>>827 The kernel in Alpha 5 is unable to access CD-ROM devices in some configurations, which means some users who were previously able to install Ubuntu will not be able to install this alpha from CD media. As a workaround, users can boot the installer with the additional "all_generic_ide" boot option. https://bugs.launchpad.net/ubuntu/+source/linux/+bug/181561 これかな? 環境によってはカーネルがCD-ROMドライブにアクセスできない事があるらしい。