kern.shutdown_timeout sysctl not working

I tried setting the value of the kern.shutdown_timeout sysctl and it failed
with:

sysctl: unknown oid 'kern.shutdown_timeout'

I am trying to increase the maximum time allowed for rc.shutdown to run due
to some custom scripting I want to wait for at the end.

>From the source code of init (ie init.c) it clearly reads the value of this
sysctl to override the default of 2 minutes:

if (sysctlbyname("kern.shutdown_timeout",
			 &shutdowntimeout,
			 &len, NULL, 0) == -1 || shutdowntimeout < 2)
	    shutdowntimeout = DEATH_SCRIPT;

But it appears that in reality this sysctl value doesn't exist.

Can I assume this is a bug and one or the other bit is wrong?

And is there anyway to fix this?

If it comes to it I can just override the default 2 minutes by altering the
#define in init.c but I would prefer to not hack the source and have to
re-edit after every src cvsup, especially since the sysctl would provide a
much neater way of accomplishing it.

I posted this question to questions a few days back but didn't get any
response there so figured I might get an answer here.

uname -a output is as follows:

FreeBSD magellan.dom.bishnet.net 5.2.1-RC2 FreeBSD 5.2.1-RC2 #1: Sun Feb 22
02:52:35 GMT 2004
dom_at_dom.bishnet.net:/u2/usr/obj/u2/usr/src/sys/MAGELLAN  i386

A quick look at cvs comments suggests that nothing has been changed that
affects this between 5.2.1-RC2 and -CURRENT

Regards,

Dominic Bishop