But so far it has only been successful in the low-end, single-application sector of the market. Although unit sales have been good, revenues are, as yet, insignificant.
The high-end server market remains the province of IBM mainframes and large-scale Unix suppliers, led by Compaq, Hewlett-Packard, Sun and IBM. The challenge for Linux companies is to move into this market, where there is serious money to be made. The release of the new Linux kernel, version 2.4, looks set to help them achieve this goal.
Linux 2.4 is, on paper, much more capable of supporting enterprise-class workloads than its predecessor, 2.2. It supports a theoretical maximum of 32 processors, up from eight, and up to 64Gbytes of main memory, compared to the previous 4Gbytes. Now the only limit to the number of concurrent processes that can be supported is the amount of memory available. File systems can be up to 2Tbytes in size.
Two of the new architectures supported, 64-bit Intel and IBM mainframe, underline the intent of the Linux community that 2.4-based systems should run on the most powerful enterprise servers.
To make effective use of these much larger machine resources, effort has been put into enhancing performance. Memory management has been improved, as has task scheduling. Networking has been enhanced through a complete rewrite of this part of the code.
These features permit a greater number of users and larger, more complex applications to be supported. According to SuSE UK managing director Rudiger Berlich, the 2.4 kernel opens up new application areas. "The new functionality has a lot of relevance for businesses. It is much easier to use it as a database server because the I/O subsystem has been much improved, and it has much greater scalability," he said.
For IBM, the new kernel will improve its ability to exploit Linux on the mainframe. Provision is already made for users to run Linux on System 390 in four ways: natively; in a logical partition; as a guest operating system under Virtual Machine (VM); and using the Virtual Image Facility (VIF).
VIF is a new capability that is essentially a reduced-functionality, easier-to-use version of VM that runs in a partition and allows multiple versions of Linux to be set up. It has been designed to provide a straightforward way of consolidating multiple standalone Linux servers onto a single machine - a technique IBM calls horizontal scaling.
According to Cliff Laking, IBM consulting IT specialist, "When you put the horizontal scalability and the increased vertical scalability together, what you end up with is something that is mighty powerful."
It is possible to run a 2.4-based system on a 9672 mainframe or a z900 eServer, although in the latter case only in 31-bit mode. To run it in 64-bit mode you need patches - chunks of enabling code - which IBM expects to have ready before the end of the second quarter.
Laking is adamant that Linux is not a replacement for any of IBM's existing mainframe operating systems. "OS/390, z/OS, VM, VSE, we see Linux existing in a co-operative kind of way. Its strength is the ability to develop applications quickly... Ultimately it is a question of the quality of service you need for the application. It is horses for courses."
This is a tacit admission that the "quality of service" offered by Linux is not as good as that offered by established mainframe operating systems.
Any new server operating system takes time to make an impact, because most IT departments prefer to wait until it is proven before entrusting production workloads to it. With Linux this is even more so, because the new kernel is not the whole operating system: Linux distributors have to integrate it within their own products.
In addition, Linux is open source, and this type of software has yet to win widespread acceptance for mission-critical applications.
The full name of the kernel release is 2.4.0. As with any "point zero" software release, people will be reluctant to adopt it until they are satisfied that it is robust enough.
It is not just a question of ensuring that all the bugs have been removed. There is also the question of how much the scalability has actually been improved.
Linux 2.2 theoretically scaled to eight processors, but in practice four was widely accepted as the upper limit.
So, although 2.4 theoretically scales to 32 processors, people are unlikely to run it on any system with more than 16. Similar considerations apply to the other scalability improvements. Everybody agrees it will scale better, but nobody can say how much better until production versions containing the 2.4 kernel have been exhaustively benchmarked.
Richard Perkins, UK manager of SCO's Server Division, is setting his sights fairly low. "I'm sure that with the 2.4 kernel Linux will not run a 500-user database," he said.
"We have to be realistic in our expectations. I know the open source movement gets things developed quickly, but you can't catch up 30 years of development in such a short space of time. It has taken 30 years for Unix, and seven to eight years for NT."
What the Linux 2.4 kernel offers to the PC user
Desktop users can expect to benefit as much as IT departments from the improved performance of the Linux 2.4 kernel. But for many enthusiasts the biggest benefit will be the increased range of device drivers supported, particularly for devices that use the Universal Serial Bus (USB).
Linux 2.2 had limited support for USB peripherals, essentially just keyboards, mice and a few printers. So desktop users who wanted to use other devices, such as scanners, disc drives, network cards and modems, had to obtain the necessary driver from the product suppliers, install it themselves, and then resolve any conflict that arose with any other installed driver.
This was a time-consuming and often infuriating process, and it certainly held back acceptance of Linux on PCs.
Now there are many more drivers supported from within the kernel. There is also improved support for digital cameras. Add to this an increase in plug-and-play capability - where you just plug a new device into the back of your PC and it is up and running without any further action needed - and Linux is now a much more attractive proposition as an alternative to Windows.
Linux is also likely to start featuring more strongly on personal digital assistants. The 2.4 kernel offers, for the first time, support for the SuperH architecture, which is used to build handheld devices that run the Windows CE operating system.