You can argue about which specific date is Linux's official birthday. Heck, even Linus Torvalds thinks there are four different dates in 1991 that might deserve the honor of being the operating system's birthday. Be that as it may, Linux is twenty years so let's take a walk though time with Linux at some of its high, and low, points.
1991: This message, sent back on August 25th 1991 to the Minix Usenet newsgroup, is usually seen at Linux's true birth. Little did Torvalds know just how wrong he'd be when he wrote, of his new free operating system that it would “just a hobby, won't be big and professional like gnu for 386(486) AT clones.”
1992: Andrew Tannenbaum, operating system guru and creator of Minix, an educational operating system version of Unix, declares “LINUX is obsolete” and Linux's first operating system war is on. In the resulting discussion, Torvalds makes a very telling comment about his vision for Linux which remains true today, “If the GNU kernel [another attempt to create a free Unix-like operating system] had been ready last spring, I'd not have bothered to even start my project: the fact is that it wasn't and still isn't. Linux wins heavily on points of being available now."
1993: There were earlier Linux distributions, such as MCC and Yggdrasil Linux but Patrick Volkerding's Slackware was the first broadly successful Linux distro and it's still being updated and used today.
1995: Linux has its first trade conference, Linux Expo. Many more will follow Today, there are over a dozen major regional and national Linux trade shows in the U.S. alone.
1998: Microsoft starts to target Linux. Eric S. Raymond, an early Linux and open-source leader, reveals the so-called Halloween Documents, which reveals that Microsoft takes Linux seriously as an enemy and starts to formulate its anti-open-source and Linux campaigns.
1999: Corel releases the first mainstream Linux desktop. While unsuccessful, it would set the path for other Linux desktop distributions, such as Ubuntu, to try to win the hearts and minds of non-technical desktop users.
2000: In 2000, IBM announced that it would invest a billion dollars in Linux in 2001. This may have been IBM's best investment ever. While commercially a huge success, it's marketing was decideily counter-culuture as you can see from IBM's Peace, Love, and Linux image.
2003: SCO, formed from the old SCO Unix company and the Caldera Linux business, turns its back on its Linux history and sues IBM and other companies and tries to prove that Linux is a copy of Unix. The company fails, but for years its FUD bedevils Linux's commercial acceptance.
2005: Any doubt about Linux being a major business player is smashed by Linus Torvalds appearance on the cover of BusinessWeek. The tagline? Linux Inc.
2008: The New York Stock Exchange, soon to be followed by many of the other major stock exchanges of the world, switches to Linux for its core operating system. Linux isn't becoming big business. Linux is big business.