An error occurred attempting to determine the process id of the DNX process hosting your application

Question

I get this error message when I\'m trying to start the application.

An error occurred attempting to determine the process id of the DNX process host

Answer 1

When upgrading from beta7 -> beta8 I had this issue and the suggestions provided by Ben M and Domysee worked for me. However, one of my colleagues was still having problems running our project which targets dnxcore50 only. If you make sure you have run the following commands:

dnvm install 1.0.0-beta8 -r coreclr
dnvm install 1.0.0-beta8 -r coreclr -arch x86

It was the second command in particular that fixed it on his machine. You can also double-check this folder has a dnx.exe in it:

%userprofile%\.dnx\runtimes\dnx-coreclr-win-x86.1.0.0-beta8\bin

Answer 2

Microsoft changed the hosting model as described in the release notes.

In project.json replace the dependency

"Microsoft.AspNet.Server.IIS": "1.0.0-beta7"

with

"Microsoft.AspNet.Server.Kestrel": "1.0.0-beta8"

---

In web.config in the handlers section remove every entry except

<add name="httpPlatformHandler" path="*" verb="*" modules="httpPlatformHandler" resourceType="Unspecified" />

The complete web.config will look like this:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <system.webServer>
    <handlers>
      <add name="httpPlatformHandler" path="*" verb="*" modules="httpPlatformHandler" resourceType="Unspecified"/>
    </handlers>
    <httpPlatform processPath="%DNX_PATH%" arguments="%DNX_ARGS%" stdoutLogEnabled="false" startupTimeLimit="3600"/>
  </system.webServer>
</configuration>

---

RC1: While using RC1 I had the error after moving the solution folder. After deleting the bin and obj folders everything worked again.
As user764754 noted, simply restarting Visual Studio can also help.

Answer 3

I've just discovered one more problem that was causing this!

web.config in project root had some dodgy IIS URL rewrite rules to enforce HTTPS. Removing those rules solved the problem.

Answer 4

I had this trouble when I'm toggling settings and have disabled the "Enable Anonymous Authentication" in the Project > Properties > Debug. Make sure that it is enabled. Close and relaunched the project then try again. Hope this helps.

Answer 5

In Visual Studio:

While following this tutorial I received a similar error.

First, I received the error: "An error occurred attempting to determine the process id of dotnet.exe..." I took the following steps.

1. I started my application without debugging CTRL+F5.
2. I was then presented with an option to accept a self-signed certificate for localhost.
3. I followed the prompts and then I was able to visit my application using the AppUrl I copied over after enabling SSL in project debug settings.

While trying a few things to solve that error I also came across this error. "An error occurred attempting to determine the process id of the DNX process hosting your application"

Which was caused by having another instance of the application running.

I hope this answer helps someone.

Answer 6

In my case in an asp net core 1.1, .net framework 4.5.2 project, the error did not refer to dnx since that is no more. Instead it referred to the project name exe. Another version of the error referred to simply being unable to connect to iis express.

The problem was the introduction of a canonical host name rewrite rule that tries to force all connections to have a host name that begins with www. e.g. redirecting gty.org to www.gty.org to conform to our ssl cert. This is fine in production but you can't force https://localhost:44347/ to begin with www and expect iis express to be able to handle it.

<rule name="CanonicalHostNameAddwww" enabled="true" stopProcessing="true">
      <match url="(.*)" ignoreCase="true" />
      <conditions logicalGrouping="MatchAll">        
        <add input="{HTTP_HOST}" negate="true" pattern="^www\." />
      </conditions>
      <action type="Redirect" url="http://www.{HTTP_HOST}{HTTP_URL}"  appendQueryString="false" redirectType="Permanent" />
</rule>

The solution was to comment out the rule when running in visual studio or add a condition:

<add input="{HTTP_HOST}" negate="true" pattern="^localhost" />