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🧪 Offline Boot Testing & Generalization of VHDX OS Images

This guide follows the Disk2vhd imaging and Azure upload process. In networks where the .vhdx is synced to local hypervisor storage, the image must be tested offline to validate bootability before being generalized and cleaned.

1. 🔌 Boot Test in Local Staging Hypervisor

Objective:

Ensure the .vhdx image boots in a virtual machine within a completely offline staging environment.

Steps:

  1. Import the .vhdx into your hypervisor (e.g., Hyper-V, Proxmox, VMware Workstation).
  2. Create a test VM:
    • Connect the disk as the primary boot volume.
    • Ensure no internet/network adapters are connected.
  3. Power on the VM.

🏢 Special Case: Ridgebrook Client Deployment

For Ridgebrook:

  • Images stored in the Azure file share:
    • Storage account: clientosimages01e2usdtc
    • File share: client-os-images-01
  • The image should be synced to the local staging hypervisor:
    • Hypervisor name: ELDERBRAIN
    • Local path:
      D:\Virtual Hard Disks\client-os-images-01
  • Ridgebrook .vhdx images should be placed into a subfolder matching their PSA company name (e.g., ridgebrook-industrial).

Once synced, follow the standard boot validation and conversion process below.

2. 🔄 Convert MBR to GPT (If Needed)

If the VM fails to boot, the .vhdx likely uses MBR instead of GPT.

✅ Option 1: MBR2GPT (Recommended)

Steps:

mbr2gpt /validate /disk:0 /allowFullOS
mbr2gpt /convert /disk:0 /allowFullOS

Make sure the OS volume is the last volume and delete any non-essential partitions (see below).

⚠️ Option 2: gptgen (Advanced / Manual Bootloader Required)

gptgen is a third-party tool that can convert MBR to GPT when MBR2GPT fails or is unsupported (e.g., on older systems or modified layouts). However, it does not set up the bootloader automatically.

Key Points:

  • You must manually recreate the EFI partition.
  • You must manually install the UEFI bootloader using bcdboot after conversion.
  • Proceed only if MBR2GPT is not usable.

Always follow up gptgen with Step 4: Rebuild BCD Bootloader.

3. 📼 Cleaning Up Partitions With DiskPart

Target Partition Layout (Post-Conversion):

Partition Purpose Size
1 EFI System 10 GB
2 Recovery 10 GB
3 OS Volume Remainder

Why fixed sizes?
Microsoft has misaligned these in the past — we standardize to 10 GB for EFI and Recovery to avoid risk.

DiskPart Steps:

diskpart
list disk
select disk 0
list partition
  • Delete unwanted partitions (OEM, redundant recovery, etc).
  • Create EFI:
create partition efi size=10240
format quick fs=fat32 label="System"
assign letter=S
  • Create Recovery (optional):
create partition primary size=10240
format quick fs=ntfs label="Recovery"
assign letter=R

4. 🥾 Rebuild BCD Bootloader

bcdboot C:\Windows /s S: /f UEFI
  • C: = OS path
  • S: = EFI partition
  • /f UEFI = Force GPT boot

5. 📽 Generalize the OS Image (Post-Boot Cleanup)

Once the VHDX boots successfully in offline staging, perform the following steps to prepare it as a reusable image.

👥 Optional: Backup & Remove User Profiles (for shared deployments)

If this image will be deployed to multiple VMs or physical workstations, it's important to remove all local user accounts and profiles to avoid SID duplication and profile conflicts.

Step 1: Backup Profiles with ProfWiz

Use ForensiT User Profile Wizard (ProfWiz) to safely back up and preserve profiles before deletion.

Step 2: Delete Local User Profiles

wmic useraccount where "name!='Administrator' and name!='DefaultAccount' and name!='Guest' and name!='WDAGUtilityAccount'" delete

for /D %%i in (C:\Users\*) do (
  rd /s /q "%%i"
)

⚠️ This permanently deletes all local user accounts and their data, except system accounts.

🔐 Clear Agent Identity & Token Data (Preserve Services)

Tool Remove From Registry Clear File System Path
NinjaRMM HKLM\SOFTWARE\NinjaRMM C:\ProgramData\NinjaRMMAgent
Blackpoint HKLM\SOFTWARE\Blackpoint C:\ProgramData\Blackpoint
Veeam Agent HKLM\SOFTWARE\Veeam\Veeam Endpoint Backup C:\ProgramData\Veeam 
reg delete "HKLM\SOFTWARE\NinjaRMM" /f
reg delete "HKLM\SOFTWARE\Blackpoint" /f
reg delete "HKLM\SOFTWARE\Veeam\Veeam Endpoint Backup" /f

rd /s /q "C:\ProgramData\NinjaRMMAgent"
rd /s /q "C:\ProgramData\Blackpoint"
rd /s /q "C:\ProgramData\Veeam"

❗ Do not delete agent service keys under HKLM\SYSTEM\CurrentControlSet\Services.

🥵 Windows Log Cleanup

del /s /q C:\Windows\System32\winevt\Logs\*.*
del /f /q %SystemRoot%\Panther\*.*

6. 💾 Optional: Skip OOBE with unattend.xml

Use an unattend.xml to skip setup UI and telemetry.

Sample Snippet

<unattend xmlns="urn:schemas-microsoft-com:unattend">
  <settings pass="oobeSystem">
    <component name="Microsoft-Windows-Shell-Setup" ...>
      <OOBE>
        <HideEULAPage>true</HideEULAPage>
        <HideWirelessSetupInOOBE>true</HideWirelessSetupInOOBE>
        <NetworkLocation>Work</NetworkLocation>
        <ProtectYourPC>3</ProtectYourPC>
        <SkipMachineOOBE>true</SkipMachineOOBE>
        <SkipUserOOBE>true</SkipUserOOBE>
      </OOBE>
      <TimeZone>Eastern Standard Time</TimeZone>
    </component>
  </settings>

  <settings pass="specialize">
    <component name="Microsoft-Windows-Feedback" ...>
      <DisableFeedback>true</DisableFeedback>
    </component>
    <component name="Microsoft-Windows-CEIPEnable" ...>
      <CEIPEnable>false</CEIPEnable>
    </component>
    <component name="Microsoft-Windows-ApplicationExperience" ...>
      <AITEnable>false</AITEnable>
    </component>
    <component name="Microsoft-Windows-ErrorReportingCore" ...>
      <DisableWerReporting>true</DisableWerReporting>
    </component>
  </settings>
</unattend>

How to Use

sysprep /generalize /oobe /shutdown /unattend:C:\Windows\System32\Sysprep\unattend.xml

✅ Final Checklist

  • Booted offline on hypervisor
  • Converted to GPT with valid partitions
  • Optional: user profiles backed up and deleted
  • Agent identities reset (binaries remain)
  • unattend.xml disables OOBE + telemetry
  • Sysprep executed successfully
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