Ubuntu

To join Collaborate Classic sessions in Ubuntu, you’ll need to install OpenJDK 7 and some extra packages

Open up the Ubuntu Software Centre. Search for, and install the following:

• OpenJDK Java 7 Runtime
• IcedTea Java Web Start
• IcedTea Java PlugIn

If you have other java runtimes installed, you will need to set OpenJDK as the default (see step two at that link).