444 CHAPTER 31 (Web domain) OPTIMIZING YOUR SYSTEM Note
444 CHAPTER 31 OPTIMIZING YOUR SYSTEM Note Actually, the /etc/rc directories don t contain the scripts. They merely contain symbolic links to scripts, which are contained in /etc/init.d. The initialization scripts take care of the basics of the system, ensuring that vital hardware and software services are started. Initialization scripts are considered critical in order for the system to run correctly. Numbered run-level scripts are more optional. They provide services the user may or may not need, depending on how the computer will be used. For example, a numbered run-level script might start the printing service. Another numbered run-level script might start the GUI components. Some users may not need either of these, so they could be removed. Ubuntu has seven groups of numbered run-level scripts, ranging from 0 through 6. Each defines the mode in which the computer is running. For example, run level 1 is single-user mode. This means that only one user can log in, and networking is disabled (usually, many other nonessential services are not activated either). Note Run level 6 is reboot mode and exists simply to reboot the system, while run level 0 is halt mode and will shut down the system. You ll probably never come into direct contact with these run levels. Instead the programs you use to shut down or restart the system, such as the System . Log Out option within GNOME, use these run levels. On Ubuntu, run levels 2 through 5 are defined as multiuser. Technically speaking, this means that they allow more than one user to log on, but actually, they re the day-to-day running modes of the computer. Run level 2 is the default run level under Ubuntu and, just as the system initialization scripts are contained in /etc/rcS.d, run level 2 scripts are contained in /etc/rc2.d, as shown in Figure 31-1. Note In fact, Ubuntu s run levels 2 through 5 are identical. Run levels 3 through 5 might be described as spares, existing merely for further expansion possibilities. For what it s worth, it s theoretically possible to utilize run levels 7, 8, and 9, but few people do so because 2 through 5 offer more than most users need. You might think that once the run-level scripts have completed, the system is ready to be used. But that s not the case. Although you ll be able to log on when the run-level scripts have finished, the GNOME desktop has yet to start, and this, too, has its own set of initialization processes. It needs to start its own set of programs, such as notification area applets, which provide handy functions like on-screen volume control.