What is it?
Linux is a version of Unix that runs on a variety of hardware platforms and is widely used for servers. As open source software, it is free, although it is distributed for a fee, along with technical support, by suppliers such as Red Hat and SuSE.
Linux has suffered a couple of setbacks in its previously unstoppable rise. One is the lawsuit by SCO Group against other Linux suppliers - and threat of suing users - claiming that some versions contain proprietary code. Although Novell and other suppliers have promised to bear litigation costs, smaller distributors and the free software community can make no such undertakings.
The other setback was the fallout from the City of Munich's decision to replace Microsoft with Linux. This was first hailed as a big win, but was subsequently stalled by patent and cost-of-ownership concerns.
Nevertheless, Linux server sales in the first quarter of the year grew 56.9%.
Microsoft had warned that Linux might break up into incompatible implementations. Now the Free Standards Group has released a specification to keep Linux from fragmenting, which is supported by Dell, Hewlett-Packard, Intel, AMD, Novell, IBM and Red Hat.
Where did it originate?
In 1991, University of Helsinki student Linus Torvalds asked for help with a free operating system he described as "just a hobby; won't be big and professional". Gartner predicts that by 2008 Linux will have 23% of the server market.
What is it for?
Linux is actually just the kernel. The tools, drivers, applications and graphical user interfaces that make up the rest of Linux come mostly from the Free Software Foundation's GNU project. Hence GNU/Linux.
Unlike Windows, designed with a file-and-print server world in mind, Linux (like Unix) was network-oriented from the outset - one reason why GUIs and other processor and bandwidth-heavy features have tended to be late-arriving options.
What makes it special?
Low cost of ownership is key, although as organisations meet the overheads of migration, Linux is proving far from free. But there is a huge armoury of freely-downloadable utilities and development tools, a large and supportive community to push development and help with problems, and a growing range of professional service organisations.
How difficult is it to master?
Like Unix, Linux administration is easier than proprietary operating systems, but only once you have mastered the basics. IBM's Developerworks Linux site warns that using Linux for a very advanced application can get "pretty hairy".
Where is it used?
Linux has moved from the "edge" - e-mail and web applications - to the centre of business computing. Gartner predicts that by 2005, 40% of large financial services organisations will have deployed Linux. Of 360 large European enterprises, Gartner found more than half already use Linux as a web server, 30% as an application server and 25% for databases.
What systems does it run on?
Supercomputers, mainframes, mid-range systems, PCs, personal digital assistants, wristwatches and cash registers. Now being shipped pre-installed on laptops.
What is coming up?
The "browser wars" seemed conclusively won by Internet Explorer, but in recent months, Netscape/Mozilla/Firefox have clawed back more than 5% of the market.
Rates of pay
Almost any IT role in almost any sector can now involve Linux, so it is difficult to give a meaningful salary range. A 2003 survey by McKendrick &Associates reported that Unix/Linux skills were better paid than Windows. Offering Linux should improve your employability.
Linux training is available from suppliers such as IBM and Red Hat. Alternatively, try free tutorials from Linux.org, IBM's Developerworks, O'Reilly's Linuxdevcenter.com and hundreds of others.
This was first published in October 2004