Ubuntu

Is it possible to make multiboot partitions of Ubuntu and red hat Linux?

Do you mean can you have two separate Linux installs on a single PC and boot between them?

I would hope so, I have one machine with 7 different operating systems and use grub to select between them.

Hello.
U have posted that you have 7 different os.
But we can have only 4 primary partitions and thus we can have maximum 4 os.

I first installed Redhat 5.
After that i installed Ubuntu 8.10.
I am unable to boot into Redhat.
In the menu Redhat is not shown as the MBR is overwritten by Ubuntu GRUB.
Now how to make the dual boot ??

If you use a seperate boot partition, you can load the kernel from a primary partition then boot into an extended partition. Many different Linux OSes can share one boot partition, too. GRUB couldn't possibly keep all its settings in the tiny amount of space a boot sector gives, it's actually smart enough to understand some partition types, to let it reach in and grab a config file. Usually /boot/grub/grub.conf, whichever partition that ended up at in your file tree. It'll be reading the new grub.conf instead of the old one now, but if you can get your old one, you can add settings from it to your new one. You can't just install lots of OSes on top of each other and expect it to work, you need to plan ahead. It may still be recoverable at this point if you can find the grub.conf from your redhat partition. Post both your new and old grub.conf files here, in code tags, and we can help you make a grub.conf that can boot either.

yes.

install redhat first. then install ubuntu as the installer can recognise most other os'es. lets say you have windows in sda1 then make a partition called sda5 (100M) for redhat boot (it has to be a logical partition or in an extended if you get that option) and sda6 for redhat os. then sda7 for redhat swap and sda8 for ubuntu boot and sda9 for ubuntu os. you can use the existing sda7 redhat swap for ubuntu too. hope this helps as this is one of many solutions.