I'm setting up an environment to install many Lenny machines at once and I need to avoid any dialog with the process, corner cases aside. One thing that consistently troubles me is that after my preseeded disk recipe creates Linux RAID-1 devices, the installer warns me about how the kernel could not re-read the partition table on each MD device. When I do a manual installation and try to use debconf-get-selections to preseed another installation, it seems to ignore the whole preseed file altogether. But reading through those selections, I couldn't find anything that seemed to suggest it would select "OK" on this extraneous warning.
For anybody else stuck on this issue, you can use the following line in your preseed file:
But you'll want to be aware of the implied risks.