How do you use grub with ubuntu and fedora installed?

You set up the grub.conf file to point to each partition. So you’d have a section that points to the Ubuntu partition and another section that points to the Fedora section. I’m assuming you have them on different partitions. If you have two different drives it might be a bit easier.

So it might look a bit like this:

timeout 30
default 0

title Ubuntu Linux
kernel (hd0,0)/boot/[name of your kernel] root=/dev/[partition of Ubuntu’s root]

title Fedora Linux
kernel (hd0,1)/boot/[name of kernel] root=/dev/[parition for Fedora]

It would be hard to be specific unless I knew how you had your drive(s) and partition(s) set up.

I’m also very much expecting each distro to be able to detect another already installed and automatically configuring Grub for this (though probably with the respective distro selected as default).