A couple of days ago I received an interesting question from fellow colleague Paudie O'Riordan, who works over in our Storage and Availability Business Unit at VMware. He was helping a customer who was interested in PXE booting/installing ESXi using UEFI which is short for Unified Extensible Firmware Interface. Historically, we only had support for PXE booting/installing ESXi using the BIOS firmware. You also could boot an ESXi ISO using UEFI, but we did not have support for UEFI when it came to booting/installing ESXi over the network using PXE and other variants such as iPXE/gPXE.

For those of you who may not know, UEFI is meant to eventually replace the legacy BIOS firmware. There are many benefits with using UEFI over BIOS, a recent article that does a good job of explaining the differences can be found here. In doing some research and pinging a few of our ESXi experts internally, I found that UEFI PXE boot support is actually possible with ESXi 6.0. Not only is it possible to PXE boot/install ESXi 6.x using UEFI, but the changes in the EFI boot image are also backwards compatible, which means you could potentially PXE boot/install an older release of ESXi.

Note: Auto Deploy still requires legacy BIOS firmware, UEFI is not currently supported today. This is something we will be addressing in the future, so stay tuned.

Not having worked with ESXi and UEFI before, I thought this would be a great opportunity for me to give this a try in my homelab which would also allow me to document the process in case others were interested. For my PXE server, I am using CentOS 6.7 Minimal (64-Bit) which runs both the DHCP and TFTP services but you can use any distro that you are comfortable with.

Step 1 - Download and install CentOS 6.7 Minimal (64-Bit)

Step 2 - Login to the CentOS system via terminal and perform the following commands which will update the system and install the DHCP and TFTP services:

yum -y update
yum -y install dhcp tftp-server

Step 3 - Download and upload an ESXi 6.x ISO to the CentOS system. In example here, I am using latest ESXi 6.0 Update 1 image (VMware-VMvisor-Installer-6.0.0.update01-3029758.x86_64.iso).

Step 4 - Extract the contents of the ESXi ISO to the TFTP directory by running the following commands:

mount -o loop VMware-VMvisor-Installer-6.0.0.update01-3029758.x86_64.iso /mnt/
cp -rf /mnt/ /var/lib/tftpboot/esxi60u1
umount /mnt/
rm VMware-VMvisor-Installer-6.0.0.update01-3029758.x86_64.iso

Step 5 - Copy the custom ESXi bootx64.efi bootloader image to the root of the extracted ESXi directory by running the following command:

cp /var/lib/tftpboot/esxi60u1/efi/boot/bootx64.efi /var/lib/tftpboot/esxi60u1/mboot.efi

Step 6 - Next, we need to edit our DHCP configuration file /etc/dhcp/dhcpd.conf to point our hosts to the mboot.efi image. Below is an example configuration and you will need to replace it with the network configuration of your environment. If you are running the TFTP server on another system, you will need to change the next-server property to the address of that system else you will just specify the same IP Address as the DHCP server.

Step 7 - Next, we will need to edit our TFTP configuration file /etc/xinetd.d/tftp to enable the TFTP service by modifying the following line from yes to no:

disable = no

Step 8 - By default, the ESXi's boot.cfg configuration file refers to all packages under / path. We will need to remove that reference and can easily do so by running the following command:

sed -i 's/\///g' /var/lib/tftpboot/esxi60u1/boot.cfg

Step 9 - Finally, we need to restart both the TFTP (under xinetd) and DHCP services. For testing purposes, I have also disabled firewall for ipv4/ipv6, of course in a real production environment you will probably want to only open the ports required for TFTP/DHCP.

/etc/init.d/xinetd restart
/etc/init.d/dhcpd restart
/etc/init.d/iptables stop
/etc/init.d/ip6tables stop

We can now boot up either a physical host that is configured to use UEFI firmware OR we can also easily test using Nested ESXi. The only change we need to make to our ESXi VM is by setting the firmware mode from BIOS to EFI which can be done using the vSphere Web/C# Client as shown in the two screenshots below:

If everything was successfully configured, we should now see our system PXE boot into ESXi installer using UEFI as seen in the screenshot below.

If you run into any issues, I would recommend checking system logs on your PXE server (/var/log/messages) to see if there are any errors. You can also troubleshoot by manually using tftp client and connecting to your TFTP Server to ensure you are able to pull down the files such as the boot.cfg by running the following command:

tftp [PXE-SERVER]
get esxi60u1/boot.cfg

For additional resources on scripted installation of ESXi also referred to as Kickstart, be sure to take a look here. I also would like to give a big shoutout and thanks to Tim Mann, one of the Engineers responsible for adding UEFI support into ESXi and for answering some of my questions while I was setting up my environment.