Linux usage has grown fast over the past several years as the operating system moved from perimeter Web servers to workloads much closer to the heart of the business, while gaining a broad following of contributors and commercial users. But the days of these easy advances may be past.

That's the message IDC analyst Al Gillen delivered to about 300 attendees at the Linux Foundation Collaboration Summit in Austin, Texas, last week. Linux has made many gains at the expense of legacy Unix systems. However, server virtualization combined with head-to-head competition with revitalized competitors, both Unix and Microsoft Windows Server, will likely slow things down.

Meanwhile, other problems plague Linux, including issues with driver development stemming from an unwillingness of some peripheral device manufacturers to reveal where they've deviated from specifications, said Chris Wright, a Linux kernel developer and conference attendee. Moreover, many Linux users fail to report bugs, whether out of laziness or ignorance of the process. Bug reporting is a priority of kernel developers, who depend on the larger community to help detect and correct problems.

BILLIONS OF REASONS
Nevertheless, Gillen stressed that Linux is still a force to be reckoned with. It's more and more frequently acting as a database server, especially for Oracle, he said, while assuming heavier business application workloads, including ERP, CRM, and financial applications. "By 2011, the logistics and manufacturing applications alone will be a $1.2 billion market on Linux; human capital management will be a $2 billion market," Gillen predicted.

He cited figures showing that for every supported copy of Linux running in the enterprise, there's another copy running unsupported, and thus unpaid for. The Linux ecosystem is twice as large as it appears in most revenue data because so many companies have support skills in-house or are willing to rely on advice from forums.

Part of the purpose of the summit, now in its second year, is to let business users interact with Linux kernel developers. One IT pro glad to have the opportunity was Ed Reaves, a Nortel technology platform manager from Research Triangle Park, N.C.

End users and server admins are happy with Linux's current five-nines uptime, Reaves said, but Nortel and other telecom companies would like to move Linux reliability to six nines, or one outage of about 30 seconds a year. In response, Nortel's Linux developers produced a block of code that restarts Linux in 20 seconds in the event of a glitch; however, that patch doesn't appear to be moving into the kernel, to the dismay of Nortel executives.

"How do you get a kernel patch released into the mainline?" Reaves asked, referring to the development process that steers additions to the kernel past reviewers and into a hierarchical code tree maintained by Linus Torvalds. That led to a discussion of the difficulties inherent in the code review process that must happen before a proposed patch makes its way into the kernel.

"The limiting resource is not development of code but review of code," said Jonathan Corbet, a kernel developer. The Nortel patch, it turns out, is a sizable block of code requiring reviewers with knowledge of a particular part of the kernel.

The first day of the summit ended with energetic debate among mobile device makers who use Linux over who was following standards and how mobile Linux devices should be developed.

"There was an amazing amount of contention. I love to see the passion," said Linux user Stefano De Panfilis, laboratory director at Engineering Informatica in Rome. And passion, of course, has long been Linux's trump card.