User Guide

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Catalyst 6500 Series Switch Cisco IOS Software Configuration Guide—Release 12.1 E

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Chapter 3 Configuring the Switch for the First Time

Modifying the Supervisor Engine Startup Configuration

These sections describe how the startup configuration on the supervisor engine works and how to modify

the configuration register and BOOT variable:

• Understanding the Supervisor Engine Boot Configuration, page 3-20

• Configuring the Software Configuration Register, page 3-21

• Specifying the Startup System Image, page 3-24

• Understanding Flash Memory, page 3-24

• BOOTLDR Environment Variable, page 3-25

• CONFIG_FILE Environment Variable, page 3-26

• Controlling Environment Variables, page 3-26

Understanding the Supervisor Engine Boot Configuration

These next sections describe how the boot configuration works on the supervisor engine.

Understanding the Supervisor Engine Boot Process

The supervisor engine boot process involves two software images: ROM monitor and supervisor engine

software. When the switch is powered up or reset, the ROM-monitor code is executed. Depending on the

NVRAM configuration, the supervisor engine either stays in ROM-monitor mode or loads the supervisor

engine software.

Two user-configurable parameters determine how the switch boots: the configuration register and the

BOOT environment variable. The configuration register is described in the “Modifying the Boot Field

and Using the boot Command” section on page 3-22. The BOOT environment variable is described in

the “Specifying the Startup System Image” section on page 3-24.

Understanding the ROM Monitor

The ROM monitor executes upon power-up, reset, or when a fatal exception occurs. The switch enters

ROM-monitor mode if the switch does not find a valid software 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 software image from bootflash or a Flash PC card.

Note For complete syntax and usage information for the ROM monitor commands, refer to the Catalyst 6500

Series Switch Cisco IOS Command Reference publication.

You can also enter ROM-monitor mode by restarting 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, regardless of whether the

configuration-register setting has the Break key disabled.