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Building and running embedded Linux .NET applications from first principles

, 23 May 2014 CPOL
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.NET applications on Yocto/OpenEmbedded Linux


This walk-through has the aim of taking you from a clean system through to including Mono in a build image using the meta-mono layer, then building and packaging an example .NET project for inclusion in that image.

You may already have Yocto installed and just be looking to work with Mono for the first time, in which case you can jump forward to the section you find most relevant, such as Build an example project on the host for testing (optional) or Adding the meta-mono layer to the Yocto build system.

The following assumptions are made. You are:

Obtain the required packages for your host system to support Yocto

First we will install the required host packages for Ubuntu as detailed in the quickstart, i.e.

  $ sudo apt-get install gawk wget git-core diffstat unzip texinfo gcc-multilib build-essential chrpath libsdl1.2-dev xterm nano 

Full details of system requirements and installation can be found in the Yocto Quickstart

Install Mono

Also install Mono on your host system as we'll use it to build and run some examples for test later

  $ sudo apt-get install mono-complete
  $ mono --version 

With Ubuntu 12.04 LTS this will install Mono version 2.10 which is now quite old (December 2011).

If you wish to install a newer build of Mono to your host system you can follow these instructions.

  $ sudo add-apt-repository ppa:directhex/monoxide
  $ sudo apt-get update
  $ sudo apt-get install mono-complete
  $ mono --version

This will install Mono 3.2.1 (August 2013)

If you wish to use the absolute latest Mono then there are instructions you can follow to build a release tarball here and from git here. Be aware this may not be straightforward and that there can be issues, such as with missing files, if you follow this process.

Additionally I have written a detailed walk-through on how to build Mono (3.4.0 tarball / git) on Windows, which can be found here.

Download and extract the Yocto 1.6 release

At the time of writing, the current release of Yocto (1.6) can be found here

  $ cd ~ 
  $ mkdir yocto
  $ wget
  $ tar xjvf poky-daisy-11.0.0.tar.bz2 

This will get you the Yocto 1.6 base meta-data and the bitbake tool. You can also add in extra layers, usually of the form "meta-foo" to provide machine support and additional functionality.

Configure the build environment to build an emulator image

  $ cd ~/yocto/poky-daisy-11.0.0
  $ source oe-init-build-env build_qemux86 

This will create a build tree in build_qemux86 although you could use a different name if you so wish with no adverse effects.

It is entirely possible to have many build trees in parallel in different folders and to switch between them using oe-init-build-env.

oe-init-build-env will create a default configuration file in conf/local/conf which will build an emulator image suitable for execution with qemu.

Build a baseline image

After configuring the environment you will be left in the build_qemux86 folder.

You should then build a baseline image, which will take some time (numbers of hours)

  $ bitbake core-image-minimal 

Build an example project on the host for testing (optional)

Building with autotools

The most straightforward way to compile non-.NET projects for different targets within Yocto is to make use of autotools.

Projects which support autotools provide a set of template files which are then used by the autotools to generate Makefiles and associated configuration files which are appropriate to build for the target environment.

Similarly it is possible to compile Mono/.NET projects using autotools.

A very basic example 'Hello World' style project called mono-helloworld has been committed to GitHub here.

If you take a look at the two source files helloworld.cs and helloworldform.cs you can see the first outputs a 'Hello World' message to the console, and the second creates a Windows Form titled 'Hello World'.

Discussion of autotools template configuration for Mono is outside the scope of this guide, but the mono-helloworld project is based on the mono-skel example which can be found in the Autotools section of the Mono Application Deployment guidelines.

The project itself builds two .NET executables, helloworld and helloworldform respectively, the first of which is a console application and the second of which is a simple Windows Forms application.

To build the project on the host independently of Yocto first clone the example repository

  $ mkdir ~/host 
  $ cd ~/host 
  $ git clone 

Then run the autotools, configure the build, and make the project

  $ cd mono-helloworld
  $ ./
  $ ./configure
  $ make 

Following a successful compilation you will have a number of new files in the root of the build folder.

There are two new .NET executables src/helloworld.exe and src/helloworldform.exe.

You can run the first with

  $ mono src/helloworld.exe 

It will output


You can run the second with

  $ mono src/helloworldform.exe 

Depending on your host environment (e.g. using SSH) you may need to explicitly set the DISPLAY variable for this to work, with

  $ export DISPLAY=:0 
  $ mono src/helloworldform.exe 

This will give you a basic Windows Forms window title

So you have now shown that you can successfully fetch configure and build the project on the host.

Next we will look at how Yocto automates the this process of fetching, configuring and building, then also installs and packages the output files.

Building with xbuild

Many individuals develop with Visual Studio, Mono Develop, Xamarin Studio or other similar integrated development environments (IDEs).

Mono provides xbuild which is the Mono implementation of Microsoft's msbuild, discussed here.

In essence this enables a developer to create a solution of projects within their IDE of choice, then use xbuild to build within the Mono environment.

A useful workflow to follow may be to develop locally with an IDE of choice, commit to a git repository upon release, then use a Yocto recipe to build and package that release into an existing image, or for provision to a package feed for update to existing targets in the field.

The mono-helloworld project discussed Building with autotools|above]] also provides a solution and project files to support build with xbuild, or indeed with an IDE such as Visual Studio.

If you have already built the examples using autotools remove the folder and start again.

  $ cd ~/host 
  $ rm -Rf mono-helloworld 

Check out the mono-helloworld project again

  $ git clone 

Run xbuild. (As you might guess from the name of the .sln file you could clone this example project to a Windows host and open it up with Visual Studio, and in fact that is how it was created)

  $ xbuild /p:Configuration=Debug mono-helloworld_vs2010.sln 

This results in a number of new files, including two new Mono/.NET executables in bin/Debug helloworld.exe and helloworldform.exe

You can run the first with

  $ mono bin/Debug/helloworld.exe 

It will output


You can run the second with

  $ mono bin/Debug/helloworldform.exe 

Depending on your host environment (e.g. using SSH) you may need to explicitly set the DISPLAY variable for this to work, with

  $ export DISPLAY=:0
  $ mono bin/Debug/helloworldform.exe 

This will give you a basic Windows Forms window title

So you have now shown that you can successfully fetch configure and build the project on the host.

Next we will look at how Yocto automates the this process of fetching, configuring and building, then also installs and packages the output files.

Adding the meta-mono layer to the Yocto build system

A preferred method for adding recipes to the build environment, and the method shown with this guide, is to place them within a new layer.

Layers isolate particular sets of build meta-data based on machine, functionality or similar, and help to keep the environment clean.

The meta-mono layer contains Mono specific recipes to support execution of .NET applications on target boards. The layer can be found here.

To use a new layer such as this you first clone the layer from its git repository and then add the layer to your bitbake configuration by editing conf/bblayers.conf.

  $ cd ~/yocto/poky-daisy-11.0.0 
  $ git clone git://
  $ cd ~/yocto/poky-daisy-11.0.0/build_qemux86
  $ nano conf/bblayers.conf

Your bblayers.conf should look similar to this

  # LAYER_CONF_VERSION is increased each time build/conf/bblayers.conf
  # changes incompatibly
  BBFILES ?= ""
  BBLAYERS ?= " \
    /home/user/yocto/poky-daisy-11.0.0/meta \
    /home/user/yocto/poky-daisy-11.0.0/meta-yocto \
    /home/user/yocto/poky-daisy-11.0.0/meta-yocto-bsp \
    /home/user/yocto/poky-daisy-11.0.0/meta \
    /home/user/yocto/poky-daisy-11.0.0/meta-yocto \

Make the new layer visible to bitbake by adding a line to BBLAYERS

  BBLAYERS ?= " \
    /home/user/yocto/poky-daisy-11.0.0/meta \
    /home/user/yocto/poky-daisy-11.0.0/meta-yocto \
    /home/user/yocto/poky-daisy-11.0.0/meta-yocto-bsp \
    /home/user/yocto/poky-daisy-11.0.0/meta-mono \

Now bitbake can see the recipes in the new layer.

You will also see when bitbake runs and shows the Build Configuration that the repository branch and hash of your layer is shown which is useful to know, particularly when comparing notes with others as to why a build fails, e.g.

  Build Configuration:
  BB_VERSION        = "1.22.0"
  BUILD_SYS         = "i686-linux"
  NATIVELSBSTRING   = "Ubuntu-12.04"
  TARGET_SYS        = "i586-poky-linux"
  MACHINE           = "qemux86"
  DISTRO            = "poky"
  DISTRO_VERSION    = "1.6"
  TUNE_FEATURES     = "m32 i586"
  TARGET_FPU        = ""
  meta-yocto-bsp    = "<unknown>:<unknown>"
  meta-mono         = "master:88c6d5f1961d58b3ec203ff19594f954c3e49cd9"

Build an image including Mono/.NET support

The meta-mono layer includes a recipe to build an image core-image-mono based on the Yocto standard image core-image-sato.

To build this image

  $ bitbake core-image-mono 

This may take a while, even if you have already built <code>core-image-minimal as additional GUI support packages need to be built.

The core-image-mono recipe can be found here and pulls in an include file from here.

You can see in the include file that extra packages are added to the standard core-image-sato image.

  IMAGE_INSTALL += "mono mono-helloworld" 

This is how you would add Mono support to your image within a recipe, or within a .bbappend file. In fact it should only be necessary to add the mono package as it is not necessary to have the examples unless you wish to for testing purposes.

The mono-helloworld recipe included here shows how to build the example project using autotools. For details see the recipe itself here, and more importantly the include file it pulls in here.

You could choose to replace mono-helloworld with mono-helloworld-xbuild which as the name suggests shows how to build the eaxmple project with xbuild.

Testing the .NET executable on an emulated target

Having built core-image-mono you can then run it up under qemu

To run up the image, simply use

   $ runqemu qemux86

This will boot the emulator, load up the image, you'll see a kernel loading and then a basic user interface.

If you find that your keymap is incorrect you might wish to set this explicitly, for example

 $ runqemu qemux86 qemuparams='-k en-gb' 


 $ runqemu qemux86 qemuparams='-k en-us'

Open up a terminal window using the appropriate icon, Log into the emulator as 'root', no password and run the examples.

You can run the first with

  $ mono helloworld.exe 

Or alternatively the recipe installs a script to wrap use of Mono, so you can use the form

  $ helloworld 

This will output


You can run the second with

  $ mono /usr/lib/helloworldform.exe 


  $ helloworldform

Depending on your host environment (e.g. using SSH) you may need to explicitly set the DISPLAY variable for this to work, with

  $ export DISPLAY=:0 
  $ mono /usr/lib/helloworld/helloworldform.exe 

This will show a test Windows Forms form titled 'Hello World'

Breakdown of an autotools recipe

This is the contents of the recipe.

 SRC_URI[md5sum] = "79b0ba0044689789a54e3d55ec400fc0"
 SRC_URI[sha256sum] = "56388435f29ce94007155acc39593c900b6d3248a7f281e83ed2101a6da455f0"

It can be seen that we provide a couple of check-sums which relate to the release tarball that will be downloaded.

Similarly this the included file which can be found here.

  SUMMARY = "Mono Hello World"
  DESCRIPTION = "Test applications for Mono console and windows forms"
  AUTHOR = "Alex J Lennon <>"
  SECTION = "mono/applications"
  PRIORITY = "optional"
  LIC_FILES_CHKSUM = "file://LICENSE;md5=783b7e40cdfb4a1344d15b1f7081af66"
  DEPENDS = "mono"
  SRC_URI = "${PV}.tar.gz"
  inherit autotools
  FILES_${PN} = "${libdir}/helloworld/helloworld.exe \
          ${bindir}/helloworld \
             ${libdir}/helloworld/helloworldform.exe \
                ${bindir}/helloworldform \
  RDEPENDS_${PN} += "mono"  

For more details on check-sums, licenses and so forth, see Adding 3rd Party Components to Yocto/OpenEmbedded Linux and the Yocto Recipe & Style Patch Guide.

We have a dependency on the mono package, and again we inherit the autotools class to make use of the bitbake autotools functionality.

Lastly we override FILES_${PN} which controls the installed files which are added to the main output package. ${libdir}, ${bindir} are standard GNU variable naming conventions for installation paths. For details see here and here.

In this case we have made sure that the helloworld executable goes to /usr/lib/helloworld/helloworld.exe as does the helloworldform.exe.

It might seem quite strange to be installing the executable assemblies to the /usr/lib location, but this is in line with Mono application deployment recommendations.

We then install wrapper scripts to /usr/bin which can be called directly to run the respective examples. These scripts take the form

  exec @MONO@ @prefix@/lib/helloworld/@APP@.exe $MONO_EXTRA_ARGS "$@" 

Breakdown of an xbuild recipe

The xbuild recipe is similar to the autotools recipe above, excepting that we override a couple of methods to ensure xbuild runs as we wish it too

This recipe can be found here.

First we include the definitions in the include file, and set the version specific check-sums for the archive to be retrieved

 SRC_URI[md5sum] = "79b0ba0044689789a54e3d55ec400fc0"
 SRC_URI[sha256sum] = "56388435f29ce94007155acc39593c900b6d3248a7f281e83ed2101a6da455f0" 

Then we set our source directory which must be correct for bitbake to find extracted files from the retrieved archive

 REALPN = "mono-helloworld"
 S = "${WORKDIR}/${REALPN}-${PV}" 

Now we override the compilation method to call xbuild to build a particular .NET configuration against the a .SLN file in the archive.

 do_compile() {
         xbuild /p:Configuration=${CONFIGURATION} ${REALPN}_vs2010.sln

Next we modify the installation method to make sure that the correct output files are installed and the executable scripts are modified to run the output assemblies

 do_install() {
        install -d "${D}${bindir}"
        install -d "${D}${libdir}/helloworld/.debug"
        install -m 0755 ${S}/bin/${CONFIGURATION}/*.mdb ${D}${libdir}/helloworld/.debug
        install -m 0755 ${S}/bin/${CONFIGURATION}/*.exe ${D}${libdir}/helloworld

        install -m 0755 ${S}/ ${D}${bindir}/helloworld
        sed -i "s|@MONO@|mono|g" ${D}${bindir}/helloworld
        sed -i "s|@prefix@|/usr|g" ${D}${bindir}/helloworld
        sed -i "s|@APP@|helloworld|g" ${D}${bindir}/helloworld
        install -m 0755 ${S}/ ${D}${bindir}/helloworldform
        sed -i "s|@MONO@|mono|g" ${D}${bindir}/helloworldform
        sed -i "s|@prefix@|/usr|g" ${D}${bindir}/helloworldform
        sed -i "s|@APP@|helloworld|g" ${D}${bindir}/helloworldform
Lastly we make sure that the .MDB debug files which are output are packaged correctly in the -dbg package. The other assemblies in ${libdir} and ${bindir} will be packaged correctly in the main output package by default
  FILES_${PN}-dbg += "${libdir}/helloworld/.debug/*" 

For more details on check-sums, licenses and so forth, see Adding 3rd Party Components to Yocto/OpenEmbedded Linux and the Yocto Recipe & Style Patch Guide.


This is a living document. Please feel free to send comments, questions, corrections to Alex Lennon.


23/05/14 v1.0 Initial Release


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)


About the Author

Alex J Lennon
CEO Dynamic Devices Ltd
United Kingdom United Kingdom
Founded Dynamic Devices in 2004 to deliver high quality embedded solutions.
Alex is an experienced engineer with a deep knowledge and wide experience of both software development and project management. He has provided cutting edge hardware and software design solutions to industry in the United States and Europe and has successfully brought a wide range of products to market.
His technical expertise includes the architectural design and development of embedded systems software, deployment of large scale assured data delivery systems and the creation of low-level device drivers in a number of languages.
During the past decade Alex has worked predominantly with Linux and Windows CE based embedded and wireless devices, customizing O.S builds, developing device drivers, and creating internet-aware mobile applications with accessible user interfaces.
Specialties:Embedded Linux and Windows CE platform ports, device driver development, application development, C#, C, Java, GSM GPRS/UMTS, Wireless, Mesh
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