Although I hate Unity, I’ve decided to continue using Ubuntu Linux. So I tried to upgrade my Ubuntu 11.10 PC automatically. It almost succeed. It fails to install grub, the boot loader of linux. In addition, I couldn’t do that with the rescue mode of my alternate CD for the clean installation. So I try the clean installation since /home volume is separated from the system volumes.
Probably, if you use LVM, Logical Volume Manager on your system partitions, the installation of grub fails in other ways than the clean installation. It was the final process. So maybe, there is a solution without this clean installation. But I don’t know. It looks better to install Ubuntu 12.04 cleanly if you use LVM by the installation with alternate CD.