Installing .NET

OpenSimulator requires .NET 8.0. The exact package you need depends on what you are doing:

• Running a prebuilt or self-built OpenSim → the .NET 8.0 Runtime.
• Building OpenSim from source → the .NET 8.0 SDK (which includes the runtime).

OpenSim no longer runs on Mono. Use the official .NET 8.0 from Microsoft.

Windows

1. Download the .NET 8.0 SDK (or Runtime) from https://dotnet.microsoft.com/en-us/download/dotnet/8.0.
2. Run the installer and follow the prompts.

3. Verify:

   dotnet --version
   

   It should print something like 8.0.xxx.

Optionally install Visual Studio 2022 or later if you want to build/debug using the IDE.

Linux

Install the .NET 8.0 SDK. On Debian/Ubuntu the quick route is the Microsoft package feed; alternatively use your distro’s packages if they provide .NET 8.

You also need libgdiplus (for image handling). If you previously had Mono 6.x complete, you already have it.

# Debian/Ubuntu example
sudo apt-get update
sudo apt-get install -y apt-utils libgdiplus libc6-dev

Then install the .NET 8 SDK following Microsoft’s instructions for your distro (https://learn.microsoft.com/dotnet/core/install/linux), then verify:

dotnet --version

macOS

1. Download the .NET 8.0 SDK for macOS from https://dotnet.microsoft.com/en-us/download/dotnet/8.0 (the .pkg installer).
2. Run it and follow the prompts.

3. Install libgdiplus via Homebrew (or MacPorts):

   brew install mono-libgdiplus
   

4. Verify:

   dotnet --version
   

Next

Once dotnet --version reports 8.0.x, continue to Building OpenSim from source.