It should be possible, but I think you're in for a painful experience. Unless you have a liveCD/USB to hand or like playing with GRUB recovery I'd try it in a VM first.
- An OS entry in grub specifies both the GRUB root (where the kernel image can be found, ie the device containing
/boot, and the kernel command line specifies the root device to use. So, there should be no reason you can't have kernels for multiple distributions in one /boot device controlled by one GRUB configuration.
.
menuentry distribution1 {
insmod part_msdos
insmod ext2
insmod gzio
set root=(hdX,msdosY)
linux /boot/vmlinuz-distribution1 root=UUID=uuid-for-distribution1-root
initrd /boot/initrd.img-distribution1
}
menuentry distribution2 {
insmod part_msdos
insmod ext2
insmod gzio
set root=(hdX,msdosY)
linux /boot/vmlinuz-distribution2 root=UUID=uuid-for-distribution2-root
initrd /boot/initrd.img-distribution2
}
Providing the kernels and initrds for the two distributions are named differently, there should not be a problem with interference between the kernel images.
However, there is likely to be problems with the grub configuration. Ubuntu certainly automatically updates this each time you update grub or the kernel, and I doubt the autogeneration will handle this configuration.
You'll need to either tweak the configuration in /etc/grub.d to handle this setup, disable autogeneration or remember to manually edit it yourself each time. You probably want to uninstall grub from one of the two distributions or you'll be dealing with this problem twice.
