3.10.4 Booting the System

		starts and stops services depending on the new run level. Most of the services are started and stopped by scripts in the /etc/rc.d/init.d directory. Each of these scripts are written following a convention whereby a service is started when the script is invoked with an argument of "start" and stopped when invoked with an argument of "stop."

		X11/XF86Config  is found on any operating system that uses the XFree86 implementation of the X Window system. This file specifies details about the graphics hardware on the machine, allowing the X Window server to optimize for monitor refresh rates, graphics card memory, and acceleration features. Most of this information can be configured using the Xconfigurator utility program, but if you have special hardware, or need to perform unique customizations, you will likely have to learn how to edit this file.

		lilo.conf is a Linux-specific file. It defines boot loader configuration parameters such as what partitions are bootable and what kernels to boot. You can maintain several different boot configurations, including the ability to boot multiple operating systems, by modifying this file. Configuration changes do not take effect immediately, and have to be committed by executing the LILO (LInux LOader) installer, /sbin/lilo.

		4.6 Tools for Program  Development

		Beowulfs, like most other large-scale parallel computers today, are primarily devel-

		opment systems. Users tend to be programmers and applications designers. Thus, program development tools are particularly important to Beowulf users. Many of these tools come from the GNU project, initiated by Richard Stallman in the 1980s to create a completely free operating system. Linux has achieved many of the goals of the GNU project, and the GNU tools have been an integral part of Linux distributions from the earliest days. These tools are available on many other architectures as well, but we focus on their use in the Linux environment.

		Together, these interoperable utilities provide the means of implementing even the largest software projects, managing its evolution, and verifying its correctness and dynamic behavior.

		Emacs

		Emacs is a powerful editor and environment for managing program development. Emacs can be used simply as a line-oriented text editor, but it also supports a