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Last updated: Jul 15, 2024

How to Fix ESXi Boot Failure in UEFI Mode?

As virtualization technology continues to evolve, ESXi remains a fundamental component in many IT infrastructures. However, one significant challenge that administrators often face is when an ESXi host fails to boot, especially in environments using UEFI (Unified Extensible Firmware Interface) configurations.

This article explores the complexities of UEFI—a modern firmware interface—and how it interacts with ESXi. We provide a detailed, step-by-step guide to help you identify and solve issues related to boot failure in your ESXi system, ensuring that your virtual environment remains stable and dependable.

No matter if the issues stem from compatibility concerns, misconfigurations, or undetermined errors, this in-depth guide is crafted to provide you with the essential knowledge and tools necessary to get your ESXi host up and running again.

Symptoms of failing to boot ESXi

These indicators are crucial for IT administrators and technicians to recognize, as they help diagnose the underlying problem. Some common indicators include:

  • No Bootable Device Found: This message indicates that the ESXi host's BIOS or UEFI firmware is unable to locate a device with a bootable ESXi installation. This could be due to disk failure, corruption of the ESXi installation, or issues with the boot order settings in BIOS/UEFI.
  • Prolonged Boot Times: If the ESXi host takes significantly longer to boot than usual, it might suggest problems with the storage devices, corrupted ESXi installation files, or hardware issues.
  • Error Messages During Boot: Error messages or warning alerts displayed during the boot process can point towards specific issues with the hardware or the ESXi installation. These messages should be noted for further troubleshooting.
  • Automatic Rebooting or System Crashes: If the ESXi host repeatedly reboots or crashes during the boot process, it could indicate hardware failures, such as issues with the RAM, CPU, or motherboard, or problems with the ESXi software itself.
  • Inaccessible Management Interfaces: Inability to access vSphere Client or ESXi's Direct Console User Interface (DCUI) after the system has supposedly booted, indicating that the boot process may not have completed successfully.
  • Unresponsive System Post-Boot: If the ESXi host appears to boot but does not respond to input or network connections, it may suggest a partial boot, where essential services or drivers have failed to load.
  • Disk or Storage Errors: Errors related to the host's storage, such as inability to access datastores or corrupted file systems, can prevent ESXi from booting correctly.
  • LED Indicators on Hardware: Many server hardware come with LED indicators that can signal hardware failures, such as disk, memory, or motherboard issues, which can impede the boot process.

Recognizing these indicators is the first step in troubleshooting ESXi boot issues, leading to a more targeted and effective resolution process.

Factors Leading to ESXi Boot Failure

Factors leading to ESXi boot failure encompass a range of issues that can arise from hardware malfunctions, software glitches, or misconfigurations. Understanding these factors is essential for diagnosing and resolving boot problems in an ESXi environment. Here are some key causes:

  • Hardware Failures: Faulty or incompatible hardware components, such as hard drives, RAM, motherboards, or CPUs, can prevent ESXi from booting. Issues like disk failure or corrupted memory modules are common culprits.
  • Storage Issues: Problems with the storage subsystem, including RAID configuration errors, failed SSDs/HDDs, or issues with SAN/NAS connectivity, can lead to boot failure. Corrupted datastores or damaged file systems on the storage devices used by ESXi can also be a cause.
  • Firmware Problems: Outdated or corrupted BIOS/UEFI firmware can lead to compatibility issues with ESXi. Firmware bugs or misconfigurations in the server's BIOS/UEFI settings can also prevent proper booting.
  • Corrupted ESXi Installation: Corruption in the ESXi installation files, whether due to improper installation, updates, or other software issues, can prevent the system from booting.
  • Network Configuration Errors: Incorrect network settings or failures in network components can impede ESXi's boot process, particularly in configurations where ESXi boots from a network location (like PXE boot).
  • Boot Loader Issues: Problems with the boot loader, such as a corrupt boot sector or misconfigured boot settings, can prevent ESXi from starting.
  • Incompatible or Corrupted Drivers: Drivers that are incompatible with the current version of ESXi or that have become corrupted can cause boot failures, especially if they are critical for the hardware initialization during the boot process.
  • Power Supply Problems: Inconsistent or inadequate power supply can lead to improper booting or system instability, which in turn affects ESXi’s ability to boot.
  • Improper Configuration Changes: Incorrect changes made to the ESXi configuration files or settings can lead to boot issues. This includes changes in the ESXi host's network settings, kernel parameters, or system security settings.
  • Virtualization Support: Lack of proper virtualization support in the BIOS/UEFI settings, or if virtualization has been disabled, can also lead to ESXi boot issues.

Reason 1 - Interaction Between the Installer and NVRAM

The Interaction Between the Installer and NVRAM as a cause of ESXi boot failure refers to issues that can arise when the ESXi installer interacts with the Non-Volatile Random-Access Memory (NVRAM) of the host machine during the installation or configuration process. NVRAM is a type of memory that retains its data even when the system's power is turned off. It is used to store critical system settings, including BIOS/UEFI configurations, boot sequence information, and hardware settings. Here's how this interaction can lead to boot issues:

  1. 1. Corrupted Boot Configuration: During installation, ESXi configures boot-related settings in the NVRAM. If these settings become corrupted or are improperly configured, the system may fail to boot. This could be due to issues with the installer, interruptions during the installation process, or hardware compatibility problems.

  2. 2. Conflicts with Existing Settings: If the host machine has existing settings stored in NVRAM (from previous installations or other operating systems), the ESXi installer might conflict with these settings. This can lead to problems where the ESXi boot loader is not correctly recognized or prioritized in the boot sequence.

  3. 3. NVRAM Space Limitations: Some systems have limited NVRAM space, and if it's already near capacity due to existing configurations, the ESXi installer might not be able to write necessary boot information. This lack of space can prevent the ESXi host from registering the correct boot settings.

  4. 4. Firmware Incompatibilities: The ESXi installer interacts with the system's firmware to configure boot settings. If there are incompatibilities between the firmware (BIOS/UEFI) and the ESXi version, it might result in incorrect or incomplete NVRAM configurations.

  5. 5. Improper Installation Media: If the installation media (like a USB drive or CD) used for ESXi installation is faulty or not prepared correctly, it can lead to incomplete or corrupted NVRAM entries, affecting the boot process.

  6. 6. Hardware-Specific Issues: Certain hardware configurations might have unique requirements or limitations regarding NVRAM, and if these are not accounted for during the installation, it can result in boot problems.

Reason 2 - Master Boot Record (MBR) or MSDOS Partition Table Issues

Master Boot Record (MBR) or MSDOS Partition Table Issues as a cause of ESXi boot failure pertains to problems associated with the disk partitioning scheme used on the boot device. Here's a detailed explanation:

  1. 1. MBR Partition Limitations: The Master Boot Record (MBR) is an older disk partitioning method that has certain limitations. One key limitation is that it supports disks up to 2TB in size and allows only four primary partitions. If ESXi is installed on a disk with an MBR scheme that exceeds these limitations, it can lead to boot failures.

  2. 2. Incompatibility with UEFI: Modern systems often use UEFI (Unified Extensible Firmware Interface) instead of the traditional BIOS. UEFI systems are typically designed to boot from the GPT (GUID Partition Table) rather than MBR. If ESXi is installed on an MBR-partitioned disk in a UEFI-configured system, it may fail to boot because UEFI might not recognize the MBR partitioning.

  3. 3. Corrupted MBR: The MBR contains critical boot information. If the MBR gets corrupted due to disk errors, malware, or improper shutdowns, it can lead to a failure in the boot process. A corrupted MBR might not properly point to the location of the ESXi bootloader.

  4. 4. Boot Loader Conflicts: If the system has multiple operating systems installed across different partitions, there could be conflicts with the boot loaders. For instance, the MBR might be configured to prioritize another boot loader over ESXi's, leading to boot issues.

  5. 5. Partition Table Errors: The MSDOS partition table, associated with MBR, can develop errors due to disk malfunctions or incorrect partition modifications. These errors can prevent the ESXi boot loader from locating the correct partition to boot from.

  6. 6. Inadequate Boot Partition Size: In an MBR scheme, if the partition size allocated for ESXi is insufficient, it can lead to issues during the boot process, as ESXi might not have enough space to load all necessary files.

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Resolving ESXi Boot Issues in UEFI Mode

Resolving ESXi boot issues in UEFI (Unified Extensible Firmware Interface) mode involves a series of troubleshooting steps and configurations adjustments to ensure compatibility and proper functioning. UEFI is a modern firmware interface that replaces the traditional BIOS, offering more advanced features like secure boot and support for larger hard drives. Here's a guide on how to address ESXi boot failures in UEFI mode:

  1. 1. Check UEFI Settings: Ensure that the UEFI settings on your server are correctly configured for ESXi. This includes disabling the secure boot feature, as some versions of ESXi might not be compatible with it. Also, check if the UEFI boot mode is enabled instead of legacy BIOS mode.

  2. 2. Verify Boot Order: In the UEFI settings, confirm that the boot order prioritizes the device where ESXi is installed. Misconfigured boot order can lead to the system trying to boot from a different device.

  3. 3. Update Firmware: Outdated UEFI firmware can cause compatibility issues with ESXi. Check for firmware updates from the server manufacturer and apply them if available.

  4. 4. Use GPT Partitioning: UEFI works best with the GPT (GUID Partition Table) rather than the older MBR (Master Boot Record) partition style. If your ESXi boot disk is using MBR, consider converting it to GPT. However, be cautious, as this conversion can lead to data loss.

  5. 5. Reinstall ESXi: If the installation is corrupted or if there were issues during the initial installation, consider reinstalling ESXi. Make sure to use a UEFI-compatible version and follow the installation instructions carefully.

  6. 6. Check Storage and Network Configuration: Ensure that storage and network configurations are properly set up, especially if you're booting ESXi from a network or a SAN/NAS device. Incorrect configurations can prevent ESXi from booting in UEFI mode.

  7. 7. Repair Boot Loader: The ESXi boot loader might be corrupted. You can use ESXi installation media to repair or reinstall the boot loader.

  8. 8. Inspect for Hardware Issues: Faulty hardware components, like hard drives, RAM, or motherboards, can cause boot failures. Conduct a hardware diagnostic to rule out physical defects.

  9. 9. Check ESXi Compatibility: Ensure that the version of ESXi you are trying to boot is compatible with your server’s hardware and UEFI firmware version.

  10. 10. Clear NVRAM: Sometimes, clearing the NVRAM (Non-Volatile Random Access Memory) can resolve boot issues. This process removes old or corrupt configuration settings that might be interfering with the boot process.

  11. 11. Consult Logs and Documentation: Check the ESXi logs for any error messages that might provide clues to the boot failure. Additionally, consulting the server's and VMware's documentation can provide model-specific guidance.

Resolving ESXi boot issues in UEFI mode often requires a systematic approach, starting from basic firmware and hardware checks, moving to more complex troubleshooting and configuration adjustments.

Guidelines for Repairing ESXi Boot VM Using DiskInternals VMFS Recovery Software

Tip: how to work with VMware Home Lab

Repairing an ESXi Boot Virtual Machine (VM) using DiskInternals VMFS Recovery software involves a series of steps designed to recover data and restore functionality to a VM that is failing to boot properly on a VMware ESXi server. DiskInternals VMFS Recovery is a specialized software tool used for recovering data from VMFS (Virtual Machine File System) partitions commonly used in VMware environments. Here's a guide on how to use this software for repairing a boot VM:

  1. 1. Download and Install DiskInternals VMFS Recovery: First, download the DiskInternals VMFS Recovery software from the official website and install it on a Windows-based machine. This computer should have enough free space to store recovered data.

  2. 2. Connect to the ESXi Server: Launch the DiskInternals VMFS Recovery software. You will need to connect to the ESXi server hosting the VMFS datastore. This can typically be done by providing the IP address and login credentials of the ESXi server within the software.

  3. 3. Scan the VMFS Datastore: Once connected, navigate to the VMFS datastore that contains the problematic VM. Initiate a scan of the datastore. The software will analyze the VMFS partition and attempt to locate all virtual machines, including those that are not booting correctly.

  4. 4. Recover the Virtual Machine: After the scan is complete, the software will display a list of found VMs. Locate the VM that is experiencing boot issues. You can then use the software’s recovery feature to recover this VM. The recovery process typically involves creating a copy of the VM’s files in a stable state.

  5. 5. Save the Recovered VM: Choose a location on your Windows machine or an external storage device to save the recovered VM. It's important to save the recovered data to a different location than the original VMFS datastore to prevent data overwriting.

  6. 6. Mount the Recovered VM: After recovery, the next step is to mount the recovered VM. You can do this by adding the VM back into your ESXi server's inventory, using either the vSphere client or other VMware management tools.

  7. 7. Verify and Boot the VM: Once the VM is mounted back onto the ESXi server, attempt to boot it. Carefully monitor the boot process for any errors or issues.

  8. 8. Backup Important Data: If the VM successfully boots, it's advisable to backup any critical data from the VM to prevent potential future data loss.

  9. 9. Assess and Repair VM Files: In some cases, you may need to assess and repair VM files or configurations if there are still issues with the VM’s operation. This could involve repairing or reinstalling virtual machine tools or drivers.

  10. 10. Consult Documentation: Throughout this process, consult the DiskInternals VMFS Recovery documentation for specific guidance on software features and troubleshooting tips.

Using VHD recovery tool is an effective way to handle data recovery and repair of a non-booting VM in an ESXi environment, especially when conventional methods fail or when dealing with corrupted VMFS datastores.


In conclusion, addressing ESXi boot failures, whether in UEFI mode or due to issues like MBR/MSDOS partition tables or installer and NVRAM interactions, requires a thorough understanding of both the hardware and software aspects of your virtualization environment. The key to effectively resolving these issues lies in systematic troubleshooting and employing the right tools and techniques.

For UEFI mode challenges, ensuring compatibility through firmware updates, proper boot sequence configuration, and using GPT partitioning are essential. In cases of corrupted boot loaders or partition table issues, understanding the underlying cause – be it hardware malfunctions, firmware incompatibilities, or corrupted installations – is crucial for effective resolution.

When dealing with more complex scenarios, such as repairing a non-booting VM, specialized tools like DiskInternals VMFS Recovery prove invaluable.

Ultimately, the resilience of an ESXi environment hinges on regular maintenance, staying updated with the latest VMware best practices, and being prepared with the right tools and knowledge to tackle boot issues. By embracing a proactive approach to these challenges, administrators can ensure the high availability and reliability of their virtual infrastructure.

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