Nutanix AHV – Boot or Convert VM from BIOS to UEFI Mode

Nutanix AHV – How to Boot a VM in BIOS or UEFI Mode (Windows & Linux Guide)

Boot mode selection plays an important role in operating system installations and long-term VM compatibility on Nutanix AHV. Many administrators often need to switch between BIOS and UEFI boot modes, especially when working with modern Windows and Linux distributions that require UEFI secure boot or GPT-based disks.

This updated guide explains what Nutanix AHV is, how BIOS and UEFI modes work in AHV, how to configure boot settings, and how to convert an existing VM from BIOS to UEFI without losing data.

Nutanix latest AHV hypervisor version support new features and updates that allow to boot Guest OS – Windows / Linux VM’s BIOS UEFI setup mode to change the VM’s BIOS settings i.e booting device sequence, Access Boot manager to enable the Secure Boot UEFI on Guest VMs.

Nutanix AOS version has built new features are supports UEFI and Secure Boot of UEFI, enable Secure Boot feature of UEFI on user guest Windows / Linux VMs running on Nutanix AHV clusters, Nutanix AHV allow to change the Windows / Linux guest VMs UEFI firmware menu to press the Fn + F2 keys on your keyboard.

What is Nutanix AHV?

Nutanix AHV (Acropolis Hypervisor) is a secure, enterprise-grade, open-source-based hypervisor that runs on Nutanix HCI. AHV is tightly integrated with Prism, offering simple VM management, networking, and lifecycle operations without additional hypervisor licensing.

AHV supports:

• Windows & Linux virtual machines
• BIOS and UEFI boot modes
• Secure Boot for supported operating systems
• Snapshot-based rollbacks
• Live migration and high availability

What is Nutanix UEFI Boot Mode?

UEFI (Unified Extensible Firmware Interface) is a modern boot firmware that replaces legacy BIOS. Nutanix AHV provides both boot modes so that users can install legacy OS in BIOS mode or modern OS in UEFI mode with better performance and security.

Benefits of UEFI mode in Nutanix AHV

• Supports GPT disk partitioning
• Faster boot time
• Required for Windows 10, 11, Windows 2016, 2019,2022 and 2025 and later, and RHEL 8,9 and later
• Supports Secure Boot (depending on version)
• Better OS compatibility for cloud-ready workloads

Advantages of UEFI Mode

The pre-operating system environment is vulnerable to attacks by possible malicious loaders. Secure boot addresses this vulnerability with UEFI secure boot using policies present in the firmware along with certificates, to ensure that only properly signed and authenticated components are allowed to execute.

UEFI firmware is a successor to legacy BIOS firmware that supports larger hard drives, faster boot time and provides more security features.

Creation and starting guest Windows / Linux VMs with UEFI firmware provide the following advantages.

• Boot faster
• Avoid legacy option ROM address constraints
• Include robust reliability and fault management
• Use UEFI drivers

You can create or update VMs with UEFI firmware by using the acli commands, Prism web console, or Prism Central UI.

Read also: Nutanix Block Vs Nutanix Node

UEFI Supported Operating System

Here is list of Operating System Windows / Linux OS supports the UEFI secure booting BIOS feature :

• Nutanix does not support converting a VM that uses IDE disks or Legacy BIOS to VMs that use Secure Boot.
• It is only supported on Q35, a new virtual hardware platform.
• It is only supported on AHV.
• Recovery of the secure boot enabled VMs is not supported on AOS 5.16.

Read more: Nutanix AHV Supported Guest OS List

Prerequisites to Boot or Convert Guest OS from BIOS to UEFI

Before switching the boot mode of any virtual machine on Nutanix AHV, it is very important to understand the technical prerequisites. Changing from BIOS to UEFI affects the way the operating system boots, the disk partition style, and the boot loader configuration. Meeting these requirements will prevent boot failures and ensure a smooth conversion.

1. Nutanix AHV Platform Requirements

To enable UEFI boot mode smoothly, ensure the following:

• The cluster must be running a supported minimum Nutanix AOS version 5.16 or later & AHV version 20190916.96or later
• Prism Element must be accessible to modify the VM configuration.
• VM must be powered off before changing the boot mode.
• VirtIO drivers should be updated to the latest version (recommended).

For AHV & AOS compatibility, you may refer to: Nutanix AHV & AOS compatibility Matrix

2. Guest Operating System Requirements

Different OS versions require different boot configurations.

Windows Requirements

• Windows Server 2016, 2019, 2022, 2025 and Windows 10/11 natively support UEFI.
• For older systems like Windows 2012/2012R2, UEFI is optional.
• Windows must use GPT partitioning to boot in UEFI mode.
• Use Microsoft’s mbr2gpt.exe utility to convert MBR to GPT.

Linux Requirements

• Modern distributions like RHEL 8+, CentOS 8+, Ubuntu 18+, and SUSE support UEFI.
• GRUB must be installed with EFI target.
• An EFI System Partition (ESP) of at least 260 MB must exist.
• GPT disk layout is recommended.

3. Virtual Machine Disk Layout Requirements

UEFI mode requires a GPT disk structure, not MBR.

For conversion from BIOS → UEFI:

• Convert the system disk to GPT.
• Verify there is sufficient unallocated space for creating an UEFI System Partition (ESP).
• Ensure the boot loader supports EFI.

Create Secure UEFI VMS From acli Command

In AHV-managed clusters, you can create a Windows / Linux VM to start with UEFI firmware by using the aCLI command. This topic describes the procedure to create a VM by using Acropolis CLI (aCLI).

Step 1: SSH to any Nutanix CVM

Step 2: Run following command to enter in acli command mode

cvm$ acli

Step 3: Create secure boot UEFI firmware VM to run following command

cvm$ vm.create uefi_boot=true nvram_container=<Container_Name>

Note: By default, the UEFI firmware and variables are stored in an NVRAM container. The UEFI variables are stored in a default NVRAM container. Nutanix recommends you to choose a storage container with at least RF2 storage policy to ensure the VM high availability for node failure scenarios.

Read also: Configure Nutanix Virtual Network with IPAM

Change VM’s BIOS Booting Firmware to UEFI

If you have migrated the UEFI firmware enabled physical server to virtual P2V / Virtual to Virtual V2V but your VM is booting up with default BIOS booting firmware. It means you need to change the VM’s BIOS booting firmware booting type.

Change VM’s BIOS booting firmware type from legacy to UEFI firmware

Step 1: shutdown your running VM on Nutanix platform

Step 2: SSH to any Nutanix CVM

Step 3: Run following command to enter in acli command mode

cvm$ acli

Step 4: Change the BIOS firmware type to UEFI firmware

cvm$ vm.update <VM_Name> uefi_boot=true

Step 5: Now Power-on the VM

Read also: Windows 10 High CPU Consumption Issue On Nutanix AHV

Boot Nutanix VM in BIOS Mode

Now you can Enter / boot your Nutanix AHV hosted Windows / Linux VM in BIOS UEFI mode to just press the Fn + F2 keys on your keyboard and can change the VM’s booting sequence, booting device, booting type, booting delay, screen resolution etc.

Just follow the steps to boot the Nutanix AHV hosted VM in BIOS mode:

Ensure that the Windows / Linux VM is in powered on state.

Step 1: Log on to Prism web console.

Step 2: Power-on VM

To go to the UEFI firmware menu, press the Fn + F2 keys on your keyboard.

Final Step: Do one of the following.

• To save the changed resolution, press the F10 key.
• To go back to the previous screen, press the Esc key.

Note: After saving the changes, the OS reflects the changed resolution.

Hopefully, You enjoyed the Nutanix new feature to boot up the Nutanix AHV hosted VM in BIOS UEFI firmware secure mode.

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Manish Kumar

I’m Manish Kumar, founder of HyperHCI.com and a senior IT consultant with 13+ years of experience in infrastructure design and cybersecurity. An official certified SME for ISC2 and Nutanix, Also, certified in CISSP, CompTIA Security+, VMware and AWS. My expertise covers HCI, virtualization, cloud computing, network and security across Nutanix, VMware, and AWS platforms Read more