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SubjectRe: what is a halted kernel supposed to do?
On Tue, 1 Apr 1997, Louis Mandelstam wrote:

> On Mon, 31 Mar 1997, Marty Leisner wrote:
>
> > What is a system supposed to do when its halted?
> >
> > My linux 2.0.29 system still responds to pings.
> >
> > My freebsd 2.2 seems to be dead.
> >
> > When we halt, everything should turn off...(pings are
> > often an indication a system is alive).
>
> I don't think this needs to be a kernel problem.
>
> You could get your shutdown script logic to simply ifconfig all your
> interfaces down before 'halting'.
>
> Does the Linux kernel even have such a thing as a 'halted' state? I would
> have a assumed we just end up with no processes running and all
> filesystems umounted.

You have discovered an interesting item. If a remote system panics, you
may not know it unless there is a fire :^)

../linux/arch/i386/kernel/process.c contains an empty procedure
called machine_halt(). This is not called on a shutdown and it
is not called during a panic. Even if it was, it would do nothing.

If you add the following code:

void machine_halt()
{
outb(0x21, 2); /* Leave ONLY the keyboard enabled */
for(;;) ;
}

If this was called after a halt or after a panic, it would give
the results you desire, i.e., the network would not work but you
could ctrl-alt-del from the keyboard.

Cheers,
Dick Johnson
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