3-20
Cisco 7600 Series Router Cisco IOS Software Configuration Guide—12.1E
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Chapter 3 Configuring the Cisco 7600 Series Router for the First Time
Modifying the Supervisor Engine Startup Configuration
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 router 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 router 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 router enters
ROM-monitor mode if the router 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 Cisco 7600
Series Router 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.
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