25-2
Catalyst 6500 Series Switch Software Configuration Guide—Release 8.7
OL-8978-04
Chapter 25 Modifying the Switch Boot Configuration
Understanding How the Switch Boot Configuration Works
Understanding the Boot Process
The boot process involves two software images: ROM monitor and supervisor engine system code. When
you power up or reset the switch, the ROM-monitor code is executed. Depending on the nonvolatile
RAM (NVRAM) configuration, the switch either stays in ROM-monitor mode or loads the supervisor
engine system code.
Two user-configurable parameters determine how the switch boots: the configuration register and the
BOOT environment variable. The configuration register is described in the
“Understanding the
Configuration Register” section on page 25-2
. The BOOT environment variable is described in the
“Understanding the BOOT Environment Variable” section on page 25-3
.
Understanding the ROM Monitor
The ROM-monitor code executes upon switch power up, reset, or when a fatal exception occurs. The
system enters ROM-monitor mode if the switch does not find a valid system image, if the NVRAM
configuration is corrupted, or if the configuration register is set to enter ROM-monitor mode. From
ROM-monitor mode, you can manually load a system image from flash memory, from a network server
file, or from bootflash.
You can enter ROM-monitor mode by restarting the switch and then pressing the
Break
key during the
first 60 seconds of startup. If you are connected through a terminal server, you can escape to the Telnet
prompt and enter the
send break
command to enter ROM-monitor mode.
Note
The
Break
key is always enabled for 60 seconds after rebooting the system, regardless of whether the
configuration-register setting has the
Break
key disabled.
The following functionality is built into the ROM monitor:
•
Power-on confidence test
•
Hardware initialization
•
Boot capability (allows manual boot and autoboot)
•
Debug utility and crash analysis
•
Monitor call interface (EMT calls—the ROM monitor provides information and some functionality
to the running system images through EMT calls)
•
File system (the ROM monitor knows the simple file system and supports the newly developed file
system through the dynamic linked file system library [MONLIB])
•
Exception handling
Understanding the Configuration Register
The configuration register determines whether the switch loads an operating system image and where
the system image is stored. The configuration register boot field determines if and how the ROM monitor
loads a supervisor engine system image at startup. You can modify the boot field to force the switch to
boot a particular system image at startup instead of using the default system image.
