I have installed DDD-3.3.9 and DBG-2.11.26 (properly, I think), using PHP 4.3.6, and have also installed DBG-CLI-2.11.0.
When I run the script, I see:

This program makes use of the Zend Scripting Language Engine:
Zend Engine v1.3.0, Copyright (c) 1998-2004 Zend Technologies with DBG v2.11.26, (C) 2000,2001,2002,2003, by Dmitri Dmitrienko

Also, the dbg section shows:

Version 2.11.26
Linked as a shared library.
Profiler compiled, enabled

Directive Local Value Master Value
debugger.enable_session_cookie On On
debugger.enabled On On
debugger.fail_silently On On
debugger.ignore_nops Off Off
debugger.JIT_enabled Off Off
debugger.JIT_host clienthost clienthost
debugger.JIT_level 3 3
debugger.JIT_port 7869 7869
debugger.profiler_enabled On On
debugger.session_nocache On On
debugger.timeout_seconds 300 300

When I try to start DDD, with or without the DBG option
( #ddd
or
#ddd --dbg )
I see a "DDD:No Debugger" message box, with the message "DBG could not be started.". The panel on the bottom shows "GNU DDD 3.3.9 (i686-pc-linux-gnu), by Dorothea L/bin/sh: line 1: exec: dbg: not found"

I also tried
and still get the message box.

Any suggestions?
Also, I'm not sure if this should be considered a separate topic: I did not apply the dbg-ddd-patch file, version 2.11-3.3.8, which is on sourceforge.
Could this be a possible cause of this problem? If the patch is necessary, where and how should it be applied?
Thanks.

dbg.so is NOT a console debugger.
You need dbg-cli

Thank you.
Resetting that path has resolved it.