Two and a half years after its chief executive donned the suit of Linux's penguin mascot on an exhibition stage, Sun seems to have fallen out of love with the open-source operating system.

Last week the firm detailed plans to focus attention largely on its own Solaris operating system for server lines, on a range of hardware platforms including Sparc, AMD Opteron, x86 and, potentially, Itanium and Power chips.

Although Sun continues to offer Red Hat and Suse Linux on systems, the firm said it is convinced Solaris can undercut Linux on price and outpace it on performance. Linux's virtues as the lowest-cost operating system that can be distributed by multiple vendors have gone, it argued.

"Because the cost of switching (operating systems) is so high, what has happened in the enterprise is that Linux has become about one company," argued Sun president Jonathan Schwartz.

"The market has tipped to Red Hat and we plan on competing very aggressively. We are agnostic with respect to what the customer wants to buy, but we are not when it comes to what we want to sell."

Confirmation of the renewed focus on Solaris might be welcomed by Sun loyalists but could hurt the firm's prospects among companies seeking to deploy Linux with the backing of an enterprise-hardened organisation. This could apply especially in Europe where Novell's Suse subsidiary comp- etes more effectively against Red Hat than is the case in North America.

Recent IT Week research shows Linux is used in 56 percent of UK firms with over 1,000 staff, one percent more than Solaris.

Clive Longbottom of analyst firm Quocirca said Sun had a dilemma. "Sun's problem is that it is a one-horse show," he said. "To bring in Linux and give it the same focus as IBM and HP have is saying that Solaris does not have a long-term future."

He said Sun was also keen to support its relatively expensive UltraSparc servers, as sales were slower than expected.

A move to make Solaris available on a wider range of hardware could be more welcome, however. As virtualisation software helps firms partition servers, the ability to run more than one operating system could become increasingly attractive.

Sun last week announced that it had made a return to profitability and showed its first year of revenue growth since 2001, after making a $795m profit on revenues of $3.1bn. However, analysts were quick to note that the profit would have been a loss were it not for Microsoft paying close to $2bn to end long-running legal conflicts.