This is more of a “Today-I-Learned” post and not a “full-blown How-To article.” If something is completely wrong, please let me know - thanks!
Fuslogvw.exe – Wait, What? Ohhh!
This might sound like a blast from the .NET past – but this little tool actually saved our day during a real customer issue.
Here’s the situation: We had a good old .NET Framework app (yes, still alive and kicking!) that worked perfectly everywhere – except on a few mysterious machines. Right on startup: Crash. No clear error, just some DLL failing to resolve its dependencies.
But! The error message did mention something called Fuslogvw.exe (Docs) – a tool I had never actually used before. So let’s take a look.
What does Fuslogvw.exe do?
In short: it logs how assemblies are loaded, where they were found, and – more importantly – where they weren’t.
If you have Visual Studio installed, you can start it via the developer prompt and type: fuslogvw.
The tool itself looks like it hasn’t changed since the Windows XP days, but hey – it gets the job done:
At the end, you get handy little reports like this one:
*** Assembly Binder Log Entry (3/5/2007 @ 12:54:20 PM) ***
The operation failed.
Bind result: hr = 0x80070002. The system cannot find the file specified.
Assembly manager loaded from: C:\WINNT\Microsoft.NET\Framework\v2.0.50727\fusion.dll
Running under executable C:\Program Files\Microsoft.NET\FrameworkSDK\Samples\Tutorials\resourcesandlocalization\graphic\cs\graphicfailtest.exe
--- A detailed error log follows.
=== Pre-bind state information ===
LOG: DisplayName = graphicfailtest.resources, Version=0.0.0.0, Culture=en-US, PublicKeyToken=null
(Fully-specified)
LOG: Appbase = C:\Program Files\Microsoft.NET\FrameworkSDK\Samples\Tutorials\resourcesandlocalization\graphic\cs\
LOG: Initial PrivatePath = NULL
LOG: Dynamic Base = NULL
LOG: Cache Base = NULL
LOG: AppName = NULL
Calling assembly : graphicfailtest, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null.
===
LOG: Processing DEVPATH.
LOG: DEVPATH is not set. Falling through to regular bind.
LOG: Policy not being applied to reference at this time (private, custom, partial, or location-based assembly bind).
LOG: Post-policy reference: graphicfailtest.resources, Version=0.0.0.0, Culture=en-US, PublicKeyToken=null
LOG: Attempting download of new URL file:///C:/Program Files/Microsoft.NET/FrameworkSDK/Samples/Tutorials/resourcesandlocalization/graphic/cs/graphicfailtest.resources.DLL.
LOG: Attempting download of new URL file:///C:/Program Files/Microsoft.NET/FrameworkSDK/Samples/Tutorials/resourcesandlocalization/graphic/cs/graphicfailtest.resources/graphicfailtest.resources.DLL.
LOG: Attempting download of new URL file:///C:/Program Files/Microsoft.NET/FrameworkSDK/Samples/Tutorials/resourcesandlocalization/graphic/cs/graphicfailtest.resources.EXE.
LOG: Attempting download of new URL file:///C:/Program Files/Microsoft.NET/FrameworkSDK/Samples/Tutorials/resourcesandlocalization/graphic/cs/graphicfailtest.resources/graphicfailtest.resources.EXE.
LOG: All probing URLs attempted and failed.
And in our case, that was exactly what we needed: One of the machines had an old, incorrect DLL sitting in the Global Assembly Cache (GAC) – something that shouldn’t have been there at all. It got loaded, messed everything up, and was a pain to track down… until Fuslogvw pointed us right to it.
What about .NET Core / modern .NET?
Fuslogvw won’t help you there – things work differently in the new world. But there are other tools like dotnet trace that can help with similar issues.
Hope this helps!
