[ILUG] (en?/dis?)-abling modem-control signals on a (not-open) serial port?

[Brian Foster]

 I'm running SUSE 9.2 and, for various not-relevant
 reasons, decided to run the YaST2 init(8) “runlevel”
 editor.  it hung during its initialisation.  after
 investigating, I determined the bash(1) command:

   isserial </dev/ttyS1

 is hanging; strace(1) shows the (bash) open(2) of
 /dev/ttyS1 is hanging.  this isn't too surprising
 since ttyS1 is the serial modem (and all this was
 done whilst I was off-line; i.e., that serial port
 is NOT open, and there is probably no other process
 trying to open it (and the permissions are not the
 issue!)).

 after a few false starts, I determined the hang is
 because the line has _somehow_ been configured to
 require various modem-control signals (i.e., it's
 not a simple 3-wire connection).  again, not too
 surprising (albeit it took me awhile to get to
 this “obvious” point!  ;-\  ).   the (admittedly
 unused) non-modem serial port is not so configured.

 but at this point I'm stuck:  how does Linux (2.6)
 configure a serial port to use (or to not use?)
 modem-control signals?   this is (now) just for my
 own curiosity since the original YaST2 problem can
 be solved by a bit of hacking on the relevant shell
 script.  I've _no_ intention of changing anything
 w.r.t. the modem or the serial port; I am (now)
 simply curious.

 ( apologies if this is described someplace; I've
  drawn a blank with quick searches for an answer.
  nor did I spot anything in /etc/init.d/*, albeit
  it's always possible I missed something? .... )

cheers!
	-blf-
-- 
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