C# Dev Kit fails to start Roslyn Language Server on Linux (.NET 9.0.1) due to invalid argument `---logLevel`

[yazn999darwish]

Environment data

• OS: Ubuntu 24.04 (x86_64)
• .NET SDK: 9.0.1
• VS Code: 1.105.0
• C# Extension: ms-dotnettools.csharp-2.96.3

C# logs

2025-10-24 11:23:12.541 [error] [stderr] Could not execute because the specified command or file was not found. 2025-10-24 11:23:12.542 [info] [stdout] Possible reasons for this include:

You intended to execute a .NET program, but dotnet---logLevel does not exist. Language server process exited with 1

Steps to reproduce

1. Install .NET 9.0.1 on Ubuntu 24.04
2. Install VS Code + C# Dev Kit extension (2.96.3)
3. Open any C# project
4. Extension tries to start Roslyn Language Server
5. Server fails with dotnet---logLevel does not exist

Expected behavior

The Roslyn Language Server should start normally with --logLevel argument.

Actual behavior

The extension passes ---logLevel (three dashes) instead of --logLevel (two dashes).
This causes dotnet to treat it as an invalid command and the server exits immediately.

Additional context

• Running the server manually with:

  /home/yazn/.dotnet/dotnet exec \
    ~/.vscode/extensions/ms-dotnettools.csharp-2.96.3/.roslyn/Microsoft.CodeAnalysis.LanguageServer.dll \
    --logLevel Information \
    --extensionLogDirectory /tmp/roslyn-logs \
    --stdio
  

works correctly.

This suggests a bug in how the extension constructs the command-line arguments.

Proposed fix

Ensure the extension uses the correct argument format

• ---logLevel

• --logLevel

and always provides the required --extensionLogDirectory parameter when launching the Roslyn Language Server.

[dibarbet]

I'm not sure what could be contributing to this. In general we are just running child_process.spawn(serverPath, ["--logLevel", "info", .., more args]).

@yazn999darwish a couple requests

1. Can you check if you have dotnet.server.path set in vscode settings? If so remove it.
2. Enable trace logging and attach the output here (you will need to set the default and restart VSCode to collect startup logs), see https://github.com/dotnet/vscode-csharp/blob/main/SUPPORT.md#collecting-general-logs)

[lonix1]

Maybe related to my issue #8682 (comment)

When another tool attempts to open a file in the current vscode window it opens two weird files --log and ms-dotnettools.csharp=info.

I'm using a similar environment: .NET 8 on ubuntu 24, but without devkit extension.