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ASP.NET Mono Specific Configuration

by Marek Habersack

Note: this document applies to the SVN trunk version of Mono (as of 10 October 2008) and to Mono 2.1 and newer

In certain situations the Mono implementation of ASP.NET must adapt to different environment conditions than those commonly found when the application runs under Microsoft .NET. To make it easier for the user to configure Mono for its controlling operating system we have added a sub-section to the <system.web> section of the Web.config file - <monoSettings>.

This article contains detailed information on the section contents.

Table of contents

Section attributes

The following table describes all the attributes currently defined for the section tag. Number in brackets preceeding each key is Mono version in which the key first appeared:

useCompilersCompatibility: a boolean which tells ASP.NET whether or not to augment compiler information read from either <system.codeDom/compilers> or <system.web/compilation> configuration sections. Defaults to true. For more details about the compiler settings available see below

verificationCompatibility: an integer which serves the same purpose as the HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\ASP.NET\VerificationCompatibility Win32 registry key (described in this article) - to let the user turn off virtual path validity verification. When Mono runs under Windows it will first check the value of the above registry key and then consult web.config to check for value of the property described here. See also this bug report.

Child elements


This is a standard add/clear/remove section which follows the same syntax as the <system.web/compilation> section. The difference is that Mono ignores all settings except for the compilerOptions one. The corresponding <system.codeDom/compilers> or <system.web/compilation> entry is augmented only if the compiler type matches. The compiler options read from this section are appended to the default ones.

Current compatibility settings

The current default configuration modifes the C# compiler entry in the following ways:

C# compiler: /nowarn:0169

Appends the /nowarn:0169 option to the compiler command line.

This prevents situations when code similar to the one shown below would throw an exception if the user configured the C# provider with the /warnlevel:3 /warnaserror options. The .NET csc compiler does not throw report this error in this particular situation:

<%@ Page Language="C#" %>
<script runat="server">
void Page_Load(object o, EventArgs e) {

Note: If you plan to use #pragma warning reset 169 anywhere in your application code, your source will fail to compile - you need to either disable the compiler compatibility settings or override the C# compiler entry removing the /nowarn:0169 option from the compilerOptions attribute.

Note: An easy way exists to prevent this error from happening. It’s sufficient to modify the code presented above by making the Page_Load method a protected one. No compiler warning will be reported then.