Deploying RHEL 9 on Amazon Web Services

1. Select the optimal cloud provider for your use case, based on your requirements and the current offer on the market. The cloud providers currently certified for running RHEL instances are:

   • Amazon Web Services (AWS)
   • Google Cloud

   • Microsoft Azure

     Note

     This document specifically talks about deploying RHEL on AWS.

2. Create a RHEL cloud instance on your chosen cloud platform. For more information, see Methods for creating RHEL cloud instances.
3. To keep your RHEL deployment up-to-date, use Red Hat Update Infrastructure (RHUI).

Procedure

1. Install Python 3 and the pip tool:

   # dnf install python3 python3-pip

2. Install the AWS command-line tools with pip:

   # pip3 install awscli

3. Set your profile. The terminal prompts you to provide your credentials, region and output format:

   $ aws configure
   AWS Access Key ID [None]:
   AWS Secret Access Key [None]:
   Default region name [None]:
   Default output format [None]:

4. Define a name for your bucket and create a bucket:

   $ BUCKET=bucketname
   $ aws s3 mb s3://$BUCKET

   Replace bucketname with the actual bucket name. It must be a globally unique name. As a result, your bucket is created.

5. To grant permission to access the S3 bucket, create a vmimport S3 Role in the AWS Identity and Access Management (IAM), if you have not already done so in the past:

   1. Create a trust-policy.json file with the trust policy configuration, in the JSON format. For example:

      {
          "Version": "2022-10-17",
          "Statement": [{
              "Effect": "Allow",
              "Principal": {
                  "Service": "vmie.amazonaws.com"
              },
              "Action": "sts:AssumeRole",
              "Condition": {
                  "StringEquals": {
                      "sts:Externalid": "vmimport"
                  }
              }
          }]
      }

   2. Create a role-policy.json file with the role policy configuration, in the JSON format. For example:

      {
          "Version": "2012-10-17",
          "Statement": [{
              "Effect": "Allow",
              "Action": ["s3:GetBucketLocation", "s3:GetObject", "s3:ListBucket"],
              "Resource": ["arn:aws:s3:::%s", "arn:aws:s3:::%s/"] }, { "Effect": "Allow", "Action": ["ec2:ModifySnapshotAttribute", "ec2:CopySnapshot", "ec2:RegisterImage", "ec2:Describe"],
              "Resource": "*"
          }]
      }
      $BUCKET $BUCKET

   3. Create a role for your Amazon Web Services account, by using the trust-policy.json file:

      $ aws iam create-role --role-name vmimport --assume-role-policy-document file://trust-policy.json

   4. Embed an inline policy document, by using the role-policy.json file:

      $ aws iam put-role-policy --role-name vmimport --policy-name vmimport --policy-document file://role-policy.json

Procedure

1. Using the text editor, create a configuration file with the following content:

   provider = "aws"
   [settings]
   accessKeyID = "AWS_ACCESS_KEY_ID"
   secretAccessKey = "AWS_SECRET_ACCESS_KEY"
   bucket = "AWS_BUCKET"
   region = "AWS_REGION"
   key = "IMAGE_KEY"

   Replace values in the fields with your credentials for accessKeyID, secretAccessKey, bucket, and region. The IMAGE_KEY value is the name of your VM Image to be uploaded to EC2.

2. Save the file as CONFIGURATION-FILE.toml and close the text editor.

3. Start the compose to upload it to AWS:

   # composer-cli compose start blueprint-name image-type image-key configuration-file.toml

   Replace:

   • blueprint-name with the name of the blueprint you created
   • image-type with the ami image type.
   • image-key with the name of your VM Image to be uploaded to EC2.

   • configuration-file.toml with the name of the configuration file of the cloud provider.

     Note

     You must have the correct AWS Identity and Access Management (IAM) settings for the bucket you are going to send your customized image to. You have to set up a policy to your bucket before you are able to upload images to it.

4. Check the status of the image build:

   # composer-cli compose status

   After the image upload process is complete, you can see the "FINISHED" status.

1. Access EC2 on the menu and select the correct region in the AWS console. The image must have the available status, to indicate that it was successfully uploaded.
2. On the dashboard, select your image and click Launch.

Procedure

1. In the RHEL image builder dashboard, click the blueprint name that you previously created.
2. Select the tab Images.

3. Click Create Image to create your customized image.

   The Create Image window opens.

   1. From the Type drop-down menu list, select Amazon Machine Image Disk (.raw).
   2. Check the Upload to AWS checkbox to upload your image to the AWS Cloud and click Next.

   3. To authenticate your access to AWS, type your AWS access key ID and AWS secret access key in the corresponding fields. Click Next.

      Note

      You can view your AWS secret access key only when you create a new Access Key ID. If you do not know your Secret Key, generate a new Access Key ID.

   4. Type the name of the image in the Image name field, type the Amazon bucket name in the Amazon S3 bucket name field and type the AWS region field for the bucket you are going to add your customized image to. Click Next.

   5. Review the information and click Finish.

      Optionally, click Back to modify any incorrect detail.

      Note

      You must have the correct IAM settings for the bucket you are going to send your customized image. This procedure uses the IAM Import and Export, so you have to set up a policy to your bucket before you are able to upload images to it. For more information, see Required Permissions for IAM Users.

4. A pop-up on the upper right informs you of the saving progress. It also informs that the image creation has been initiated, the progress of this image creation and the subsequent upload to the AWS Cloud.

   After the process is complete, you can see the Image build complete status.

5. In a browser, access Service→EC2.

   1. On the AWS console dashboard menu, choose the correct region. The image must have the Available status, to indicate that it is uploaded.
   2. On the AWS dashboard, select your image and click Launch.
6. A new window opens. Choose an instance type according to the resources you need to start your image. Click Review and Launch.
7. Review your instance start details. You can edit each section if you need to make any changes. Click Launch

8. Before you start the instance, select a public key to access it.

   You can either use the key pair you already have or you can create a new key pair.

   Follow the next steps to create a new key pair in EC2 and attach it to the new instance.

   1. From the drop-down menu list, select Create a new key pair.
   2. Enter the name to the new key pair. It generates a new key pair.
   3. Click Download Key Pair to save the new key pair on your local system.

9. Then, you can click Launch Instance to start your instance.

   You can check the status of the instance, which displays as Initializing.

10. After the instance status is running, the Connect button becomes available.

11. Click Connect. A window appears with instructions on how to connect by using SSH.

    1. Select A standalone SSH client as the preferred connection method to and open a terminal.

    2. In the location you store your private key, ensure that your key is publicly viewable for SSH to work. To do so, run the command:

       $ chmod 400 <_your-instance-name.pem_>

    3. Connect to your instance by using its Public DNS:

       $ ssh -i <_your-instance-name.pem_> ec2-user@<_your-instance-IP-address_>

    4. Type yes to confirm that you want to continue connecting.

       As a result, you are connected to your instance over SSH.

Procedure

1. Launch the AWS Console.
2. Click on your AWS Account ID to display the drop-down menu and select My Security Credentials.
3. Click Users.
4. Select the user and open the Summary screen.
5. Click the Security credentials tab.
6. Click Create access key.
7. Download the .csv file (or save both keys). You need to enter these keys when creating the fencing device.

Procedure

1. From the AWS EC2 Dashboard, select Images and then AMIs.
2. Right-click the image you want to use and select Launch.

3. Choose an Instance Type that meets or exceeds the requirements of your workload. Depending on your HA application, each instance requires different capacity.

   See Amazon EC2 Instance Types for information about instance types.

4. Click Next: Configure Instance Details.

   1. Enter the Number of instances you want to create for the cluster. This example procedure uses three cluster nodes.

      Note

      Do not launch into an Auto Scaling Group.

   2. For Network, select the virtual private cloud (VPC) you created in Set up the AWS environment. Select the subnet for the instance to create a new subnet.

   3. Select Enable for Auto-assign Public IP. These are the minimum selections you need to make for Configure Instance Details. Depending on your specific HA application, you can make additional selections.

      Note

      These are the minimum configuration options necessary to create a basic instance. Review additional options based on your HA application requirements.

5. Click Next: Add Storage and verify that you have required storage for your HA application. You do not need to change these settings, unless your HA application requires other storage options.
6. Click Next: Configure Security Group. Select the existing security group you created in Setting up the AWS environment.
7. Click Review and Launch and verify your selections.
8. Click Launch. Select an existing key pair or create a new key pair. For selecting a key pair, see Setting up the AWS environment.
9. Click Launch Instances.

10. Click View Instances. You can name the instance(s).

    Note

    Also, you can launch instances by using the AWS CLI. See Launching, Listing, and Terminating Amazon EC2 Instances in the Amazon documentation for more information.

Procedure

1. Move the key file from the Downloads directory to your Home directory or to your ~/.ssh directory.

2. Change the permissions of the key file so that only the root user can read it:

   # chmod 400 KeyName.pem

Procedure

1. Launch the AWS Console and select the EC2 instance.
2. Click Connect and select A standalone SSH client.
3. From your SSH terminal session, connect to the instance by using the AWS example provided in the pop-up window. Add the correct path to your KeyName.pem file if the path is not shown in the example.

Procedure

1. Remove the AWS Red Hat Update Infrastructure (RHUI) client.

   $ sudo -i
   # dnf -y remove rh-amazon-rhui-client*

2. Register the VM with Red Hat.

   # subscription-manager register

3. Disable all repositories.

   # subscription-manager repos --disable=*

4. Enable the RHEL 9 Server HA repositories.

   # subscription-manager repos --enable=rhel-9-for-x86_64-highavailability-rpms

5. Update the RHEL AWS instance.

   # dnf update -y

6. Install the Red Hat High Availability Add-On software packages, along with the AWS fencing agent from the High Availability channel.

   # dnf install pcs pacemaker fence-agents-aws

7. The user hacluster was created during the pcs and pacemaker installation in the previous step. Create a password for hacluster on all cluster nodes. Use the same password for all nodes.

   # passwd hacluster

8. Add the high availability service to the RHEL Firewall if firewalld.service is installed.

   # firewall-cmd --permanent --add-service=high-availability
   # firewall-cmd --reload

9. Start the pcs service and enable it to start on boot.

   # systemctl start pcsd.service
   # systemctl enable pcsd.service

10. Edit /etc/hosts and add RHEL host names and internal IP addresses. For more information, see the Red Hat Knowledgebase solution How should the /etc/hosts file be set up on RHEL cluster nodes?.

Procedure

1. On one of the nodes, enter the following command to authenticate the pcs user hacluster. In the command, specify the name of each node in the cluster.

   # pcs host auth <hostname1> <hostname2> <hostname3>

   Example:

   [root@node01 clouduser]# pcs host auth node01 node02 node03
   Username: hacluster
   Password:
   node01: Authorized
   node02: Authorized
   node03: Authorized

2. Create the cluster.

   # pcs cluster setup <cluster_name> <hostname1> <hostname2> <hostname3>

   Example:

   [root@node01 clouduser]# pcs cluster setup new_cluster node01 node02 node03
   
   [...]
   
   Synchronizing pcsd certificates on nodes node01, node02, node03...
   node02: Success
   node03: Success
   node01: Success
   Restarting pcsd on the nodes in order to reload the certificates...
   node02: Success
   node03: Success
   node01: Success

Verification

1. Enable the cluster.

   [root@node01 clouduser]# pcs cluster enable --all
   node02: Cluster Enabled
   node03: Cluster Enabled
   node01: Cluster Enabled

2. Start the cluster.

   [root@node01 clouduser]# pcs cluster start --all
   node02: Starting Cluster...
   node03: Starting Cluster...
   node01: Starting Cluster...

Procedure

1. Create a shared block volume by using the AWS command create-volume.

   $ aws ec2 create-volume --availability-zone <availability_zone> --no-encrypted --size 1024 --volume-type io1 --iops 51200 --multi-attach-enabled

   For example, the following command creates a volume in the us-east-1a availability zone.

   $ aws ec2 create-volume --availability-zone us-east-1a --no-encrypted --size 1024 --volume-type io1 --iops 51200 --multi-attach-enabled
   
   {
       "AvailabilityZone": "us-east-1a",
       "CreateTime": "2020-08-27T19:16:42.000Z",
       "Encrypted": false,
       "Size": 1024,
       "SnapshotId": "",
       "State": "creating",
       "VolumeId": "vol-042a5652867304f09",
       "Iops": 51200,
       "Tags": [ ],
       "VolumeType": "io1"
   }

   Note

   You need the VolumeId in the next step.

2. For each instance in your cluster, attach a shared block volume by using the AWS command attach-volume. Use your <instance_id> and <volume_id>.

   $ aws ec2 attach-volume --device /dev/xvdd --instance-id <instance_id> --volume-id <volume_id>

   For example, the following command attaches a shared block volume vol-042a5652867304f09 to instance i-0eb803361c2c887f2.

   $ aws ec2 attach-volume --device /dev/xvdd --instance-id i-0eb803361c2c887f2 --volume-id vol-042a5652867304f09
   
   {
       "AttachTime": "2020-08-27T19:26:16.086Z",
       "Device": "/dev/xvdd",
       "InstanceId": "i-0eb803361c2c887f2",
       "State": "attaching",
       "VolumeId": "vol-042a5652867304f09"
   }

Verification

1. For each instance in your cluster, verify that the block device is available by using the ssh command with your instance <ip_address>.

   # ssh <ip_address> "hostname ; lsblk -d | grep ' 1T '"

   For example, the following command lists details including the hostname and block device for the instance IP 198.51.100.3.

   # ssh 198.51.100.3 "hostname ; lsblk -d | grep ' 1T '"
   
   nodea
   nvme2n1 259:1    0   1T  0 disk

2. Use the ssh command to verify that each instance in your cluster uses the same shared disk.

   # ssh <ip_address> "hostname ; lsblk -d | grep ' 1T ' | awk '{print \$1}' | xargs -i udevadm info --query=all --name=/dev/{} | grep '^E: ID_SERIAL='"

   For example, the following command lists details including the hostname and shared disk volume ID for the instance IP address 198.51.100.3.

   # ssh 198.51.100.3 "hostname ; lsblk -d | grep ' 1T ' | awk '{print \$1}' | xargs -i udevadm info --query=all --name=/dev/{} | grep '^E: ID_SERIAL='"
   
   nodea
   E: ID_SERIAL=Amazon Elastic Block Store_vol0fa5342e7aedf09f7

1. A receiver collects telemetry data from data sources, such as applications and services.
2. After the receiver ingest data, it passes to a processing phase, in which a chain of processors may be defined to transform the data.
3. The exporter sends the telemetry data to the required destination.

Procedure

1. Install the opentelemetry-collector package on a RHEL instance:

   # dnf install -y opentelemetry-collector

2. Enable and start the service to transfer the logs from the RHEL instance to AWS CloudWatch Logs:

   # systemctl enable --now opentelemetry-collector.service

3. To configure the OTel Collector to forward journald logs from the RHEL instance, create and edit the /etc/opentelemetry-collector/configs/10-cloudwatch-exporter.yaml file:

   ...
   exporters:
     awscloudwatchlogs:
       log_group_name: testing-logs-emf
       log_stream_name: testing-integrations-stream-emf
       raw_log: true
       region: us-east-1
       endpoint: logs.us-east-1.amazonaws.com
       log_retention: 365
       tags:
         sampleKey: sampleValue
   service:
     pipelines:
       logs:
         receivers:
           - journald
         exporters:
           - awscloudwatchlogs
   ...

4. Restart the OTel Collector service:

   # systemctl restart opentelemetry-collector.service

5. Create an IAM role for AWS CloudWatch agent from AWS console. For instructions, see Create IAM roles and users for use with the CloudWatch agent.
6. Attach the role to the RHEL instance through AWS Console. For instructions, see Attach an IAM role to an instance.
7. Restart the RHEL instance from AWS console to enable log exportation automatically.

8. Optional: If you no longer want to export logs, stop logs transfer from the RHEL instance:

   # systemctl stop opentelemetry-collector.service

9. Optional: If you no longer need this service, permanently disable logs transfer:

   # systemctl disable opentelemetry-collector.service

Procedure

1. Check the platform status of the RHEL Marketplace AMI instance:

   $ sudo mokutil --sb-state

   SecureBoot disabled
   Platform is in Setup Mode

   The setup mode allows updating the Secure Boot UEFI variables within the instance.

2. Generate a custom_db.cer custom certificate:

   $ openssl req -quiet \
   -newkey rsa:3072 \
   -nodes -keyout custom_db.key \
   -new -x509 -sha256 \
   -days 3650 \
   -subj "/CN=Signature Database key/" \
   --outform DER -out custom_db.cer

3. Generate UEFI variables file by using the virt-fw-vars utility:

   $ virt-fw-vars --enroll-redhat \
   --add-db-cert OvmfEnrollDefaultKeys custom_db.cer \
   --set-dbx /usr/share/edk2/ovmf/DBX* \
   --output-auth .

   For details, see the virt-fw-vars(1) man page on your system.

4. Convert UEFI variables to the Extensible Firmware Interface (EFI) Signature List (ESL) format:

   $ for f in PK KEK db dbx; do tail -c +41 $f.auth > $f.esl; done

   Note

   Each GUID is an assigned value and represents an EFI parameter

   • 8be4df61-93ca-11d2-aa0d-00e098032b8c: EFI_GLOBAL_VARIABLE_GUID
   • d719b2cb-3d3a-4596-a3bc-dad00e67656f: EFI_IMAGE_SECURITY_DATABASE_GUID

   The EFI_GLOBAL_VARIABLE_GUID parameter maintains settings of the bootable devices and boot managers, while the EFI_IMAGE_SECURITY_DATABASE_GUID parameter represents the image security database for Secure Boot variables db, dbx, and storage of required keys and certificates.

5. Transfer the database certificates to the target instance, use the efivar utility to manage UEFI environment variables.

   1. To transfer PK.esl, enter:

      $ sudo efivar -w -n 8be4df61-93ca-11d2-aa0d-00e098032b8c-PK -f PK.esl

   2. To transfer KEK.esl, enter:

      $ sudo efivar -w -n 8be4df61-93ca-11d2-aa0d-00e098032b8c-KEK -f KEK.esl

   3. To transfer db.esl, enter:

      $ sudo efivar -w -n d719b2cb-3d3a-4596-a3bc-dad00e67656f-db -f db.esl

   4. To transfer the dbx.esl UEFI revocation list file for x64 architecture, enter:

      $ sudo efivar -w -n d719b2cb-3d3a-4596-a3bc-dad00e67656f-dbx -f dbx.esl

6. Reboot the instance from the AWS console.

Procedure

1. Generate a custom certificate custom_db.cer:

   $ openssl req -quiet \
   -newkey rsa:3072 \
   -nodes -keyout custom_db.key \
   -new -x509 -sha256 \
   -days 3650 -subj "/CN=Signature Database key/" \
   --outform DER -out custom_db.cer

2. Use the virt-fw-vars utility to generate the aws_blob.bin binary file from keys, database certificates, and the UEFI variable store:

   $ virt-fw-vars --enroll-redhat \
   --add-db-cert OvmfEnrollDefaultKeys custom_db.cer \
   --set-dbx /usr/share/edk2/ovmf/DBX* \
   --output-aws aws_blob.bin

   The customized blob consists of:

   • PK.cer, KEK.cer, db, and dbx from the edk2-ovmf package
   • The custom_db.cer generated certificate

3. Use the awscli2 utility to create and register the AMI from a disk snapshot with the required Secure Boot variables:

   $ aws ec2 register-image \
   --name rhel-9-secure-boot \
   --architecture x86_64 \
   --virtualization-type hvm \
   --root-device-name "/dev/sda1" \
   --block-device-mappings "{\"DeviceName\": \"/dev/sda1\",\"Ebs\": {\"SnapshotId\": \"<snap-02d4db3813ff9b98e>\"}}" \
   --ena-support --boot-mode uefi \
   --region eu-central-1 \
   --uefi-data $(cat aws_blob.bin)
   --output json

   {
       "ImageId": "example-amazon-id"
   }

4. Reboot the instance from the AWS Console.

1. Initialization and measurement: A SEV-SNP enabled hypervisor sets the initial state of a VM. This hypervisor loads firmware binary into the VM memory and sets the initial register state. AMD Secure Processor (SP) measures the initial state of the VM and provides details to verify the initial state of the VM.
2. Firmware: The VM initiates the UEFI firmware. The firmware might include either stateful or stateless Virtual Trusted Platform Module (vTPM) implementation. Stateful vTPM maintains persistent cryptographic state across VM reboots and migrations, whereas stateless vTPM generates fresh cryptographic state for each VM session without persistence. Virtual Machine Privilege Levels (VMPL) technology isolates vTPM from the guest. VMPL offers hardware-enforced privilege isolation between different VM components and the hypervisor.

3. vTPM: Depending on your cloud service provider, for stateful vTPM implementation, the UEFI firmware might perform a remote attestation to decrypt the persistent state of vTPM.

   1. The vTPM also measures facts about the boot process such as Secure Boot state, certificates used for signing boot artifacts, UEFI binary hashes, and so on.

4. Shim: When the UEFI firmware finishes the initialization process, it searches for the extended firmware interface (EFI) system partition. Then, the UEFI firmware verifies and executes the first stage boot loader from there. For RHEL, this is shim. The shim program allows non-Microsoft operating systems to load the second stage boot loader from the EFI system partition.

   1. shim uses a Red Hat certificate to verify the second stage boot loader (grub) or Red Hat Unified Kernel Image (UKI).
   2. grub or UKI unpacks, verifies, and executes Linux kernel and initial RAM filesystem (initramfs), and the kernel command line. This process ensures that the Linux kernel is loaded in a trusted and secured environment.

5. Initramfs: In initramfs, vTPM information automatically unlocks the encrypted root partition in case of full disk encryption technology.

   1. When the root volume becomes available, initramfs transfers the execution flow to the root volume.
6. Attestation: The VM tenant gets access to the system and can perform a remote attestation to ensure that the accessed VM is an untampered Confidential Virtual Machine (CVM). Attestation is performed based on information from AMD SP and vTPM. This process confirms the authenticity and reliability of the initial CPU and memory state of the RHEL instance and AMD processor.
7. TEE: This process creates a Trusted Execution Environment (TEE) to ensure that booting of the VM is in a trusted and secured environment.

Procedure

1. Check if SEV-SNP is enabled for the RHEL instance:

   $ aws ec2 describe-instances --instance-ids <example_instance_id> \
   --region <example_region>

   ...
   "CpuOptions": {
   "CoreCount": 2,
   "ThreadsPerCore": 2,
   "AmdSevSnp": "enabled"
   },
   ...

2. If SEV-SNP is not enabled, get ID of a RHEL Amazon Machine Image (AMI):

   $ aws ec2 describe-images \
   --owners 309956199498 \
   --query 'sort_by(Images, &Name)[].[CreationDate,Name,ImageId]' \*
   --filters "Name=name,Values=RHEL-9" \*
   --region us-east-1 \
   --output table

   Note

   Do not modify the command option --owners 309956199498. This is the account ID for displaying Red Hat images. If you need to list images for AWS GovCloud, use --region us-gov-west-1 and --owners 219670896067.

3. Launch a RHEL instance with SEV-SNP enabled:

   $ aws ec2 run-instances \
   --image-id <example-rhel-9-ami-id> \
   --instance-type m6a.4xlarge \
   --key-name <example_key_pair_name> \
   --subnet-id <example_subnet_id> \
   --cpu-options AmdSevSnp=enabled

Procedure

1. UEFI Firmware: The boot process starts from the Unified Extensible Firmware Interface (UEFI) firmware. For boot, Red Hat Enterprise Linux (RHEL) UKI requires UEFI firmware, because legacy basic input/output system (BIOS) firmware is not supported.
2. Shim boot loader: Use the shim boot loader for booting rather than directly booting the UKI from the UEFI firmware. shim includes additional security mechanisms such as Machine Owner Key (MOK) and Secure Boot Advanced Targeting (SBAT).
3. Signature verification (Secure Boot UEFI mechanism): During boot, shim reads the UKI binary and the secure boot UEFI mechanism verifies the signature of UKI against trusted keys stored in the Secure Boot Allowed Signature Database (db) of the system, the MOK database, and the built-in database of the shim binary. If the signature key is valid, the verification passes.

4. SBAT verification: Immediately after signature verification, the shim boot loader verifies the SBAT rules at startup.

   During SBAT verification, the system compares generation numbers, for components such as systemd.rhel or linux.rhel, embedded in the UKI by using the .sbat section against values in the shim boot loader. If the generation number for a component in the shim is higher than the generation number in the UKI, the binary gets automatically discarded, even if it was signed by a trusted key.

   Note that the generation number is a version identifier for UEFI applications, such as shim and grub.

5. Unpacking and Execution: If verification passes, control passes from shim to the systemd-stub code in the UKI to continue the boot process.

6. systemd-stub add-ons: During execution, systemd-stub unpacks and extracts the contents of the .cmdline section, the plain text kernel command line, and the .initrd section, the temporary root file system, for the boot process.

   Note that systemd-stub reads UKI add-ons and verifies their signatures to safely extend the kernel command line of UKI by appending the .cmdline content from add-ons. systemd-stub reads add-ons from two locations:

   • Global (UKI-independent) add-ons from the /loader/addons/ directory on the Extensible Firmware Interface (EFI) System Partition (ESP).
   • Per-UKI add-ons from the /EFI/Linux/<UKI-name>.extra.d/ directory on the ESP.

7. Control passes from systemd-stub to the Linux kernel and the operating system boot process continues.

   From this point, secure boot with UKI mechanisms follows the standard kernel boot process.