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Troubleshooting Overview 9-9
9
9.4.4 POST and OpenBoot
POST and OpenBoot work together in the system to test and manage system
hardware.
POST resides in the OpenBoot PROM on each CPU/Memory board, I/O board,
and Disk board. When the system is turned on, or if a system reset is issued,
POST detects and tests buses, power supplies, boards, CPUs, SIMMs, and
many board functions. POST controls the status LEDs on the system front
panel and all boards. POST displays diagnostic and error messages on a
console terminal, if available.
Only POST can configure the system hardware, and only POST can enable hot-
pluggable boards. If a new unit (board or modular power supply) is added to
the card cage after the system has booted, the new unit will not work until the
system is rebooted, at which time POST reconfigures the system, using the
units that are found in the system at that time.
OpenBoot provides basic environmental monitoring, including detection of
overheating conditions and out-of-tolerance voltages. For example, if an
overheated board is found, OpenBoot issues a warning message. If the
temperature passes the danger level, POST will put the overheated board(s) in
low power mode.
OpenBoot also provides a set of commands and diagnostics at the ok prompt.
For example, you can use OpenBoot to set NVRAM variables that reserve a
board or a set of SIMMs for hot-sparing.
The following OpenBoot commands may be useful for diagnosing problems:
9.4.4.1 show-devs Command
Use the show-devs command to list the devices that are included in the
system configuration.
9.4.4.2 printenv Command
Use the printenv command to display the system configuration variables
stored in the system NVRAM. The display includes the current values for these
variables, as well as the default values.