One of the challenges of administering Linux is that Linux isn't a single OS. Instead, it's a collection of OSs, all built around the same kernel. Each of these variant OSs is known as a distribution. A distribution consists of a Linux kernel; a distribution-specific installation program; a wide assortment of support tools, user programs, and so on; and a set of default startup and configuration scripts. Different distributions frequently use different versions of the Linux kernel and of support programs. Indeed, they sometimes ship with different programs entirely to fill particular roles, such as sendmail, Exim, or Postfix for a mail server. For these reasons, Linux distributions can vary substantially in overall feel and in many administrative details.
Many books on Linux fail to address the variability among Linux distributions. They intentionally focus on just one distribution, or provide coverage of others in a cursory manner. One of the goals of this book, though, is to cover several of the most popular Linux distributions explicitly. Specifically, I cover Caldera OpenLinux 3.1, Debian GNU/Linux 2.2, Mandrake 8.1, Red Hat 7.2, Slackware 7.0, SuSE 7.3, and TurboLinux 7.0. To be sure, I can't cover every detail for each of these OSs, but I point out where they differ in important ways, such as where each places network startup scripts and what FTP servers each includes. Some chapters ”notably those on server startup tools, LPD print servers, SMTP mail servers, and FTP servers ”cover multiple servers in order to be applicable to the default configurations for each of these seven major Linux distributions.