Nearly half of all enterprises will be running mission-critical business applications on Linux in five years' time, according to survey of IT directors and chief information officers (CIOs).

The research, carried out by US IT analyst Saugatuck Research predicts a steep rise in adoption where the number of companies in "early or full deployment" of mission-critical applications on Linux would grow by 40% from 2007-2009, accelerating to grow by 80% between 2009 and 2011.

Although only 18% of businesses will be using Linux in business-critical roles by the end of 2007, vendors, service providers and IT execs need to take notice of the trend and reposition themselves to meet it, the researchers claimed.

"Linux 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.

"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," they said.

The research, which questioned 133 businesses worldwide, also found software as a service (SaaS) and application hosting suppliers will also get a boost from Linux, as it cuts software and maintenance costs and brings greater standardization, the researchers said.

Guptil and McNee said: "Open source, especially Linux, is being legitimised by the major enterprise vendors, and user executives are more than happy to believe them.”

They said it was easy to understand Microsoft's thawing toward the open source operating system in the face of such demand, following its strategic deal with Novell last year to support Linux given Windows’ continued growth as the other main server platform of choice.

But they added that "most large vendors remain tied to legacy cash-cow operating systems" and need to reposition themselves on Linux fast.