Nearly half of all enterprises will be running mission-critical business applications on Linux in five years' time. That's according to a survey of IT directors, vice-presidents and CIOs (chief information officers) carried out by Saugatuck Research, which questioned 133 businesses worldwide.

The company predicts a steep rise: only 18 percent of businesses will be using Linux in business-critical roles by the end of 2007.

"Linux OSes [operating systems] – and open source-based software in general – have reached critical marketplace mass," said the study's authors, Bruce Guptill and Bill McNee of Saugatuck Research.

They predicted that the number of companies in "early or full deployment" of mission-critical applications on Linux would grow by 40 percent from 2007-2009, and would then accelerate to grow by 80 percent from 2009-2011.

Vendors, service providers and IT execs alike all need to take notice of the trend and reposition themselves to meet it, the researchers claimed.

"Recent Linux deals and announcements by Oracle and Microsoft have only reinforced the 'open source is enterprise-grade' message that IBM, Unisys and others have been preaching for years," Guptill and McNee said.

"In short, open source, especially Linux, is being legitimised by the major enterprise vendors, and user executives are more than happy to believe them. Microsoft's thawing toward Linux is now easier to understand when faced with such data – even as Windows continues to grow as the other main server platform of choice."

'Software as a Service' and application hosting suppliers will also get a boost from Linux, as it cuts software and maintenance costs and brings greater standardisation, the researchers said.

They added though that "most large vendors remain tied to legacy cash-cow OSes" and need to reposition themselves on Linux fast.