GRUB allows a number of useful commands in its command line
interface. Some of the commands accept options after their name; these
options should be separated from the command and other options on that
line by space characters.
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.
When using the install command the user must
specify the following:
<stage-1>
— Signifies a device, partition, and file where
the first boot loader image can be found, such as
(hd0,0)/grub/stage1.
<install-disk>
— Specifies the disk where the stage 1 boot loader should be
installed, such as (hd0).
<stage-2>
— Passes to the stage 1 boot loader the location of the
stage 2 boot loader is located, such as
(hd0,0)/grub/stage2.
p<config-file>
— This option tells the install command
to look for the menu configuration file specified by
<config-file>.
An example of a valid path to the configuration file is
(hd0,0)/grub/grub.conf.
Warning
The install command will overwrite any
other information in the MBR. If executed, any information (other
than GRUB information) that is used to boot other operating
systems, will be lost.
kernel
<kernel-file-name><option-1><option-N> —
Specifies the kernel file to load from GRUB's root file system 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 file system, such as
(hd0,0). An option is also passed to the kernel
specifying that when loading the root file system for the Linux
kernel, it 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 a specific device
and partition, such as (hd0,0), and mounts
the partition so that files can be read.
rootnoverify
<device-and-partition>
— Performs the same functions 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.
