serial console and spurious breaks

Hello

I have several NetBSD/macppc and NetBSD/amd64 machines using
serial consoles.
If I unplug the serial port, or if I power cycle the serial
remote device, o
the NetBSD box will catch a BREAK on the console, and will
drop in ddb. 

Anyone has a workaround for that? The ability to drop in ddb
using a break
is really useful, but unplanned server downtime just because
a serial cable
was unplugged is a shame.

-- 
Emmanuel Dreyfus
manunetbsd.org

On Mon, 23 Jul 2007 14:00:46 +0000
Emmanuel Dreyfus <manuNetBSD.org> wrote:

> Hello
> 
> I have several NetBSD/macppc and NetBSD/amd64 machines
using serial
> consoles. If I unplug the serial port, or if I power
cycle the serial
> remote device, o the NetBSD box will catch a BREAK on
the console,
> and will drop in ddb. 
> 
> Anyone has a workaround for that? The ability to drop
in ddb using a
> break is really useful, but unplanned server downtime
just because a
> serial cable was unplugged is a shame.
> 
Set ddb.fromconsole=0 in sysctl.conf.  Also see the
hw.cnmagic sysctl.


		--Steve Bellovin, http://www.cs.columbi
a.edu/~smb

On Mon, Jul 23, 2007 at 10:07:54AM -0400, Steven M. Bellovin
wrote:
> > break is really useful, but unplanned server
downtime just because a
> > serial cable was unplugged is a shame.
> Set ddb.fromconsole=0 in sysctl.conf. 

I'd like to retain the ability to drop into ddb from the
console, I just
want to avound getting there if I unplug the cable.

> Also see the hw.cnmagic sysctl.

How can this be used? I see cnmagic(9), but what value could
I use? 
It's x27x02 right now

-- 
Emmanuel Dreyfus
manunetbsd.org

On Mon Jul 23 2007 at 11:00:54 -0400, Thor Lancelot Simon
wrote:
> On Mon, Jul 23, 2007 at 02:00:46PM +0000, Emmanuel
Dreyfus wrote:
> > Hello
> > 
> > I have several NetBSD/macppc and NetBSD/amd64
machines using serial consoles.
> > If I unplug the serial port, or if I power cycle
the serial remote device, o
> > the NetBSD box will catch a BREAK on the console,
and will drop in ddb. 
> 
> This is why we have the hw.cnmagic sysctl setting.  I
generally set it to
> 
ddb (<control-a>ddb) on my systems.

Just a side-note: entering ddb through cnmagic on a com
console leaves
the com spinlock locked and will prevent some tasks such as
pfind().
This, of course, should be fixed (or I should at least
send-pr it).

-- 
Antti Kantee <pookaiki.fi>                     Of course
he runs NetBSD
http://www.iki.fi/pooka/
                         http://www.NetBSD.org/
    "la qualité la plus indispensable du cuisinier est
l'exactitude"