Sun, Jan 16, 2005 at 04:26:27PM +0100, ali (Anders Lindgren):
> I run a headless sparc64 with serial console (ttya). Occassionally,
> however, I want to temporarily use ttyb to enable my box as a serial
> console for other headless machines -- but connecting/disconnecting
> anything on ttyb invariably causes enough of a power flux on the port to
> emulate a serial BREAK, at which point the kernel drops into ddb.
> If I am on location I suppose I can just say continue in ddb and be happy,
> but it is still inconvenient, at best.
> 
> I couldn't find much on google apart from an old kernel patch to
> completely disable ddb on serial BREAK, and ddb(4) had no enlightenment
> for me either.
> 
> I presume it is not possible to tell the kernel to ignore BREAKs on serial
> ports that don't have a console device attached to them? Could I easily
> patch it to work this way myself?

see cnmagic(9).  the key sequence to trigger the bugger can be changed
to something other than break.