Use UEFI Secure Boot

Secure Boot is supported in UEFI installations only. It is not used when booting StarlingX as a legacy boot target.

StarlingX currently does not support switching from legacy to UEFI mode after a system has been installed. Doing so requires a reinstallation of the system. This also means that upgrading from a legacy install to a secure boot install (UEFI) is not supported.

When upgrading a StarlingX system from a version which does not support secure boot to a version that does, do not enable secure boot in UEFI firmware until the upgrade is complete.

For each node that is going to use secure boot, you must populate the StarlingX public certificate/key in the UEFI Secure Boot authorized database in accordance with the board manufacturer’s process. This must be done for each node before starting installation.

You may need to work with your hardware vendor to have the certificate installed.

There is often an option in the UEFI setup utility which allows a user to browse to a file containing a certificate to be loaded in the authorized database. This option may be hidden in the UEFI setup utility unless UEFI mode is enabled, and secure boot is enabled.

Many motherboards ship with Microsoft secure boot certificates pre-programmed in the UEFI certificate database. These certificates may be required to boot UEFI drivers for video cards, RAID controllers, or NICs (for example, the PXE boot software for a NIC may have been signed by a Microsoft certificate). While certificates can usually be removed from the certificate database (again, this is UEFI implementation specific) it may be required that you keep the Microsoft certificates to allow for complete system operation.

Mixed combinations of secure boot and non-secure boot nodes are supported. For example, a controller node may secure boot, while a worker node may not. Secure boot must be enabled in the UEFI firmware of each node for that node to be protected.

Build considerations for signing packages for UEFI Secure Boot

The StarlingX build environment has provisions for calling out to a signing server for purposes of creating a secure boot load. At this time StarlingX does not include an implementation of the signing server. The following describes how the signing process is intended to work in the context of a CentOS build. You may find it helpful in implementing your own signing server.

The following environmental variables should be defined before attempting to request a secure boot signing:

export SIGNING_SERVER=<signing-host>
export SIGNING_USER=<signing-user>
export SIGNING_SERVER_SCRIPT=<path-to-signing-script>

build-pkgs further requires that $USER be set to “jenkins”, and export FORMAL_BUILD=1`.

If the above criteria is met, it calls into sign-secure-boot.

This is an example of the call sequence:

# 1. Set up the server side directory for files transfers.

# 2. upload the original package

# 3. Request that the package be signed

# 4. Download the file from the signing server

Within the signing server there are two keys used for signing, known as the boot key and the shim key. The public boot key file must be manually added to the secure boot keychain in the firmware. The boot key signs the first executable loaded, contained in the shim package. The first executable must then install the public shim key file (automatically) before passing control to the grub, and ultimately the kernel, both of which are signed by the private shim key.

Three packages need to be passed to the signing server. The RPMs need to be unpacked, the relevant binaries signed with the correct keys, and the RPMs reassembled.



Files to sign


boot shim

BOOTX64, shim, shimx64 MokManager, fallback, mmx64, fbx64



grubx64.efi, gcdx64.efi




shim files that are required to be signed might might include a .efi or .EFI suffix.

Some files may be absent in newer packages.



Keys and certificates:

  • boot.crt - Certificate to boot (to be programmed in firmware)

  • boot.key - Private key with which to sign shim

  • shim.crt - Certificated embedded within shim used to validate kernel, grub

  • shim.key - Private key with which to sign kernel/grub

Key generation:

openssl req -new -x509 -newkey rsa:2048 -keyout $KEY.key -out $KEY.pem -days 3650
openssl x509 -in $KEY.pem -out $KEY.crt -outform DER


boot.crt should be copied to cgcs-root/build-tools/certificates/TiBoot.crt for inclusion during the build-iso step.