How to enter DDB through a terminal server / remote console ... ?

[Robert Watson]

On Wed, 28 Jun 2006, User Freebsd wrote:

> On Wed, 28 Jun 2006, Robert Watson wrote:
>
>> On Wed, 28 Jun 2006, User Freebsd wrote:
>> 
>>> 'k, now that I'm up to 3 6-STABLE servers that are deadlocking, I'm 
>>> spending time with the remote tech today to get a serial console put 
>>> online ... how do I drop into DDB remotely, where the serial console is 
>>> going through a Portmaster Terminal server?  issuing CTL-ALT-ESC, I doubt, 
>>> will work, will it?
>> 
>> If configured to use a serial console (console="comconsole" in 
>> loader.conf), you can enter the debugger with BREAK_TO_DEBUGGER in the 
>> kernel config by sending a serial break.  With my portmasters, I telnet to 
>> a TCP port to connect to the serial console, so I send a telnet break, 
>> using ^]send break.
>
> Have you ever had a problem with this warning: "(useful for remote 
> diagnostics, but also dangerous if you generate a spurious BREAK on the 
> serial port!)" in the handbook?

Yes.  It's unusual, but once in a while I get a nervous serial port.  If you 
experience this, type "Cont" to continue, and then recompile your kernel with 
ALT_BREAK_TO_DEBUGGER but without BREAK_TO_DEBUGGER.  Here's the notes entry:

# Solaris implements a new BREAK which is initiated by a character
# sequence CR ~ ^b which is similar to a familiar pattern used on
# Sun servers by the Remote Console.
options         ALT_BREAK_TO_DEBUGGER

I've not had problem a problem on any recent hardware except for my soekris.

Robert N M Watson
Computer Laboratory
University of Cambridge