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Catalyst 2950 and Catalyst 2955 Switch Software Configuration Guide
OL-10101-02
Chapter 4 Assigning the Switch IP Address and Default Gateway
Modifying the Startup Configuration
Controlling Environment Variables
You enter the boot loader mode only through a switch console connection configured for 9600 bps.
Unplug the switch power cord, and press the switch Mode button while reconnecting the power cord.
Release the Mode button a second or two after the LED above port 1X turns off. Then the boot loader
switch: prompt appears.
The switch boot loader software provides support for nonvolatile environment variables, which can be
used to control how the boot loader, or any other software running on the system, behaves. Boot loader
environment variables are similar to environment variables that can be set on UNIX or DOS systems.
Environment variables that have values are stored in the flash file system in various files as shown in
Table 4-4.
Each line in these files contains an environment variable name and an equal sign followed by the value
of the variable. A variable has no value if it is not listed in this file; it has a value if it is listed in the file
even if the value is a null string. A variable that is set to a null string (for example, “ ”) is a variable with
a value. Many environment variables are predefined and have default values.
Environment variables store two kinds of data:
• Data that controls code, which does not read the Cisco IOS configuration file. For example, the name
of a boot loader helper file, which extends or patches the functionality of the boot loader can be
stored as an environment variable.
• Data that controls code, which is responsible for reading the Cisco IOS configuration file. For
example, the name of the Cisco IOS configuration file can be stored as an environment variable.
You can change the settings of the environment variables by accessing the boot loader or by using Cisco
IOS commands. It is not necessary to alter the setting of the environment variables.
Note For complete syntax and usage information for the boot loader commands and environment variables,
see the command reference for this release.
Ta b l e 4-4 Environment Variables Storage Location
Environment Variable Location (file system:filename)
BAUD, ENABLE_BREAK, CONFIG_BUFSIZE,
CONFIG_FILE, MANUAL_BOOT, PS1
flash:env_vars
BOOT, BOOTHLPR, HELPER, HELPER_CONFIG_FILE flash:system_env_vars