Installation guide

82 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

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

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

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

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

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.

• kernel kernel-file-name option-1 option-N — Speciﬁes the kernel ﬁle to

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-

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

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.