using tip on machine that has COMCONSOLE set to serial

[Bruce Evans]

On Tue, 16 Sep 2003, Don Bowman wrote:

> This may be a dumb question, but I have
> a situation where machine A and B both have
> enabled serial console. I'm ssh'ing into A to
> try and debug a problem on B. I'm trying to
> use tip, but am getting interference from the
> fact that A also has a serial console.
>
> If i disable the getty, its a bit better.
>
> Is there a way to make this work reliably, or
> am I SOL?

Not completely reliably.  In -current you can try switching off the
serial console, but IIRC the switching code has problems in precisely
this area -- it doesn't turn off the lowest levels of consoleness.

Turning off getty is a good idea.  cua* with getty on ttyd* may work,
but it is necessary to turn off CLOCAL on the console snd maybe fiddle
with carrider on the line so that getty blocks in open.  CLOCAL defaults
to on for serial consoles and is locked on.  Speeds are also locked for
consoles.

Turning off anything that writes to the console (e.g., syslogd) is a good
idea if you haven't turned off the console.  I sometimes turn off low
level writes by writing machine code in ddb.  On i386's, writing byte 0xc3
at printf turns off all kernel printfs (fortunately nothing checks their
return value :-).  Overwriting byte 0xe8 with byte 0xb8 in calls to printf
turns off individual printfs.

Bruce