init s and rc0 script

[Michal Bizik]

Greetings,

I am new on tru64 system, i started to look around a bit and stoped by rc0 script wich is doing all the job during the system shutdown. One thing i just can't get is that in inittab the single user mode is deffined as:

ss:Ss:wait:/sbin/rc0 shutdown < /dev/console > /dev/console 2>&1

but then when i open rc0 the end of this script is like:

if [ "$ARGONE" = shutdown ]; then
/sbin/init S
else
echo "The system is down."
sync
/sbin/halt -q

so its calling the "init S" command again and thats very strange. How is it possible that this sequence doesn't loop the whole system into executing "rc0 shutdown" again and again...? i see no other condition in the script wich could block the loop...

Thank you

[Michal Bizik]

no one knows the answer?

Could you guys atleast tell me whats the line

/sbin/kill -USR1 $SPECIALPID

doing?

It looks like it sends USR1 signal to the init process. But what does it mean for the init?
How is init interpreting the USR1 signal?

[Dennis Handly]

>I see no other condition in the script wich could block the loop.

On HP-UX, you only execute the rc0 scripts if you transition to that runlevel. Not if you are already at that runlevel.

>It looks like it sends USR1 signal to the init process. But what does it mean for the init?

Yes, it sends USR1 to $SPECIALPID.
You'll need to look at the documentation for init(8).
Unfortunately I don't see anything obvious:
http://h30097.www3.hp.com/docs/base_doc/DOCUMENTATION/V50_HTML/MAN/MAN8/0166____.HTM
http://h30097.www3.hp.com/docs/base_doc/DOCUMENTATION/V50_HTML/MAN/MAN1/0237____.HTM

[Michal Bizik]

Yeah thats why im asking. Coz init man pages shows nothing about this signal :/

Its obvios that init do not load rc0 again when the system is in single user already. But where is the condition?

[Matti_Kurkela]

The inittab line that runs /sbin/rc0 is of type "wait". That means it is run only once when entering runlevel S or s. It is not run again as long as the system stays in the single-user runlevel.

So, running "init S" would cause the main init process to "think" something like "OK, we're already in single-user mode and we already did /sbin/rc0, so there is nothing at all to do."

The point of having "/sbin/init S" instead of just exiting the script is mysterious to me: perhaps some side-effect of re-executing /sbin/init is desired? (It might be triggering the main init process to re-read the inittab file, in case it's been changed; perhaps this is for firmware updates or some other thing that requires system to automatically go to single-user mode, do something and return to normal mode.)

At that point, the single-user shell (or root login prompt, if single-user mode can be password-protected in tru64) is invoked, most likely by program code embedded in /sbin/init itself. That is likely to be the same code that gets executed if you are booting a system whose inittab file has accidentally become empty or deleted.

The only way to know for sure would be to read the source code of /sbin/init.

MK