A new report from Gartner is raising questions about how to accurately measure use of the Linux operating system. In a phone survey of 724 IT professionals, Gartner asked what kind of servers had been purchased last fall, and what operating system had been installed on it since, if any. The study found that Linux-based systems accounted for 8.6% of traditional server shipments in the United States during the third quarter.

But Linux advocates think those numbers are skewed. "I suspect that an awful lot of servers--and home computers--get counted as Windows machines because that is how they were sold, even if they now run Linux," wrote Robin Miller on his site Newsforge.com, a Web site focused on open-source computing.

In fact, other research firms have come up with much larger numbers when they have tried to estimate Linux installations. IDC analyst Dan Kunetsky estimates that Linux accounts for 27% of the server market, and AllNetResearch says 39%.

"Linux users are absolutely undercounted," says Garrison Hoffman, a software engineer who uses Linux on his own Web server. "They don't count any of the people who just downloaded it and installed it on their machines, like I did."

"The bottom line is that it's very difficult to get hard and fast numbers on something that's still an underground movement," says Hoffman. "What's really important isn't how many users there are, but that people are still talking about it."