"It became clear to me that I needed to direct the same level of attention and effort in support of my family ... that I have invested in Red Hat for nearly a decade," Szulik said during a conference call to discuss the management change and the company's strong third-quarter financial results.

In an interview after the call, Szulik declined to elaborate on who is ill but said he had kept Red Hat officials and friends "in the loop" about the situation.

"So when the decision came, [board members] ... were certainly disappointed, but I think they respected my decision," said Szulik, 51. "My intent was always to be at Red Hat until I was 62 1/2 and get the gold watch."

In selecting Whitehurst, Szulik said he wanted a leader with an open mind and a successful record in leading a global business.

While at Delta, Whitehurst helped manage a company with 55,000 employees and $17 billion in annual revenue. He helped the airline emerge from bankruptcy protection this year but was passed over for Delta's top job and stepped down in August.

Red Hat's board considered a "huge number" of candidates, both within the software industry and in other fields, said Red Hat board member W. Steve Albrecht.

"The board was thrilled with Matthew," Albrecht said. "Matthew would have been our choice to be CEO for years to come."

One Wall Street analyst questioned the secretive search process and said that few people were aware that the company had hired a national executive search firm several months ago.

"I've never seen a management change like this," said Katherine Egbert, an analyst with Jeffries & Co. in San Francisco.

She was particularly perplexed about why the incoming CEO did not participate in the conference call. "It was odd," Egbert said. "It's hard to know what the future direction of the company will be when you can't ask the new CEO."

Whitehurst couldn't be reached for comment Thursday. In a prepared statement, Whitehurst said that he is privileged to join an outstanding company. "Red Hat has changed the way people consume technology," he said.

Whitehurst starts with a base annual salary of $700,000, Red Hat reported in a filing submitted Thursday to the Securities and Exchange Commission. He also will receive stock options and is eligible for other bonuses.

He has a bachelor's degree in computer science and is "kind of a technology fanatic, really," Albrecht said. "He's been a star wherever he's gone."

Whitehurst takes over at a time when Red Hat is proving itself a contender in the global software market. Red Hat sells Linux software, which is used to run business computers, much like Microsoft's Windows.

Szulik became Red Hat's second CEO in 1999 and helped transform the company into the world's largest distributor of Linux software and one of Microsoft's fiercest rivals.

The company, which was founded in 1993, now employs 2,200. That includes about 500 at its headquarters on N.C. State University's Centennial Campus, which will be closed next week so workers can celebrate Christmas.

The company reported Thursday that third-quarter profit surged 39 percent from a year ago, to $20.3 million. Revenue rose 28 percent to $135.4 million. The results were boosted by stronger sales in Asia and Latin America, Red Hat finance chief Charlie Peters said.

Red Hat released the CEO news and financial results after the close of regular stock market trading, when the stock rose 53 cents to $18.79. The shares climbed as high as $20.20 in after-hours trading.