Why does the S5 init run "/bin/su" in single-user mode

[Mike Wescott]

>  From: dan at rna.UUCP (Dan Ts'o)
>  Newsgroups: net.bugs.usg
>  Subject: RE: Why does the S5 init run "/bin/su" in single-user mode
>  
>  Hi,
>	  One reason I might do such a thing is to prevent passers-by from
>  booting the system and getting a root shell. On my system, I replaced
>  init's call to /bin/sh to /bin/login to achieve the same thing. I felt that
>  the rare chance that /bin/login, /etc/passwd were corrupted but NOT /bin/sh
>  was small compared to the value of not being able to get an easy root shell.

Actually using login prevents this, but not /bin/su.  Having been kicked off
by a root uid proc /bin/su doesn't ask for a password. To make it difficult to
reboot a Sys5 machine and get a root permission shell we change the default
initial run level to kick off a single getty - login - shell sequence. And
this does permit the creation of non-root operators for booting, fsck, et. al.

BTW, we DID have a lightning storm that fouled up our disk; login, getty,
/etc/passwd were all ok, but su, rm and a few others were corrupted.  The
machine didn't go down but you couldn't repair it except from the console.
(We disable root logins except from the console.) Unfortunately, we tried
rebooting first and went from a system that was crippled to one that looped
endlessly trying to exec a froogged up /bin/su.

As for the original question of why init kicks off /bin/su in the single user
state...the question is still open.

	Mike Wescott
	NCR Corp
	mcnc!ncsu!ncrcae!wescott