Why does the S5 init run "/bin/su" instead of "/bin/sh" single-user?

[Jack Jansen]

I guess that they did it for security reasons. If you run "su"
in stead of "sh", you don't have to lock your machine room if
you want to make sure that no-one can log in as superuser.
 I did something like this, with one exception : If "su"
cannot find the password file it returns a funny exit status, and
if "init" gets this funny return, it will still start "sh". This
way, you get your security, but you can still boot if the passwordfile
is corrupted.

	Jack Jansen, {philabs|decvax}!mcvax!vu44!jack