While many enterprises are still wary of using the open source platform, citing the limited number of applications that run on the system, it is becoming entrenched among application service providers (ASPs) that use the Intel hardware platform.
The operating system has always been prominent among ASPs, given its strength in running edge-of-the-network applications such as Apache Web server.
According to analyst group IDC, the Linux installed base, now at 3.5 million units and will climb to 8.6 million server units by 2005.
By contrast, Unix will drop from 2.61 million units to 2.53 million units. But Windows will still lead the way with an installed base of 8.6 million units in 2002 and 13.84 million server units in 2005.
Rival analyst Gartner Dataquest said Linux revenues in the first quarter of 2002 grew by 54%, while other operating systems faced double-digit declines compared with the same period in 2001.
Year-on-year shipments for Linux grew by nearly 48% while other platforms declined or had slight growth, according to Dataquest.
ASP Salesforce.com, which provides online CRM applications, is firmly in the Linux camp. "All of our Web and application servers are Linux," said Dave Mollenhoff, chief technology officer of Salesforce.com.
Mollenhoff said that Linux offers advantages in reliability, price, and CPU power. The company uses Red Hat Linux on approximately 20 two-processor Dell Computer systems to run Apache Web server and Resin application server.
"We think it's great because it's much more reliable than any alternative operating systems at that level," including Windows, Mollenhoff said.
Eric Packman, chief technology officer and cofounder of Coradient, a provider of monitoring and management services for ASPs, agreed that Linux is popular among service providers.
"The vast majority [of ASPs] I know use Linux up front [as a Web server] because [it's] really cheap and really fast," he said. "So any time you want to handle a larger load of customers and more people that turn up [at a Web site], you can turn on a bunch of Linux machines."
Oracle uses Linux in its application outsourcing, and sees Linux becoming a deployment platform for applications.
"We're starting to see (a) real shift" to Linux adoption, said Doug Kennedy, vice-president of the platform alliances, systems platform division at Oracle. "The combination of Red Hat and the Intel servers, we believe, is the best economic model for us to run our [outsourcing] business right now."
Oracle is deploying its E-Business Suite of applications on Red Hat Advanced Server, Kennedy said. The Red Hat Linux variant breaks down previous barriers to functionality, while featuring enterprise-class support, he said.
Oracle also operates a facility that allows its sales staff to access a pool of 370 Dell servers running Linux when doing remote product demos for customers.
"It's a pretty significant move when you're betting your business on running well in front of a live audience," Kennedy said.
But not all service providers running Linux are hooked. Digital Impact expects to drop the operating system, at least temporarily. The company, which provides outsourced online direct-mail marketing for clients, plans to consolidate to two operating systems, most likely Solaris and Windows NT, said Gerardo Capiel, chief technology officer and co-founder of the ASP.
"Even though the licence costs are a lot less, we have to have people to support three different operating systems," Capiel said. Linux may be cut, he added, "because not all our applications run on that OS".
"When you're relying on products such as Oracle or Documention, you're just not going to find a lot of support. Either they just don't have a flavour for that OS or they just don't support it [very well]," Capiel said.
Capiel said that Apache Web server tends to run best on Linux but there were problems with Java on Linux. "We're a Java shop and the JVMs (Java Virtual Machines) on Linux have never been exactly the fastest," Capiel said.
Salesforce.com opts to run its Oracle database on Sun Solaris rather than Linux. "Solaris is Oracle's primary build platform, so we get fixes faster," Mollenhoff said.
Mollenhoff also cited a scalability issue. Salesforce.com can run its database on a 20-processor Sun Enterprise 10000 system, which is not possible with Linux on Intel.
Microsoft, not surprisingly, remains sceptical about Linux's continued success. Peter Houston, senior director of the Windows servers product management group, said Linux would continue to make some inroads as a commodity platform for Web servers or network infrastructure servers and also for one-of-a-kind systems such as those used in the oil and gas industry.
However, he said Linux suffered from poor co-ordination of development effort of the core operating system and file system.
Linux is capturing a lot of basic infrastructure workload historically deployed on Unix, such as print file and Web servers, said analyst Al Gillen, research director of systems software at IDC. But Linux application software "is in relatively short supply", Gillen said.