Missing symbol for ntdll in Microsoft's Symbol Server

Question

Missing symbol for ntdll in Microsoft's Symbol Server

Bemblekar, Vishal (GE Digital) 0

Hello, myself Vishal from GE Vernova.

While analysing an urgent escalation dump from the customer using windbg.exe, I received an error for downloading ntdll.dll symbols as below,

User's image

The above details clearly shows that associated PDB file for ntdll.dll is missing from MS symbol Server. As it is an escalated issue I can't proceed without necessary PDB so blocked very badly.

I tried with “. symopt +40” as well but didn't worked for me because of unknown reason.

**OS **details from where dump has been captured is as below,

User's image

And ntdll.dll associated PDB details are as below,

User's image

Please guide me asap how can I proceed with my investigation further.

Note -: I tried accessing symbol server with both https and http but same result. It is for x86 application.

Best Regards,

Vishal

3 answers

Your answer

Answer 1

Thank you for reaching out . I understand you are unable to download the nrdll.dll PDB symbols from the Microsoft symbol server while analyzing a Windows 8.1 Dump using WinDbg, And are receiving a “path not found" error.

Let's go through the possible causes and steps to resolve the issue

1. verify symbols server path

ensure your WinDbg symbol path is correctly set. Please use the following recommended symbol path:

.sympath srv*C:\Symbols*https://msd1.microsoft.com/download/symbols

then reload the symbols:

.symfix
.reload /f ntdll.dll

note: always use https over http, as http is deprecated for symbol access.

2. Check OS build compatibility

the dump is from Windows 8.1(6.3.9600.22072) a long term servicing (LTSB) escrow build (winblue-ltsb_escrow_240624-1833), Which may not have its symbol package publicly available yet.

Microsoft symbol server hosts symbols for released and supported builds only. If the build is from an internal or prerelease channel (LTSB escrow), its symbols might be available only via Microsoft internal symbol servers.

If you are part of GE vernova’s enterprise agreement, please contact your Microsoft premiere/unified support representative to request private symbol access for this LTSB build.

3. Use local symbols (if available )

if you have access to the same build of Windows 8.1 from which the dump originated:

Copy ntdll.dll and its corresponding .pdb file from that system’s %SystemRoot%\System32 directory.
Place them in your local symbol cache directory (e.g., C:\Symbols\ntdll.pdb<GUID>).

Then reload symbols manually:

  .sympath+ C:\Symbols
  .reload /f ntdll.dll

4. Check PDB GUID mismatch

From your log:

pdb sig : 92AA387A-F400-4D72-B2E5-0E5DA5667537

If the public symbol server does not contain this GUID version of ntdll.pdb, WinDbg will fail with”path not found”. This indicates your specific build ofntdll.dll the first slightly from publicly released binaries.

You can verify this by checking:

!sym noise
.reload /f ntdll.dll

this command will show which PDB CUID WinDbg is requesting and whether any close matches exist.

**5. **Alternative symbol retrieval

if you're debugging is blocked and private symbols are not available:

Use the exports symbols only (.symopt+0x40), which allows partial debugging
Focus on user-mode modules or managed code paths where full symbols are not mandatory.
Use the following:
```
  .symopt+0x40
  .reload /f ntdll.dll
```

**6. **Reference:

for more details:

Please let us know if you require any further assistance we’re happy to help. If you found this information useful, kindly mark this as "Accept Answer".

Adiba Khan 1,440 Reputation points Microsoft External Staff

2025-11-14T05:43:44.6033333+00:00

"Hope you're doing well. We're following up on the ticket. Please let us know before 19 Nov whether the issue persists or has been resolved, after that we'll close this thread and If the issue has been resolved, kindly mark the response as answered."
Adiba Khan 1,440 Reputation points Microsoft External Staff

2025-11-18T05:58:07.0066667+00:00

"Hope you're doing well. We're following up on the ticket. Please let us know before 19 Nov whether the issue persists or has been resolved, after that we'll close this thread and If the issue has been resolved, kindly mark the response as answered."

Answer 2

Bemblekar, Vishal (GE Digital) 0

Hi Adiba, whatever you suggested are very basic things which I already tried and those are not working so raised query here.... If you have some other solution or some way to make those necessary PDBs available or so please let me know...

Thanks,

Vishal

Adiba Khan 1,440 Reputation points Microsoft External Staff

2025-11-19T09:01:41.64+00:00
Thank you for your update . I understand your concern.Since the standard troubleshooting steps did not resolve the issue, I reviewed the symbol request details and I can now confirm the following.

**1.      **Your requested PDB does not exist on the public Microsoft Symbol server

The PDB signature you provided:

92AA387A-F400-4D72-B2E5-0E5DA5667537

Corresponds to a Windows 8.1 LTSB escrow build

WINBLUE_LTSB_ESCROW_240624-1833 OS version:6.3.9600.22072

This is not a publicly released build.

Because of this, The PDB for this specific ntddll.dll was never published to the public symbol server( msdl.microsoft.com).

This is why your winDbg logs repeatedly show:

SYMSRV: file.ptr :not found SYMSRV: ntdll.pdb : not found

Even with correct symbol paths, this PDB cannot be downloadd because it does not exist on the public server.

**2.      **Why this happens

Symbols for:

Escrow builds

Pre-release OS versions

Internal servicing branches are only available on Microsoft’s internal symbol servers, not on the public one.

Since your dump originates from a private branch of windows 8.1 the failure is expected.

**3.      **Available solutions

Option A: Request Private Symbol Access (recommended for escalations)

If your organization has Microsoft Premier/Unified Support , you can initiate a request internally to access the required private symbols.

Option B: Use symbols from the Customer’s machine

If you still have access to the machine where the dump was captured:

1.      Copy the following from %SystemRoot%\System32:

Ntdll.dll

Matching ntdll.pdb (if present)

2.      Place them in your local symbol directory, e.g.,:

C:\Symbols\ntdll.pdb\92AA387AF4004D72B2E50E5DA5667537\

3.      Reload:

.sympath+ C:\Symbols .reload /f ntdll.dll

This will load the exact matching symbols if they exists locally.

Option C: Continue debugging with export-only symbols

If you cannot get the private PDB, you can still proceed using export symbols:

.symopt+0x40 .reload /f ntdll.dll

This allows call stacks and user-mode debugging to continue, though with limited kernel insight.

The problem is not with your configuration- the PDB for your OS build is simply not available publicly. To proceed further with a full investigation, private symbol access is required.

Please let us know if you require any further assistance we’re happy to help. If you found this information useful, kindly mark this as "Accept Answer".
Adiba Khan 1,440 Reputation points Microsoft External Staff

2025-11-24T05:22:36.3033333+00:00

"Hope you're doing well. We're following up on the ticket. Please let us know before 27 November whether the issue persists or has been resolved, after that we'll close this thread and If the issue has been resolved, kindly mark the response as answered."

Answer 3

Bemblekar, Vishal (GE Digital) 0

Hi Adiba, thanks for your input. With that, our issue did not resolve but we have got direction to proceed further.

Best Regards,

Vishal

Adiba Khan 1,440 Reputation points Microsoft External Staff

2025-11-24T07:31:38.8466667+00:00

Thank you for the update, and i am glad to hear the information helped provide a direction for your next steps. I kindly ask if you feel the answer has helped you in any way please consider accepting the answer it as the confirmed information. Doing so helps the system recognize that the topic has been confirmed, and it provides a valuable reference for other users who may encounter similar questions in the future. It also contributes to building a stronger community and helps increase your reputation score on the platform. We are closing this thread now if you need any further assistance, while proceeding with the investigation or require clarification on symbol availability, please feel free to reach out by raising new thread, we’re happy to support you further needed.

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Missing symbol for ntdll in Microsoft's Symbol Server

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