Secure Boot

If you install ESXi via a Kickstart script and make use of the %firstboot option to execute commands on the first boot of the ESXi host after installation, you should be aware of its incompatibility with the Secure Boot feature. If you install ESXi where Secure Boot is enabled, the Kickstart will install ESXi normally only execute up to the %post section. However, it will not execute the %firstboot scripts and if you look at the /var/log/kickstart.log after the host boots, you should see the following message:

INFO UEFI Secure Boot Enabled, skipping execution of /var/lib/vmware/firstboot/001.firstboot_001

If you have Secure Boot enabled, %firstboot is not supported. The reason for this is Secure Boot mandates only known tardisks which can hold executable scripts, and a kickstart script is an unknown source so it can not run when Secure Boot is enabled. If you wish to continue using %firstboot scripts, the only option is to disable Secure Boot and then re-enable it after the installation. A preferred alternative is to convert your %firstboot logic into an external script which can then be applied using the vSphere API (recommended method) and this way you can still customize your ESXi host after the initial installations. I have already filed an internal documentation bug to add a note regarding Secure Boot and %firstboot, hopefully that will roll out with the net documentation refresh.

Several weeks back I was chatting with a few of our Engineers from the Core Platform Team (vSphere) and they had shared an interesting tidbit which I thought I was worth mentioning to my readers. When creating a Virtual Machine in either vSphere or Fusion/Workstation, customers have the option to override the default and specify the specific Firmware boot option whether that is BIOS or UEFI.

Like most customers, I do not even bother touching this setting and I just assume the system defaults are sufficient. Interestingly, for Microsoft Windows 10 and Windows Server 2016, there are some important implications to be aware of on whether BIOS or UEFI is used. This is especially important since the default firmware type in vSphere for these OSes are BIOS.