2.1 Key Commands Used Throughout the Chapter

2.2 Boot Process

During the boot process, the system tests the hardware, loads and runs the operating system, and configures devices. To boot the operating system, the following resources are required:

• A boot image that can be loaded after the machine is turned on or reset.

• Access to the root and /usr file systems.

There are three types of system boots:

• Hard Disk Boot

  A machine is started for normal operations with the key in the normal position. On PCI-based systems with no key locking, this is the default startup mode.

• Diskless Network Boot

  A diskless or dataless workstation is started remotely over a network. A machine is started for normal operations with the key in the normal position. One or more remote file servers provide the files and programs that diskless or dataless workstations need to boot.

• Service Boot

  A machine is started from a hard disk, network, tape, or CD-ROM with the key set in the service position. This condition is also called maintenance mode. In maintenance mode, a system administrator can perform tasks, such as installing new or updated software and running diagnostic checks.

During a hard disk boot, the boot image is found on a local disk created when the operating system was installed. During the boot process, the system configures all devices found in the machine and initializes other basic software required for the system to operate (such as the Logical Volume Manager). At the end of this process, the file systems are mounted and ready for use.

The same general requirements apply to diskless network clients. They also require a boot image and access to the operating system file tree. Diskless network clients have no local file systems and get all their information by way of remote access.

The system finds all information necessary for the boot process on its disk drive. When the system is started by turning on the power switch (a cold boot) or restarted with the reboot or shutdown commands (a warm boot), a number of events must occur before the system is ready for use. These events can be divided into the following phases:

1. Read Only Storage (ROS) Kernel Init Phase

   During this stage, problems with the motherboard are checked, and the ROS initial program load searches for the bootlist. Once the bootlist is found, the boot image is read into the memory, and system initialization starts.

2. Base Device Configuration Phase

   All devices are configured in this phase with the help of cfgmgr command.

3. System Boot Phase

   In this phase of the boot process, all the logical volumes are varied on, paging is started, and the /etc/inittab file is processed.

2.3 Power On Sequence LEDs and Audio Signals