How to Start a VMDK File Without a VMX File: Recovery and Manual Boot Guide
In VMware environments, the VMDK file contains the virtual machine’s disk data, while the VMX file defines its configuration and hardware settings. Normally, both are required for a VM to boot. But what happens if the VMX file is missing, corrupted, or accidentally deleted? Many administrators find themselves with only a VMDK and no configuration file to launch the VM.
This guide explains how to start a VMDK file without a VMX, covering practical recovery methods, manual reconstruction techniques, and troubleshooting steps. Whether you’re dealing with datastore corruption, failed migration, or accidental deletion, you’ll learn how to rebuild the VM configuration, attach the existing disk, and validate a successful boot.
Can You Run a VMDK Without a VMX File?
The VMX file plays a critical role in VMware environments: it defines the virtual machine’s hardware configuration — CPU, memory, disk controllers, network adapters, and firmware settings. Without it, VMware doesn’t know how to interpret or boot the VMDK disk file.
What happens when the VMX is missing or corrupted
- VMware cannot register or start the VM directly.
- The VMDK remains intact, but it’s just a disk image without instructions on how to use it.
- Attempts to boot may fail with errors or result in a blank screen.
Conditions where a VMDK can still be started
- By creating a new VM and attaching the existing VMDK.
- By manually reconstructing a VMX file that points to the disk.
- By using VMware Converter or recovery tools to rebuild the configuration.
Key risks when running a VMDK without its original VMX
- Wrong disk controller mapping (SCSI vs IDE vs NVMe) can cause boot errors.
- Boot failure if firmware type (BIOS vs EFI) doesn’t match the OS.
- Broken UUIDs leading to conflicts or duplicate identifiers.
- Missing NVRAM file causing loss of boot order or firmware variables.
Core Methods to Start a VMDK Without VMX
Method 1 — Create a New VM and Attach Existing VMDK
The most straightforward way to start a VMDK without its original VMX file is to build a new virtual machine and link the disk manually.
Workflow:
- 1. Manual VM creation — In VMware Workstation or ESXi, create a new custom virtual machine.
- 2. Select the correct guest OS type — Match the operating system inside the VMDK to ensure proper drivers and compatibility.
- 3. Choose the right disk controller — Options include LSI Logic, VMware Paravirtual (PVSCSI), or IDE. Selecting the wrong controller often leads to boot errors.
- 4. Attach the existing virtual disk — Instead of creating a new disk, point the VM to the existing VMDK file.
- 5. VMware will automatically generate a new VMX configuration file, allowing the VM to boot from the recovered disk.
Method 2 — Rebuild a VMX File Manually
If automated creation isn’t possible, you can manually reconstruct a VMX file to reference the VMDK.
Key requirements:
- Required VMX parameters — CPU count, RAM size, firmware type (BIOS/EFI), disk controller, and network adapter.
- Matching disk path and adapter type — Ensure the VMX points to the correct VMDK file and uses the right controller (SCSI, IDE, NVMe).
- CPU, RAM, firmware, and boot config — Define hardware resources and boot order explicitly.
- Common VMX syntax mistakes — Typos, missing quotation marks, or incorrect parameter names can prevent VMware from loading the VM.
Example snippet for disk linkage:
scsi0.present = "TRUE"
scsi0:0.present = "TRUE"
scsi0:0.fileName = "disk.vmdk"
scsi0:0.deviceType = "disk"
| VMX Parameter | Purpose | Example |
|---|---|---|
| scsi0.present | Enables disk controller | TRUE |
| scsi0:0.fileName | Links VMDK disk | disk.vmdk |
| guestOS | Defines OS type | windows9-64 |
| firmware | BIOS or EFI boot | bios |
How to Identify Correct Boot Settings From the VMDK
When starting a VMDK without its original VMX file, one of the biggest challenges is determining the correct boot settings. The disk itself contains clues that can help you reconstruct the proper configuration.
- Detecting OS type from disk structure. By examining the contents of the VMDK (or mounting it in another VM), you can identify whether it contains Windows, Linux, or another OS. File system type (NTFS, ext4, etc.) is a strong indicator of the guest OS.
- BIOS vs EFI boot mode. Modern operating systems often rely on EFI, while older ones use BIOS. If the disk contains EFI system partitions, you’ll need to configure the VMX to use EFI firmware.
- MBR vs GPT partition scheme. Inspecting the partition table reveals whether the disk uses MBR or GPT. MBR typically pairs with BIOS, while GPT is usually tied to EFI. Matching this correctly prevents boot errors.
- Using disk descriptor file for clues. VMDK files often include a descriptor that specifies geometry, adapter type, and other metadata. Reviewing this information can guide you in setting the right disk controller and firmware in the VMX.
Mounting a VMDK Without a VM for Data Access
Sometimes the goal isn’t to boot the virtual machine but simply to access the data stored inside the VMDK. In these cases, you can mount the disk directly without needing a VMX file.
- When booting is not required. If you only need to recover files, documents, or application data, mounting the VMDK as a secondary disk is faster and safer than attempting a full VM boot.
- Mounting disk in VMware Workstation / ESXi. VMware allows you to add an existing VMDK to another virtual machine as an additional drive. This way, the host VM can read the disk contents without relying on the missing VMX.
- Using disk as secondary drive. Attach the VMDK to a healthy VM running the same or compatible operating system. The guest OS will recognize the disk and allow you to browse its partitions.
- Extracting critical files safely. Once mounted, copy out important files, databases, or configuration data. This method avoids boot errors and reduces the risk of further corruption.
Common Errors When Starting a VMDK Without VMX
Attempting to boot a VMDK without its original VMX file often leads to errors. Recognizing these issues helps administrators quickly identify the root cause and apply the right fix.
- “Operating System Not Found”. Occurs when the VM firmware type (BIOS vs EFI) doesn’t match the disk’s partition scheme, or when the bootloader is missing.
- Boot loop or kernel panic. The guest OS may enter a loop or crash if hardware settings in the new VM don’t align with the original configuration (e.g., wrong CPU features or mismatched memory).
- Disk controller mismatch. Using IDE instead of SCSI, or the wrong VMware Paravirtual controller, can cause inaccessible boot device errors. Always match the controller type to the OS requirements.
- Missing snapshot chain. If the VMDK is part of a snapshot chain and only a delta file is attached, the VM cannot boot. Consolidate snapshots or recover the base disk before starting.
- Descriptor file errors. A corrupted or missing VMDK descriptor file prevents VMware from recognizing the disk. Rebuild or repair the descriptor to restore proper disk linkage.
Repairing Broken or Incomplete VMDK Files
When a VMDK file is damaged or incomplete, VMware may refuse to boot the VM or even recognize the disk. Repairing the file requires careful validation of its structure and metadata.
- Checking descriptor vs flat disk consistency. A VMDK typically consists of a small descriptor file and a larger flat disk file. If the descriptor points to the wrong size, geometry, or file name, VMware cannot mount the disk. Compare and correct these values to restore consistency.
- Fixing corrupted VMDK header. The header contains essential metadata about the disk. Corruption here can make the file unreadable. Specialized recovery tools or manual hex editing may be required to repair header values.
- Rebuilding snapshot chain. If the VMDK is part of a snapshot chain, missing or broken delta files will prevent boot. Consolidate snapshots or reconstruct the chain by re‑linking descriptor files to the correct parent disks.
- Converting disk format to restore bootability. In cases of severe corruption, converting the VMDK into another format (such as RAW or QCOW2 using
qemu-img) can bypass VMware’s strict validation, allowing you to recover data or rebuild the VM.
Recovering VM Data When VMX and VMDK Are Damaged
Why VM Files Fail
Virtual machine files can become damaged or lost due to several common scenarios:
- VMX deletion or overwrite — accidental removal of the configuration file.
- VMFS datastore corruption — hardware or filesystem errors leading to inaccessible VM files.
- Interrupted VM migration or copy — incomplete transfers leaving partial or broken files.
- Snapshot chain break — missing or corrupted delta files preventing proper disk reconstruction.
Restoring VMDK and VM Configuration
When both VMX and VMDK are affected, recovery requires a layered approach:
- Recover deleted VMX files — restore or rebuild configuration files to re‑register the VM.
- Rebuild virtual machine from raw disk — create a new VM and attach the recovered disk manually.
- Extract files from unreadable VMDK — mount the disk in another VM or convert it to a different format to salvage data.
Example: DiskInternals VMFS Recovery™
A specialized tool like DiskInternals VMFS Recovery™ can streamline the process:
- Scan damaged VMFS datastore to locate lost VM files.
- Recover deleted or lost VMDK and VMX together, ensuring disk and configuration integrity.
- Restore full virtual machine structure for re‑registration in VMware.
- Extract data without overwriting datastore, preserving original files during recovery.
Manual VMX Reconstruction vs New VM Attachment
| Method | Difficulty | Risk | Best Use Case |
|---|---|---|---|
| Create new VM + attach VMDK | Low | Low | Fast recovery |
| Manual VMX rebuild | Medium | Medium | Exact VM restore |
| Disk mount only | Low | None | File extraction |
| Full VM recovery software | Medium | Low | Corrupted datastore |
Advanced Troubleshooting
Even after reconstructing or recovering VMX and VMDK files, deeper technical issues can prevent a virtual machine from starting correctly. These advanced problems often require careful adjustments inside VMware or within the guest OS itself.
- Fixing UUID and MAC conflicts. When re‑registering a VM, VMware may detect duplicate UUIDs or MAC addresses. This can cause conflicts with other VMs on the same network. Allow VMware to generate new identifiers or manually edit the VMX file to assign unique values.
- Correcting virtual hardware version mismatch. Each VMX specifies a hardware compatibility version. If the VMX references a newer version than the host supports, the VM won’t start. Downgrade the hardware version in the VMX or upgrade the host to match.
- Resolving snapshot dependency issues. Broken or missing snapshot files can prevent a VM from booting. Consolidate snapshots into a single VMDK or rebuild the snapshot chain by re‑linking descriptor files to their parent disks.
- Repairing bootloader inside guest OS. Even with correct VMX and VMDK linkage, the guest OS may fail to boot if its bootloader is corrupted. Use OS‑specific recovery tools (e.g., Windows Recovery Environment or Linux GRUB repair) to rebuild the bootloader and restore boot functionality.
Best Practices to Prevent VMX Loss
Losing a VMX file can make a virtual machine unbootable, even if the VMDK remains intact. Preventive measures ensure that configuration files are always available and recoverable.
- Keep VM configuration backups. VMX files are small but essential. Include them in scheduled backups alongside VMDKs to guarantee quick restoration.
- Avoid manual datastore edits. Directly deleting or modifying files in the datastore risks breaking VM structures. Always use VMware tools or vSphere client operations instead of manual edits.
- Consolidate snapshots regularly. Long snapshot chains increase the risk of corruption and complicate recovery. Consolidating snapshots ensures disk integrity and reduces dependency on multiple delta files.
- Verify VM integrity after migration or storage move. After moving a VM between datastores or hosts, confirm that the VMX correctly references the VMDK and that the VM boots successfully.
Final Checklist Before Booting Reconstructed VM
Before powering on a reconstructed virtual machine, confirm these critical settings to avoid boot errors and ensure stability:
- Disk controller matches original OS. Verify that the VM uses the same controller type (LSI Logic, VMware Paravirtual, IDE, NVMe) as the original configuration. A mismatch can cause “inaccessible boot device” errors.
- Firmware type correct (BIOS/EFI). Align the VM firmware with the disk’s partition scheme (MBR → BIOS, GPT → EFI). Incorrect firmware settings often lead to “Operating System Not Found.”
- No broken snapshot chain. Ensure all snapshot files are consolidated or correctly linked. A missing delta file will prevent the VM from booting.
- VM boots and filesystem mounts correctly. Power on the VM and confirm that the guest OS loads without kernel panic or boot loops, and that the filesystem is accessible.
- Backup created after successful recovery. Once the VM is stable, immediately back up both VMX and VMDK files to secure the restored environment against future loss.