Chapter 4. Boot Loaders

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4.5.1. Menu Interface

If GRUB was automatically configured by the Red Hat Linux installation program, this is the inter 

face shown by default. A menu of operating systems or kernels preconfigured with their own boot

commands are displayed as a list, ordered by name. Use the arrow keys to select an option other than

the default selection and press the [Enter] key to boot it. Alternatively, a timeout period is set, so that

GRUB will start loading the default option.

From the menu interface, press the [e] key to enter the entry editor interface or the [c] key to load a

command line interface.

See Section 4.7 for more information on configuring this interface.

4.5.2. Menu Entry Editor Interface

To access the menu entry editor, press the [e] key from the boot loader menu. The GRUB commands

for that entry are displayed here, and users may alter these command lines before booting the operating

system by adding a command line ([o] inserts the new line after the current line and [O] before it),

editing one ([e]), or deleting one ([d]).

After all changes are made, hit the [b] key to execute the commands and boot the operating system.

The [Esc] key discards any changes and reloads the standard menu interface. The [c] key will load the

command line interface.

4.5.3. Command Line Interface

The command line is the most basic GRUB interface, but it is also the one that grants the most control.

The command line makes it possible to type any relevant GRUB commands followed by the [Enter]

key to execute them. This interface features some advanced shell like features, including [Tab] key

completion, based on context, and [Ctrl] key combinations when typing commands, such as [Ctrl] [a]

to move to the beginning of a line, and [Ctrl] [e] to move to the end of a line. In addition, the arrow,

[Home], [End], and [Delete] keys work as they do in the

bash

shell.

See Section 4.6, for a list of common commands.

4.5.4. Order of Interface Use

When the GRUB environment loads the second stage boot loader, it looks for its configuration file.

When found, it uses the configuration file to build the menu list and displays the boot menu interface.

If the configuration file cannot be found, or if the configuration file is unreadable, GRUB will load the

command line interface to allow users to manually type the commands necessary to boot an operating

system.

If the configuration file is not valid, GRUB will print out the error and ask for input. This can be

very helpful, because users will then be able to see precisely where the problem occurred and fix it

in the file. Pressing any key will reload the menu interface, where it is then possible to edit the menu

option and correct the problem based on the error reported by GRUB. If the correction fails, the error

is reported and GRUB will begin again.

4.6. GRUB Commands

GRUB allows a number of useful commands in its command line interface. Some of the commands

accept options after their name, and these options should be separated from the command and other

options on that line by space characters.