Submitter reported additional information re initramfs-tools to d-s390 mailing list [1]. Most relevant information (console messages) duplicated below.
Freeing unused kernel memory: 120k freed Loading, please wait... Begin: Initializing /dev ... /sbin/udevsynthesize: 13: /lib/udev/udevsynthesize: not found Done. Begin: Loading modules ... Done. Begin: Running /scripts/init-premount ... Done. Begin: Mounting root file system ... Begin: Running /scripts/local-top ... Done. ALERT× /dev/dasd/0.0.0108/part1 does not exist. Dropping to a shell× [1] http://lists.debian.org/debian-s390/2005/11/msg00017.html
