What's the difference between SDK and Runtime in .NET Core?

Solution 1:

According to the .Net Core Guide, .NET Core is composed of the following items

• A .NET runtime, which provides a type system, assembly loading, a garbage collector, native interop and other basic services.
• A set of framework libraries, which provide primitive data types, app composition types and fundamental utilities.
• A set of SDK tools and language compilers that enable the base developer experience, available in the .NET Core SDK.
• The 'dotnet' app host, which is used to launch .NET Core apps. It selects the runtime and hosts the runtime, provides an assembly loading policy and launches the app. The same host is also used to launch SDK tools in much the same way.

The SDK is all of the stuff that is needed/makes developing a .NET Core application easier, such as the CLI and a compiler.

The runtime is the "virtual machine" that hosts/runs the application and abstracts all the interaction with the base operating system.

Only the latter is required to run the application, but the former is needed to develop the application.

Solution 2:

Runtime: to run apps

SDK (Runtime + Tooling): to build and run apps

Solution 3:

I'm not inventing anything here. Just copy-pasting the definitions from https://dotnet.microsoft.com/download

The software development kit (SDK) includes everything you need to build and run .NET Core applications, using command-line tools and any editor (like Visual Studio).

The runtime includes everything you need to run .NET Core applications. The runtime is also included in the SDK.

Solution 4:

Sharing from Rick Strahl's post: Which .NET Core Runtime Download do you need?

Only the .NET Core Runtime is required to run an application and provides information about the install.

To develop, build and publish an application will require an SDK.

dotnet.exe installs with a runtime install, but it only provides core features to provide info to run an application and provide info about the install: dotnet mydll.dll and dotnet --info. To build, publish or do anything else you need to install the SDK.

Running the following command will provide information about the install:

dotnet --info

If the command fails it means you do not have the .NET Core runtime installed or available in the system's PATH.

Below is a sample output of the command.

$ dotnet --info
.NET Core SDK (reflecting any global.json):
 Version:   2.2.101
 Commit:    236713b0b7

Runtime Environment:
 OS Name:     Mac OS X
 OS Version:  10.13
 OS Platform: Darwin
 RID:         osx.10.13-x64
 Base Path:   /usr/local/share/dotnet/sdk/2.2.101/

Host (useful for support):
  Version: 2.2.0
  Commit:  1249f08fed

.NET Core SDKs installed:
  2.1.4 [/usr/local/share/dotnet/sdk]
  2.1.302 [/usr/local/share/dotnet/sdk]
  2.2.101 [/usr/local/share/dotnet/sdk]

.NET Core runtimes installed:
  Microsoft.AspNetCore.All 2.1.2 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.2.0 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.App 2.1.2 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.2.0 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 2.0.5 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.2 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.2.0 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]

To install additional .NET Core runtimes or SDKs:
  https://aka.ms/dotnet-download

The output tells you:

• The installed SDK version
• The active runtime version that's running this dotnet command
• A list of all installed runtimes and SDKs

Installing an SDK also installs the runtime.

macOS homebrew specific

Installing the homebrew-cask dotnet will conflict with the dotnet-sdk, so to get both the runtime, and the sdk install dotnet-sdk

brew cask install dotnet-sdk

In short, the runtime will allow your OS to run compiled C-Sharp, C# programs, and the sdk will allow you to compile programs written in C-Sharp, C#.

It's important to understand that you can have multiple runtimes and multiple SDKs installed and each project can use a different one. The runtime is determined by your project's runtime specifier in the .csproj file:

<TargetFramework>netcoreapp2.1</TargetFramework>

The SDK is either the last globally installed SDK which is the default, or you can explicitly override the SDK in a global.json placed in the solution root folder. The following explicitly forces my project to use the last RC SDK, instead of the RTM version:

{
 "sdk": {
   "version": "2.1.300-rc.31211"
 }
}

Generally, there should be no need to use a specific lower SDK version as the SDK is backwards compatible and can compile various versions of .NET Core applicatino back to v1.0. IOW, it's OK to use the latest SDK in almost all cases.

.NET Core Runtimes

The .NET Core Runtimes are the smallest self-contained and specific component and contain the absolute minimum to run just .NET Core on a specific platform.

Note it a runtime install does not include the ASP.NET Core meta package runtime dependencies, so if your application references Microsoft.AspNetCore.App or Microsoft.AspNetCore.All you have to seperately download the ASP.NET Core package. However, if you explicitly reference all ASP.NET Core Nuget packages rather than using the meta packages, those packages are deployed as part of your application and it can run with just the runtime.

Essentially you are trading installation package size vs. a runtime pre-install requirement.

References:

• Which .NET Core Runtime Download do you need?