On Mon, 21 Dec 1998, Arun K. Khan wrote:
> Until now, I was under the impression, that once a specific device is
> locked it cannot be used by another process (to ensure availablity of
> service by the locking process). If the **same** device can be used by
> (each using it's locking mechanism) mgetty/diald/minicom respectively then
> I am interested in finding out how it can be done. I would appreciate if
It's simple: the locking is purely advisory. That is, the presence of the
lock file does NOTHING to prevent another app from trying to open the
"locked" device. Depending on the device and the actions of the locking
app, such an attempt may or may not succeed. The prescribed way of
handling these locks and getting the apps to share one device for
sequential access is quite a bit more involved.
> I have not seen any clear views on this. Some say /dev/cua* are the old
> serial devices provided for backward compatibility and that only /dev/ttyS*
> should be used to call out/in. Some say, use ttyS* to call in and cua* to
> call out. Fr FreeBSD serial devices see above.
/dev/cua* WILL be going away in the future. They were an attempt to solve
the various problems involved in using the UUCP-style lock file method of
sharing access. Their use is discouraged at this time, as it has ben for
over a year now. I *think* that 2.2 will have a "mild annoyance" log
entry whenever /dev/cua* is used, but I may be misremembering, or the plan
may have changed since I heard about it.
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