Controlling Environment Variables - Cisco WS-C3550-12G Software Configuration Manual
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Chapter 4
Assigning the Switch IP Address and Default Gateway
Controlling Environment Variables
With a normally operating switch, 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. You can release the Mode button a second or two after the LED
above port 1X goes off. Then the boot loader switch: prompt is displayed.
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
Table 4-4
Environment Variable
BAUD, ENABLE_BREAK, CONFIG_BUFSIZE,
CONFIG_FILE, MANUAL_BOOT, PS1
BOOT, BOOTHLPR, HELPER, HELPER_CONFIG_FILE
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:
•
•
You can change the settings of the environment variables by accessing the boot loader or by using IOS
commands. Under normal circumstances, it is not necessary to alter the setting of the environment
variables.
For complete syntax and usage information for the boot loader commands and environment variables,
Note
refer to the Catalyst 3550 Multilayer Switch Command Reference for this release.
78-11194-03
4-4.
Environment Variables Storage Location
Data that controls code, which does not read the 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 IOS configuration file. For example,
the name of the IOS configuration file can be stored as an environment variable.
Location (file system:filename)
flash:env_vars
flash:system_env_vars
Catalyst 3550 Multilayer Switch Software Configuration Guide
Modifying the Startup Configuration
4-15
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