Restarting an Ubuntu upgrade

I’m currently trying to upgrade a machine using an Ubuntu CD. This is normally pretty painless – stick the CD in, follow the prompts and away you go. Unfortunately I chose the wrong option and cancelled the upgrade, and couldn’t get it to restart again.

After a bit of head scratching I figured it out:

$ sudo sh /cdrom/cdromupgrade

You need to specify the full path, otherwise the process fails.