The systemd-based initrd (default here, since this host has a ZFS
root) locks the root account by default, so sulogin refuses a shell
if something in the initrd fails and it drops to emergency mode --
confirmed live: it just loops re-entering the target instead of
prompting, making an initrd-level ZFS import failure impossible to
diagnose from the console. Only affects the pre-switch-root initrd
shell, not the installed system's own login.