When more than one operating system is present on the system's mass storage devices, both the location of the operating systems and the type of media on which they are stored determine which operating system is loaded. The primary boot path in Stable Storage determines the default boot path. Stable Storage is the memory in Series 800 computers reserved for maintaining critical configuration parameters used during system boot. For example, the primary and alternate boot paths, console path, and autoboot settings are stored in Stable Storage.
The Boot ROM contains general-purpose software developed to support both present and future Hewlett-Packard operating systems. This section describes how the ROM boots the HP- UX operating system.
When you turn the computer on, the Boot ROM goes through the following sequence:
1. Performs System Processing Unit (SPU) self-test.
2. Reads the console path from Stable Storage, tests it, and assigns a display terminal for use as a system console.
3. Reads the boot device path from Stable Storage, searches for the paths on Model 825, 835, and 845 computers using a capability called "autosearch", or lets you enter the path from the system console and tests the boot device path.
4. Loads the Initial System Loader (ISL) into memory.
The media on which your bootable system resides has a boot area and a root partition. The boot area contains the bootstrap program and other files needed for bringing up the system. See isl(lM) in the HP-UX Reference for more information on these files. The disk section where the boot area resides is /dev/dsk/cOdOs6. The root partition contains a file, called hp-ux, which is the operating system. The typical disk section for the root partition on a system using an HP-IB interface card is /dev/dsk/cOdOsO.
2-16 System Startup
System Boot Overview At powerup or reset:
1. The processor self test is executed from PDC (Processor Dependent Code).
2. The PDC locates the system console and tests the console path using 1/0-Dependent Code. The boot and console paths are kept in Stable Storage. Stable Storage memory is static RAM.
3. The PDC checks to see if the autoboot flag is set. If not, the system asks for a boot path. If set, the system prompts the console with the following message:
Booting from default lpath
To interrupt, press any key within 10 seconds
If you press a key the system asks if booting will be done from the primary autoboot path, the secondary autoboot path, or ask for an alternate path.
4. The PDC loads the ISL (Initial System Load). The ISL loads an operating system (HP- UX in this case).
Once the operating system is loaded, the Boot ROM passes program control to the operating system. The operating system then controls the system until you re- boot the system. The section in this chapter called "HP- UX Startup Sequence" describes what HP- UX does between the time it takes control and the time you see the login: prompt.
Boot ROM Search Sequence (Series 800)
The Boot ROM initializes the primary boot path, loads ISL, and allows you to select either the manual or autoboot mode. On Model 825, 835, and 845 computers, an additional mode called autosearch is available when autoboot is enabled. In manual mode, you can select the boot device from all the available peripheral devices. In autoboot mode, the Boot ROM automatically boots the operating system from the primary boot path defined in Stable Storage.
Autoboot
You should use autoboot except for first-time installation and operating system reconfiguration. The ISL autoboot on command enables autoboot. No reboot
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or automatic reboot on panic is possible. Panic is a condition when the system becomes inoperative due to an abnormal condition detected by the kernel.
Before using autoboot, make sure the boot device is fully powered up and ready for operation before you turn on your computer. Autoboot is selected if you let the 10 second override period expire.
Manual Boot
Manual boot can be entered by pressing any key during the 10-second override period in the beginning of the autoboot sequence. \Vhen manual mode is activated, the Boot ROM prompts for the path to be used. The primary boot path is not altered or disabled.
If you do not want to boot automatically from the primary boot path during the boot process, disable the autoboot flag in Stable Storage. You can do this using the 1SL autoboot off command. However, this is not normally done because the autoboot feature makes your system administration tasks more efficient. Disabling autoboot requires your intervention each time the system is rebooted. To re-enable autoboot, use the 1SL autoboot on command.
2·18 System Startup
Autosearch
Many Series 800 computers have a feature called autosearch. If the system cannot locate the console using the console path from Stable Storage, it
searches for a console device. Then, if the system cannot locate the boot device using the primary or alternate boot paths and the autosearch flag is set, the system continues to search for a boot device.
The autosearch flag is much like the autoboot flag. It is in Stable Storage and can be enabled or disabled. Use the 1S1 autosearch on command to enable autosearch and the 1S1 autosearch off command to disable the feature.
When autosearch is invoked (if the two paths specified in Stable Storage fail), the following messages appear on the console:
Autosearch for boot device enabled.
To override, press any key within 10 seconds.
If you press a key, the system responds:
Do you want to continue an interactive search? (Y or N)?>
If you answer "no," autosearch halts at that point and proceeds to manual boot. If you answer "yes," the system searches for a boot path, states it, and asks you if you want to boot from it. If you respond "yes," the system uses that path. Otherwise, it presents other logical paths until you respond positively or until it finds no other paths. It then proceeds to manual boot.
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