Linux ---how to install another linux distribution

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Install the new OS in a new partion.
Dont install the grub while the installation of the second OS.

After the installation go to the older OS and edit the "/boot/grub/grub.conf" like appending the below line with the existing file(Assume Fedora core 3 is the new OS )

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title Fedora Core 3
root (hd0,8)
kernel /boot/vmlinuz-2.6.20-8 ro root=/dev/hda9
initrd /initrd-2.6.20-8.img

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The commands and the usages(change the parameter according to you settings):

title: for the text displayed on the grub interface.
root: to specify the root partiotion.
hd0 :- the primary harddisk (grub starts the counting from 0)
8 :- the 9th partition (hda9) where the os is installed (/ is mounted)
kernel : specifies kernel image the parameters
initrd : (init ram disk) is requied for ext3 type file system.

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