To boot the system without boot media, you usually need to
install a boot loader. A boot loader is the first software program that runs
when a computer starts. It is responsible for loading and transferring
control to the operating system kernel software. The kernel, in turn,
initializes the rest of the operating system.
GRUB (GRand Unified Bootloader), which is installed by default, is a
very powerful boot loader. GRUB can load a variety of free operating
systems, as well as proprietary operating systems with chain-loading (the
mechanism for loading unsupported operating systems, such as DOS or Windows,
by loading another boot loader).
Figure 4-14. Boot Loader Configuration
If you do not want to install GRUB as your boot loader, click
Change boot loader, where you can choose not to
install a boot loader at all.
If you already have a boot loader that can boot Red Hat Enterprise Linux and do not want to
overwrite your current boot loader, choose Do not install a boot
loader by clicking on the Change boot
If you choose not to install GRUB for any
reason, you will not be able to boot the system directly, and you must use
another boot method (such as a commercial boot loader application). Use
this option only if you are sure you have another way of booting the system!
Every bootable partition is listed, including partitions used by other
operating systems. The partition holding the system's root file system has
a Label of Red Hat Enterprise Linux (for
GRUB). Other partitions may also have boot labels. To add or change the boot
label for other partitions that have been detected by the installation
program, click once on the partition to select it. Once selected, you can
change the boot label by clicking the Edit button.
Select Default beside the preferred boot partition
to choose your default bootable OS. You cannot move forward in the
installation unless you choose a default boot image.
The Label column lists
what you must enter at the boot prompt, in non-graphical boot loaders, in
order to boot the desired operating system.
Once you have loaded the GRUB boot screen, use the arrow keys to
choose a boot label or type [e] for edit. You are presented
with a list of items in the configuration file for the boot label you have
Boot loader passwords provide a security mechanism in an environment where
physical access to your server is available.
If you are installing a boot loader, you should create a password to
protect your system. Without a boot loader password, users with access to
your system can pass options to the kernel which can compromise your system
security. With a boot loader password in place, the password must first be
entered before selecting any non-standard boot options. However, it is still
possible for someone with physical access to the machine to boot from a
diskette, CD-ROM, or USB media if the BIOS supports it. Security plans which
include boot loader passwords should also address alternate boot methods.
If you choose to use a boot loader password to enhance your system
security, be sure to select the checkbox labeled Use a boot loader
Once selected, enter a password and confirm it.
To configure more advance boot loader options, such as changing the
drive order or passing options to the kernel, be sure Configure
advanced boot loader options is selected before clicking
Now that you have chosen which boot loader to install, you can also
determine where you want the boot loader to be installed. You may install
the boot loader in one of two places:
The master boot record (MBR) — This is the recommended place
to install a boot loader, unless the MBR already starts another
operating system loader, such as System Commander. The MBR is a
special area on your hard drive that is automatically loaded by your
computer's BIOS, and is the earliest point at which the boot loader
can take control of the boot process. If you install it in the MBR,
when your machine boots, GRUB presents a boot prompt. You can then
boot Red Hat Enterprise Linux or any other operating system that you have configured
the boot loader to boot.
The first sector of your boot partition — This is
recommended if you are already using another boot loader on your
system. In this case, your other boot loader takes control
first. You can then configure that boot loader to start GRUB,
which then boots Red Hat Enterprise Linux.
Figure 4-15. Boot Loader Installation
If you have a RAID card, be aware that some
BIOSes do not support booting from the RAID card. In cases such as these,
the boot loader should not be installed on the MBR of
the RAID array. Rather, the boot loader should be installed on the MBR of
the same drive as the /boot/ partition was
If your system only uses Red Hat Enterprise Linux, you should choose the
Click the Change Drive Order button if you
would like to rearrange the drive order or if your BIOS does not return
the correct drive order. Changing the drive order may be useful if you
have multiple SCSI adapters, or both SCSI and IDE adapters, and you want
to boot from the SCSI device.
The Force LBA32 (not normally required) option
allows you to exceed the 1024 cylinder limit for the
/boot/ partition. If you have a system which supports
the LBA32 extension for booting operating systems above the 1024 cylinder
limit, and you want to place your /boot/ partition
above cylinder 1024, you should select this option.
While partitioning your hard drive, keep in mind that
the BIOS in some older systems cannot access more than the first 1024
cylinders on a hard drive. If this is the case, leave enough room for the
/boot Linux partition on the first 1024 cylinders of
your hard drive to boot Linux. The other Linux partitions can be after
In parted, 1024 cylinders equals 528MB. For
more information, refer to:
To add default options to the boot command, enter them into the
Kernel parameters field. Any options you enter are
passed to the Linux kernel every time it boots.
Rescue mode provides the ability to boot a small Red Hat Enterprise Linux environment
entirely from boot media or some other boot method instead of the system's
hard drive. There may be times when you are unable to get Red Hat Enterprise Linux running
completely enough to access files on your system's hard drive. Using
rescue mode, you can access the files stored on your system's hard drive,
even if you cannot actually run Red Hat Enterprise Linux from that hard drive. If you need
to use rescue mode, try the following method:
Using the CD-ROM to boot an x86, AMD64, or Intel® EM64T
system, type linux rescue at the
installation boot prompt. Itanium users should type
elilo linux rescue to enter rescue mode.
For additional information, refer to the
Red Hat Enterprise Linux System Administration Guide.
If you do not wish to use a boot loader, you have several
You can load Linux from MS-DOS. Unfortunately, this
requires a copy of the Linux kernel (and an initial RAM disk, if you
have a SCSI adapter) to be available on an MS-DOS partition. The
only way to accomplish this is to boot your Red Hat Enterprise Linux system using some
other method (for example, from a boot CD-ROM) and then copy the
kernel to an MS-DOS partition. LOADLIN is available from
and associated mirror sites.
SYSLINUX is an MS-DOS program very similar to LOADLIN. It is
also available from
and associated mirror sites.
- Commercial boot loaders
You can load Linux using commercial boot loaders. For
example, System Commander and Partition Magic are able to boot Linux
(but still require GRUB to be installed in your Linux root
Boot loaders such as LOADLIN and System Commander are considered to
be third-party boot loaders and are not supported by Red Hat.
This section is specific to SMP motherboards only. SMP, short for
Symmetric Multiprocessing, is a computer architecture providing fast
performance by making multiple CPUs available to complete individual
processes simultaneously (multiprocessing).
If the installation program detects an SMP motherboard on your system,
it automatically creates two boot loader entries.
An SMP kernel is installed by default on
Intel® Pentium® 4 systems with
The two GRUB entries are Red Hat Enterprise Linux (kernel
version) and Red Hat Enterprise Linux
(kernel version-smp). The
Red Hat Enterprise Linux (kernel
version-smp) boots by default. However, if
you have trouble with the SMP kernel, you can elect to boot the
Red Hat Enterprise Linux (kernel
version) entry instead. You retain all the
functionality as before, but only operate with a single processor.