.Net and Asp.Net on MacOs & Mono instead of Windows (using Visual Studio or JetBrains Rider)

Mono goes a long way in running code written for .Net on Windows. It is all very much easier if you either start with cross-platform in mind, or if you move to .Net Core; but even for existing .Net Framework projects mono can run runs most things including Asp.Net.

Here's my checklist from a couple of years of opening .Net Framework solution files on a Mac and finding they don't build first time.

Most of these require you to edit the .csproj file to make it cross-platform, so a basic grasp of msbuild is very helpful.

  1. For AspNet: inside the PropertyGroup section near the top of the csproj file, add an element:

    <WebProjectOutputDir Condition="$(WebProjectOutputDir) == '' AND $(OS) == 'Unix' ">bin/</WebProjectOutputDir>

    Use this if you get a 'The “KillProcess” task was not given a value for the required parameter “ImagePath” (MSB4044)' error message; or if the build output shows you are trying to create files in an top-level absolute /bin/ path.

  2. For AspNet: Add Condition="'$OS'!='Unix'" to the reference to Microsoft.Web.Infrastructure.dll AND delete the file from the website bin directory.

    <Reference Condition="'$OS'!='Unix'" Include="Microsoft.Web.Infrastructure, Version=, Culture=neutral, PublicKeyToken=31bf3856ad364e35, processorArchitecture=MSIL">
  3. For all project types—but, only if you need to use the netCore dotnet build tooling to build an NetFramework project on unix. mono's msbuild does not need this. Add this section somewhere in the csproj file (I put it right at the bottom), to resolve NetFramework4 reference paths:

    <PropertyGroup Condition="$(TargetFramework.StartsWith('net4')) and '$(OS)' == 'Unix'">
    <!-- When compiling .NET SDK 2.0 projects targeting .NET 4.x on Mono using 'dotnet build' you -->
    <!-- have to teach MSBuild where the Mono copy of the reference asssemblies is -->
    <!-- Look in the standard install locations -->
    <BaseFrameworkPathOverrideForMono Condition="'$(BaseFrameworkPathOverrideForMono)' == '' AND EXISTS('/Library/Frameworks/Mono.framework/Versions/Current/lib/mono')">/Library/Frameworks/Mono.framework/Versions/Current/lib/mono</BaseFrameworkPathOverrideForMono>
    <BaseFrameworkPathOverrideForMono Condition="'$(BaseFrameworkPathOverrideForMono)' == '' AND EXISTS('/usr/lib/mono')">/usr/lib/mono</BaseFrameworkPathOverrideForMono>
    <BaseFrameworkPathOverrideForMono Condition="'$(BaseFrameworkPathOverrideForMono)' == '' AND EXISTS('/usr/local/lib/mono')">/usr/local/lib/mono</BaseFrameworkPathOverrideForMono>
    <!-- If we found Mono reference assemblies, then use them -->
    <FrameworkPathOverride Condition="'$(BaseFrameworkPathOverrideForMono)' != '' AND '$(TargetFramework)' == 'net40'">$(BaseFrameworkPathOverrideForMono)/4.0-api</FrameworkPathOverride>
    <FrameworkPathOverride Condition="'$(BaseFrameworkPathOverrideForMono)' != '' AND '$(TargetFramework)' == 'net45'">$(BaseFrameworkPathOverrideForMono)/4.5-api</FrameworkPathOverride>
    <FrameworkPathOverride Condition="'$(BaseFrameworkPathOverrideForMono)' != '' AND '$(TargetFramework)' == 'net451'">$(BaseFrameworkPathOverrideForMono)/4.5.1-api</FrameworkPathOverride>
    <FrameworkPathOverride Condition="'$(BaseFrameworkPathOverrideForMono)' != '' AND '$(TargetFramework)' == 'net452'">$(BaseFrameworkPathOverrideForMono)/4.5.2-api</FrameworkPathOverride>
    <FrameworkPathOverride Condition="'$(BaseFrameworkPathOverrideForMono)' != '' AND '$(TargetFramework)' == 'net46'">$(BaseFrameworkPathOverrideForMono)/4.6-api</FrameworkPathOverride>
    <FrameworkPathOverride Condition="'$(BaseFrameworkPathOverrideForMono)' != '' AND '$(TargetFramework)' == 'net461'">$(BaseFrameworkPathOverrideForMono)/4.6.1-api</FrameworkPathOverride>
    <FrameworkPathOverride Condition="'$(BaseFrameworkPathOverrideForMono)' != '' AND '$(TargetFramework)' == 'net462'">$(BaseFrameworkPathOverrideForMono)/4.6.2-api</FrameworkPathOverride>
    <FrameworkPathOverride Condition="'$(BaseFrameworkPathOverrideForMono)' != '' AND '$(TargetFramework)' == 'net47'">$(BaseFrameworkPathOverrideForMono)/4.7-api</FrameworkPathOverride>
    <FrameworkPathOverride Condition="'$(BaseFrameworkPathOverrideForMono)' != '' AND '$(TargetFramework)' == 'net471'">$(BaseFrameworkPathOverrideForMono)/4.7.1-api</FrameworkPathOverride>
    <FrameworkPathOverride Condition="'$(BaseFrameworkPathOverrideForMono)' != '' AND '$(TargetFramework)' == 'net472'">$(BaseFrameworkPathOverrideForMono)/4.7.2-api</FrameworkPathOverride>
    <EnableFrameworkPathOverride Condition="'$(BaseFrameworkPathOverrideForMono)' != ''">true</EnableFrameworkPathOverride>
    <!-- Add the Facades directory.  Not sure how else to do this. Necessary at least for .NET 4.5 -->
    <AssemblySearchPaths Condition="'$(BaseFrameworkPathOverrideForMono)' != ''">$(FrameworkPathOverride)/Facades;$(AssemblySearchPaths)</AssemblySearchPaths>
  4. For projects that have lived through C# evolution from C# 5 to C# 7: You may need to remove duplicate references to e.g. System.ValueTuple. Add Condition="'$(OS)' != 'Unix'" to the reference. This applies to Types that MS put on NuGet.org during the evolution. idk why msbuild builds without complain on Windows but not on Unices.

    <Reference Condition="'$(OS)' != 'Unix'" Include="System.ValueTuple, Version=, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51, processorArchitecture=MSIL">
  5. For References to Microsoft.VisualStudio.TestTools.UnitTesting: Add a nuget reference to MSTEST V2 from nuget.org and make it conditional on the OS

    <ItemGroup Condition="'$(OS)' == 'Unix'">
    <Reference Include="MSTest.TestFramework" Version="2.1.1">
    <Reference Include="coverlet.collector" Version="1.3.0" >

    Note this will only get you to a successful build. To run the tests on unix you then have to download and build https://github.com/microsoft/vstest and run it with e.g.
    mono ~/Source/Repos/vstest/artifacts/Debug/net451/ubuntu.18.04-x64/vstest.console.exe --TestAdapterPath:~/Source/Repos/vstest/test/Microsoft.TestPlatform.Common.UnitTests/bin/Debug/net451/ MyTestUnitTestProjectName.dll.

  6. Case Sensitivity & mis-cased references
    Windows programmers are used to a case-insensitive filesystem. So if code or config contains references to files, you may need to correct mismatched casing. Usually a 'FileNotFoundException' will tell you if you have this problem.

  7. The Registry, and other Permissions
    See this post for more: https://www.cafe-encounter.net/p1510/asp-net-mvc4-net-framework-version-4-5-c-razor-template-for-mono-on-mac-and-linux

Using the command line

It is helpful to be somewhat familiar with microsoft docs on MSBuild Concepts since msbuild will be issuing most of your build errors. If you have installed mono then you can run msbuild from the command line with extra diagnostics e.g.

msbuild -v:d >> build.log

you can also run web applications from the command just by running


from the project directory.

Original Text from 2011

For reasons best not examined too closely I switch between between Mac and PC which, since I earn my crust largely with .Net development, means switching between Visual Studio and MS.Net and MonoDevelop with Mono.

Mono is very impressive, it is not at all a half hearted effort, and it does some stuff that MS haven't done. But when switching environments, there's always the occasional gotcha. Here are some that have got me, and some solutions.

  • Gotcha: Linq Expressions don't work on Mono?
    Solution: Add a reference to System.Core to your project.
  • Question: What version of NUnit is built in to mono?As of Feb 2011, it's nunit 2.4.8.

HowTo: Linux, Nginx, Mono, Asp.Net Mvc

These are notes I made for getting an application written for Asp.Net Mvc (It was probably Mvc 3-ish) to run on a Centos server.

Note that some of the issues/solutions may vary across Linux variants. The interface Nginx-Mono is FastCGI, which they both support. The Mono webserver is xsp4.

Of course, running cross platform is all much easier these days if you use .Net Core and Kestrel 🙂 And een for Net Framework running on Mono, the work done since Microsoft bought Xamarin has been really helpful for e.g. Mvc compatibility.

The Reading List

The Checklist

Ensure nginx has read execute permissions on your application directory and all parent directories

nginx conf section for webapp

With the Asp.Net website listening on port 9001

server {
listen 8080;
server_name your-public-facing-nginx-server-name.com;

# use /smoketest/ to confirm that nginx is reading this config 
# and has read/execute access to the 
# /usr/share/nginx directories and files:

location /smoketest/ {
root /usr/share/nginx/smoketestredir;
index index.html;

# pass XSP to FastCGI server listening on
# use a different port for each ASP.NET site you create
# (port 9000 is often taken by PHP on default webserver setups)

location / {

# replace fastcgi with this to confirm nginx read address
# to files in root /usr/share/nginx/mywebapplication;
fastcgi_index index.html;

include /etc/nginx/fastcgi_params;
fastcgi_param  PATH_INFO          "";
fastcgi_param  SCRIPT_FILENAME    $document_root$fastcgi_script_name;

fastcgi_buffers 16 16k;
fastcgi_buffer_size 32k;

Systemd Startup Script

vim /etc/systemd/system/fastcgi-mono-hdmbreas.service

Description=FastCgi-mono-server4 for Application

ExecStart=/bin/fastcgi-mono-server4 --applications /:/usr/share/nginx/hdmbreas/hdm-fe-web --socket=tcp:

systemctl daemon-reload
systemctl start fastcgi-mono-app.service
systemctl status fastcgi-mono-app.service
systemctl status fastcgi-mono-app.service

Error: [error] 7216#0: *119 upstream sent too big header while reading response header

  • Considering setting the buffer size
  • Considering setting the busy buffer size
  • e.g. nginx config: fastcgi_buffers 16 16k; fastcgi_buffer_size 32k;

Watching Errors

Watch errors with tail -F /var/log/nginx/error.log

Adding your Outlook.com account to MacOs as an Exchange account.

Is simple when you know how. Possibly harder if, like me, your outlook login is not an outlook.com email address, but your own domain.

System Preferences -> Add Internet Account -> Choose the Big Exchange Button

MacOs System Preferences with “Internet Accounts” Highlighted
MacOs System Preferences with “Internet Accounts” Highlighted

First, get an app-password from your outlook.com account
Then note the Exchange server URL: https://outlook.office365.com/EWS/Exchange.asmx
Then, try to add your account just by typing in your email address and the app-password you got.
If that doesn't work, and you get the “Unable to verify account name or password” paste the Exchange server URL into the two boxes for Internal URL and External URL:

MacOs Mojave Add an Outlook.com account
MacOs Mojave Add an Outlook.com account

And that works for me™ on MacOs Mojave in 2019.

PowerShell String.Split() Off-by-Method-Overload Error

This seemed to me an error and I and was on the point of raising it as a bug on the Powershell github repo:

PS> "\this".Split( [char]'\', [StringSplitOptions]::RemoveEmptyEntries).Length
# >> 2

Presumably it is because [StringSplitOptions]::RemoveEmptyEntries is coerced to a [char] and so the line is parsed as:

PS> "\this".Split( ([char]'\', [StringSplitOptions]::RemoveEmptyEntries) ).Length

Instead of as

PS> \this".Split( (,[char]'\'), [StringSplitOptions]::RemoveEmptyEntries).Length

If the first parameter is a string not a character then it works as expected:

PS> "\this".Split( '\', [StringSplitOptions]::RemoveEmptyEntries).Length
# >> 1

But the really unfortunate case is :

PS> "\this".Split( [System.IO.Path]::DirectorySeparatorChar, [StringSplitOptions]::RemoveEmptyEntries).Length
# >> 2

which results in

PS> "\this".Split( [System.IO.Path]::DirectorySeparatorChar, [StringSplitOptions]::RemoveEmptyEntries).[0]
# >> $null
# instead of
# >> "this"

It turns out that it's fixed in Powershell 6 Beta; or to be more precise, it doesn't happen in PowerShell 6. What changed is that the underlying .Net framework has added new overloads to String.Split():

string[] Split(char separator, System.StringSplitOptions options)                                                                                    
string[] Split(char separator, int count, System.StringSplitOptions options)                                                                         
string[] Split(string separator, System.StringSplitOptions options)                                                                                  
string[] Split(string separator, int count, System.StringSplitOptions options)                                                                       

Whereas PowerShell 5 only has these overloads available:

string[] Split(Params char[] separator)                                                                                                              
string[] Split(char[] separator, int count)                                                                                                          
string[] Split(char[] separator, System.StringSplitOptions options)                                                                                  
string[] Split(char[] separator, int count, System.StringSplitOptions options)                                                                       
string[] Split(string[] separator, System.StringSplitOptions options)                                                                                
string[] Split(string[] separator, int count, System.StringSplitOptions options)                                                                     

And so the best-match overload that PowerShell 6 chooses is different to PowerShell 5's best match.