I need to know exactly how to add a new disrto to a Windows 7 dual boot. I am using 2 hard drives and one grub bootloader [not using BIOS]
Was told to just add / of the 3rd distro in a resized partition. When I did the 3rd distro worked fine but the ubuntu that was up and running fine before wouldn't load because it couldn't find /home.
This can't be that difficult. I am just missing something.
I think your older Ubuntu's /etc/fstab wasn't using UUIDs to identify the partitions (instead, something like /dev/sdaX). Thus when you resized partitions, there may have been a change in the numbering, and thus a missing /home partition. Either that, or it was using UUIDs, and you somehow modified the /home partition, causing its UUID to change.
Either way, check the fstab of the new system to see what the /home entry should look like. If that file isn't using UUIDs, note the correct partition number, and look up its UUID:
sudo blkid
# Or
ls -l /dev/disk/by-uuid/
Then fix the entries in both systems to use the correct UUID (by using UUID=<uuid> instead of /dev/sdaX in the fstab).
I've done this before myself, though it was a long time ago. You're using grub so that makes it easy. I'm assuming you've got Windows installed on 1 drive and Ubuntu on the 2nd drive, if that isn't the case then forgive me.
However, the key for installing a 3rd installation is you need it to have its own root and home - though if memory serves they can use the same swap partition so long as you don't use hibernate (as that uses the swap partition). So when you install the 3rd OS, you just need to make room for it's partitions. When installing, tell it you want to do custom partitions, shrink your Ubuntu partition to make room for the new install. Create a new partition (2 if you are using separate home and root, or 3 if you want it to have its own dedicated swap partition). Tell the new distro to install there. As a matter of safety if it gives me the option to specify mount points for the other partitions I always specify them to avoid confusion in the OS.
So if I've got Ubuntu A on the system with a swap and a main partition and install Ubuntu B, when installing I make sure Ubuntu B knows I want it to mount the Ubuntu A partition in something like /dual-boot/Ubuntu-A or the like, so that the OS doesn't get confused as to where root and home are. The installer should detect that you've got GRUB installed and simply install the extra boot options to it.
If you end up with either Linux distro not able to find home then you'll need to look at that distro's fstab and find out what it is trying to mount. Also, for simplicity, some google searches on dual booting 2 linux distros could be handy. The Windows bootloader is called from GRUB and thus as long as GRUB always knows where to find it, you're good on that one.
As additional resources, I'd look at the following links:
Remember, as a general rule as long as Grub knows where to find the distro you want to boot you're fine. If I had to guess, previously, you mentioned that it couldn't find home and that might have simply been a matter of the new installer changing the partition map, it doesn't know the other distro exists so if it tried to claim your old home as root, or as its home, or swapped them around, etc... Then you're going to have issues. That's why you do the mapping manually.
