[.NET 9] `RuntimeInformation.RuntimeIdentifier` includes unexpected OS details on Linux repo installs

[ptr727]

Description

Per docs it is expected that RuntimeInformation.RuntimeIdentifier returns OS agnostic RID's.

In my testing the RID's returned on some Linux installs includes the OS name, this is not expected, and breaks usage of the reported RID. (I use the RID to download single file dotnet tools)

Note that the issue may be related to how the SDK/runtime was built and installed, as the behavior on Windows (.NET sourced rom Msft, and Debian (.NET sourced from install script) appear to work, while the SDK/runtime installed using the OS native repository does not produce the correct results.

Summary:
Win11 Msft download : Ok
Debian https://dot.net/v1/dotnet-install.sh : Ok
Ubuntu dotnet-runtime-9.0 : Fail
Alpine dotnet9-runtime : Fail

Reproduction Steps

Windows 11 x64, .NET 9 SDK installed: (Ok)
dotnet --info -> RID: win-x64
Console.WriteLine(RuntimeInformation.RuntimeIdentifier); -> win-x64

Alpine, docker alpine:latest, apk add dotnet9-runtime (Fail)
dotnet --info -> RID: alpine.3.21-x64 (expected linux-musl-x64)
Console.WriteLine(RuntimeInformation.RuntimeIdentifier); -> alpine.3.21-x64 (expected linux-musl-x64)

Debian, docker debian:stable-slim, https://dot.net/v1/dotnet-install.sh (Ok)
dotnet --info -> RID: linux-x64
Console.WriteLine(RuntimeInformation.RuntimeIdentifier); -> linux-x64

Ubuntu, docker ubuntu:rolling, dotnet-runtime-9.0 (Fail)
dotnet --info -> RID: ubuntu.24.10-x64 (expected linux-x64)
Console.WriteLine(RuntimeInformation.RuntimeIdentifier); -> ubuntu.24.10-x64 (expected linux-x64)

Expected behavior

RID returned in dotnet --info and RuntimeInformation.RuntimeIdentifier is consistent with documentation.

Actual behavior

See reproduction steps, it appears that .NET installed via Linux native repos do not return the correct RID.

Regression?

I last tested this behavior in .NET v7 and it worked then, but that was a long time ago.

Known Workarounds

Always install using Msft helper script, but that is not recommended for production use.

Configuration

.NET 9.0.3

See description for install steps on Docker.

Other information

No response

[pra2892]

This issue with RuntimeInformation.RuntimeIdentifier returning OS-specific details on Linux when installed from native repositories can be problematic when you need consistent RIDs.

Here's a possible solution that normalizes the RID to the expected format:

using System;
using System.Runtime.InteropServices;
using System.Text.RegularExpressions;

class Program
{
    static void Main()
    {
        // Get the raw RID as reported by the runtime
        string rawRid = RuntimeInformation.RuntimeIdentifier;
        Console.WriteLine($"Raw RID: {rawRid}");
        
        // Get the normalized RID
        string normalizedRid = GetNormalizedRuntimeIdentifier();
        Console.WriteLine($"Normalized RID: {normalizedRid}");
    }
    
    /// <summary>
    /// Gets a normalized runtime identifier that's consistent across different installation methods.
    /// </summary>
    public static string GetNormalizedRuntimeIdentifier()
    {
        string rid = RuntimeInformation.RuntimeIdentifier;
        
        // If already in the expected format, return as is
        if (rid == "win-x64" || rid == "win-arm64" || 
            rid == "linux-x64" || rid == "linux-arm64" || 
            rid == "linux-musl-x64" || rid == "linux-musl-arm64" ||
            rid == "osx-x64" || rid == "osx-arm64")
        {
            return rid;
        }
        
        // Handle OS-specific RIDs from native repositories
        
        // Extract architecture (should be the part after the last dash)
        string architecture = "x64"; // Default
        if (rid.Contains("-"))
        {
            architecture = rid.Substring(rid.LastIndexOf('-') + 1);
        }
        
        // Determine OS and variant
        if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
        {
            return $"win-{architecture}";
        }
        else if (RuntimeInformation.IsOSPlatform(OSPlatform.Linux))
        {
            // Check if it's Alpine Linux (musl-based)
            if (rid.Contains("alpine") || IsAlpineLinux())
            {
                return $"linux-musl-{architecture}";
            }
            return $"linux-{architecture}";
        }
        else if (RuntimeInformation.IsOSPlatform(OSPlatform.OSX))
        {
            return $"osx-{architecture}";
        }
        
        // Fallback to the original RID if we can't normalize it
        return rid;
    }
    
    /// <summary>
    /// Checks if the current Linux distribution is Alpine (musl-based).
    /// </summary>
    private static bool IsAlpineLinux()
    {
        try
        {
            // Check for /etc/os-release file which contains distribution info
            if (File.Exists("/etc/os-release"))
            {
                string content = File.ReadAllText("/etc/os-release");
                return content.Contains("ID=alpine") || content.Contains("ID=\"alpine\"");
            }
            
            // Alternative check for /etc/alpine-release
            return File.Exists("/etc/alpine-release");
        }
        catch
        {
            return false;
        }
    }
}

This solution:

1. Creates a GetNormalizedRuntimeIdentifier() method that returns a consistent RID format regardless of installation method
2. Handles the specific cases mentioned in your issue (Windows, standard Linux, and Alpine Linux)
3. Includes a helper method to detect Alpine Linux specifically, which needs the "linux-musl-x64" RID

You can use this normalized RID for your tool downloads instead of directly using RuntimeInformation.RuntimeIdentifier. This should work across all installation methods, including native repository installations.

For production use, you might want to add more comprehensive detection for other Linux distributions or edge cases, but this covers the main scenarios you described in the issue.

Thank You,

Prashant Yadav

[ptr727]

For production use, you might want to add more comprehensive detection for other Linux distributions or edge cases, but this covers the main scenarios you described in the issue.

Thank you, this is a temporary workaround, I do believe the repo based installers should report the correct information, and workarounds should not be required.

I'd like to hear from dotnet if this is in fact a repo installer issue, how they interact with maintainers to get it fixed, and maybe add tests to assure correct RID behavior?

[dotnet-policy-service]

Tagging subscribers to this area: @vitek-karas, @agocke, @VSadov
See info in area-owners.md if you want to be subscribed.

[jkotas]

This is expected. The distro package managers install distro-specific .NET runtime. The distro-specific .NET runtime has RuntimeIdentifier specific to that distro.

What are you trying to do? If you just need to check whether you are running on Linux, there is OperatingSystem.IsLinux() API for that.

cc @dotnet/distro-maintainers

[ptr727]

I am trying to get the RID so that I can download the correct single file test tool.

The method of using dotnet --info is very widely used to get the RID. So making the result of dotnet --info and RuntimeInformation.RuntimeIdentifier non-deterministic is very troublesome, and it is contrary to the documentation.

I expect some form of method that returns the RID in a deterministic way, that matches the documentation, regardless of how the runtime was installed.

[agocke]

@elinor-fung Looks like the documentation isn't quite right. It says that the RID on ubuntu will be linux-x64, but that's dependent on whether they're using a portable or non-portable build, right?

[am11]

I guess more problematic is the behavior of published apps, which differ from dotnet run:

$ dotnet run
ubuntu.25.04-arm64

# dotnet publish -p:PublishSingleFile=true -o publish-singlefile
$ publish-singlefile/app1 
linux-arm64

# dotnet publish -p:PublishAot=true -o publish-aot
$ publish-aot/app1        
linux-arm64

At minimum, we should make it consistently return the same RID, either portable or non-portable. This is informational API for telemetry purposes etc. For other use-cases, OperatingSystem.IsXx APIs are preferred as @jkotas has pointed out. However, that does not cover cases like linux-musl-{arch} for which we have to detect libc flavor by shelling out to environment or P/Invoking. Ideally, both pieces of information are useful for non-portable builds: effective RID (for telemetry etc.) and portable RIDs (for native assets / runtime.json NuGet/Home#10571 etc.).

[ptr727]

Thank you for continuing to investigate.

I do want to call out that the .NET diagnostic tooling expects normalized RID's, so I'd still prefer some solution where dotnet --info (as I mentioned before this is used in grep all over github to get the RID) or some other CLI accessible command returns the normalized RID as expected by .NET tooling, or that all .NET tooling support whatever RID is returned from other .NET CLI tools.

[elinor-fung]

@elinor-fung Looks like the documentation isn't quite right. It says that the RID on ubuntu will be linux-x64, but that's dependent on whether they're using a portable or non-portable build, right?

It should probably call that out explicitly. The example is technically correct (version of Ubuntu from when they didn't produce their own packages), but confusing. Tried to clarify in: dotnet/dotnet-api-docs#11203