Installation guide

Starting Up and Shutting Down the

System

This chapter describes procedures for starting up and shutting down the

operating system and includes a discussion of:

• Boot operation

• Different startup states and the corresponding boot preparation

• Run levels

• Resolving problems that occur during the boot operation

Refer to the Installation Guide for information about installing the system

and performing the initial boot operation. The information in this chapter

assumes that you are booting or rebooting an installed operating system.

Shutting down the system is a routine task that you should perform

periodically. Usually, you can shut down the system easily and with

minimal disruption to system users. Occasionally, you must shut down the

system rapidly, causing a moderate degree of disruption to users. Under

some circumstances (that are out of your control), the system shuts itself

down suddenly, causing substantial disruption to users.

3.1 Understanding the Boot Operation

When you boot the operating system, you initiate a set of tasks that the

system must perform to operate successfully. The system is vulnerable

during startup since it is loading the kernel into memory and initializing

routines that it depends on for operation. Consequently, you should

understand what is happening during the system boot, and be prepared to

respond if problems occur.

Although certain boot operations are hardware dependent, some features

typically apply to all systems. For example:

• The system always boots either automatically or manually.

In an automatic boot, the system controls the entire operation. When

you boot the system to multiuser mode, or shut down the system with

the reboot ﬂag, or when the system panics and recovers, you are relying

Starting Up and Shutting Down the System 3–1