Fuslogvw.exe (Assembly Binding Log Viewer)

Updated: March 2012

The Assembly Binding Log Viewer displays details for assembly binds. This information helps you diagnose why the .NET Framework cannot locate an assembly at run time. These failures are usually the result of an assembly deployed to the wrong location, a native image that is no longer valid, or a mismatch in version numbers or cultures. The common language runtime's failure to locate an assembly typically shows up as a TypeLoadException in your application.

This tool is automatically installed with Visual Studio and with the Windows SDK. To run the tool, we recommend that you use the Visual Studio Command Prompt or the Windows SDK Command Prompt (CMD Shell). These utilities enable you to run the tool easily, without navigating to the installation folder. For more information, see Visual Studio and Windows SDK Command Prompts.

Important noteImportant

You must run fuslogvw.exe with administrator privileges.

  • If you have Visual Studio installed on your computer: On the taskbar, click Start, click All Programs, click Visual Studio, click Visual Studio Tools, right-click Visual Studio Command Prompt, and then click Run as administrator from the shortcut menu.

    -or-

    If you have the Windows SDK installed on your computer: On the taskbar, click Start, click All Programs, click the folder for the Windows SDK, right-click Command Prompt (or CMD Shell), and then click Run as administrator from the shortcut menu.

  • At the administrator command prompt, type the following:

fuslogvw

The viewer displays an entry for each failed assembly bind. For each failure, the viewer describes the application that initiated the bind; the assembly the bind is for, including name, version, culture and public key; and the date and time of the failure.

To change the log location view

  1. Select the Default option button to view bind failures for all application types. By default, log entries are stored in per-user directories on disk in the wininet cache.

  2. Select the Custom option button to view bind failures in a custom directory that you specify. You must specify the custom location where you want the runtime to store the logs by setting the custom log location in the Log Settings dialog to a valid directory name. This directory should be clean, and only contain files that the runtime generates. If it contains an executable that generates a failure to be logged, the failure will not be logged because the tool tries to create a directory with the same name as the executable. In addition, an attempt to run an executable from the log location will fail.

    NoteNote

    The default bind location is preferable to the custom bind location. The runtime stores the default bind location in the wininet cache, and therefore automatically cleans it out. If you specify a custom bind location, you are responsible for cleaning it out.

To view details about a specific failure

  1. Select the application name of the desired entry in the viewer.

  2. Click the View Log button. Alternately, you can double-click the selected entry.

    The tool displays the following details about the selected bind failure:

    • The specific reason the bind failed, such as "file not found" or "version mismatch".

    • Information about the application that initiated the bind, including its name, the application's root directory (AppBase), and a description of the private search path, if there is one.

    • The identity of the assembly the tool is looking for.

    • A description of any Application, Publisher, or Administrator version policies that have been applied.

    • Whether the assembly was found in the global assembly cache.

    • A list of all probing URLs.

The following sample log entry shows detailed information about a failed assembly bind.

*** 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/en-US/graphicfailtest.resources.DLL.
LOG: Attempting download of new URL file:///C:/Program Files/Microsoft.NET/FrameworkSDK/Samples/Tutorials/resourcesandlocalization/graphic/cs/en-US/graphicfailtest.resources/graphicfailtest.resources.DLL.
LOG: Attempting download of new URL file:///C:/Program Files/Microsoft.NET/FrameworkSDK/Samples/Tutorials/resourcesandlocalization/graphic/cs/en-US/graphicfailtest.resources.EXE.
LOG: Attempting download of new URL file:///C:/Program Files/Microsoft.NET/FrameworkSDK/Samples/Tutorials/resourcesandlocalization/graphic/cs/en-US/graphicfailtest.resources/graphicfailtest.resources.EXE.
LOG: All probing URLs attempted and failed.

To delete a single entry from the log

  1. Select an entry in the viewer.

  2. Click the Delete Entry button.

To delete all entries from the log

  • Click the Delete All button.

To refresh the user interface

  • Click the Refresh button. The viewer does not automatically detect new log entries while it is running. You must use the Refresh button to display them.

To change the log settings

  • Click the Settings button to open the Log Settings dialog.

To view the About dialog

  • Click the About button.

By default, Fuslogvw.exe logs normal assembly bind requests. Alternatively, you can log assembly binds for native images that were created using the Ngen.exe (Native Image Generator).

To log assembly binds for native images

  • In the Log Categories group, select the Native Images option button.

The following log shows a failure caused by a dependency that did not exist when the native image was created for the application. If the dependencies at run time differ from the dependencies when Ngen.exe is run, binding to a native image is not allowed.

*** Assembly Binder Log Entry  (12/8/2006 @ 5:22:07 PM) ***

The operation failed.
Bind result: hr = 0x80070002. The system cannot find the file specified.

Assembly manager loaded from:  E:\Windows\Microsoft.NET\Framework64\v2.0.50727\mscorwks.dll
Running under executable  E:\test\App.exe
--- A detailed error log follows. 

LOG: Start binding of native image App, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null.
LOG: IL assembly loaded from E:\test\App.exe.
LOG: Start validating native image App, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null.
LOG: Start validating all the dependencies.
LOG: [Level 1]Start validating native image dependency mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089.
LOG: Dependency evaluation succeeded.
LOG: [Level 1]Start validating IL dependency b, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null.
WRN: Dependency assembly was not found at ngen time, but is found at binding time. Disallow using this native image.
WRN: No matching native image found.
LOG: Bind to native image assembly did not succeed. Use IL image.

The following log shows a native image binding failure that occurred because the security settings on the computer when the application was run were different from the security settings at the time the native image was created.

*** Assembly Binder Log Entry  (12/8/2006 @ 5:29:09 PM) ***

The operation failed.
Bind result: hr = 0x80004005. Unspecified error

Assembly manager loaded from:  E:\Windows\Microsoft.NET\Framework64\v2.0.50727\mscorwks.dll
Running under executable  E:\test\Application101622.exe
--- A detailed error log follows. 

LOG: Start binding of native image Application101622, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null.
LOG: IL assembly loaded from E:\test\Application101622.exe.
LOG: Start validating native image Application101622, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null.
LOG: Start validating all the dependencies.
LOG: [Level 1]Start validating native image dependency mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089.
LOG: Dependency evaluation succeeded.
LOG: [Level 1]Start validating IL dependency Dependency101622, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null.
LOG: Dependency evaluation succeeded.
LOG: Validation of dependencies succeeded.
LOG: Start loading all the dependencies into load context.
LOG: Loading of dependencies succeeded.
LOG: Bind to native image succeeded.
Native image has correct version information.
Attempting to use native image E:\Windows\assembly\NativeImages_v2.0.50727_64\Application101622\1ac7fadabec4f72575d807501e9fdc72\Application101622.ni.exe.
Rejecting native image because it failed the security check. The assembly's permissions must have changed since the time it was ngenned, or it is running with a different security context.
Discarding native image.

You can use the Log Settings dialog to perform the following actions.

To disable logging

  • Select the Log disabled option button. Note that this option is selected by default.

To log assembly binds in exceptions

  • Select the Log in exception text option button. Only the least detailed fusion log information is logged in exception text. To view full information, use one of the other settings.

    See the Important note regarding assemblies that are loaded as domain neutral.

To log assembly bind failures

  • Select the Log bind failures to disk option button.

    See the Important note regarding assemblies that are loaded as domain neutral.

To log all assembly binds

  • Select the Log all binds to disk option button.

    See the Important note regarding assemblies that are loaded as domain neutral.

Important noteImportant

When an assembly is loaded as domain neutral, for example by setting the LoaderOptimization property to LoaderOptimization.MultiDomain or LoaderOptimization.MultiDomainHost, turning on logging might leak memory in some cases. This can happen if a log entry is made when a domain-neutral module is loaded into an application domain, and later the application domain is unloaded. The log entry might not be released until the process ends. Some debuggers automatically turn on logging.

To enable a custom log path

  1. Select the Enable custom log path option button.

  2. Enter the path into the Custom log path text box.

NoteNote

The Fuslogvw.exe (Assembly Binding Log Viewer) uses the Internet Explorer (IE) cache to store its binding log. Due to occasional corruption in the IE cache, the Fuslogvw.exe (Assembly Binding Log Viewer) can sometimes stop showing new binding logs in the viewing window. As a result of this corruption, the .NET binding infrastructure (fusion) cannot write to or read from the binding log. (This issue is not encountered if you use a custom log path.) To fix the corruption and allow fusion to show binding logs again, clear the IE cache by deleting temporary internet files from within the IE Internet Options dialog.

If your unmanaged application hosts the common language runtime by implementing the IHostAssemblyManager and IHostAssemblyStore interfaces, log entries can't be stored in the wininet cache. To view log entries for custom hosts that implement these interfaces, you must specify an alternate log path.

Date

History

Reason

March 2012

Clarified that fuslogvw.exe must be run with administrator privileges.

Customer feedback.

April 2011

Added information about using the Visual Studio and Windows SDK Command Prompts.

Information enhancement.

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