Totally weird. Today /dev/disk/by-id/ata* in fstab couldn't be dealt with upon boot, but I still could login as root (with only the root partition mounted), whereupon I did reboot(8), and miraculously this time the boot went smoothly! So one does not need to rerun lilo, nor change /etc/fstab at all. Just reboot. I suppose if that doesn't work, then just reboot again.