Mono FAQ

From Mono Homepage. This document should be synced from time to time.


A Spanish translation is also available


Question 1: What is Mono exactly?

The Mono Project is an open development initiative sponsored by Ximian that is working to develop an open source, Unix version of the Microsoft .NET development platform. Its objective is to enable Unix developers to build and deploy cross-platform .NET Applications. The project will implement various technologies developed by Microsoft that have now been submitted to the ECMA for standardization.

Question 2: What is the difference between Mono and the .NET Initiative?

The ".NET Initiative" is a somewhat nebulous company-wide effort by Microsoft, one part of which is a cross-platform development framework. Mono is an implementation of the development framework, but not an implementation of anything else related to the .NET Initiative, such as Passport, software-as-a-service, or corporate re-branding.

Question 3: What technologies are included in Mono?

Mono contains a number of components useful for building new software:

Windows has compilers that target the virtual machine from a number of languages: Managed C++, Java Script, Eiffel, Component Pascal, APL, Cobol, Perl, Python, Scheme, Smalltalk, Standard ML, Haskell, Mercury and Oberon.

The CLR and the Common Type System (CTS) enables applications and libraries to be written in a collection of different languages that target the byte code

This means for example that if you define a class to do algebraic manipulation in C#, that class can be reused from any other language that supports the CLI. You could create a class in C#, subclass it in C++ and instantiate it in an Eiffel program.

A single object system, threading system, class libraries, and garbage collection system can be shared across all these languages.

Question 4: Where can I find the specification for these technologies?

You can find the information here:



Question 5: Will you implement the .NET Framework SDK class libraries?

Yes, we will be implementing the APIs of the .NET Framework SDK class libraries.

Question 6: Will you offer an ECMA-compliant set of class libraries?

Eventually we will. Our current focus is on inter-operating with the Microsoft SDK, but we will also offer an ECMA compliant set of libraries.

Question 7: What does the name "Mono" mean?

Mono is the word for `monkey' in Spanish. We like monkeys.

Question 8: Is Mono usable?

The JIT engine is usable on Intel x86 machines. An interpreter can be used on other non-Intel x86 machines.

The class libraries are mature enough to run some real applications (the compiler for instance, and every day more and more applications are natively developed with Mono).

Question 9: When will you ship it?

Different parts of Mono will achieve usability at different stages, once we are comfortable with the compiler, we will release "Mono Core", which contains everything needed to develop applications with the base class libraries, this will happen soon and in the meantime you can download daily snapshots of our work. Also the full ASP.NET support is close to completion.

Other higher level class libraries (ASP.NET, ADO.NET, WinForms) will be released when they become stable.

Question 10: What major components will you include in Mono?

Hopefully everything that Microsoft ships on their Framework (ADO.NET, ASP.NET, WinForms), and we encourage third party developers to create reusable components that work on both Mono and Windows.

Question 11: How can I contribute?

Check the contributing section.

Question 12: Aren't you just copying someone else's work?

We are interested in providing the best tools for programmers to develop applications for Free Operating Systems. We also want to help provide the interoperability that will allow those systems to fit in with other standards.

For more background, read the Mono Project white paper. the project.

Question 13: Miguel said once that Mono was being implemented in COBOL. Is that true?.

No. It was a joke.

The Ximian Role in the Mono Project

Question 14: Why is Ximian working on .NET?

Ximian is interested in providing the best tools for programmers to develop applications for Free Operating Systems.

For more information, read the project rationale page.

Question 15: Will Ximian be able to take on a project of this size?

Of course not. Ximian a supporter of the Mono project, but the only way to implement something of this size is for the entire free software community to get involved. Visit the contributing page if you'd like to help out.

Question 16: What pieces will Ximian be working on?

We will devote most of our resources to work on the pieces which are on the critical path to release a development and execution environment. Once the project is at a stage where it is useful in the real world, it will achieve a critical mass of developers to improve it further.

Question 17: Will Ximian offer Mono commercially?

When Mono is ready to be shipped Ximian will offer a commercial support and services for Mono.

Question 18: Does Ximian provide consulting services around Mono?

Yes, Ximian does provide consulting services around Mono to make it suitable to your needs. Porting the runtime engine, customizing it, working on specific classes or tuning the code for your particular needs.

Question 19: Will you wait until Mono is finished?

Mono will ship on various stages as they mature. Some people require only a subset of the technologies, those will ship first.

More advanced features will take more time to develop. A support time line will be available in June 2002.

Mono and GNOME

Question 20: How is Mono related to GNOME?

In a number of ways. This project was born out of the need of providing improved tools for the GNOME community, and will use existing components that have been developed for GNOME when they are available. For example, we plan to use Gtk+ and Libart to implement Winforms and the Drawing2D API and are considering GObject support.

Question 21: Has the GNOME Foundation or the GNOME team adopted Mono?

Mono is too new to be adopted by those groups. We hope that the tools that we will provide will be adopted by free software programmers including the GNOME Foundation members and the GNOME project generally.

Question 22: Should GNOME programmers switch over to Mono now?

It is still far to early for discussions of "switching over." No pieces of Mono will be ready within the next six months, and a complete implementation is roughly one year away.

We encourage GNOME developers to continue using the existing tools, libraries and components. Improvements made to GNOME will have an impact on Mono, as they would be the "back-end" for various classes.

Question 23: Will Mono include compatibility with Bonobo components? What is the relationship between Mono and Bonobo?

Yes, we will provide a set of classes for implementing and using Bonobo components from within Mono. Mono should allow you to write Bonobo components more easily, just like .NET on Windows allows you to export .NET components to COM.

Question 24: Does Mono depend on GNOME?

No, Mono does not depend on GNOME. We use a few packages produced by the GNOME team like the `glib' library.

Question 25: But will I be able to build GNOME applications?

Yes, we will enable people to write GNOME applications using Mono.

Question 26: Do you have C# bindings for GNOME?.

Yes, we currently bind libgnome, libgnomecanvas, and libgnomeui -- although I dare say I have no idea how functional the bindings are outside of what I tested in the sample app. I imagine other libraries under the GNOME framework will be added on an as-needed (and as-requested) basis...although a truly good bonobo binding will have to wait on the CORBA remoting support which has been started recently.

GUI applications

Question 27: Will Mono enable GUI applications to be authored?

Yes, you will be able to build GUI applications. Indeed, that is our main focus. We will provide both the Windows.Forms API and the Gtk# API.

Question 28: What is the difference between Gtk# and System.Windows.Forms?

Gtk# is a set of bindings for the Gtk+ toolkit for C# (and other CIL-enabled languages). System.Windows.Forms is an API defined by Microsoft to build GUI applications.

Question 29: Will I be able to run my smart clients on systems powered by Mono?

As long as your applications are 100% .NET and do not make use of P/Invoke to call Win32 functions, your smart client applications will run on Mono platforms.

Question 30: Where can I learn more about Gtk#?

The following Question 31: What can I do with Gtk#?.

Gtk# is becoming very usable and you can create applications and applets like those you see in a GNOME desktop environment. It's easy to install so it's worth a try.

Question 32: How can I compile my HelloWorld.cs which uses Gtk#?.

Try: mcs --unsafe -o HelloWorld.exe -r glib-sharp -r pango-sharp -r atk-sharp -r gdk-sharp -r gtk-sharp -r gdk-imaging-sharp HelloWorld.cs

Question 33: Is there any way how to connect DataAdapter to some GTK# controls?

There is a sample file called `DbClient' in gtk-sharp/samples that you might to look at. It is a sample program in Gtk# that adds/updates/deletes information on a Postgress database. When we have the new table/tree widgets, I am sure someone would write an adapter for System.Data (in Gtk2 the tree/list widgets are written using a view/model, so you only need to write a model that maps to the database). You can have a look at gtk-sharp/sample/DbClient, where there is a GTK# application that uses System.Data. It does not use DataAdapter, but DataReader though.

Question 34: Do you have an estimate for when Windows.Forms will be released?

We do not know, volunteers are working on this, but there is no set date yet. The current approach is using the Wine Library to implement it.

Mono and Microsoft

Question 35: Is Microsoft helping Ximian with this project?

There is no high level communication between Ximian and Microsoft at this point, but engineers who work on .NET or the ECMA groups have been very friendly, and very nice to answer our questions, or clarify part of the specification for us.

Microsoft is interested in other implementations of .NET and are willing to help make the ECMA spec more accurate for this purpose.

Ximian was also invited to participate in the ECMA committee meetings for C# and the CLI.

Question 36: Is Microsoft or Corel paying Ximian to do this?


Question 37: Do you fear that Microsoft will change the spec and render Mono useless?

No. Microsoft proved with the CLI and the C# language that it was possible to create a powerful foundation for many languages to inter-operate. We will always have that.

Even if changes happened in the platform which were undocumented, the existing platform would a value on its own.

Question 38: Are you writing Mono from the ECMA specs?

Yes, we are writing them from the ECMA specs and the published materials in print about .NET.

Question 39: If my applications use Mono, will I have to pay a service fee?

No. Mono is not related to Microsoft's initiative of software-as-a-service.

Question 40: Is the Mono Project is related to the Microsoft Hailstorm effort? Is Ximian endorsing Hailstorm?

No. The Mono Project is focused on providing a compatible set of tools for the Microsoft .NET development platform. It does not address, require, or otherwise endorse the MS Passport-based Hailstorm single sign-on system that is part of Windows XP and other services.

Question 41: Will Mono or .NET applications depend on Microsoft Passport?

No. MS Passport is unrelated to running .NET compatible applications produced with the Mono tools. The only thing you will need is a just-in-time compiler (JIT).

Question 42: What is a 100% .NET application?

A `100% .NET application' is one that only uses the APIs defined under the System namespace and does not use PInvoke. These applications would in theory run unmodified on Windows, Linux, HP-UX, Solaris, MacOS X and others.

Question 43: If Microsoft will release a port of their .NET platform under the `Shared Source' license, why should I bother with anything else?

The Shared Source implementation will be expensive and its uses will be tightly restricted, especially for commercial use. We are working towards an implementation that will grant a number of important rights to recipients: use for any purpose, redistribution, modification, and redistribution of modifications.

This is what we call Free Software

Question 44: Is Mono a free implementation of Passport?

No. Mono is just a runtime, a compiler and a set of class libraries.

Question 45: Will the System.Web.Security.PassportIdentity class mean that my software will depend on Passport? No. Applications may use that API to contact a Passport site, but are not required to do so.

As long as your application does not use Passport, you will not need Passport.

Question 46: Will Mono running on Linux make Passport available for Linux?

No. However, the Passport toolkit for Linux-based web servers is available from Microsoft.

Question 47: Will Mono allow me to run Microsoft Office on Linux?

No, it will not. Microsoft Office is a Windows application. To learn more about running Windows applications on Intel Unix systems refer to the Wine Project.

Question 48: Will I be able to compile a Microsoft VB.NET application and execute the resultant MSIL file under MONO on Linux without converting to C# and recompiling?

Once we have a complete VisualBasic runtime, yes.

Question 49: Can mono run the WebMatrix?

No. That requires System.Windows.Forms support which is not currently implemented.

Question 50: Does mono have something like Passport? Will mono have a server side Passport/Similar framework for XSP as well as client classes?

Not yet, but the client side API for authentication is not the problem. We will likely have a lot of other authentication APIs, like the Liberty Alliance APIs. The problem is people on the web provider end that might use this for authentication.

Mono Platforms

Question 51: What operating systems does Mono run on?

Mono is known to run on Linux, Unix and Windows systems.

Question 52: What architectures does Mono support?

Mono today ships with a Just-in-Time compiler for x86-based systems. It is tested regularly on Linux, FreeBSD and Windows (with the XP/NT core).

There is also an interpreter, which is slower that runs on the s390, SPARC and PowerPC architectures.

Question 53: Can Mono run on Windows 9x, or ME editions?

Mono requires Unicode versions of Win32 APIs to run, and only a handful of *W functions is supported under Win9x.

There is Microsoft Layer for Unicode that provides implementation of these APIs on 9x systems.

Unfortunately it uses linker trick for delayed load that is not supported by ld, so some sort of adapter is necessary. You will need MSLU and one of the following libs to link Mono to unicows.dll or alternatively search the net for "libunicows".

No changes to Mono source code required, the only thing is to make sure that linker will resolve imports to adapter library instead of Win32 libs. This is achieved by inserting -lunimono before -lkerner32/user32 in the linker's specs file.

Mono and Portable.NET

Question 54: What are the differences between Mono and Portable.NET?

Most of Mono is being written using C#, with only a few parts written in C (The JIT engine, the runtime, the interfaces to the garbage collection system).

It is easier to describe what is unique about Mono:

Web Services

Question 55: How is Mono related to Web Services?

Mono is only related to Web Services in that it will implement the same set of classes that have been authored in the .NET Framework to simplify and streamline the process of building Web Services.

But most importantly, Mono is an Open Source implementation of the .NET Framework.

Question 56: Can I author Web Services with Mono?

You will be able to write Web Services on .NET that run on Mono and vice-versa.

Question 57: If Mono implements the SDK classes, will I be able to write and execute .NET Web Services with it? Yes. When the project is finished, you will be able to use the same technologies that are available through the .NET Framework SDK on Windows to write Web Services.

Question 58: What about Soup? Can I use Soup without Mono?

Soup is a library for GNOME applications to create SOAP servers and SOAP clients, and can be used without Mono. You can browse the source code for soup using GNOME's Bonsai.

Question 59: Can I use CORBA?

Yes. The CLI contains enough information about a class that exposing it to other RPC systems (like CORBA) is really simple, and does not even require support from an object.

We will be implementing CORBA inter-operation as an extension to the Mono classes so that we can integrate with Bonobo, just like Microsoft provides COM inter-operation classes and support mechanisms.

Question 60: Can I serialize my objects to other things other than XML?

Yes, although the serializing tools have not yet been planned, and you would probably have to implement them yourself.

Question 61: Will Mono use ORBit?

No. Mono will be using a new implementation of CORBA that isn't still started.


Question 62: What is MonoDoc?

MonoDoc is a graphical documentation editor and viewer. Currently, MonoDoc consists of a Gtk# application and is in heavy development. There is also a Qt# version of it.

Development Tools and Issues

Question 63: Will it be possible to use the CLI features without using byte codes or the JIT?

Yes. The CLI engine will be made available as a shared library. The garbage collection engine, the threading abstraction, the object system, the dynamic type code system and the JIT will be available for C developers to integrate with their applications if they wish to do so.

Question 64: Will you have new development tools?

With any luck, Free Software enthusiasts will contribute tools to improve the developer environment. These tools could be developed initially using the Microsoft implementation of the CLI and then executed later with Mono.

Question 65: What kind of rules make the Common Intermediate Language useful for JITers?

The main rule is that the stack in the CLI is not a general purpose stack. You are not allowed to use it for other purposes than computing values and passing arguments to functions or return values.

At any given call or return instruction, the types on the stack have to be the same independently of the flow of execution of your code.

Question 66: Is it true that the CIL is ideal for JITing and not efficient for interpreters?

The CIL is better suited to be JITed than JVM byte codes, but you can interpret them as trivially as you can interpret JVM byte codes.

Question 67: Isn't it a little bit confusing to have the name of "XSP" (the same as in the Apache Project) for the ASP.NET support in Mono?.

In Mono, xsp is just the name of the C# code generator for ASP.NET pages. In the Apache Project, it is a term for the "eXtensible Server Pages" technology so as they are very different things, they don't conflict.

Question 68: What about using something like Jabber instead of the System.Messaging namespace?.

In short, MSMQ is not something like Jabber, but asynchronous messaging through queues. Useful queues do more than serialize messages, they are also platform bridges.

Question 69: Are you supporting XMLDocument and relatives?.

Currently, we aren't implementing them yet. It would require updates to most of the XmlNode derivatives so it's not a trivial task. We are currently focusing on getting XPath support working.

Question 70: Is there any plan to develop an aspx server for Mono?.

The web server turned out to be very simple compared to the rest of the work. Gonzalo has got the page generator mostly done (a module called xsp, who has nothing to do with the XSP term used in the Apache Project). Patrik has done a lot of the work to get the ProcessRequest to work. You can try to help in the final touches to the System.Web classes and writing regression tests for the widgets we have.

Question 71: Is there any way I can develop the class libraries using Linux yet?

Yes. Some class libraries can be developed on Linux. Search for Paolo's post (he lists which classes can be compiled fine now).

Question 72: Is there any way I can install a known working copy of mono in /usr, and an experimental copy somewhere else, and have both copies use their own libraries? (I'm still not very good at library paths in Linux)

Yes. Just use two installation prefixes.

Question 73: How should I write tests or a tests suite?

If you do a test suite for C#, you might want to keep it independent of the Mono C# compiler, so that other compiler implementations can later use it.

Question 74: Would it be too terrible to have another corlib signed as mscorlib?

We rename corlib to mscorlib also when saving the PE files, in fact, the runtime can execute program created by mono just fine.

Question 75: Is there a relatively straightforward way to repeat the steps taken by Paolo to get Mono completely self-hosted on Linux?

To build the compiler and class libraries in Linux, run:

If you want to produce and distribute a monocharge tarball, run: make -f makefile.gnu dist Of course you have to run these in the top level mcs directory.

Question 76: Is it possible to build a C# file to some sort of intermediate format which can linked into a final module, like the traditional .c -> .o -> .so path? You could do: mcs /target:module file1.cs, mcs /target:module file2.cs, mcs /target:exe file1.dll file2.dll /out:mybin.exe

Question 77: Is there any plans for implementing remoting in the near future?, When will work in System.Runtime.Remoting.dll start?

The remoting infrastructure is in place. Some of the channels and formatters are not.

Question 78: I'm wondering if there are any plans to start using nant to build the class lib + test lib. i think that every project need/should use an automated build process and nant + a couple of tools enables this. is the problem that the compiler can't run nant yet?

Maybe well be doing some sort of automated build process + testing when the summer finish.

Mono and ASP.NET

Question 79: Is Mono supporting ASP.NET?

Yes. The development of the support for ASP.NET comes in various stages, here is what Gonzalo has been working on: 1. The Parser. 2. Getting the parser to generate output compatible with ASP.NET. 3. Running the sample output with the real Microsoft runtime but using our generated page. 4. Running the sample with our classes with the .NET runtime. 5. Running our sample code with our classes with our runtime. This is the process we are following. Currently Gonzalo has reached point 5.

Question 80: Do I need install cygwin to work on ASP.NET in mono or Linux is enough since it is self host right now.

Linux is enough.

Question 81: Any plan to make ASP.NET in mono works with Apache in Linux?.

Yes, we have plans to do so, but we need to wait for Patrik's patches to HttpRuntime. Once that is there, writing a mod_mono should be trivial (look at mono/samples/embed for a sample embedded application).

Mono and ADO.NET

Question 82: What is the status of ADO.NET support?. Could I start migrating applications from MS.NET to Mono?.

You could start right now using the ADO.NET support in mono, of course, if you want to help filling the missing gaps while you develop your app :-) Well, what I mean is that we're not that far to having full ADO.NET support in Mono, and we've got a lot of working things, so if we could get more help, we'd finish it really soon :-)

Question 83: In developing the data architecture for the application are there and objects I should stay away from in order to insure the smoothest possible transition (minimum code rewrite) to Mono's ADO.NET implementation? (For example, strongly typed datasets versus untyped datasets, etc...)

We are implementing all the classes in Microsoft .NET's System.Data, so you can be sure that things will work the same in Mono as with the Microsoft implementation.

Question 84: Does Mono can to connect to Sybase by using Mono.Data.*?

Yes. use Mono.Data.SybaseClient. First of all you have to create a SybaseConnection, and then, from it, use it as any other IDbConnection-based class.

Mono and Java

Question 85: Why don't you use Java? After all, there are many languages that target the Java VM.

You can get very good tools for doing Java development on free systems right now. Red Hat has contributed a GCC front-end for Java that can take Java sources or Java byte codes and generate native executables; Transvirtual has implemented Kaffe a JIT engine for Java; Intel also has a Java VM called ORP.

The JVM is not designed to be a general purpose virtual machine. The Common Intermediate Language (CIL), on the other hand, is designed to be a target for a wide variety of programming languages, and has a set of rules designed to be optimal for JITers.

Question 86: Could Java target the CLI?

Yes, Java could target the CLI. We have details on a project that someone could take on to make this happen.

Microsoft has an implementation of the Java language called J# that can target the CIL execution engine.

Question 87: Is it possible to write a JVM byte code to CIL converter?

Yes, it is possible. Here are a few starting point:

Question 88: Could mono become a hybrid CIL/java platform?

No. It is quite far from the philosophy of the project. The idea of Mono is, to have only _one_ VM, on which all can run. And if there existing a binary-converter from Java-.class to IL and if there existing something like J-Sharp on Mono, you can write programs in Java, which than can run on Mono. You do not need two bindings (like your example: GTK-Sharp _and_ Java-Gnome). You need only _one_ of it (GTK-Sharp). Thats the idea of Mono. An other point is, that there are no people, who use Open Source-JVMs. They all prefer Suns original. But for Unix there don't exist a .NET-Framework. So it is possible, that in the future Mono is the standard .NET for Unixes.

Question 89: Do you plan to implement a Javascript compiler?

Yes. Eto Demerzal has started a Rhino port to C#. After this is completed, we will begin developing the JavaScript compiler.

Question 90: Can Mono or .NET share system classes (loaded from mscore.dll and other libs) or will it behave like Sun's Java VM?

What you can do with mono is to load different applications in their own application domain: this is a feature of the CLR that allows sandboxing applications inside a single process space. This is usualy exploited to compartmentalize different parts of the same app, but it can also be effectively used to reduce the startup and memory overhead. Using different appdomains the runtime representation of types and methods is shared across applications.

Extending Mono

Question 91: Would you allow other classes other than those in the specification?

Yes. The Microsoft class collection is very big, but it is by no means complete. It would be nice to have a port of `Camel' (the Mail API used by Evolution inspired by Java Mail) for Mono applications.

You might also want to look into implementing CORBA for Mono. Not only because it would be useful, but because it sounds like a fun thing to do, given the fact that the CLI is such a type rich system.

For more information on extending Mono, see our ideas page.

Question 92: Do you plan to Embrace and Extend .NET?

Embracing a good technology is good. Extending technologies in incompatible ways is bad for the users, so we do not plan on extending the technologies.

If you have innovative ideas, and want to create new classes, we encourage you to make those classes operate correctly well in both Mono and .NET.

Question 93: Is there any way I can develop the class libraries using Linux yet?

Yes. Some class libraries can be developed on Linux. Search for Paolo's post (he lists which classes can be compiled fine now).

Question 94: Is there any way I can install a known working copy of mono in /usr, and an experimental copy somewhere else, and have both copies use their own libraries? (I'm still not very good at library paths in Linux)

Yes. Just use two installation prefixes.


Question 95: Will Mono only work on Linux?

Currently, we are doing our work on Linux-based systems and Windows. We do not expect many Linux-isms in the code, so it should be easy to port Mono to other UNIX variants.

Question 96: What about Mono on non Linux-based systems?

Our main intention at Ximian is to be able to develop GNOME applications with Mono, but if you are interested in providing a port of the Winforms classes to other platforms (frame buffer or MacOS X for example), we would gladly integrate them, as long they are under an open source license.

Question 97: What operating systems/CPUs do you support

Mono currently runs on Linux, Windows, Solaris and FreeBSD. There is a JIT engine available for x86 processors that can generate code and optimizations tailored for a particular CPU.

Interpreters exist for the SPARC, PowerPC and StrongARM CPUs.

Question 98: Does Mono run on Windows?

Yes. You can get pre-compiled binaries from

Question 99: Does Mono run on Linux?

Yes. You can get pre-compiled binaries from

Question 100: Will I require Cygwin to run mono?

No. Cygwin is only required to build Mono.

Question 101: Will Mono depend on GNOME?

It will depend only if you are using a particular assembly (for example, for doing GUI applications). If you are just interested in Mono for implementing a `Hello World Enterprise P2P Web Service', you will not need any GNOME components.

Question 102: Is anyone working on porting Mono to IA-64?

Nobody is working on such port.

Question 103: If I were about to start a Mono port to IA-64,would the same lburg code generator work for IA-64 also? or anything else need to be used for code generation(as the processor architecture is totally different from IA32)

The lburg approach can be use for any processor architecture. But you might think in another better approach.

Question 104: Do you plan to port Rhino to C#?.

Eto Demerzal has started a Rhino port to C#.

Question 105: Has anyone succeeded in building a Mac version of the C# environment. If so can you explain how?

You could try to check with the Darwin people, or the Fink people. Mono/C# is self hosting on Linux/PPC which is the hard part, so it should be relatively simple to get it to work on MacOS

Reusing Existing Code

Question 106: What projects will you reuse or build upon?

We want to get Mono in the hands of programmers soon. We are interested in reusing existing open source software.

Question 107: What about Intel's research JIT framework, ORP?

At this time, we are investigating whether we can use elements of ORP for Mono. ORP is a research JIT engine that has a clearly defined API that splits the JIT from the GC system and the actual byte code implementation.

We are using some pieces of ORP (Their code generation interface) and we use it as a source of inspiration for optimizations. Paolo and Dietmar consider ORP as being one of the best JIT engines out there (and their research work and papers are very useful if you are interested in JIT technology).

Question 108: What about using GNU Lightning?

We are not using GNU Lightning. Our JIT is using an instruction selector based on tree-pattern matching, and a code generation interface that is very tied to the current architecture.

Question 109: Will I be able to use Microsoft SQL Server 2000 or will I need to switch to a specific Open Source Database. Will I need to recode?

There should not be any need to recode.

Question 110: What do I need to watch out for when programming in VB.NET so that I'm sure to be able to run those apps on Linux?

Not making any PInvoke or DLL calls should and not using anything in the Microsoft.* namespaces should suffice. Also do not use any Methods/Classes marked as "This type/method supports the .NET Framework infrastructure and is not intended to be used directly from your code." even if you know what these classes/methods do.

Question 111: Will built-in reporting be supported for crystal reports? This is a heavily used part of our system.

Probably not. Crystal Reports are propriety. Someone may try to emulate the behavior, but no-one has yet volunteered.

Question 112: Who about writing to the registry? As I understand it, Linux does not have a counterpart to the registry. Should I avoid relying on that feature?

Try to avoid it. Although there would be a emulation for registry in Mono too. GNOME does have a registry like mechanism for configuration. But Even if gnome has a configuration system similar to the registry, the keys will not be equal, so you will probably end up having to do some runtime detection, and depending on this load an assembly that has your platform-specific hacks.

Question 113: System.Data.SqlClient with FreeTDS, will you port parts of these to C# and use them?

if their license is compatible with mono's, yes, we'd think about porting them. If not, we'll continue with the plan of using FreeTDS.

Mono and GCC

Question 114: Are you working on a GCC front-end to C#? A GCC back-end that will generate CIL images? What about making a front-end to GCC that takes CIL images and generates native code?

We are currently seeking volunteers for those projects. Visit the contributing section if you are interested.

Question 115: But would this work around the GPL in the GCC compiler and allow people to work on non-free front-ends?

People can already do this by targeting the JVM byte codes (there are about 130 compilers for various languages that target the JVM).

Question 116: Why are you writing a JIT engine instead of a front-end to GCC?

We want the JIT engine and runtime engine because they will be able to execute CIL executables generated on Windows, and so no recompilation will be necessary.


Question 117: How fast will Mono be?

We can not predict the future, but a conservative estimate is that it would be at least `as fast as other JIT engines'.

We would like to ship various JIT engines with Mono, just like Microsoft has done with their .NET development platform. We could provide a faster, JIT for fast load times but lower performance, and an and an optimizing JIT that would be slower at generating code but produce more optimal output.

The CIL has some advantages over the Java byte code: it is really an intermediate representation and there are a number of restrictions on how you can emit CIL code that simplify creating better JIT engines.

For example, on the CIL, the stack is not really an abstraction available for the code generator to use at will. Rather, it is a way of creating a postfix representation of the parsed tree. At any given call point or return point, the contents of the stack are expected to contain the same object types independently of how the instruction was reached.


Question 118: Will I be able to write proprietary applications that run with Mono?

Yes. The licensing scheme is planned to allow proprietary developers to write applications with Mono.

Question 119: What license or licenses are you using for the Mono Project?

The C# Compiler is released under the terms of the GNU GPL. The runtime libraries are under the GNU Library GPL. And the class libraries are released under the terms of the MIT X11 license.

The Mono runtime and the Mono C# Compiler are also available under a proprietary license for those who can not use the LGPL and the GPL in their code.

For licensing details, contact

Question 120: I would like to contribute code to Mono under a particular license. What licenses will you accept?

We will have to evaluate the licenses for compatibility first, but as a general rule, we will accept the code under the same terms of the "container" module.

Question 121: Is the Mono


Question 122: Could patents be used to completely disable Mono (either submarine patents filed now, or changes made by Microsoft specifically to create patent problems)?

No. First, its basic functional capabilities have pre-existed too long to be held up by patents. The basic components of Mono are technologically equivalent to Sun's Java technology, which has been around for years.

Mono will also implement multi-language and multi-architecture support, but there are previous technologies such as UCSD p-code and ANDF that also support multiple languages using a common intermediate language. The libraries are similar to other language's libraries, so again, they're too similar to be patentable in large measure.

However, if Microsoft does patent some technology, then our plan is to either (1) work around it, (2) chop out patented pieces, (3) find prior art that would render the patent useless. Not providing a patented capability would weaken the interoperability, but it would still provide the free software / open source software community with good development tools, which is the primary reason for developing Mono.

Miscellaneous Questions

Question 123: You say that the CLI allows multiple languages to execute on the same environment. Isn't this the purpose of CORBA?

The key difference between CORBA (and COM) and the CLI is that the CLI allows "data-level interoperability" because every language/component uses the same data layout and memory management.

This means you can operate directly upon the data types that someone else provides, without having to go via their interfaces. It also means you don't have to "marshal" (convert) parameters (data layouts are the same, so you can just pass components directly) and you don't have to worry about memory management, because all languages/components share the same garbage collector and address space. This means much less copying and no need for reference counting.

Question 124: Will you support COM?

The runtime will support XPCOM on Unix systems and COM on Windows. Most of the code for dynamic trampolines exists already.

Question 125: Will Ximian offer certifications on Mono or related technologies?.

It's possible. But there is no plan about this. So the short answer is no.

Question 126: Are there any Boehm's GC binaries?

Yes. You can find RPMs here, though if your distribution provides the correct packages, you should use those. The suggested version of the Boehm GC is 6.1.

Question 127: How can I report a bug?

The best thing is to track down the bug and provide a simple test to reproduce the bug. You can then add the bug to the bugtracking system.

Please provide information about what version of mono you're using and any relevant details to be able to reproduce the bug. Note that bugs reported on the mailing-list may be easily forgotten, so it's better to file them in the bug tracking system.

Question 128: Does mcs support the same command line options as the MS C# compiler?

The Mono C# compiler now supports the same command line arguments as the Microsoft C# compiler does.

Question 129: How about getting searchable archives on

You can perform a search on the mono-related mailing lists here.

Question 130: When using mono from cvs or from a snapshot, I get an error messaage saying that Mono and the runtime are out of sync. How do I fix that?

If you use mono from cvs, you need to be prepared for changes in the runtime internals. This means that you should keep a working setup before blindling updating (a working setup may just be the last released tarball or a recent binary snapshot). Usually, compiling corlib with mcs before recompiling the C runtime does the right thing (but occasionally you may need to do it the other way around).

Question 131: Why are you going for a GtkHtml implementation?

GtkHTML is just a lightweight HTML rendering engine that does not support CSS, so we need it to look decent for those of us that will be using the documentation in our day-to-day work on Linux. The Web-based interfaces lack the agility that you get from a native GUI tool to browse your documentation. Probably later on, we will write scripts and generate a full documentation set that is web-browsable, but we need a command-line and GUI tools that we can use natively on Linux when disconnected from the Web (and that has better interactions than a web page).

Question 132: Is there a command-line tool that allows me to access .NET interactively?

There are several but one that is free software and uses MCS is the one Dennis Lu from Rice University is working on; a REPL C# interpreter.

Question 133: Is it possible to use Visual C++ with Mono?.

Well, It's possible to run VC++ generated apps under Mono though.

Mono Common Problems

If you are having problems compiling or running Mono software or if you think that you found a bug, etc. Please visit the Mono Common Problems document and try there.

[AUTHOR: Johannes Roith is working on this]