Re: Delivering SIGKILL to init

On Tue, 2006-Sep-19 17:55:50 +1000, Peter Jeremy wrote:
Prompted by some discussion elsewhere, I've been trying to send
SIGKILL to init. If I ktrace kill(1), I can see "kill(1,9)" which
returns 0 but the signal is never delivered. If I sent (eg) SIGXCPU
then init dies and the kernel panics (as expected). I've looked
through sys/kern/kern_* and can't see anywhere that special cases
the delivery of SIGKILL to init.

For anyone else interested:

I was pointed to code in kern_sig.c:issignal() by a friend. The
signal action handling switch (about line 2172 in -stable) ignores
any signals marked SIG_DFL for "system" processes (those with a
PID of 1 or less). Since SIGKILL is marked SIG_DFL (because it
can't be changed), this means SIGKILL isn't delivered. SIGXCPU
(and a variety of other signals) have a handler defined by init
so they aren't SIG_DFL and therefore are delivered.

--
Peter Jeremy

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