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 Add kernel arguments to nodes.

note

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.

Procedure

1. Inspect the system status by running the following command:

   # 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

2. 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 by running the following command:

   # 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

3. If an update is available, apply the update so that the changes take effect on the next reboot by running the following command:

   # 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 boot loader automatically by using a machine config

You can automatically update the boot loader with bootupd by creating 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 because unexpected interruptions of the update operation might lead to unbootable nodes. If you enable this configuration, make sure to avoid interrupting nodes during the boot process while the boot loader update is in progress. The boot loader update operation generally completes quickly thus the risk is low.

Procedure

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

   Example output

   variant: openshift
   version: 4.22.0
   metadata:
     name: 99-worker-chrony
     labels:
       machineconfiguration.openshift.io/role: worker
   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

   On control plane nodes, substitute master for worker in metadata.name and metadata.labels.machineconfiguration.openshift.io/role.

2. Generate a MachineConfig object file, 99-worker-bootupctl-update.yaml, containing the configuration to be delivered to the nodes by running the following command:

   $ 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 by running the following command:

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