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Using corerun To Run .NET Core Application

In page Using your .NET Core Runtime Build with dotnet cli gives detailed instructions on using the standard command line host and SDK, dotnet.exe to run a .NET application with the modified build of the .NET Core runtime built here. This is the preferred mechanism for you to officially deploy your changes to other people since dotnet.exe and Nuget insure that you end up with a consistent set of DLLs that can work together.

However packing and unpacking the runtime DLLs adds extra steps to the deployment process and when you are in the tight code-build-debug loop these extra steps are an issue.

For this situation there is an alternative host to dotnet.exe called corerun.exe that is well suited for this. It does not know about Nuget at all, and has very simple rules. It needs to find the .NET Core runtime (that is coreclr.dll) and additionally any class library DLLs (e.g. System.Runtime.dll System.IO.dll ...).

It does this by looking at two environment variables.

  • CORE_ROOT - The directory where to find the runtime DLLs itself (e.g. CoreCLR.dll).
    Defaults to be next to the corerun.exe host itself.
  • CORE_LIBRARIES - A Semicolon separated list of directories to look for DLLS to resolve any assembly references. It defaults CORE_ROOT if it is not specified.

These simple rules can be used in a number of ways

Getting the class library from the shared system-wide runtime

Consider that you already have a .NET application DLL called HelloWorld.dll and wish to run it (You could make such a DLL by using 'dotnet new' 'dotnet restore' 'dotnet build' in a 'HelloWorld' directory).

If you execute the following

    set PATH=%PATH%;%CoreCLR%\bin\Product\Windows_NT.x64.Debug
    set CORE_LIBRARIES=%ProgramFiles%\dotnet\shared\Microsoft.NETCore.App\1.0.0

    corerun HelloWorld.dll

for Linux use /usr/share for %Program Files%

Where %CoreCLR% is the base of your CoreCLR repository, then it will run your HelloWorld. application. You can see why this works. The first line puts build output directory (Your OS, architecture, and buildType may be different) and thus corerun.exe you just built is on your path. The second line tells corerun.exe where to find class library files, in this case we tell it to find them where the installation of dotnet.exe placed its copy. (Note that version number in the path above may change)

Thus when you run 'corerun HelloWorld.dll' Corerun knows where to get the DLLs it needs. Notice that once you set up the path and CORE_LIBRARIES environment, after a rebuild you can simply use corerun to run your application (you don't have to move DLLs around)

Using corerun.exe to Execute a Published Application

When 'dotnet publish' publishes an application it deploys all the class libraries needed as well. Thus if you simply change the CORE_LIBRARIES definition in the previous instructions to point at that publication directory but RUN the corerun from your build output the effect will be that you run your new runtime getting all the other code needed from that deployed application. This is very convenient because you don't need to modify the deployed application in order to test your new runtime.

How CoreCLR Tests use corerun.exe

When you execute 'tests\runTest.cmd' one of the things that it does is set up a directory where it gathers the CoreCLR that has just been built with the pieces of the class library that tests need. It places this runtime in the directory


off the CoreCLR Repository. The way the tests are expected to work is that you set the environment variable CORE_ROOT to this directory (you don't have to set CORE_LIBRARIES) and you can run any tests. For example after building the tests (running build-test at the repository base) and running 'test\runtest') you can do the following

    set PATH=%PATH%;%CoreCLR%\bin\Product\Windows_NT.x64.Debug
    set CORE_ROOT=%CoreCLR%\bin\tests\Windows_NT.x64.Debug\Tests\Core_Root 

sets you up so that corerun can run any of the test. For example

    corerun bin\tests\Windows_NT.X64.Debug\GC\Features\Finalizer\finalizeio\finalizeio\finalizeio.exe 

runs the finalizerio test.