shim-x64-15-8.el8_1.x86_64
# bootupctl update
Updated: grub2-efi-x64-1:2.04-31.el8_4.1.x86_64,shim-x64-15-8.el8_1.x86_64
variant: openshift version: 4.12.0 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
butane 99-worker-bootupctl-update.bu -o 99-worker-bootupctl-update.yaml
oc apply -f ./99-worker-bootupctl-update.yaml