MULTI-BOOT GRUB ( "Chainloading" )
Imagine you want to use the Grub of your favorite distro to include the options to boot all the other distros you want to install ( or already have instaled ) on your computer.
The trick is, that if you have all boot loaders ( except the one from your favorite distro ) installed in the / partition of the distros they belong to, you can use "chainloading": You will only need to add 3 lines in the /boot/grub/menu.lst ( of your favorite distro ), using an example of Fedora on partition hda13:
This way ( and this is very important ) if the Fedora kernel gets upgraded during an ( automatic ) update process you will automatically boot the new installed kernel even when using the Grub bootloader that lives in the MBR.
You can chainload as many distros as you like, here are a few more examples taken from a forum post to Urmas who has PCLos, Mandriva, OpenSUSE and Slackware booting from his Ubuntu Grub:
|# for PCLos on hda5
# for mandriva on hda7
# for SUSE on hda9
# for Slackware on hda11
NOTE: For the way Grub numbers the partitions please read: Grub the bootloader
-- May 12 2007 --