The installation instructions in this chapter refer to MySQL 4.0.21, which is the current production version of the software. This version number can be read as minor release number 21 of the major version 4.0 software. MySQL AB, the company responsible for creating and distributing MySQL, uses minor release numbers for updates containing security enhancements or bug fixes. Minor releases do not follow a set release schedule; when enhancements or fixes are added to the code and thoroughly tested, MySQL AB releases a new version, with a new minor version number.
It is possible that by the time you purchase this book, the minor version number will have changed, to 4.0.21 or beyond. If that is the case, you should read the list of changes at http://www.mysql.com/doc/en/News-4.0.x.html for any changes regarding the installation or configuration process, which makes up the bulk of this chapter.
Although it is unlikely that any installation instructions will change between minor version updates, you should get in the habit of always checking the changelog of software that you install and maintain. If a minor version change does occur during the time you are reading this book, but no installation changes are noted in the changelog, simply make a mental note and substitute the new version number wherever it appears in the installation instructions and accompanying figures.