Java and Linux should have been a natural: on the one hand we have a language that can run on any OS; on the other, an OS that can be custom tailored to a vast range of computing needs.

Should have been, would have been, could have been. Maybe some day even will be. Today, however, the failure of Java to evoke more than relatively mild interest in the Linux community is the complex result of both philosophical and technical differences between the Java and Linux communities and technologies.

The philosophical differences revolve around the terms open source and free. Java is neither, all claims to the contrary. Linux, at least in theory, is both.

Further, there's a none-to-subtle bifurcation in the Linux community that Java advocates must understand. A significant segment of the Linux community stresses the word free. The other half lives by different economic rules, but nonetheless is devoted to open source. At the risk of making a sweeping generalization, the bastion of free software advocates is the students and researchers of the world's universities. They're a critical piece of the Linux formula, providing a massive amount of free brainpower that's helping develop Linux and the body of software that surrounds the OS.

The commercial strength of open source and Linux lies with those who use Linux to build products for market, folks whose love of Linux is in their ability to custom-tailor every aspect of the OS to their own particular needs. These are folks who will and do pay for Linux if they have to, as long as it's open source. They're also a critical piece of the Linux formula without which Linux would be merely the stuff of computer science classes and esoteric research projects.

For the first group, the free software advocates, Java will never be popular until the day Sun releases the source code under an acceptable license, either the well-known GNU General Public License (GPL) or one very much like it. Now let's remember what GNU stands for: "GNU's Not UNIX." Then let's remember that Java comes from Sun, and Sun's forte is definitely UNIX. Let's not talk about Sun's concept of a "community" license. It doesn't cut bait with the open source community.

The dislike of Microsoft in the Linux community is, of course, legion. But spend enough time talking with Linux folks, especially the free software part of the community, and it soon becomes clear that Sun isn't popular either.

The result is that for a significant chunk of the Linux community Java is simply not an alternative. It's the wrong religion. If Sun ever does make good on its occasional hints that maybe it will GPL Java, and that's a very big if, it won't be the Linux folks changing religions.

That leaves the rest of the Linux community, the guys that don't got religion. Folks at commercial Linux companies say a large segment of their community would love to use Java but it just doesn't fit.

Where Java's missed the boat so far is in its acceptability to the embedded community. Most of the talk about Linux on the desktop is just that - talk. Linux's real strength lies in embedded widgetry of all ilks. In that market Linux is starting to make a major dent in what had been a purely proprietary OS market.

Embedded Linux developers sneer at the footprint of a Java Virtual Machine. There's simply too much code to stuff into the smaller embedded applications, they say. There's no good implementation of Java for real time, the criticism continues. Real time - be it deterministic hard real time, soft real time, "near" real time - is the holy grail of the embedded community.

Another worry of the Linux community, indeed of the embedded community in general, is the stability of the Java code base. Unlike desktop computers with a few years' life span, it's not unusual to find embedded devices that are expected to run unattended for 10-15 years. Java is simply changing too fast right now to provide the comfort level that embedded developers need.

To be sure, at the higher end of embedded, particularly anything hooked to the Internet, Java support is de rigueur. But it's grudging and doesn't go far beyond stuffing a JVM into widgetry such as Internet terminals. Linux-based Web servers, ironically, may dish up more Java than any other type of server in the world. But they don't have to run Java - that's done on the client. And Windows owns the clients.

The fact is that the Linux world starts with good old C. The more adventurous Linux developers are discovering C++ with all its warts and pimples. Many say they'd love to try Java, but they think Java tools and compilers need more time to mature. Some are even saying that time may be running out. The really avant garde are already poring over Microsoft's C#, which Microsoft fancies is a sort of super-Java blending the best of C++ and Java, and keeping their fingers crossed that it won't be a Windows-only creature.