Booting of HP-UX

The Series 700 and 800 bootstrap process involves the execution of three software components:

processor-dependent code or pdc
initial system loader or isl
HP-UX secondary system loader - hpux

What's displayed on the console?

When the HP system is reset or first powered on, the screen blanks and a HP logo is displayed on the console. At this point, the ESC key can be pressed to use the isl interactively. A prompt of BOOT_ADMIN> is offered.

If you do press ESC several low-level commands that list the hardware configuration of the machine are available. For example the SCSI bus(es) can be search to verify new SCSI devices and and the automatic boot device can be set.

If you do not press ESC, then the system searches for the automatic boot device, reads and executes hpux which loads the kernel. The next prompt that is offered is the Console login.

What's happening?

After the processor is reset, pdc, the processor-dependent code (firmware), performs a self-test and initializes the processor. It then loads and transfers control to the operating-system independent initial system loader, isl. This program loads and transfers control to the hpux utility, the HP-UX specific bootstrap loader. Which then downloads the HP-UX kernel object file from an HP-UX filesystem and transfers control to the loaded kernel image. The kernel image in HP-UX 9.X systems is the file /hp-ux, for HP-UX 10.0 and above it is /stand/vmunix.

System Initialization

Once the kernel is loaded, the /etc/init daemon is executed. It in turns starts up many other processes and uses the /etc/inittab file to loaded site specific programs and configuration scripts. This file usually has /etc/init create processes that allow users to log on to the system. It also controls autonomous processes required by any particular system.

The /etc/init daemon considers the system to be in a run level or initialization state at any given time. The processes created by init for each of these run levels is defined in the /etc/inittab file.