SYSLIB0005: The global assembly cache (GAC) is not supported

.NET Core and .NET 5 and later versions eliminate the concept of the global assembly cache (GAC) that was present in .NET Framework. To help steer developers away from these APIs, some GAC-related APIs are marked as obsolete, starting in .NET 5. Using these APIs generates warning SYSLIB0005 at compile time.

The following GAC-related APIs are marked obsolete:

• Assembly.GlobalAssemblyCache

  Libraries and apps should not use the GlobalAssemblyCache API to make determinations about run-time behavior, as it always returns false in .NET Core and .NET 5+.

Workarounds

If your application queries the GlobalAssemblyCache property, consider removing the call. If you use the GlobalAssemblyCache value to choose between an "assembly in the GAC"-flow vs. an "assembly not in the GAC"-flow at run time, reconsider whether the flow still makes sense for a .NET 5+ application.

Suppress a warning

If you must use the obsolete APIs, you can suppress the warning in code or in your project file.

To suppress only a single violation, add preprocessor directives to your source file to disable and then re-enable the warning.

// Disable the warning.
#pragma warning disable SYSLIB0005

// Code that uses obsolete API.
// ...

// Re-enable the warning.
#pragma warning restore SYSLIB0005

To suppress all the SYSLIB0005 warnings in your project, add a <NoWarn> property to your project file.

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
   ...
   <NoWarn>$(NoWarn);SYSLIB0005</NoWarn>
  </PropertyGroup>
</Project>

For more information, see Suppress warnings.

See also

• Global assembly cache