The library hostpolicy.dll was not found

问题

I have a simple .NET Core project (console app) that I'm trying to compile and run. dotnet build succeeds, but I get the following error when I do dotnet run:

λ dotnet run
Project RazorPrecompiler (.NETCoreApp,Version=v1.0) was previously compiled. Skipping compilation.
A fatal error was encountered. The library 'hostpolicy.dll' required to execute the application was not found in [path].

My project.json looks like this:

{
  "buildOptions": {
    "warningsAsErrors": true
  },
  "dependencies": {
    "Microsoft.AspNetCore.Razor": "1.0.0",
    "Microsoft.NETCore.App": {
      "type": "platform",
      "version": "1.0.0"
    }
  },
  "description": "Precompiles Razor views.",
  "frameworks": {
    "netcoreapp1.0": {
      "imports": [ ]
    }
  },
  "version": "1.2.0"
}

What is hostpolicy.dll, and why is it missing?

回答1:

Update for dotnet core 2.0 and beyond: the file appname.runtimeconfig.json (for both debug and release configuration) is needed in the same path as appname.dll.

It contains:

{
  "runtimeOptions": {
    "tfm": "netcoreapp2.0",
    "framework": {
      "name": "Microsoft.NETCore.App",
      "version": "2.0.0"
    }
  }
}

then dotnet.exe exec "path/to/appname.dll" [appargs] works.

回答2:

This error message is unhelpful. The actual problem is a missing emitEntryPoint property:

  "buildOptions": {
    ...
    "emitEntryPoint": true
  },

Once this is added, the compiler will let you know about any other problems (like a missing static void Main() method). Successfully compiling the project will result in an output that dotnet run can execute.

回答3:

For me it was a stupid mistake: I started a wrong file.

回答4:

For me the issue was with the version mismatch. I had a different ".Net core SDK" version installed and a different version was specified in .json file.

Once I modified the version in my .json file the application started working fine.

回答5:

In my case it was because I was publishing a self-contained application for the wrong target. My intent was to run on alpine linux, but I was building for libc when I should have been building for musl.

The failing package was built using:

dotnet publish --self-contained true --runtime linux-x64 --framework netcoreapp2.1 --output /app

Changing the RID:

dotnet publish --self-contained true --runtime linux-musl-x64 --framework netcoreapp2.1 --output /app

produced a functional package. Notice the RID changed from linux-x64 to linux-musl-x64. If I had read the .NET Core RID Catalog page this could have been avoided. 😅

回答6:

For me with ASP.NET Core 2.0 on Azure, it was the appname.deps.json that did the trick.

回答7:

I had this same problem with a .NET Core 3.0 WPF app, but I found that my app wouldn't run in Visual Studio 2019 either.

I discovered on the project properties page (right-click on project > Properties) that the Target framework was set to .NET Core 3.0.

I'd recently updated VS 2019 which had also installed .NET Core 3.1, so I switched to that in the dropdown, and it worked again.

(I also had to update my shortcut to point to the netcoreapp3.1 folder instead of the previous netcoreapp3.0 folder.)

回答8:

Promoting voltrevo's comment as an answer as I believe this should be the most common case of the problem. When you build your solution, sometimes you might get 2 directories with outputs bin and obj. 'Bin' directory has everything that is needed to run dotnet.exe command. Just run from the bin directory and things should be good. :)

回答9:

This occurred when a Visual Studio 2019 preview upgrade .Net Core to the latest preview (specifically .Net Core 3.1.100-preview2-014569).

Reinstalling/repairing .Net Core 3.0.100 solved the problem for me.

回答10:

The solution may be executing the cmd as administrator (at least, for me it was).

来源：https://stackoverflow.com/questions/38085430/the-library-hostpolicy-dll-was-not-found

标签

.net

.net-core

dotnet-cli