"line monitor" for Linux...?

[Jeff Gordon <jeff.gordon@wellnow.com>]

Under OS/2, a nifty utility called Poor Man's LIne Monitor (PMLM) was
included with Ray Gwinn's SIO com ports drivers. PMLM allowed one to
watch was passing through the serial port during online conversations
-- very useful for debugging connections and for retrieving forgotten
encrypted passwords, etc.

I don't find a "line monitor" for linux -- is it because there's a
system command that would accomplish the same thing...?

Same general category:  OS/2's "iptrace" command recorded packet 
conversations between clients and servers on TCP et al.  Is there 
a linux equivalent?
-- 

 -- Jeff --   <http://www.wellnow.com>

 "There's nothing left in the world to prove.  All that's worth doing
  is to love one another, using whatever means are available to serve."