3.5 Configuring a Tri-boot with GRUB

For GRUB experts, kindly proceed and make the modifications as required in the menu.lst file in CentOS. For GRUB newbies, there is a wealth of information available at: http://www.gnu.org/software/grub/grub.html most of which is self-explanatory and easy to understand. If there is something that you do not understand, shoot me a mail.

GNU GRUB stands for the GRand Unified Bootloader, which is a very powerful boot loader program for PCs. Detailed manual for GRUB (version 0.97) can be accessed by:

• Online: http://www.gnu.org/software/grub/manual/ wherein different formats are available for easy perusal.
• CentOS: Open a terminal, type in: info grub which opens up the Detailed manual for GRUB (version 0.97) on your screen.

In Section 4.1 of the manual for GRUB (version 0.97), lies the secret of how to boot OSes successfully. As mentioned therein, GRUB has two distinct boot methods - either booting the OS directly or when GRUB is unable to provide native support to the OS in question, it fires the boot loader of the OS via a chain-loading mechanism; thereby enabling the OS to boot successfully. For CentOS 5.2, GRUB loads the OS directly, whereas for WinXP it needs to fire up the boot loader for Windows via chain-loading mechanism. One point which readers ought to keep in mind is that chain-loading mechanism normally operates on the assumption that the boot loader is embedded in the boot sector of the active partition on which the OS is installed.

= =  STEPS TO FOLLOW = =

Step1: Login to CentOS 5.2, open a terminal, gain superuser rights (referred to as root) by using the su command and providing the password that you had provided whilst installation.

[ghosh@pluton ~]$ su

Step2: Once you have root access, type the following commands at the terminal:

This creates a backup file for the grub.conf file which is the configuration file for GNU GRUB boot loader. In the listing of all files on the screen, you can also see menu.lst -> ./grub.conf which means menu.lst is a soft or symbolic link to the GRUB configuration file grub.conf.

Step3: [root@pluton grub]# vi grub.conf

Step4: My grub.conf is displayed on the screen:

Step5: Edit the file contents and add the lines which are marked in blue.

# grub.conf generated by anaconda
#
# Note that you do not have to rerun grub after making changes to this file
# NOTICE: You do not have a /boot partition. This means that
#                  all kernel and initrd paths are relative to /, e.g.
#                  root (hd0,2)
#                  kernel /boot/vmlinuz-version ro root=/dev/sda3
#                  initrd /boot/initrd-version.img
# boot=/dev/hda
default=1
timeout=60
splashimage=(hd0,2)/boot/grub/splash.xpm.gz
hiddenmenu

title Windows
           rootnoverify (hd0,0)
           chainloader +1

title OpenSolaris
           rootnoverify (hd0,1)
           savedefault
           makeactive
           chainloader +1

title CentOS (2.6.18-92.el5)
           root (hd0,2)
           kernel /boot/bzImage.2.6.18-92.el5  ro  root=LABEL=/    rhgb   quiet    crashkernel=512M@16M
           initrd /boot/initrd-.2.6.18-92.el5.img

Step6: I have rearranged the code in accordance to the geometrical layout of the partitions in the hard disk. WinXP first, followed by OpenSolaris slice and finally, the CentOS partition. Save and exit vi editor.

Step7: [root@pluton grub]# /sbin/reboot

This restarts the PC. When the system finally comes up, press any key to see the GNU GRUB version 0.97 screen, which displays:

Windows
OpenSolaris
CentOS (2.6.18-92.e15)

• Selecting Windows and pressing <ENTER> boots your system into WinXP.
• Selecting OpenSolaris and pressing <ENTER> loads the OpenSolaris GRUB boot loader via chain-loading mechanism. It has our earlier OpenSolaris entries plus the WinXP boot entry. Check whether all working correctly or not.
• Selecting CentOS (2.6.18-92.e15) and pressing <ENTER> boots CentOS 5.2.

Thus, as promised, we have:

a) Successfully partitioned a new single hard disk drive into primary and extended partitions with WinXP FAT32, OpenSolaris ZFS and Linux ext3 filesystems on them.
b) Successfully installed Microsoft WinXP on the first primary partition of the hard disk.
c) Successfully installed OpenSolaris 2008.11 on the second primary partition of the hard disk.
d) Successfully installed CentOS 5.2 on the third primary partition of the hard disk (with Linux swap on a logical disk drive of the extended partition).
e) Successfully edited the GRUB configuration file /boot/grub/grub.conf and configured a tri-boot system with WinXP, OpenSolaris and CentOS OSes.

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