When Sun Microsystems Inc rolls out the latest overhaul of its flagship software for running computer networks on Monday, executives are likely to tout enhancements such as diagnostic tools that increase productivity by a third. But the big eyebrow raiser of Solaris 10 will be its price: free. The dramatic discount — previous versions of Solaris sold for hundreds or thousands of dollars — is a response to the growing threat that free and open-source software such as Linux poses to traditional software companies including Sun and Microsoft Corp. It’s also the centre of Sun’s strategy to regain at least some of its former shine.‘‘It’s a brilliant strategic move,’’ said Bill Raduchel, Sun’s former chief strategist. ‘‘The tech world is funny — you often give away your most valuable assets.’’Such a step has been debated within Sun for at least 10 years, said Raduchel, now chief executive of Ruckus Network Inc. It was Sun President Jonathan Schwaz, promoted this year from a position heading software strategy, who made the decision, believing the once-mighty company had little choice. Sun could easily lose its bet, dropping revenue and hastening Solaris’ slide toward irrelevance. ‘‘For it to work, Sun must execute flawlessly,’’ Meta Group analyst Nick Gall said. ‘‘That’s often a code word for ‘doubtful.’’Sun’s computer servers and software powered the Internet boom, and the Santa Clara-based company suffered particularly heavy losses when the boom went bust. Sun shares, which once traded as high as a split-adjusted $64.66 a share, have languished below $10 for more than two years. They rose 10 cents to $4.86 on Nasdaq last Friday, up from a 52-week low of $3.31 in August.Although sales have inched up in recent quarters, Sun’s recovery has been hamstrung by the popularity of Linux. Linux and Solaris share a similar architecture — both are descendants of decades-old Unix systems — and similar functions, with both powering big corporate computers and networks.Solaris is still better, many say. But Linux is free and is continually improved by the volunteer efforts of thousands of programmers who examine and tinker with the underlying code. That combination makes it attractive to corporate customers who can design or commission custom applications cheaply. Solaris’ code, highly regarded for its security, speed and stability, is still secret, but Schwartz said most of it would soon be opened up. For years, Sun sold millions of copies of Solaris, which helped the company win the biggest share of what had been a surging market for Unix computer servers. As Linux began taking hold several years ago with the combination of free software and cheap computers, Sun also began offering Solaris for use on other companies’ less expensive hardware. That didn’t stem the tide.Sun has watched Unix variants made by IBM and Hewlett-Packard decline, especially as those companies have pushed Linux on the machines they sell. — LAT-WP