ubuntu-latest not respecting latest installed .NET SDK - Results in build error

[thomhurst]

Description

Here's my build. It's on a matrix to build on ubuntu, windows and mac.

As you can see, windows and mac pass. But ubuntu complains that it only has .NET 8 and not .NET 9.

However you can see in the step above I'm installing the .NET 9 SDK by doing:

      - name: Setup .NET
        uses: actions/setup-dotnet@v4
        with:
          dotnet-version: 9.0.x

That runs and says:

dotnet-install: Attempting to download using aka.ms link https://builds.dotnet.microsoft.com/dotnet/Sdk/9.0.102/dotnet-sdk-9.0.102-linux-x64.tar.gz
dotnet-install: Remote file https://builds.dotnet.microsoft.com/dotnet/Sdk/9.0.102/dotnet-sdk-9.0.102-linux-x64.tar.gz size is 210604728 bytes.
dotnet-install: Extracting archive from https://builds.dotnet.microsoft.com/dotnet/Sdk/9.0.102/dotnet-sdk-9.0.102-linux-x64.tar.gz
dotnet-install: Downloaded file size is 210604728 bytes.
dotnet-install: The remote and local file sizes are equal.
dotnet-install: Installed version is 9.0.102
dotnet-install: Adding to current process PATH: /usr/share/dotnet. Note: This change will be visible only when sourcing script.
dotnet-install: Note that the script does not resolve dependencies during installation.
dotnet-install: To check the list of dependencies, go to https://learn.microsoft.com/dotnet/core/install, select your operating system and check the "Dependencies" section.
dotnet-install: Installation finished successfully.

Then the next step is to run my .NET 9 app, and it fails with a .NET 8 SDK error:

Run sudo -E dotnet run -c Release --allCategories=Singleton
Error: /usr/lib/dotnet/sdk/8.0.111/Sdks/Microsoft.NET.Sdk/targets/Microsoft.NET.TargetFrameworkInference.targets(166,5): error NETSDK1045: The current .NET SDK does not support targeting .NET 9.0. Either target .NET 8.0 or lower, or use a version of the .NET SDK that supports .NET 9.0. Download the .NET SDK from https://aka.ms/dotnet/download [/home/runner/work/Inject.NET/Inject.NET/Benchmarks/Benchmarks.csproj]

Platforms affected

• Azure DevOps
• GitHub Actions - Standard Runners
• GitHub Actions - Larger Runners

Runner images affected

• Ubuntu 20.04
• Ubuntu 22.04
• Ubuntu 24.04
• macOS 12
• macOS 13
• macOS 13 Arm64
• macOS 14
• macOS 14 Arm64
• macOS 15
• macOS 15 Arm64
• Windows Server 2019
• Windows Server 2022
• Windows Server 2025

Image version and build link

https://github.com/thomhurst/Inject.NET/actions/runs/12807345586/job/35707734799

Is it regression?

Yes

Expected behavior

https://github.com/thomhurst/Inject.NET/actions/runs/12738696095

Actual behavior

.NET 9 SDK is installed but isn't used when trying to run a .NET 9 app

Repro steps

Install .NET 9 SDK

Run .NET 9 app

[Prabhatkumar59]

Hi @thomhurst - Thank you for bringing this issue to our attention. We will look into this issue closely and will update you after investigating.