title: error MSB3644: The reference assemblies for framework ".NETFramework,Version=v3.5" were not found - ubuntu
body: <p>I'm running a <code>dotnet build</code> command on a legacy project originally created by someone else I don't know, under Windows some many years ago, but on my <code>Linux Ubuntu 16.04</code> laptop it gives me the error:</p>
  
  <pre><code>/home/stephane/programs/dotnet-sdk-2.2.204-linux-x64/sdk/2.2.204/Microsoft.Common.CurrentVersion.targets(1183,5): error MSB3644: The reference assemblies for framework ".NETFramework,Version=v3.5" were not found.
  </code></pre>
  
  <p>I downloaded and installed the <code>dotnet</code> SDK yesterday, with the <code>dotnet-sdk-2.2.204-linux-x64</code> archive, and the configuration info is:</p>
  
  <pre><code>$ dotnet --info
  .NET Core SDK (reflecting any global.json):
   Version:   2.2.204
   Commit:    8757db13ec
  
  Runtime Environment:
   OS Name:     ubuntu
   OS Version:  16.04
   OS Platform: Linux
   RID:         ubuntu.16.04-x64
   Base Path:   /home/stephane/programs/dotnet-sdk-2.2.204-linux-x64/sdk/2.2.204/
  
  Host (useful for support):
    Version: 2.2.5
    Commit:  0a3c9209c0
  
  .NET Core SDKs installed:
    2.2.204 [/home/stephane/programs/dotnet-sdk-2.2.204-linux-x64/sdk]
  
  .NET Core runtimes installed:
    Microsoft.AspNetCore.All 2.2.5 [/home/stephane/programs/dotnet-sdk-2.2.204-linux-x64/shared/Microsoft.AspNetCore.All]
    Microsoft.AspNetCore.App 2.2.5 [/home/stephane/programs/dotnet-sdk-2.2.204-linux-x64/shared/Microsoft.AspNetCore.App]
    Microsoft.NETCore.App 2.2.5 [/home/stephane/programs/dotnet-sdk-2.2.204-linux-x64/shared/Microsoft.NETCore.App]
  
  To install additional .NET Core runtimes or SDKs:
    https://aka.ms/dotnet-download
  </code></pre>
  
  <p>And the <code>.csproj</code> file contains:</p>
  
  <pre><code>&lt;Project ToolsVersion="3.5" DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003"&gt;
    &lt;PropertyGroup&gt;
      &lt;ProjectGuid&gt;{1F89C6A7-BCC7-4B9A-AF06-4BA515541489}&lt;/ProjectGuid&gt;
      &lt;Configuration Condition=" '$(Configuration)' == '' "&gt;Debug&lt;/Configuration&gt;
      &lt;Platform Condition=" '$(Platform)' == '' "&gt;x86&lt;/Platform&gt;
      &lt;OutputType&gt;WinExe&lt;/OutputType&gt;
      &lt;RootNamespace&gt;RoseauWin&lt;/RootNamespace&gt;
      &lt;AssemblyName&gt;RoseauWin&lt;/AssemblyName&gt;
      &lt;TargetFrameworkVersion&gt;v3.5&lt;/TargetFrameworkVersion&gt;
      &lt;AppDesignerFolder&gt;Properties&lt;/AppDesignerFolder&gt;
    &lt;/PropertyGroup&gt;
    &lt;PropertyGroup Condition=" '$(Platform)' == 'x86' "&gt;
      &lt;PlatformTarget&gt;x86&lt;/PlatformTarget&gt;
    &lt;/PropertyGroup&gt;
    &lt;PropertyGroup Condition=" '$(Configuration)' == 'Debug' "&gt;
      &lt;OutputPath&gt;bin\Debug\&lt;/OutputPath&gt;
      &lt;DebugSymbols&gt;True&lt;/DebugSymbols&gt;
      &lt;DebugType&gt;Full&lt;/DebugType&gt;
      &lt;Optimize&gt;False&lt;/Optimize&gt;
      &lt;CheckForOverflowUnderflow&gt;True&lt;/CheckForOverflowUnderflow&gt;
      &lt;DefineConstants&gt;DEBUG;TRACE&lt;/DefineConstants&gt;
    &lt;/PropertyGroup&gt;
    &lt;PropertyGroup Condition=" '$(Configuration)' == 'Release' "&gt;
      &lt;OutputPath&gt;bin\Release\&lt;/OutputPath&gt;
      &lt;DebugSymbols&gt;False&lt;/DebugSymbols&gt;
      &lt;DebugType&gt;None&lt;/DebugType&gt;
      &lt;Optimize&gt;True&lt;/Optimize&gt;
      &lt;CheckForOverflowUnderflow&gt;False&lt;/CheckForOverflowUnderflow&gt;
      &lt;DefineConstants&gt;TRACE&lt;/DefineConstants&gt;
    &lt;/PropertyGroup&gt;
    &lt;Import Project="$(MSBuildBinPath)\Microsoft.CSharp.targets" /&gt;
    &lt;ItemGroup&gt;
      &lt;Reference Include="Sanford.Multimedia"&gt;
        &lt;HintPath&gt;..\Sanford.Multimedia.Midi\bin\Debug\Sanford.Multimedia.dll&lt;/HintPath&gt;
      &lt;/Reference&gt;
      &lt;Reference Include="System" /&gt;
      &lt;Reference Include="System.Configuration" /&gt;
      &lt;Reference Include="System.Core"&gt;
        &lt;RequiredTargetFramework&gt;3.5&lt;/RequiredTargetFramework&gt;
      &lt;/Reference&gt;
      &lt;Reference Include="System.Core"&gt;
        &lt;RequiredTargetFramework&gt;3.5&lt;/RequiredTargetFramework&gt;
      &lt;/Reference&gt;
      &lt;Reference Include="System.Data" /&gt;
      &lt;Reference Include="System.Data.DataSetExtensions"&gt;
        &lt;RequiredTargetFramework&gt;3.5&lt;/RequiredTargetFramework&gt;
      &lt;/Reference&gt;
      &lt;Reference Include="System.Drawing" /&gt;
      &lt;Reference Include="System.Windows.Forms" /&gt;
      &lt;Reference Include="System.Xml" /&gt;
      &lt;Reference Include="System.Xml.Linq"&gt;
        &lt;RequiredTargetFramework&gt;3.5&lt;/RequiredTargetFramework&gt;
      &lt;/Reference&gt;
    &lt;/ItemGroup&gt;
    &lt;ItemGroup&gt;
      &lt;Compile Include="MainForm.cs" /&gt;
      &lt;Compile Include="MainForm.Designer.cs"&gt;
        &lt;DependentUpon&gt;MainForm.cs&lt;/DependentUpon&gt;
      &lt;/Compile&gt;
      &lt;Compile Include="Program.cs" /&gt;
      &lt;Compile Include="Properties\AssemblyInfo.cs" /&gt;
      &lt;EmbeddedResource Include="MainForm.resx"&gt;
        &lt;DependentUpon&gt;MainForm.cs&lt;/DependentUpon&gt;
      &lt;/EmbeddedResource&gt;
    &lt;/ItemGroup&gt;
    &lt;ItemGroup&gt;
      &lt;ProjectReference Include="..\Roseau.ComponentModel\Roseau.ComponentModel.csproj"&gt;
        &lt;Project&gt;{28F134E7-F044-4153-A8AE-0C18E6351635}&lt;/Project&gt;
        &lt;Name&gt;Roseau.ComponentModel&lt;/Name&gt;
      &lt;/ProjectReference&gt;
      &lt;ProjectReference Include="..\Roseau.Music.Generators\Roseau.Music.Generators.csproj"&gt;
        &lt;Project&gt;{DBE17471-321A-400D-97A9-ADCEBFE960EA}&lt;/Project&gt;
        &lt;Name&gt;Roseau.Music.Generators&lt;/Name&gt;
      &lt;/ProjectReference&gt;
      &lt;ProjectReference Include="..\Roseau.Music.Midi\Roseau.Music.Midi.csproj"&gt;
        &lt;Project&gt;{FF7B26FF-AB13-4FCC-AC85-9FD04C2D0F1A}&lt;/Project&gt;
        &lt;Name&gt;Roseau.Music.Midi&lt;/Name&gt;
      &lt;/ProjectReference&gt;
      &lt;ProjectReference Include="..\Roseau.Music\Roseau.Music.csproj"&gt;
        &lt;Project&gt;{9A4CF19C-B0A7-4D74-8B01-C479FE8C3019}&lt;/Project&gt;
        &lt;Name&gt;Roseau.Music&lt;/Name&gt;
      &lt;/ProjectReference&gt;
      &lt;ProjectReference Include="..\Roseau.Probability\Roseau.Probability.csproj"&gt;
        &lt;Project&gt;{CA266A83-CB09-4A37-9160-0E67B7035C9C}&lt;/Project&gt;
        &lt;Name&gt;Roseau.Probability&lt;/Name&gt;
      &lt;/ProjectReference&gt;
      &lt;ProjectReference Include="..\Roseau.Windows.Forms\Roseau.Windows.Forms.csproj"&gt;
        &lt;Project&gt;{CCAC8FF9-E2BD-4B76-B479-72D91D1170BD}&lt;/Project&gt;
        &lt;Name&gt;Roseau.Windows.Forms&lt;/Name&gt;
      &lt;/ProjectReference&gt;
      &lt;ProjectReference Include="..\Sanford.Multimedia.Midi\Sanford.Multimedia.Midi.csproj"&gt;
        &lt;Project&gt;{4269C72A-8D3A-4737-8F89-72EAA33EA9E1}&lt;/Project&gt;
        &lt;Name&gt;Sanford.Multimedia.Midi&lt;/Name&gt;
      &lt;/ProjectReference&gt;
    &lt;/ItemGroup&gt;
  &lt;/Project&gt;
  </code></pre>
  
  <p>Is this above file a build file ? An equivalent to a <code>pom.xml</code> file in a Maven Java application ?</p>
  
  <p>I never touched a <code>.Net</code> application before.</p>
  
  <p>What is this <code>ToolsVersion="3.5"</code> and <code>&lt;TargetFrameworkVersion&gt;v3.5&lt;/TargetFrameworkVersion&gt;</code> ?</p>
  
  <p>Can I edit this file ? What version can I change ?</p>
  
  <p>I've seen this <a href="https://docs.microsoft.com/en-us/dotnet/core/porting/libraries" rel="nofollow noreferrer">page</a> and I hope I won't have to acquire so much knowledge just to build it. After all, I'm rewritting this application from scratch in Java and Typescript.</p>