How can I run PowerShell with the .NET 4 runtime?

Question

I am updating a PowerShell script that manages some .NET assemblies. The script was written for assemblies built against .NET 2 (the same version of the framework that PowerShell runs with), but now needs to work with .NET 4 assemblies as well as .NET 2 assemblies.

Since .NET 4 supports running applications built against older versions of the framework, it seems like the simplest solution is to launch PowerShell with the .NET 4 runtime when I need to run it against .NET 4 assemblies.

How can I run PowerShell with the .NET 4 runtime?

Answer 1

PowerShell (the engine) runs fine under .NET 4.0. PowerShell (the console host and the ISE) do not, simply because they were compiled against older versions of .NET. There's a registry setting that will change the .NET framework loaded systemwide, which will in turn allow PowerShell to use .NET 4.0 classes:

reg add hklm\software\microsoft\.netframework /v OnlyUseLatestCLR /t REG_DWORD /d 1
reg add hklm\software\wow6432node\microsoft\.netframework /v OnlyUseLatestCLR /t REG_DWORD /d 1

To update just the ISE to use .NET 4.0, you can change the configuration ($psHome\powershell_ise.exe.config) file to have a chunk like this:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
    <startup>
      <supportedRuntime version="v4.0.30319" />
    </startup>
</configuration>

You can build .NET 4.0 applications that call PowerShell using the PowerShell API (System.Management.Automation.PowerShell) just fine, but these steps will help get the in-the-box PowerShell hosts to work under .NET 4.0.

---

Remove the registry keys when you don't need them any more. These are machine-wide keys and forcibly migrate ALL applications to .NET 4.0, even applications using .net 2 and .net 3.5

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Answer 2

Actually, you can get PowerShell to run using .NET 4 without affecting other .NET applications. I needed to do so to use the new HttpWebRequest "Host" property, however changing the "OnlyUseLatestCLR" broke Fiddler as that could not be used under .NET 4.

The developers of PowerShell obviously foresaw this happening, and they added a registry key to specify what version of the Framework it should use. One slight issue is that you need to take ownership of the registry key before changing it, as even administrators do not have access.

• HKLM:\Software\Microsoft\Powershell\1\PowerShellEngine\RuntimeVersion (64 bit and 32 bit)
• HKLM:\Software\Wow6432Node\Microsoft\Powershell\1\PowerShellEngine\RuntimeVersion (32 bit on 64 bit machine)

Change the value of that key to the required version. Keep in mind though that some snapins may no longer load unless they are .NET 4 compatible (WASP is the only one I have had trouble with, but I don't really use it anyway). VMWare, SQL Server 2008, PSCX, Active Directory (Microsoft and Quest Software) and SCOM all work fine.

Answer 3

If you're still stuck on PowerShell v1.0 or v2.0, here is my variation on Jason Stangroome's excellent answer.

Create a powershell4.cmd somewhere on your path with the following contents:

@echo off
:: http://stackoverflow.com/questions/7308586/using-batch-echo-with-special-characters
if exist %~dp0powershell.exe.activation_config goto :run
echo.^<?xml version="1.0" encoding="utf-8" ?^>                 > %~dp0powershell.exe.activation_config
echo.^<configuration^>                                        >> %~dp0powershell.exe.activation_config
echo.  ^<startup useLegacyV2RuntimeActivationPolicy="true"^>  >> %~dp0powershell.exe.activation_config
echo.    ^<supportedRuntime version="v4.0"/^>                 >> %~dp0powershell.exe.activation_config
echo.  ^</startup^>                                           >> %~dp0powershell.exe.activation_config
echo.^</configuration^>                                       >> %~dp0powershell.exe.activation_config
:run
:: point COMPLUS_ApplicationMigrationRuntimeActivationConfigPath to the directory that this cmd file lives in
:: and the directory contains a powershell.exe.activation_config file which matches the executable name powershell.exe
set COMPLUS_ApplicationMigrationRuntimeActivationConfigPath=%~dp0
%SystemRoot%\System32\WindowsPowerShell\v1.0\powershell.exe %*
set COMPLUS_ApplicationMigrationRuntimeActivationConfigPath=

This will allow you to launch an instance of the powershell console running under .NET 4.0.

You can see the difference on my system where I have PowerShell 2.0 by examining the output of the following two commands run from cmd.

C:\>powershell -ExecutionPolicy ByPass -Command $PSVersionTable

Name                           Value
----                           -----
CLRVersion                     2.0.50727.5485
BuildVersion                   6.1.7601.17514
PSVersion                      2.0
WSManStackVersion              2.0
PSCompatibleVersions           {1.0, 2.0}
SerializationVersion           1.1.0.1
PSRemotingProtocolVersion      2.1


C:\>powershell4.cmd -ExecutionPolicy ByPass -Command $PSVersionTable

Name                           Value
----                           -----
PSVersion                      2.0
PSCompatibleVersions           {1.0, 2.0}
BuildVersion                   6.1.7601.17514
CLRVersion                     4.0.30319.18408
WSManStackVersion              2.0
PSRemotingProtocolVersion      2.1
SerializationVersion           1.1.0.1

Answer 4

If you don't want to modify the registry or app.config files, an alternate way is to create a simple .NET 4 console app that mimicks what PowerShell.exe does and hosts the PowerShell ConsoleShell.

See Option 2 – Hosting Windows PowerShell yourself

First, add a reference to the System.Management.Automation and Microsoft.PowerShell.ConsoleHost assemblies which can be found under %programfiles%\Reference Assemblies\Microsoft\WindowsPowerShell\v1.0

Then use the following code:

using System;
using System.Management.Automation.Runspaces;
using Microsoft.PowerShell;

namespace PSHostCLRv4
{
    class Program
    {
        static int Main(string[] args)
        {
            var config = RunspaceConfiguration.Create();
                return ConsoleShell.Start(
                config,
                "Windows PowerShell - Hosted on CLR v4\nCopyright (C) 2010 Microsoft Corporation. All rights reserved.",
                "",
                args
            );
        }
    }
}

Answer 5

If you only need to execute a single command, script block, or script file in .NET 4, try using Activation Configuration Files from .NET 4 to start only a single instance of PowerShell using version 4 of the CLR.

Full details:

http://blog.codeassassin.com/2011/03/23/executing-individual-powershell-commands-using-net-4/

An example PowerShell module:

https://gist.github.com/882528

Answer 6

The other answers are from before 2012, and they focus on "hacking" PowerShell 1.0 or PowerShell 2.0 into targeting newer versions of the .NET Framework and Common Language Runtime (CLR).

However, as has been written in many comments, since 2012 (when PowerShell 3.0 came) a much better solution is to install the newest version of PowerShell. It will automatically target CLR v4.0.30319. This means .NET 4.0, 4.5, 4.5.1, 4.5.2, or 4.6 (expected in 2015) since all of these versions are in-place replacements of each other. Use $PSVersionTable or see the Determine installed PowerShell version thread if you are unsure of your PowerShell version.

At the time of writing, the newest version of PowerShell is 4.0, and it can be downloaded with the Windows Management Framework (Google search link).