You should install the JDK (the one from Oracle, not OpenJDK) first, and then the jMonkey SDK. If jMonkeyEngine SDK cannot find a valid JDK although you have it installed, then you have to specify the location manually.

1. Go to your jMonkeyEngine SDK installation directory.
   Mac users right-click jMonkeyApplication.app (which actually is a directory) in the Finder and select "Show package contents".
2. Navigate to the etc directory.
   Mac users navigate to Contents/Resources/jmonkeyplatform/etc/.
3. Open the file jmonkeyplatform.conf in a text editor.
4. Uncomment the following line and enter the path to the JDK:

   jdkhome="/path/to/jdk"

On Windows and Linux make sure you have the latest driver installed. Make sure its the one supplied by the card manufacturer and not just the OS-default one. On OSX, make sure you have the latest update for your MacOS.

On some Linux and Windows systems, the SDK might perform unstable and quit with native VM crashes or "x errors". There are a few things one can try to remedy those issues.

First of all theres the new “OpenGL” settings page in the SDK global settings where you can enable the "heavyweight" canvas, which solved some issues for some people. The settings panel can be found under Tools→Options on Windows and Linux and in the main menu (or by pressing Apple-Comma) for MacOSX.

If you cannot start the SDK, edit the file config/Preferences/com/jme3/gde/core.properties in the SDK settings folder (see above). If it doesn't exist, create the file including all folders. Add the line use_lwjgl_canvas=true. To try OpenGL1 compatibility mode (works for both canvas settings) add use_opengl_1=true.

The OS-built-in look and feel might cause issues, you can change the LAF by using the appropriate command line switch (or add it to the [app folder]/etc/jmonkeyplatform.conf file, without the "- -" prefix).

--laf javax.swing.plaf.metal.MetalLookAndFeel

Compiz on Linux might cause issues, if you set its rendering quality to "medium" these should go away. * Appearance→Set Special effects to → “Medium”

If you have problems updating the SDK, try deleting all files from jmonkeyplatform/update/download and/or [settings folder]/update/download depending on your system (see below for the settings folder location).

To completely remove and/or reinstall the SDK it is vital that the settings folder is deleted too. The location can be seen through the "about" menu and is as following for the different OS's:

• Windows: C:\Users\<username>\AppData\Roaming\.jmonkeyplatform
• Windows (alt): C:\Users\<username>\.jmonkeyplatform\
• MacOSX: /Users/<username>/Library/Application Support/jmonkeyplatform
• Ubuntu: /home/<username>/.jmonkeyplatform

To see or post the error output of the SDK in the forum, you can find the log of the application in the settings folder above too, the file is called var/log/messages.log

When an exception happens in the SDK, a small warning sign appears in the lower right corner of the main window. Double-click it to open a window that allows you to see the exception stack trace. When posting about issues in the forum, always post the stack trace along with a description of what happens and how it can be reproduced.

For a list of known issues and possible workarounds see the following link: List of known issues on googlecode