The library hostpolicy.dll was not found

K

25

121

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:

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?

Kangaroo answered 28/6, 2016 at 20:12 Comment(3)

I ran into this error when trying to run a custom DotnetCliTool with Visual Studio 2017 RC3 that was missing a runtimeconfig.json. The next VS version will pack it by default. github.com/dotnet/cli/issues/5593#issuecomment-277638612 – Salena 6/2, 2017 at 15:50

The same error may be shown, if you run dotnet MyApp.exe, just run MyApp.exe "The library 'hostpolicy.dll' required" if run from deploy folder, but emitEntryPoint is true – Ellenaellender 29/10, 2017 at 12:43

With the release of asp.net core 2.1 the webjob publish task has a bug/regression that can cause this error if you're targeting the full framework. The fix for this is to pin the sdk to 2.1.200 until it's fixed. You can also delete the run.cmd files to quickly get your production jobs running again. – Uralaltaic 8/6, 2018 at 23:26

K

26

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.

Kangaroo answered 28/6, 2016 at 20:12 Comment(12)

Since this is still happening in rtm it might be worth noting in the github repo just in case. – Kept 30/6, 2016 at 5:57

@NickAcosta - I guess these kind of issues are why tooling is preview2 and not rtm (the milestone for the bug is 1.0.0-rtm). Only runtime is rtm. – Facia 30/6, 2016 at 17:20

How does this work with the new Visual Studio 2017 RC projects, where Microsoft has ditched project.json is support of .csproj files? As far as I can tell, my project is set up to create an executable. – Pinafore 24/12, 2016 at 13:44

@UmarFarooqKhawaja I'd recommend posting a new question. – Kangaroo 27/12, 2016 at 16:42

I've seen this happen with csproj files too, targeting netcoreapp1.1 in a aspnetcore project. – Jennajenne 4/1, 2017 at 13:25

Yes, I have a csproj targeting 1.1 and I have this error on first compile. The app always runs if I compile two times in a row..... – Epiboly 16/1, 2017 at 20:10

@Epiboly Do you know of a fix so you don't have to run it twice? I have the same issue. – Soll 25/1, 2017 at 20:46

@Soll - I do not have a fix, but I have logged it as a bug here: github.com/dotnet/sdk/issues/672 Some folks are having success with the nightly builds, but I am not. The GitHub issue is on their radar and listed as a known issue. – Epiboly 26/1, 2017 at 23:23

@Epiboly Awesome! Thanks! – Soll 26/1, 2017 at 23:33

@Soll - Updating to 1.1.1 with the security fix and updating to the latest 2017RC solved this problem for me. – Epiboly 29/1, 2017 at 19:20

@Epiboly I'm going to try it out. Thanks for the updates. You're a real champ! – Soll 29/1, 2017 at 19:21

Thanks @Epiboly updating from version 1.1 to 1.1.1 fixed my issue – Epiphenomenon 25/1, 2018 at 7:30

L

71

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.

Laboy answered 11/9, 2017 at 15:28 Comment(3)

This answer was partly relevant to me as I'm using dotnet core 2.0 too. Not sure if I did something weird to my workspace, but I also found that I had .dll in both obj and bin directories. I was in obj, and realized that the one in bin had this .runtimeconfig.json file already. Running that one worked without changes. – Stuff 2/12, 2017 at 7:33

This was the solution for me with dotnet core 3.0 preview 8 also – Tamarind 14/8, 2019 at 16:38

How is this file appname.runtimeconfig.json generated? If I specify output as exe, it's there. But if it's build as library (and run as dotnet app.dll, it's not there. – Springclean 14/3, 2022 at 3:45

K

26

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

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