There is one additional location you should check, although it's unlikely that the settings here are the problem:N.B.: This is from a Fedora 19 setup, but I don't think that it's any different from the F18 file.

Thanks for the help, but /etc/dracut.conf.d has contained those files since Feb. Methinks the problem might be the POSTIN script in the kernel*rpm. It invokes /sbin/new-kernel-pkg with a now-illegal command option. It no longer likes "--package kernel". I don't know enough about rpm to figure out what happens next, but the initramfs file it creates is probably the default one. It can't even find the ext4 boot partition containing grub. With ext4.ko and lvm.ko built into the kernel, /lib/modules in the initramfs image doesn't contain those. Perhaps if /lib/modules/`uname -m`/kernel/drivers/ata, which is easily found in /lib/modules/`uname -m`/modules.block, it may have a chance, but the initramsfs has to be as small as possible so it fits in /proc/meminfo/MemTotal. I don't know, maybe parse /proc/mounts for boot and root, maybe get the device names from /etc/fstab?

[Please accept my humble apology. I suffer from what the docs classify as a serious illness, which apparently affects my patience. I know everyone tried to help without all of the facts necessary to effectively triage this issue. For that, I am indeed grateful.]

Well the sbin/new-kernel-pkg file is a shell script, so you could just edit it so it would do the right thing with the unexpected argument.