Shares of Red Hat Inc., a distributor of the Linux operating system, fell after the company forecast third-quarter revenue below estimates of $449 million to $452 million. Red Hat’s billings growth of 17 percent for the second quarter also disappointed investors. Total revenue rose to $445.9 million from $374.4 million a year earlier. Net income rose to $46.8 million, or 25 cents, from $40.8 million, or 21 cents, a year earlier. Red Hat also said it would buy Ireland’s mobile application service provider FeedHenry for $82 million. FeedHenry operates a Burlington office.