Re: Modem /dev/cua vs /dev/ttyS (The Long, True answer to this reappearing question)
Serial device locking by convention uses files in a special directory which
are named according to the name of the device. Unless all references to the
device use the same name, this locking fails. That's why cua devices are no
longer used. Why were they ever used? Because old versions of unix had two
different devices for the same serial port, one on which an open would hang
until the device asserted Carrier Detect (which getty's used) and another
which open would return without having Carrier Detect (used for program which
wanted to dial out on the modem). In the modern world we have the same device
for both uses and control this type of behavior by passing flags to the open
system call. For a while the old cua device files were kept around so that old
programs which referenced serial lines as cuaX would still work. This however
created a lot of problems because the locking convention fell apart unless
everyone used the same device name. Thus cua devices were forever banished.
Robert D. Hilliard wrote:
> Maybe someone more knowledgable can answer this, I can't. I have
> never had any problems with /dev/ttyS? devices in a script. I have
> been hearing that /dev/cua? devices are deprecated for years, and they
> haven't been included in the debian distribution since rex.
>
> Bob
>
> On Tue, 10 Feb 1998, Steve Hsieh <steveh@eecs.umich.edu> wrote:
> >
> > Use of /dev/cua? may be deprecated, but I can't get scripts to work with
> > /dev/ttyS?, only /dev/cua?. Can anone explain why?
>
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--
Jens B. Jorgensen
jjorgens@bdsinc.com
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