We like Linux. Of all the Unix and Unix-like systems we’ve used, many now forgotten,* Linux is our favorite. It’s an excellent server platform, a good desktop, and the center of much innovation in the current computing world. Linux probably has the broadest reach of any operating system, from tiny systems the size of phone jacks, to cell phones, to supercomputer clusters bigger than your high school. It has infiltrated the fields of telecommunications, embedded systems, satellites, medical equipment, military systems, computer graphics, and—last but not least—desktop computing. In a relatively short time, Linux progressed from a Finnish hacker’s hobby to a toptier enterprise-level system backed by high rollers such as IBM and Oracle. The user base has grown from about 30,000 people in 1995 to hundreds of millions today. During the Internet boom of the 1990s, many Unix administrators were surprised to find that Linux on PC hardware could outperform more expensive Unix workstations and servers. Many Windows and Novell administrators saw that Linux could handle DNS, email, and file services more reliably and with less support personnel than their current platforms. The growth of the Internet, and especially the Web, fueled a rapid expansion in the use of Linux servers and the need for people to manage them. This book is for Linux system administrators. However, you may be a grizzled Unix veteran, a brave MCSE, or a stoic mainframer. You’re exploring new territory and need a map and compass. Some of the ground will be familiar, but some will be terra incognita. This book covers many topics that have only recently joined the mainstream, for instance load-balanced clusters and virtualization. The success of the Internet and open source software is changing business. Google, Amazon, eBay, and others have built huge server farms with commodity hardware and relatively few administrators compared to traditional mainframe and PC installations.