Running c# extension on older hardware without .net 9 support

Discussions
1

Do anyone have some tips regarding running cursor c# extentions on older MacBooks?

Newer .net versions don’t support older MacBooks. It seems like the c# extension is compiled with .net 9. Therefore the extension tries to download .net version 9 but it can’t install (the newest OS for my Mac does not support .net 9) and then fails.

I have tried the workarounds in the settings trying to make cursor use .net 8 but it seems to ignore this.

3

You’re right — newer .NET runtimes being required by extensions can break things on older macOS machines. Here’s a clear, practical set of steps and options you can try to get the C# (Cursor) extension working on an older Mac that cannot run .NET 9.

Quick checklist first

  • Confirm macOS version and CPU (Intel vs Apple Silicon). That determines which runtimes you can install.

  • Determine which runtime the extension actually needs (some extensions target .NET 9, others run on .NET 8 or earlier).

  • Keep a backup of your workspace/settings before making changes.

Options (ordered from least invasive to most)

  1. Force the extension to use .NET 8 runtime (if possible)

  • Many C#/OmniSharp/Language Server implementations will look for a runtime via environment variables or extension settings. Check settings for:

    • “OmniSharp: Use Modern Net” / “omnisharp.path” / “omnisharp.useGlobalMono” (if using OmniSharp) or the extension’s runtime selection.

  • Set the extension to use a system-installed .NET (e.g., .NET 8) instead of downloading .NET 9:

    • Install .NET 8 (if supported on your macOS). Use the official installer from Microsoft or Homebrew (brew install --cask dotnet-sdk8 if available).

    • Set environment variable DOTNET_ROOT to the .NET 8 install path and restart your editor:

      • macOS example: add to ~/.zshrc (or ~/.bash_profile):

        export DOTNET_ROOT="/usr/local/share/dotnet"   # adapt to actual install path
export PATH="$DOTNET_ROOT:$PATH"

    • If the extension has a setting for “useGlobalDotnet” or “useLocalDotnet”, enable it so it uses the system runtime.

Note: Some extensions still try to download a bundled runtime regardless — they may ignore settings. Proceed to other options if this fails.

  1. Install older compatible extension version

  • Find the extension’s release history (marketplace or GitHub). Identify a version that targets .NET 8 (or earlier).

  • Install that older extension build in your editor:

    • VS Code: Use “Install Another Version…” from the extensions panel or download the .vsix from the project releases and install manually.

  • Lock updates for that extension so it doesn’t auto-upgrade to a .NET 9–requiring version.

  1. Use Mono (for OmniSharp) — if your stack supports it

  • If the extension is OmniSharp-based and your projects are compatible, installing Mono can let OmniSharp run without requiring a modern dotnet runtime.

  • Install Mono:

    • Via Homebrew: brew install mono (or get the pkg from the Mono project).

  • Set OmniSharp to use Mono:

    • In editor settings: "omnisharp.useGlobalMono": "always" (or equivalent).

  • Note: Mono support is diminishing for some modern C# features and SDK-style projects, but it can work for many cases.

  1. Run the language server externally on a supported machine and connect remotely

  • Set up a small VM or another computer (could be a cloud instance or a newer Mac you have access to) that can run .NET 9 and the extension/language server.

  • Forward the language server connection to your old Mac (via SSH port forwarding or the editor’s remote extension). Example approaches:

    • VS Code Remote - SSH: develop on the remote machine while using the older Mac as a thin client.

    • Run the language server on the remote and configure your editor to connect to it (advanced).

  1. Container / VM on your machine (if CPU/OS permits)

  • If your Mac can run a lightweight Linux VM (Parallels, UTM, VMware Fusion), install a supported Linux image with .NET 9 and run the extension/language server in the VM. Use editor remote features to connect.

  • Performance on very old hardware may be limited, but it isolates the runtime requirement.

  1. Patch or fork the extension (advanced)

  • If the extension is open source and the change is primarily target framework version, you can:

    • Clone the repo, change target framework to net8.0 (if code is compatible), build, and install the custom .vsix.

    • This requires dev tools and may not be trivial if the extension uses net9-only APIs.

  • Only recommended if you’re comfortable building from source.

  1. Consider alternative C# tooling
  • If the current extension is unfixable on your hardware, try alternative C# extensions or language servers that support older runtimes (search OmniSharp variants, or lightweight linters/IntelliSense plugins).

Troubleshooting checklist (if things still fail)

  • Verify which dotnet runtimes are installed: dotnet --list-runtimes and dotnet --list-sdks.

  • Look at the extension logs: enable verbose logging for the extension/language server to see why it attempts to download .NET 9.

  • Check file permissions and installer errors — sometimes the runtime download fails because of permissions or missing installers for older macOS.

  • Confirm the editor is reading your environment (some GUI apps don’t inherit shell environment variables; launch your editor from terminal to test).

What I need from you to help further

  • macOS version (e.g., 10.14 Mojave, 11.7 Big Sur, 12.x Monterey, etc.).

  • CPU type (Intel or Apple Silicon M1/M2).

  • Exact editor and extension name/version (e.g., VS Code — “C# for Visual Studio Code (powered by OmniSharp)” version X, or “Cursor C#” if that’s a specific extension).

  • Output of dotnet --info (if dotnet is installed).

  • Any logs/error messages the extension shows when it fails.

Give me those details and I’ll recommend the exact commands/settings or a step-by-step recipe that fits your machine.