Red Hat, which has made its fortune displacing Solaris, is now going to collaborate with Sun to advance open source Java, which Red Hat is particularly partial to given its JBoss investment.

This is the third time this year that Sun has laid down with one of its enemies. It also cut deals with Microsoft and IBM.

Red Hat will get a fully compatible open source Java Development Kit (JDK) for its Linux operating system out of the deal. All it has to do now is build it - and that includes a Java Runtime Environment (JRE) - and optimize the runtime for JBoss-on-Linux.

Red Hat's IcedTea project - which brings together Fedora, the early access version of Red Hat Linux, and JBoss.org technologies on Linux - gets pushed. It's supposed to supply free alternatives to some of the pieces of the OpenJDK project that are still proprietary.

It is unclear exactly what Sun gets out of the alliance that it can put on its bottom line.

Red Hat says that in the name of all its engineers it's signed Sun's broad contributor agreement, covering their participation in all Sun-led open source projects.

It's going to share its developers' contributions with Sun as part of the OpenJDK community. Being a contributor, Red Hat gets access to the OpenJDK code base.

It's also signed Sun's OpenJDK Community TCK license agreement, which gives it access to the precious test suites that determine whether Java SE implementations derived from the OpenJDK project comply with the Java SE 6 specification.

Red Hat says it's the first major software vendor to license the Java SE TCK (Technology Compatibility Kit).

Red Hat is already a voting member of the executive committee for SE/EE.

JBoss was previously involved with the development of Java EE.