If there was any doubt about whether Linux is gaining ground in enterprise data centers, this week's LinuxWorld in San Francisco should put that to rest. Consider this: Microsoft is leading a session.

That session, titled, "Managing Linux in a Mixed Environment . . . at Microsoft?" and to be led by Bill Hilf, director of Microsoft's platform technology strategy organization, is just one of several sessions and workshops that will look at how Linux fits into an overall data center architecture.

Microsoft's role at the show highlights the growing maturity of Linux, analysts say. Rather than helping IT managers decide if Linux fits in their environments, the show now is more geared to where the operating system fits and what open source products best fit on top of it. Talk also will center on beefing up security for Linux, running Linux in virtualized and grid environments, and enhancing management tools for Linux.

Show organizer IDG World Expo, a sister company of Network World, says it expects more than 11,000 people to attend. Last year, 11,400 showed up, while 8,300 people came to LinuxWorld in Boston in February. The number of exhibitors at this week's show has increased from about 180 last year to 200, organizers say.

The growing interest from vendors and customers illustrates the evolution of Linux into a mainstream operating system, analysts say. According to a Forrester Research study, Linux ranks third, behind Windows Server 2000/2003 and IBM z/OS, as an operating system that respondents consider strategic. And 26 of the 56 respondents in the May survey said they are using Linux in their data centers.

"At this point, Linux is a done deal," says Michael Goulde, an analyst at Forrester. IT managers "are going to see what they can do with Linux and open source and how to expand their use of it, rather than just looking at how they can initially adopt it."

IT managers attending the show also will get a look at how the Linux community is hoping to grow. Novell, for example, plans to announce that it will open up a version of its SuSE Linux to users and developers. The goal of the OpenSuSE project is to expand the adoption of Linux by making it more easily accessible, says Greg Mancusi-Ungaro, director of marketing for Linux and open source at Novell.