1-3. ROM Monitor The ROM monitor is a ROM-based program that is executed on power up or reset of the switch. The ROM monitor interface can be accessed if the user presses Ctrl+Break during the boot process. If the switch fails to load an operating system or if the value of 0 is specified in the BOOT field of the configuration register, the switch enters ROM monitor mode. If the switch encounters a fatal exception from which it cannot recover, it enters ROM monitor mode. Like the COS and Cisco IOS Software interfaces, ROM monitor is a CLI. ROM monitor offers a limited number of commands associated with booting recovery of the switch. ROM monitor offers a limited help facility and basic history functions to aid users. ROM monitor allows for Xmodem asynchronous transfers to aid in the recovery of OSs.
Using the ROM Monitor Command Set Many switches have a ROM monitor command set that enables the user to interact with the switch to recover operating systems or alter boot variables during the boot process. The ROM monitor has a basic set of commands and a help facility to aid the user. The following steps outline the use of the ROM monitor facility. 1. | User interface modes
rommon1>
The rommon interface is a simple CLI that allows users to recover from fatal errors or change the boot parameters of the switch. The rommon interface offers a single mode with a limited set of commands typically associated with booting the switch and managing environment parameters.
| 2. | User interface features
- a. Entering commands
rommon> command
The rommon command line interprets input a line at a time like the COS and Cisco IOS Software CLI.
- b. Help
You can enter a question mark (?) at the beginning of a rommon> prompt to get a list of available commands for rommon.
- c. History
The rommon interface keeps a history of the previous 16 commands a user typed. To view the history, use the command history or the letter h to view the list of commands in history. When the history is listed, users should see a numeric value to the left of each command. The user can recall the commands by using the repeat value or r value, where the value is the number to the left of the command shown during a history listing.
| 3. | Viewing and changing configuration variables
- a. Viewing the configuration variables
rommon> set
The ROM monitor loads the configuration variables for the switch before giving the user access to the prompt. These variables include the location of the configuration file and the boot image that ROM monitor will look for. Use the command set with no options to view these variables.
- b. Setting the configuration variables
rommon> PARAMETER=value
To set a configuration variable, use the parameter value exactly as it shows in the set command (these are case-sensitive) followed by a value. To nullify a configuration variable, leave the value blank. For example, use the following command to clear the boot image that was specified for the switch.
rommon> BOOT=
NOTE When you're in the ROM monitor, it is important to note that any variable or parameter you set should be in all uppercase and any command that is typed should be all lowercase. If you mistype the case, the ROM monitor cannot process the command. - c. Saving the configuration variables
rommon> sync
To save the configuration variables, use the command sync. This command saves the new variables to NVRAM to be used the next time the switch is reset.
- d. Loading the new configuration variables
rommon> reset
To load the configuration variables to the ROM monitor, you must power cycle or reset the switch. To reset the switch, use the command reset.
| 4. | Booting a switch in rommon mode
- a. Viewing the images on Flash devices
rommon> dir [device:]
ROM monitor is responsible for loading the COS or Cisco IOS Software images for a device. To view an image, use the command dir followed by the device name such as dir bootflash: or dir slot0:.
- b. Booting an image from Flash
rommon> boot [device:filename]
To boot from ROM monitor, use the command boot. The command boot without any device or filename uses the BOOT field in the configuration variables. If the field is empty or the file is invalid, the user is returned to the rommon> prompt. If you specify the name of the file when using the boot command, the variable is ignored and the file is booted.
CAUTION Boot variables and filenames are case-sensitive. If you specify an invalid name or miss a character or a case setting in the name, the file will not be found and the switch will return you to the rommon mode. It might be useful to view the Flash device and highlight and copy the filename into a buffer using the edit commands in the terminal application.
| 5. | Xmodem transfers
rommon> xmodem
This command initiates an Xmodem receive for the ROM monitor. Using this command, you can boot a switch from a file located on a PC attached to the console port. Use the terminal software on your PC to start an asynchronous transfer using Xmodem and send a file from the PC hard drive to the ROM monitor Flash device. After the switch has booted from the PC, the OS will be active and a valid file can be copied into flash memory . This process can take a very long time and should be considered a last resort to recovering a lost or damaged image.
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