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Process terminated. Couldn't find a valid ICU package installed on the system in Asp.Net Core 3 - ubuntu

I am trying to run a Asp.Net Core 3 application in Ubuntu 19.10 thru terminal using dotnet run command but it does not seem to work. I get this error.
Process terminated. Couldn't find a valid ICU package installed on the system.
Set the configuration flag System.Globalization.Invariant to true if you want
to run with no globalization support.
at System.Environment.FailFast(System.String)
at System.Globalization.GlobalizationMode.GetGlobalizationInvariantMode()
at System.Globalization.GlobalizationMode..cctor()
at System.Globalization.CultureData.CreateCultureWithInvariantData()
at System.Globalization.CultureData.get_Invariant()
at System.Globalization.CultureInfo..cctor()
at System.StringComparer..cctor()
at System.StringComparer.get_OrdinalIgnoreCase()
at Microsoft.Extensions.Configuration.ConfigurationProvider..ctor()
at Microsoft.Extensions.Configuration.EnvironmentVariables.EnvironmentVariablesConfigurationSource.Build(Microsoft.Extensions.Configuration.IConfigurationBuilder)
at Microsoft.Extensions.Configuration.ConfigurationBuilder.Build()
at Microsoft.AspNetCore.Hosting.GenericWebHostBuilder..ctor(Microsoft.Extensions.Hosting.IHostBuilder)
at Microsoft.Extensions.Hosting.GenericHostWebHostBuilderExtensions.ConfigureWebHost(Microsoft.Extensions.Hosting.IHostBuilder, System.Action'1<Microsoft.AspNetCore.Hosting.IWebHostBuilder>)
at Microsoft.Extensions.Hosting.GenericHostBuilderExtensions.ConfigureWebHostDefaults(Microsoft.Extensions.Hosting.IHostBuilder, System.Action'1<Microsoft.AspNetCore.Hosting.IWebHostBuilder>)
at WebApplication.Program.CreateHostBuilder(System.String[])
at WebApplication.Program.Main(System.String[])
I installed the dotnet core sdk using the ubuntu store and after that I also installed Rider IDE.
The weird thing here is that when I run the app using Rider it runs fine, the only issue is using terminal dotnet core commands.
Does anybody know what might be the issue ?
The application is created using Rider. I don't think that this plays a role but just as a side fact.
I know there are also other ways to install dotnet core in ubuntu but since the sdk is available in the ubuntu story I thought it should work out of the box and of course its an easier choice.
Also tried this one but does not seem to work for me. Still the same issue happens after running the commands.

The alternative solution as described in Microsoft documentation is to set environment variable before running your app
export DOTNET_SYSTEM_GLOBALIZATION_INVARIANT=1

If you want to run with no globalization support, you need to get "System.Globalization.Invariant": true into your published output AppName.runtimeconfig.json file as shown in the example below:
{
"runtimeOptions": {
"tfm": "netcoreapp3.0",
"configProperties": {
"System.GC.Server": true,
"System.Globalization.Invariant": true
}
}
}
You can add it manually every time you deploy by adding or updating the AppName.runtimeconfig.json file. Better yet, add it once to a runtimeconfig.template.json file like this:
{
"configProperties": {
"System.Globalization.Invariant": true
}
}
Make sure that runtimeconfig.template.json is included in build/publish.

It seem the package libicu63 will provide the ico support for dotnet on Linux, at least on Debian'ish distros.
Update:
And it seems it's "missing" when doing a small installing of Debian (i.e. deselect all applications/system-options in the installation program, except for SSH server)

The trick around it on Ubuntu 20.04 based on this thread https://github.com/dotnet/core/issues/2186#issuecomment-671105420
$export DOTNET_SYSTEM_GLOBALIZATION_INVARIANT=1

Yes. When installing Github action in Debian. It is also required.
As the response from MrCalvin,
sudo apt-get update && sudo apt-get install -qqq libicu63 resolve my issue.

edit your .bashrc file by adding the following line, e.g.:
nano ~/.bashrc
add
export DOTNET_SYSTEM_GLOBALIZATION_INVARIANT=1
Ctrl+o, Ctrl+x
restart terminal and run pwsh again

I had this issue while trying to run Umbraco version 9.2.0. Fiddling with System.Globalization.Invariant was not a good solution as it broke globalization in the backoffice. This issue has been solved in v9.4: https://github.com/umbraco/Umbraco-CMS/pull/11961
I didn't want to upgrade my Umbraco version to solve this, so I just copied the change in that commit to my project.
Simply go into the .csproj file of your web project and change the ICU package reference lines to:
<!-- Force windows to use ICU. Otherwise Windows 10 2019H1+ will do it, but older windows 10 and most if not all winodws servers will run NLS -->
<ItemGroup>
<PackageReference Include="Microsoft.ICU.ICU4C.Runtime" Version="68.2.0.9" />
<RuntimeHostConfigurationOption
Condition="$(RuntimeIdentifier.StartsWith('linux')) Or $(RuntimeIdentifier.StartsWith('win')) Or ('$(RuntimeIdentifier)' == '' And !$([MSBuild]::IsOSPlatform('osx')))"
Include="System.Globalization.AppLocalIcu"
Value="68.2.0.9" />
</ItemGroup>

In my case, I followed the Windows documentation to install SDK dependencies and Runtime, watch out for the corresponding version to each Linux distribution to avoid compatibility issues.

This helped me override the default ICU version to the one that's installed on the machine running arch linux.
export CLR_ICU_VERSION_OVERRIDE=$(pacman -Q icu | awk '{split($0,a," ");print a[2]}' | awk '{split($0,a,"-");print a[1]}')

The NPM script 'start' exited without indicating that the create-react-app server was listening for requests

I faced with this problem:
The NPM script 'start' exited without indicating that the create-react-app server was listening for requests. The error output was: 'rimraf' is not recognized as an internal or external command,
operable program or batch file.
npm ERR! code ELIFECYCLE
npm ERR! errno 1
npm ERR! CallerPanelProject#0.1.0 start: `rimraf ./build && react-scripts start`
npm ERR! Exit status 1
npm ERR!
npm ERR! Failed at the CallerPanelProject#0.1.0 start script.
npm ERR! This is probably not a problem with npm. There is likely additional logging output above.
npm ERR! A complete log of this run can be found in:
))
TSystem.Threading.Tasks.Task<TResult>.GetResultCore(bool waitCompletionNotification)

I had this problem when made the Node SPA app inside ASP .NET Core and tried to perform start node app in the Production mode. In Development mode everything was OK.
This line in Stratup.cs file caused the problem:
spa.UseReactDevelopmentServer(npmScript: "start");
a source of the problem is: in the production mode Node app has been bundled already, i.e. it has no package.json and other Node related files, so start request is not possible to do.
A good way to fix that is to put start in to the clause:
if (env.IsDevelopment())
{
spa.UseReactDevelopmentServer(npmScript: "start");
}

You might have missed installing the dependencies in your source project. That is why it is unable to start to run your application without references.
Run npm install in your source project would resolve the issue

I ran into this problem, after starting afresh with Visual Studio 2019 after a longer break from it (so prette clean setup). It happened when I just tried to set up the simplest ASP.NET Core app, these are the steps I followed / roughly:
Check logs in "Event Viewer" for your app - there I found
"Could not find 'aspnetcorev2_inprocess.dll'. Exception message:
It was not possible to find any compatible framework version
The framework 'Microsoft.AspNetCore.App', version '2.2.0' was not found."
Went into Visual Studio Installer (Visual Studio | Tools | Get Tools and Features).
Select the "Individual Components" tab.
Check all (applicable) modules under .NET for ".NET Core .."-anything (I took them all).
Hit "Install while loading"
Restart Visual Studio.
Voila: ASP.NET core app started without errors.

I solved my problem by running "npm install rimraf" in the project folder.

A similar error as #JamesPoulose but I had installed npm. The problem was I installed it when Visual Studio was open. Event Viewer therefore showed me this error:
Category: Microsoft.AspNetCore.SpaServices
EventId: 0
'npm' is not recognized as an internal or external command,
A simple restart of Visual Studio fixed it.

In my case, it was a very silly problem. After re-installing my Windows, I missed installing npm altogether and then running npm install.

My colleague, Dave Wilson, fixed this for me. Went to our react project folder and deleted the node_modules. Next went to the command prompt and npm i in the project folder. Checked the output of npm i and saw that Python was not installed when the module fibres has a dependency on it. Installed python and added it to PATH in system variables. The key thing is to check the output of npm i.

I ran into this issue when Selecting HTTPS instead of HTTP. When running it on your localhost. Inside your visual studio project: Properties/launchSettings.json, change "applicationULR" to route to http instead of https(see image)
settings change

ASP .NET CORE 2.0 - Unable to start service on Debian

I have a problem with .Net Core ConsoleApp. I am trying to run it on DebianOS 9.0 as daemon. As far I did:
1. Create app in Visual Studio.
2. Publish app from Visual Studio fox x64-linux
3. Copy code to DebianOS
4. Create service in /etc/systemd/system/newservice.service
Code of my service looks like:
[Unit]
Description=Test
DefaultDependencies=no
[Service]
ExecStart=/var/SystemdExample/ConsoleApp.dll
WorkingDirectory=/var/SystemdExample
Restart=always
RestartSec=10
User=netuser
SyslogIdentifier=ConsoleAppEx
Group=netuser
[Install]
WantedBy=multi.user.target
When i try to run it with systemctl start newservice.service
The return of this command is something like:
'newservice.service: Main process exited, code=exited, status=203/EXEC'
Nothing else. Someone have idea how to resolve this?

You cannot run the DDL directly, you have to call it as parameter of dotnet
Something like this :
ExecStart=/usr/bin/dotnet /var/path/to/your/app/hellomvc.dll

For me:
status=203/EXEC indicating the execution is not running correctly.
Please check the path/location of the dotnet when you was installing, because it may not be in /usr/bin/dotnet.
Double check the location of your dll as well.
Do something like below:
ExecStart=/root/dotnet6/dotnet /root/YourAppFolder/YourAppName.dll

Deploy a C# Stateful Service Fabric application from Visual Studio to Linux

EDIT 04/06/18 => Updated question with last status
So I have this working .Net 4.6 Stateful Service that currently run on my Windows Service Fabric cluster deployed on Azure.
Starting from 09/2017, I should be able to move to Linux: https://blogs.msdn.microsoft.com/azureservicefabric/2017/09/25/service-fabric-6-0-release/
So I'm trying to deploy it on Linux so I can save costs.
First things first, I've migrated all my code from .Net 4.6 to .Net Core 2.0. Now I can compile my binaries without issues. I've basically created new .Net Core projects and then moved all my source code from .Net 4.6 projects to the new .Net Core ones.
Then I've updated my Service Fabric application. I removed my previous SF services from my sfproj, then I've added my new .Net Core ones.
Looks like there is a warning (nothing on the output window though), but it's here anyway if I try to create a new empty Statful service using .Net core 2.0 through the template provided by Service Fabric Tools 2.0 (beta):
So I'm going to live with it.
On my dev machine, I've modified the 2 csproj projects that contain my Stateful services so they can run locally as Windows executables. I've used the win7-x64 runtimeIdentifier.
Running my SF cluster locally on my Windows machine is fine.
Then I've slightly changed the previous csproj files for Linux. I used the ubuntu.16.10-x64 runtimeIdentifier.
Also I've changed the ServiceManifest.xml file to target the linux-compatible binary:
<!-- Code package is your service executable. -->
<CodePackage Name="Code" Version="1.9.6">
<EntryPoint>
<ExeHost>
<Program>entryPoint.sh</Program>
</ExeHost>
</EntryPoint>
</CodePackage>
entryPoint.sh is a basic script that eventually executes:
dotnet $DIR/MyService.dll
Then I've successfully deployed to my secured SF Linux cluster from Visual Studio. Unfortunately I have the following errors for both my stateful services:
Error event: SourceId='System.Hosting',
Property='CodePackageActivation:Code:EntryPoint'. There was an error
during CodePackage activation.The service host terminated with exit
code:134
Looks like my binary crashes when starting. So here are my questions:
Is the approach right to deploy a C# .Net Core SF stateful service on Linux from Visual Studio?
EDIT: looking inside the LinuxsyslogVer2v0 table, I get the following error:
starthost.sh[100041]: Unhandled Exception:
System.IO.FileLoadException: Could not load file or assembly
'System.Threading.Thread, Version=4.1.0.0, Culture=neutral,
PublicKeyToken=b03f5f7f11d50a3a'. The located assembly's manifest
definition does not match the assembly reference. (Exception from
HRESULT: 0x80131040)
I found the following bug report: https://github.com/dotnet/sdk/issues/1502
Unfortunately, I still get the error without using MSBuild (using dotnet deploy).
EDIT: further clarification:
My boss want me to run on Linux because starting from D1v2 machines, it's half the price compared to Windows machines (no license etc.)
My .NET Core 2.0 services successfully run on Windows. So the .NET Core port should be fine.

So, this was a real pain in the ass to get it working properly. But it works. Well, kind of.
First, Reliable Services are still in preview on Linux: https://github.com/Microsoft/service-fabric/issues/71
Full Linux support should come very soon (actually it should be available already according to the previous link...).
Now for the details about how to procede, here is some information to help others, because there is just nothing about that on Microsoft documentation and I literally lost 3 days trying to make it work.
1. Do use .NET Core 2.0 for your projects.
It is supported on Linux. On preview for now, but it works.
2. Do use the right RID for your projects.
As of today (April 2018), the right RID to use is ubuntu.16.04-x64.
Edit the csproj files of your Reliable Service projects and set the RID like this:
<Project Sdk="Microsoft.NET.Sdk">
<PropertyGroup>
<OutputType>Exe</OutputType>
<TargetFramework>netcoreapp2.0</TargetFramework>
<IsServiceFabricServiceProject>True</IsServiceFabricServiceProject>
<RuntimeIdentifier>ubuntu.16.04-x64</RuntimeIdentifier>
<Platforms>AnyCPU;x64</Platforms>
</PropertyGroup>
The fun part is, you should be able to provide multiple RIDs using the RuntimeIdentifiers parameter (with a S at the end) like that:
<PropertyGroup>
<OutputType>Exe</OutputType>
<TargetFramework>netcoreapp2.0</TargetFramework>
<IsServiceFabricServiceProject>True</IsServiceFabricServiceProject>
<RuntimeIdentifiers>win7x64;ubuntu.16.04-x64</RuntimeIdentifiers>
<Platforms>AnyCPU;x64</Platforms>
</PropertyGroup>
So you could build Windows binaries and Linux binaries at the same time.
But it simply doesn't work. When building the project from Visual Studio, I end up with the following directory only:
bin/Debug/netcoreapp2.0/
Only DLLs, no valid entry point. No win7-x64 folder, no ubuntu.16.04-x64, no nothing.
This is a bug, supposed to be fixed, but it's not (I use Visual Studio 15.6.2 all up-to-date as of today). See https://github.com/dotnet/core/issues/1039
3. You need a valid Entry Point for your service.
On Windows it's an executable file (*.exe). On Linux it's not. I ended up getting the Linux C# example and copied/pasted the entry point. https://learn.microsoft.com/en-us/azure/service-fabric/service-fabric-create-your-first-linux-application-with-csharp
So basically I now have on my ServiceManifest.xml file of each Reliable Service the following EntryPoint :
<?xml version="1.0" encoding="utf-8"?>
<ServiceManifest Name="XXXX"
Version="1.0.0"
xmlns="http://schemas.microsoft.com/2011/01/fabric"
xmlns:xsd="http://www.w3.org/2001/XMLSchema"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
<ServiceTypes>
<!-- This is the name of your ServiceType.
This name must match the string used in RegisterServiceType call in Program.cs. -->
<StatefulServiceType ServiceTypeName="YYY" HasPersistedState="true" />
</ServiceTypes>
<!-- Code package is your service executable. -->
<CodePackage Name="Code" Version="1.0.0">
<EntryPoint>
<ExeHost>
<Program>entryPoint.sh</Program>
</ExeHost>
</EntryPoint>
</CodePackage>
entryPoint.sh is as follows:
#!/usr/bin/env bash
check_errs()
{
# Function. Parameter 1 is the return code
if [ "${1}" -ne "0" ]; then
# make our script exit with the right error code.
exit ${1}
fi
}
DIR=`dirname $0`
echo 0x3f > /proc/self/coredump_filter
source $DIR/dotnet-include.sh
dotnet $DIR/NAME_OF_YOUR_SERVICE_DLL.dll $#
check_errs $?
dotnet-include.sh is as follows:
#!/bin/bash
. /etc/os-release
linuxDistrib=$ID
if [ $linuxDistrib = "rhel" ]; then
source scl_source enable rh-dotnet20
exitCode=$?
if [ $exitCode != 0 ]; then
echo "Failed: source scl_source enable rh-dotnet20 : ExitCode: $exitCode"
exit $exitCode
fi
fi
Both are inside the PackageRoot folder. I specified for both their properties so the Build Action is "Content" and the Copy to Output Directory is "Copy always".
4. Do NOT build using MSBuild !!
Yeah it is supposed to build Linux packages too, or at least it seems so, because MSBuild is able to produce the following files when you right click on your project and click "Build":
Don't trust the apparent success of the operation, it will miserably FAIL to properly execute when deployed. Some *.so files missing and other issues. MSBuild is buggy as hell and misbehaves regarding dependencies.
See for instance this bug report: https://github.com/dotnet/sdk/issues/1502
Still not fixed after almost a year...
Or https://github.com/dotnet/core/issues/977 (got this one, too).
5. Do write some PowerShell script to build the stuff by yourself.
I ended up reinventing the wheel using the following script to build my package:
# Creating binaries for service 1
cd DIRECTORY_OF_MY_SERVICE_1
dotnet publish -c Release -r ubuntu.16.04-x64
# Creating binaries for service 2
cd ..\DIRECTORY_OF_MY_SERVICE_2
dotnet publish -c Release -r ubuntu.16.04-x64
# Creating binaries for service 3
cd ..\DIRECTORY_OF_MY_SERVICE_3
dotnet publish -c Release -r ubuntu.16.04-x64
# Copying ApplicationManifest.xml
cd ..
mkdir PKG\ServiceFabricApplication
echo F|xcopy "ServiceFabricApplication\ApplicationPackageRoot\ApplicationManifest.xml" "PKG\ServiceFabricApplication\ApplicationManifest.xml" /sy
# Copying Service1 files
mkdir "PKG\ServiceFabricApplication\Service1Pkg"
mkdir "PKG\ServiceFabricApplication\Service1Pkg\Code"
xcopy "Service1\PackageRoot\*" "PKG\ServiceFabricApplication\Service1Pkg" /sy /D
xcopy "Service1\bin\Release\netcoreapp2.0\ubuntu.16.04-x64\publish\*" "PKG\ServiceFabricApplication\Service1Pkg\Code" /sy
# Copying Service2 files
mkdir "PKG\ServiceFabricApplication\Service2Pkg"
mkdir "PKG\ServiceFabricApplication\Service2Pkg\Code"
xcopy "Service2\PackageRoot\*" "PKG\ServiceFabricApplication\Service2Pkg" /sy /D
xcopy "Service2\bin\Release\netcoreapp2.0\ubuntu.16.04-x64\publish\*" "PKG\ServiceFabricApplication\Service2Pkg\Code" /sy
# Copying Service3 files
mkdir "PKG\ServiceFabricApplication\Service3Pkg"
mkdir "PKG\ServiceFabricApplication\Service3Pkg\Code"
xcopy "Service3\PackageRoot\*" "PKG\ServiceFabricApplication\Service3Pkg" /sy /D
xcopy "Service3\bin\Release\netcoreapp2.0\ubuntu.16.04-x64\publish\*" "PKG\ServiceFabricApplication\Service3Pkg\Code" /sy
# Compresses the package
Write-host "Compressing package..."
Copy-ServiceFabricApplicationPackage -ApplicationPackagePath .\PKG\ServiceFabricApplication -CompressPackage -SkipCopy
sfproj file is a Visual Studio / MSBuild related project, so you need to build everything by yourself.
The script above produces the same content as the pkg folder created by MSBuild when building your sfproj using Visual Studio. It copies everything on a PKG folder at the root of your solution.
The package structure is detailed here: https://github.com/MicrosoftDocs/azure-docs/blob/master/articles/service-fabric/service-fabric-package-apps.md
6. Now it's time to deploy!
At this point I didn't trusted Visual Studio anymore, so I built my own PowerShell script:
. .\ServiceFabricApplication\Scripts\Deploy-FabricApplication.ps1 -ApplicationPackagePath '.\PKG\ServiceFabricApplication' -PublishProfileFile '.\ServiceFabricApplication\PublishProfiles\Cloud.xml' -DeployOnly:$false -ApplicationParameter:#{} -UnregisterUnusedApplicationVersionsAfterUpgrade $false -OverrideUpgradeBehavior 'None' -OverwriteBehavior 'SameAppTypeAndVersion' -SkipPackageValidation:$false -ErrorAction Stop
It reuses the Deploy-FabricApplication.ps1 script provided by the Service Fabric project template inside the sfproj project. This script parses the Cloud.xml PublishProfile and deploys to your service fabric cluster.
So you specifies the rights values on both PublishProfiles/Cloud.xml and ApplicationParameters/Cloud.xml then execute the script.
It only works if you have the certificate used to secure the cluster installed on your machine, of course.
Do note the first dot '.' is important, because if you don't use it, you'll have the following error:
Get-ServiceFabricClusterManifest : Cluster connection instance is null
See https://stackoverflow.com/a/38104087/870604
Oh, and as there are bugs on the Service Fabric SDK too, you might want to shutdown your local SF cluster too...
https://github.com/Azure/service-fabric-issues/issues/821
7. Now it's time for another deception.
It simply doesn't work, the service crashes on startup. After searching hours inside the LinuxsyslogVer2v0 Azure Storage table (the log table for Linux, located in one of the two Azure Storage Accounts created automatically with the SF cluster), I found that Microsoft own Nuget Packages were buggy too.
Specifically, the Nuget package Microsoft.Azure.Devices doesn't work on version 1.6.0. An issue with a reference of a dll not found or whatever. I rollbacked to a previous version, namely 1.5.1, and it was fixed.
At this point I didn't had anymore energy to create another Github issue about that. Sorry MS, I'm not your QA team, I'm getting tired.
8. Build again using the first PowerShell script, deploy using the second PowerShell script, and you're done.
You've finally deployed C# Reliable Services using .NET Core 2.0 from Visual Studio (kind of, as it's buggy and I used PowerShell) on Windows to a Linux SF Cluster.
Now I still have issues with my ASP.NET Core service, but it will be a story for another day.
Conclusion: TL;DR
The whole thing is a mess. Bugs everywhere. In the SDK, in the tools, in some of Microsoft Nuget Packages. Awful experience. But it is supported (in preview for now) and you can make it work. Hope this post will help...

I was having similar issues, but I believe this is the issue:
In this release, .NET Core 2.0 services are only supported on Service Fabric for Windows. Full cross-platform support for .NET Core 2.0 services on Windows and Linux is coming soon.
From the Service Fabric 6.1 Release Notes
So no Linux as long as you are targeting .net core 2.0.

I have success deploy to Linux service fabric with this help
Open all the service .csproj files and update the RuntimeIdentifier as shown below
<PropertyGroup>
<OutputType>Exe</OutputType>
<TargetFramework>netcoreapp2.0</TargetFramework>
<IsServiceFabricServiceProject>True</IsServiceFabricServiceProject>
<RuntimeIdentifier>linux-x64</RuntimeIdentifier>
</PropertyGroup>
Update the ServiceManifest.xml to remove .exe extension as shown below
<CodePackage Name="Code" Version="1.0.0">
<EntryPoint>
<ExeHost>
<Program>Web1</Program>
</ExeHost>
</EntryPoint>
</CodePackage>
See https://blogs.msdn.microsoft.com/premier_developer/2018/05/27/running-net-core-2-0-applications-in-a-linux-service-fabric-cluster-on-azure/
*Visual Studio 15.7.3

How to run .net console application (built on windows) on Linux using .net core [duplicate]

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?

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.

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.

If I'm not mistaken, one scenario when you can hit the issue is this: You have an integration project that references another application project (not library). In this case, dependentProject.runtimeconfig.json won't be copied to your integration project's output folder and you won't be able to run dependentProject.exe binary because it will throw The library hostpolicy.dll was not found..
There is a Github issue for this and a workaround.
Edit: Should be fixed in .NET SDK 5.0.200.

I had similar problem running tests in VS19.
========== Starting test run ==========
Testhost process exited with error: A fatal error was encountered. The
library 'hostpolicy.dll' required to execute the application was not
found in 'C:\Program Files\dotnet'. Failed to run as a self-contained
app.
After digging into it I found the source of the problem:
The full path the the .runtimeconfig.json in the test binary folder was above 255 characters. Renaming the module, so the file path becomes shorter, resolved the problem.

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.

I'm not sure why but I ran in to the problem when executing the .exe file in my \bin folder while the .exe in my \obj folder works fine.

I am having this problem in Dotnet Core 3.1 Console application.
If you are publishing your application, make sure that your target runtime set to the specific runtime that you had installed in your target machine.
If you set to portable it will pick whatever runtime that it feels comfortable (which you might not have it installed)

I had this happen with .NET 6.0 where somehow the appname.runtimeconfig.dev.json file was not being generated in the bin/Debug/net6.0/ directory.
The fix was modifying the .csproj file and include this fragment inside the <PropertyGroup> element:
<GenerateRuntimeConfigDevFile>true</GenerateRuntimeConfigDevFile>
I found this solution while searching with https://www.google.com/search?q=net60+runtimeconfig.dev.json at Breaking change: runtimeconfig.dev.json file not generated - .NET | Microsoft Learn with the solution at MSBuild properties for Microsoft.NET.Sdk - .NET | Microsoft Learn:
GenerateRuntimeConfigDevFile
Starting with the .NET 6 SDK, the [Appname].runtimesettings.dev.json file is no longer generated by default at compile time. If you still want this file to be generated, set the GenerateRuntimeConfigDevFile property to true.
<PropertyGroup>
<GenerateRuntimeConfigDevFile>true</GenerateRuntimeConfigDevFile>
</PropertyGroup>
After applying this to the .csproj file and re-building the project, debugging from Visual Studio Code worked fine including stopping at the breakpoints that I had set previously.

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.

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. 😅

Maybe you didn't want to do a "Console .Net Core" project but a "Console .Net Framework" project. It solves the problem, for me...

My problem was that I have 2 .NET Core App projects and one is dependent on the other.
(so I can then execute that application from that other application)
But .NET Core applications (with default config) need <assembly name>.runtimeconfig.json file (to get some launch config) which isn't copied by default.
The only solution that worked for me was adding to Project Properties > Build Events (of the dependent project) this command:
COPY "$(SolutionDir)<dependency name>\$(OutDir)<dependency assymbly name>.runtimeconfig.json" "$(SolutionDir)$(ProjectName)\$(OutDir)" /Y
But you can also copy the <dependency assembly name>.runtimeconfig.json file by hand to the dependent project.
Note that there should be a better more generic way to do this for every .NET Core App Project automatically.

This error is quite generic. So the real problem can be anything.
In my case (if helps anyone with same issue), I created a Class Library project instead of a Console Application project.
A Class Library DLL can't be runned with MSBuild, even if it has a Main method.
Only Console Application DDL can be runned as dotnet <appname>.dll

I was getting similar error while running Unit tests using VSTest#2 task in Azure Devops.
In my case, the problem was with my testAssemblyVer2 value. I was giving wrong pattern for test dlls.
Below one worked for me.(if you are getting this error with VSTest)
- task: VSTest#2
displayName: 'Running UnitTests'
inputs:
testSelector: 'testAssemblies'
testAssemblyVer2: |
$(System.DefaultWorkingDirectory)\SrcFolder\BBBB.UnitTests\**\bin\**\*.BBBB.UnitTests.dll
$(System.DefaultWorkingDirectory)\SrcFolder\AAAAa.UnitTests\**\bin\**\*.AAAA.UnitTests.dll
!**\*TestAdapter.dll
!**\obj\**
platform: x64
configuration: Debug
codeCoverageEnabled: true
So try to give correct pattern value for testAssemblyVer2 input. Make sure its filtering only the required dlls.

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.)

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. :)

For me with ASP.NET Core 2.0 on Azure, it was the appname.deps.json that did the trick. You need to copy it from your build directory to Azure.

For me, the error occurred during the SonarQube coverage scan due to one of the projects had a project reference to a MSTest project.

I faced this problem and it took me couple of days to figure out the solution.
Go to Visual Studio Installer.
Click on 'More' option of the Visual Studio.
Select 'Repair'.
It'll take some time for the download and installation.
Once it's completed restart the machine and try again.
This should solve the issue.

Add the OutputType on the PropertyGroup and issue is solved
<Project Sdk="Microsoft.NET.Sdk">
<PropertyGroup>
<OutputType>Exe</OutputType>
<TargetFramework>net5.0</TargetFramework>
</PropertyGroup>
</Project>
more about this MSBuild can be found here