Sales of new Linux operating system licences fell 5% from 2000 to 2001, according to a survey released last week by research company IDC. Over the next five years, revenue from the sale of Linux systems is expected to grow from $80m (£52.25m) in 2001 to $280m in 2006.
The decline in Linux revenue from new licence shipments was part of a wider decline in server software during 2001, according to IDC. Additionally, the number of units of server operating systems shipped in 2001 was flat compared with the previous year.
Microsoft's Windows operating system was the only system to show revenue growth from 2000 to 2001, said Al Gillen, research director of system software at IDC.
IDC tracks its data for new licence revenue by adding up all of the copies of an operating system sold as part of a configured system or in a box.
This tracking method has not always been a good indicator of how widely Linux is deployed because the operating system can be downloaded freely from the Web.
Additionally, users can install a single copy of Linux on any number of computers, which is not possible for Windows users because of licensing restrictions. As a result, revenue collected from the sale of Linux licences does not correlate directly with how widely it is distributed, according to Gillen.
"Historically, it's been harder to track. But that's changing," Gillen said.
IDC research showed that customers are changing their habits over how they deploy Linux in the enterprise. Increasingly, Linux users will install a single copy of Linux on no more than two or three machines, Gillen said.
"It's our belief that over time the industry is going to move to a smaller number of deployments [per copy]," he added.
This shift is partly the result of business models being constructed around the open-source operating system by vendors such as Red Hat, SuSE Linux and IBM.
"The vendors are moving to a model where they are offering support for only one machine per licence," Gillen said.
Under that model, customers must purchase a licence for every server that they want supported by the vendor. Red Hat, which holds the lion's share of the Linux server software market, follows that licensing model.