How to enable assembly bind failure logging (Fusion) in .NET

Question

How do I enable assembly bind failure logging (Fusion) in .NET?

Answer 1

This is not an answer but a word of warning:

• If you ever enable this logging, DO NOT FORGET TO DISABLE IT or you will regret it later.

I did forget, and I ended up with several GB of small log files with HTM extension in C:\Windows\System32\config\systemprofile\AppData\Local\Microsoft\Windows\INetCache\IE folder — it was apparently logging all assembly bindings from applications running under NT AUTHORITY\SYSTEM account.

The number of files was greater than 3 million and neither Total Commander nor Windows Explorer could display the contents or folder size without hanging.

After disabling logging and a reboot for good measure, I ran the deletion from command prompt.

It took more than 15 minutes to delete all the files on a Samsung 970 Pro SSD which was showing 100% disk usage all the time — my high-end PC workstation was brought down to its knees by this delete operation and remained only partially responsive until it finished.

Answer 2

There's so much wrong with the Assembly Binding Log Viewer (FUSLOGVW.exe) that I decided to write an alternative viewer named Fusion++ and put it on GitHub. It uses the same mechanics internally but parses the logs for you. You don't have to care for any settings at all, not even log paths 😉

You can get the latest release from here or via chocolatey (choco install fusionplusplus).

I hope you and some of the visitors in here can save some worthy lifetime minutes with it.

Answer 3

Add the following values to

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Fusion
Add:
DWORD ForceLog set value to 1
DWORD LogFailures set value to 1
DWORD LogResourceBinds set value to 1
DWORD EnableLog set value to 1
String LogPath set value to folder for logs (e.g. C:\FusionLog\)

Make sure you include the backslash after the folder name and that the Folder exists.

You need to restart the program that you're running to force it to read those registry settings.

By the way, don't forget to turn off fusion logging when not needed.

Answer 4

I usually use the Fusion Log Viewer (Fuslogvw.exe from a Visual Studio command prompt or Fusion Log Viewer from the start menu) - my standard setup is:

• Open Fusion Log Viewer as administrator
• Click settings
• Check the Enable custom log path checkbox
• Enter the location you want logs to get written to, for example, c:\FusionLogs (Important: make sure that you have actually created this folder in the file system.)
• Make sure that the right level of logging is on (I sometimes just select Log all binds to disk just to make sure things are working right)
• Click OK
• Set the log location option to Custom

Remember to turn of logging off once you're done!

(I just posted this on a similar question - I think it's relevant here too.)

Answer 5

You can run this Powershell script as administrator to enable FL:

Set-ItemProperty -Path HKLM:\Software\Microsoft\Fusion -Name ForceLog         -Value 1               -Type DWord
Set-ItemProperty -Path HKLM:\Software\Microsoft\Fusion -Name LogFailures      -Value 1               -Type DWord
Set-ItemProperty -Path HKLM:\Software\Microsoft\Fusion -Name LogResourceBinds -Value 1               -Type DWord
Set-ItemProperty -Path HKLM:\Software\Microsoft\Fusion -Name LogPath          -Value 'C:\FusionLog\' -Type String
mkdir C:\FusionLog -Force

and this one to disable:

Remove-ItemProperty -Path HKLM:\Software\Microsoft\Fusion -Name ForceLog
Remove-ItemProperty -Path HKLM:\Software\Microsoft\Fusion -Name LogFailures
Remove-ItemProperty -Path HKLM:\Software\Microsoft\Fusion -Name LogResourceBinds
Remove-ItemProperty -Path HKLM:\Software\Microsoft\Fusion -Name LogPath

Answer 6

For those who are a bit lazy, I recommend running this as a bat file for when ever you want to enable it:

reg add "HKLM\Software\Microsoft\Fusion" /v EnableLog /t REG_DWORD /d 1 /f
reg add "HKLM\Software\Microsoft\Fusion" /v ForceLog /t REG_DWORD /d 1 /f
reg add "HKLM\Software\Microsoft\Fusion" /v LogFailures /t REG_DWORD /d 1 /f
reg add "HKLM\Software\Microsoft\Fusion" /v LogResourceBinds /t REG_DWORD /d 1 /f
reg add "HKLM\Software\Microsoft\Fusion" /v LogPath /t REG_SZ /d C:\FusionLog\

if not exist "C:\FusionLog\" mkdir C:\FusionLog

Answer 7

In my case helped type disk name in lower case

Wrong - C:\someFolder

Correct - c:\someFolder

Answer 8

Just in case you're wondering about the location of FusionLog.exe - You know you have it, but you cannot find it? I was looking for FUSLOVW in last few years over and over again. After move to .NET 4.5 number of version of FUSION LOG has exploded. Her are places where it can be found on your disk, depending on software which you have installed:

C:\Program Files (x86)\Microsoft SDKs\Windows\v8.0A\bin\NETFX 4.0 Tools\x64

C:\Program Files (x86)\Microsoft SDKs\Windows\v7.0A\Bin\x64

C:\Program Files (x86)\Microsoft SDKs\Windows\v8.1A\bin\NETFX 4.5.1 Tools\x64

C:\Program Files (x86)\Microsoft SDKs\Windows\v8.0A\bin\NETFX 4.0 Tools

C:\Program Files (x86)\Microsoft SDKs\Windows\v8.1A\bin\NETFX 4.5.1 Tools

C:\Program Files (x86)\Microsoft SDKs\Windows\v7.0A\Bin

Answer 9

Instead of using a ugly log file, you can also activate Fusion log via ETW/xperf by turning on the DotnetRuntime Private provider (Microsoft-Windows-DotNETRuntimePrivate) with GUID 763FD754-7086-4DFE-95EB-C01A46FAF4CA and the FusionKeyword keyword (0x4) on.

@echo off
echo Press a key when ready to start...
pause
echo .
echo ...Capturing...
echo .

"C:\Program Files (x86)\Windows Kits\8.1\Windows Performance Toolkit\xperf.exe" -on PROC_THREAD+LOADER+PROFILE -stackwalk Profile -buffersize 1024 -MaxFile 2048 -FileMode Circular -f Kernel.etl
"C:\Program Files (x86)\Windows Kits\8.1\Windows Performance Toolkit\xperf.exe" -start ClrSession -on Microsoft-Windows-DotNETRuntime:0x8118:0x5:'stack'+763FD754-7086-4DFE-95EB-C01A46FAF4CA:0x4:0x5 -f clr.etl -buffersize 1024

echo Press a key when you want to stop...
pause
pause
echo .
echo ...Stopping...
echo .

"C:\Program Files (x86)\Windows Kits\8.1\Windows Performance Toolkit\xperf.exe" -start ClrRundownSession -on Microsoft-Windows-DotNETRuntime:0x8118:0x5:'stack'+Microsoft-Windows-DotNETRuntimeRundown:0x118:0x5:'stack' -f clr_DCend.etl -buffersize 1024 

timeout /t 15

set XPERF_CreateNGenPdbs=1

"C:\Program Files (x86)\Windows Kits\8.1\Windows Performance Toolkit\xperf.exe" -stop ClrSession ClrRundownSession 
"C:\Program Files (x86)\Windows Kits\8.1\Windows Performance Toolkit\xperf.exe" -stop
"C:\Program Files (x86)\Windows Kits\8.1\Windows Performance Toolkit\xperf.exe" -merge kernel.etl clr.etl clr_DCend.etl Result.etl -compress
del kernel.etl
del clr.etl
del clr_DCend.etl

When you now open the ETL file in PerfView and look under the Events table, you can find the Fusion data:

Answer 10

Just a tiny bit of info that might help others; if you do something along the lines of searching all assemblies in some directory for classes that inherit/implement classes/interfaces, then make sure you clean out stale assemblies if you get this error pertaining to one of your own assemblies.

The scenario would be something like:

1. Assembly A loads all assemblies in some folder
2. Assembly B in this folder is stale, but references assembly C
3. Assembly C exists, but namespaces, class names or some other detail might have changed in the time that has passed since assembly B became stale (in my case a namespace was changed through a refactoring process)

In short: A ---loads--> B (stale) ---references---> C

If this happens, the only telltale sign is the namespace and classname in the error message. Examine it closely. If you can't find it anywhere in your solution, you are likely trying to load a stale assembly.

Answer 11

Set the following registry value:

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Fusion!EnableLog] (DWORD) to 1

To disable, set to 0 or delete the value.

[edit ]:Save the following text to a file, e.g FusionEnableLog.reg, in Windows Registry Editor Format:

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Fusion]
"EnableLog"=dword:00000001

Then run the file from windows explorer and ignore the warning about possible damage.

Answer 12

If you have the Windows SDK installed on your machine, you'll find the "Fusion Log Viewer" under Microsoft SDK\Tools (just type "Fusion" in the start menu on Vista or Windows 7/8). Launch it, click the Settings button, and select "Log bind failure" or "Log all binds".

If these buttons are disabled, go back to the start menu, right-click the Log Viewer, and select "Run as Administrator".

Answer 13

If you already have logging enabled and you still get this error on Windows 7 64 bit, try this in IIS 7.5:

1. Create a new application pool

2. Go to the Advanced Settings of this application pool

3. Set the Enable 32-Bit Application to True

4. Point your web application to use this new pool

Answer 14

The Fusion Log Settings Viewer changer script is bar none the best way to do this.

In ASP.NET, it has been tricky at times to get this to work correctly. This script works great and was listed on Scott Hanselman's Power Tool list as well. I've personally used it for years and its never let me down.