On Fri, 14 Apr 2000, Jon Lindgren wrote:

> What happens when a serial console is disconnected from a running 1.4.x
> machine?  I've a few sparcs which will be running 1.4.1 or 1.4.2, however,
> I've only one vt420 :-( so I'll have to use a serial switch or
> equiv.  I've seen messages from people before (perhaps not on this port,
> sorry, can't remember) regarding halting the system when the serial
> console is removed.
> 
> I'd also be worried about serial traffic queuing up due to no DCD or such.

Just set the line to be a direct connect ("local" in /etc/ttys I
think) and lack of DCD won't be a problem.

The other problem with disconnecting the serial console, which Dan
addressed, is that often times machines are set up so that sending a
"break" signal (a continuous stream of "0" bits even when the stop bits
are supposed to be there) will interrupt the kernel. It's the equivalent
of Control-Power on newer mac's at the keyboard.

The problem is that when you unhook the cable, the data pins float, and
they might float to where the signal looks like a break signal,
interrupting the kernel.

Dan's resistor changes will fix that.

Take care,

Bill