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Chapter 4. Boot Loaders

The following is a list useful commands:

  boot

  Boots the operating system or chain loader that has been previously specified and loaded.

  chainloader

file name

  Loads the specified file as a chain loader. To grab the file at the

0

1

first sector of the specified partition, use

+1

as the file's name.

  displaymem

  Displays the current use of memory, based on information from the BIOS. This is

useful to determine how much RAM a system has prior to booting it.

  initrd

file name

  Enables users to specify an initial RAM disk to use when booting. An

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initrd

is necessary when the kernel needs certain modules in order to boot properly, such as when

the root partition is formated with the ext3 file system.

  install

stage 1

install disk

stage 2

p

config file

  Installs

2

342

352

3

2

3

GRUB to the system MBR.

Warning

The install command will overwrite any other information in the MBR. If executed, any informa 

tion (other than GRUB information) that is used to boot other operating systems, will be lost.

Make sure you know what you are doing before executing this command.

This command can be configured in several different ways. However, it is required to specify a

stage 1

, which signifies a device, partition, and file where the first boot loader image can be

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found, such as

(hd0,0)/grub/stage1

. In addition, specify the disk where the stage 1 boot loader

should be installed, such as

(hd0)

.

The

stage 2

section tells the stage 1 boot loader where the stage 2 boot loader is located, such

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1

as

(hd0,0)/grub/stage2

. The

p

option tells the

install

command that a menu configuration

file is being specified in the

config file

section, such as

(hd0,0)/grub/grub.conf

.

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1

  kernel

kernel file name

option 1

option N

  Specifies the kernel file to

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160

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1

load from GRUB's root filesystem when using direct loading to boot the operating system. Options

can follow the

kernel

command and will be passed to the kernel when it is loaded.

For Red Hat Linux, an example

kernel

command looks like the following:

kernel /vmlinuz root=/dev/hda5

This line specifies that the

vmlinuz

file is loaded from GRUB's root filesystem, such as

(hd0,0)

.

An option is also passed to the kernel specifying that the root filesystem for the Linux kernel when

it loads should be on

hda5

, the fifth partition on the first IDE hard drive. Multiple options may be

placed after this option, if needed.

  root

device and partition

  Configures GRUB's root partition to be the particular de 

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vice and partition, such as

(hd0,0)

, and mounts the partition so that files can be read.

  rootnoverify

device and partition

  Does the same thing as the

root

command but

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does not mount the partition.

Commands other than these are available. Type

info grub

for a full list of commands.

4.7. GRUB Menu Configuration File

The configuration file, which is used to create the list in GRUB's menu interface of operating systems

to boot, essentially allows the user to select a pre set group of commands to execute. The commands

given in Section 4.6 can be used, as well as some special commands that are only available in the

configuration file.