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Moonlight, an open source implementation of Silverlight for Unix systems

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This is Moonlight, an open source implementation of Silverlight 1.0, 2.0, 3.0 and 4.0 for Unix systems.

See for more information.


For standard Unix configuration/installation instructions, see the INSTALL file.


At this time, Moonlight trunk (this release) requires you to use
trunk to get the required dependency (e.g. latest Mono.Cecil) and
compilers (e.g. the new 'mcs' compiler). To build mono, do like this:

git clone git:// system-mono
cd system-mono && ./ && make && sudo make install

Note that here we checkout mono to a different directory than below.

To build Moonlight, you'll also need to get the source code for mono and mono-basic repositories from a specific revision from trunk.

Do this like this: git clone git:// moon git clone git:// mono cd mono && git reset --hard f41f710 && cd .. git clone git:// mono-basic cd mono-basic && git reset --hard 4ef1fbe && cd ..

To build pixel shader support, you need to get a specific revision of the mesa repository.

Do this like this: git clone git:// cd mesa && git reset --hard 3ed0a099c && cd ..

The revision the codecs currently are at is: 15e2b1b2 (only applicable to buildbots and developers on the Moonlight team). For SVN users, the revision is: 10364

The package wnck-sharp is also required, it can be found in the gnome-desktop-sharp repository on github: Alternatively, on ubuntu/debian, the gnome-desktop-sharp2 package provides it.

Compiling Mono for Moonlight

Automatic Mode (recommended)

This is recommended if you haven't built Mono before. This is also recommended if you have clean mono and mcs checkouts that you are going to use just for Moonlight.

In this mode, you don't have to build Mono before building Moonlight, so you just do

        cd moon
        make && make install

This will configure your Mono source tree with the minimum options required to build it for Moonlight. At the moment, these are:

--with-moonlight=only --with-profile4=no --enable-minimal=aot,interpreter
--with-ikvm-native=no --with-mcs-docs=no --disable-nls --disable-mono-debugger

This Mono configuration will not be suitable for anything except Moonlight.

If you want to use SGen with Moonlight, you'll need use the following option when running


Warning: Moonlight+Sgen has not been fully tested yet, and is likely unstable. Enable this at your own risk

Build only Mode (advanced)

This is recommended if you have built Mono before and you would like Moonlight to use your existing Mono source tree. This is for advanced users only - make sure you know what you're doing.

In this mode, Moonlight will not touch your existing Mono configuration, it will build the parts it needs. Since it doesn't do a full build of mono+mcs, it's faster than a normal mono+mcs build.

Before building moon, you need to make sure your mono configuration includes the following options:


And you need to configure mono-basic like this:

--with-moonlight-yes --moonlight-sdk-path=<mono checkout>/mcs/class/lib/moonlight_raw

To build moon in this mode, configure it with the following options:


If you want to use SGen with Moonlight, you'll need to use the following option:

--with-sgen=yes --with-moon-gc=sgen

Warning: Moonlight+SGen has not been fully tested yet, and is likely unstable. Enable this at your own risk

Manual Mode (really advanced)

On this mode, moon will not configure or build mono, you have to do it yourself. To activate this mode, configure moon with --with-manual-mono=yes

Configuration options

If your mono/mcs checkout is not in the same place where you have your moon
source, you can configure moon with:


If you want to use ffmpeg with Moonlight, you need at least r20911 of ffmpeg and r30099 of libswscale:

svn co -r 20911 svn:// &amp;&amp; cd trunk/libswscale &amp;&amp; svn up -r 30099

Installing and Testing

If you want to test your newly installed Moonlight, do this:

make test-plugin

This will install it into your ~/.mozilla/plugins which will let both Firefox and Chrome pick it.


A custom profiler is available which allows you to track which objects
are being kept alive by strong GCHandles and also see the stacktrace
for every gchandle that was not freed.

This profiler is only built if you pass --with-object-tracking=yes to autogen and then subsequently be enabled as follows:

export MOON_PROFILER=gchandle

On application shutdown, right before the appdomain is freed, a GCHandle 'leak' report will be printed. This will show all the objects being retained in memory because they have a strong gchandle attached to them. If you want to see where the gchandles were allocated you just have to export the following variable. This example will print the stacktraces of all the unfreed strong gchandles for the Uri type:


If multiple strong handles are targetting the same CLR object, these will be grouped together. This makes it easy to see if 10,000 handles are targetting the same object or if its 10,000 different objects.

Runtime Options

There are a couple of runtime-parameters that affect Moonlight behavior
and turn on/off certain features. Those options are specified through
the MOONLIGHT_OVERRIDES env variable. The more interesting ones are:

  • shapecache=yes/no

    Use some extra memory for caching shapes. Increases memory usage but helps with performance (off by default). The shape cache size is 6MB max.

  • render=ftb/btf

    Use front-to-back or back-to-front rendering (ftb is the default).

  • cache=show/hide

    Show the (shape) cache usage statistics. In plugin mode they're available through the right-click popup menu (hide by default).

  • converter=yuv/ffmpeg

    Use native mmx/sse2 conversion code or ffmpeg to do the yuv -> rgb colorspace conversion (by default we use the native yuv code).

To launch Firefox with shape caching and ffmpeg converters use:

$&gt; MOONLIGHT_OVERRIDES="shapecache=yes,converter=ffmpeg" firefox

Other options include:

  • ms-codecs=yes/no

  • ffmpeg-codecs=yes/no

    Controls which sets of codecs to use, the Microsoft ones or the ffmpeg ones.

  • timesource=manual/system

    Defaults to `system'.

Also if --with-debug=yes option was provided to configure script, the MOONLIGHT_DEBUG env variable controls which debug output is printed on the console. Valid values are:

    alsa, alsa-ex, audio, audio-ex, pulse, pulse-ex, httpstreaming, 
    markers, markers-ex, mms, mediaplayer, mediaplayer-ex, pipeline, 
    pipeline-error, framereaderloop, ui, ffmpeg, codecs, dependencyobject, 
    downloader, font, layout, media, mediaelement, mediaelement-ex, 
    buffering, asf, playlist, playlist-warn, text, xaml

Moonlight currently contains two ASX parsers. The default parser is a custom parser that accounts for some of ASX's oddities such as quotes in attribute strings and non case sensitive element names (ie ). The older parser uses a true xml parser, so will not handle these oddities well, however it has been more heavily tested. To use the older expat based playlist parser set the env variable MOONLIGHT_USE_EXPAT_ASXPARSER=1.

There are two XAML parsers available in Moonlight. An unmanaged one that is used for Silverlight 1, 2 and 3 applications and a managed one that is used for silverlight 4 (and above) applications. The parser is determined at runtime after the app manifest is read. The unmanaged parser is always used to parse the app manifest. After that the correct parser is determined based on Deployment::RuntimeVersion.

You can force moonlight to use the managed parser on all sites by setting the MOON_USE_MANAGED_XAML_PARSER environment variable.

You can force moonlight to use the unmanaged parser on all sites by setting the MOON_DONT_USE_MANAGED_XAML_PARSER environment variable.


The C and C++ code that makes up the engine is dual-licensed
under the LGPL v2 license and is also available commercially
for developers interested in using Moonlight on embedded
systems or other systems where the end-user can not upgrade
the LGPL code on his own.

The C# tests in test/2.0/Microsoft.Silverlight.Testing are copyrighted by Microsoft and released by them under the open source MS-PL license.

The C# controls in class/Microsoft.SilverlightControls/ and class/WPF.Toolkit are copyrighted by Microsoft and released by them under the open source MS-PL license.

Technical Details

For implementation details and notes, see the NOTES file.

Test Suite

To run the test suite, make sure that the output from
configure indicates that the tests will be run.  Once this is
done, you can run the tests like this:

To run the Moonlight Unit Tests:

cd moon/test/2.0/moon-unit
make test

Firefox 3

The original Silverlight.js shipped by Microsoft was incompatible
with Firefox 3.  We have released a greasemonkey script 
(data/silverlight-ff3-quirks.user.js) that will patch this behaviour
for some sites.

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