Re: agetty question

blender@xxxxxxxxx wrote:
any clues how to find some info?

The Natural Philosopher napisal(a):
blender@xxxxxxxxx wrote:
\
Hi all !!

I have one question.

Is it possible to write to serial port while agetty is "listening"
(initiated by initab)?

Best Regards
David

Used to be. There is some negotiation that allows another process to
'steal' the port from getty, IIRC.

Man agetty?

Certainly all serial ports could be used by modem programs like cu even with getty programs hanging off the back. So you could use the modem to accept calls and dial out with as well.

I haven't got agetty here - just Linux getty - or cu...try looking for source code for cu and see what it does..

Something in my brain is telling me that the serial port has two interfaces, one that getty attaches to and another that can be opened by another program...can't remember the syntax, but on some systems it uses to be the same /dev/tty[sS] but with upper case for the getty one. Or at least it had on SCO unix.

Hmm. There's also pseudo terminals..I am buggered if I can remember what does what..

Anyway there is another program that opens serial ports whilst getty is hung on them - pppd. So you can dial outwards and connect to a router etc.

It looks like MY linux (Debian) only uses one instance of the port - /dev/ttyS[1-4]

That has a straight getty hung on it, and also pppd uses it (or would if I had it configured)

I am FAIRLY sure that even with a getty on, you can open and close and read and write a serial device...some magic ensures that YOUR open disables and kills the getty, which is respawned after you close the device.






.

Relevant Pages

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