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Jato, an open source implementation of the JVM

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What is Jato

Jato is an implementation of the Java virtual machine. It includes a VM and a JIT compiler for the x86 machine architecture and supports the JNI API. Jato uses Boehm GC as its garbage collector and relies on GNU Classpath to provide essential Java APIs.

Compilation and Installation

Getting the Sources

Fetch the latest sources with:

git clone git://

Build Requirements

Before installing Jato ensure you have the following software installed on your system:

  • GNU Classpath CVS HEAD. You can use the git mirror to obtain the sources:


  • Eclipse Java Compiler

Fedora 15:

sudo yum install binutils-devel bison glib2-devel libffi-devel libzip-devel

Ubuntu 10.10:

sudo apt-get install ecj libffi-dev binutils-dev libzip-dev libglib2.0-dev bison


pacman -S eclipse-ecj classpath libzip libffi

Building GNU Classpath

GNU Classpath is no longer packaged with Ubuntu 10.10 and later versions so you need to build and install it yourself to run Jato. First download the sources from:

and then install the following dependencies that are required to build GNU Classpath:

sudo apt-get install openjdk-6-jdk antlr libgconf2-dev libgtk2.0-dev ecj fastjar pccts

You can then compile GNU Classpath:

./configure --disable-Werror --disable-plugin ; make

and install it to /usr/local:

sudo make install

Building the Software

Compile the VM:


Testing and Installation

You can run all Jato unit and regression tests with the command:

make check

All tests should pass.

In addition, you can download and run bunch of real-world tests with the command:

make torture

Note! This step is optional and can take a long time.

You can now install Jato with:

make install

Using Jato

Jato uses the same command line options as 'java'. You can execute a single class with:

jato <class name>

To specify classpath use:

jato -cp <jar files or directories> <class name>

You can also execute a Jar file with:

jato -jar <jar file>

Jato also supports variety of command line options for debugging and tracing purposes. See the file Documentation/options.txt for details.

Copyright and License

Copyright (C) 2005-2012 Pekka Enberg and contributors

Jato is available under the GNU General Public License (GPL) version 2 with the following clarification and special exception:

Linking this library statically or dynamically with other modules is making a
combined work based on this library. Thus, the terms and conditions of the
GNU General Public License cover the whole combination.

As a special exception, the copyright holders of this library give you
permission to link this library with independent modules to produce an
executable, regardless of the license terms of these independent modules, and
to copy and distribute the resulting executable under terms of your choice,
provided that you also meet, for each linked independent module, the terms
and conditions of the license of that module. An independent module is a
module which is not derived from or based on this library. If you modify this
library, you may extend this exception to your version of the library, but
you are not obligated to do so. If you do not wish to do so, delete this
exception statement from your version.

Thanks and Acknowledgements

I would like to thank the following people and organizations for supporting Jato development:

  • Google for including Jato in Summer of Code 2008 and 2009.

  • for providing git hosting for Jato.

  • Reaktor Innovations Oy for sponsoring initial Jato development back in 2005.

Thank you!

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