From: utzoo!utcsrgv!dave
Newsgroups: net.unix-wizards
Title: Re: Dialing In/Out through same port
Article-I.D.: utcsrgv.1302
Posted: Tue Apr 19 09:30:34 1983
Received: Tue Apr 19 14:44:11 1983
References: sri-arpa.902

There's an even simpler way, though slightly grungier, than what
Paul Milazzo suggests. Simply have a program which edits /etc/ttys,
and sets the entry for the line used both ways to 0 (for dialout)
or 1 (for dialin), followed by a "kill -2 1" to reinitialize the
existence/nonexistence of getty on that line. When uucp wants to call
out, it simply calls this program before it starts (to do away with
getty) and calls it again when it's done (to bring getty back).
Of course, the program has to be setuid, and you have to make
sure two people aren't trying to muck with /etc/ttys at the same
time. And you may need to send a stty hup to the line to make the
modem hang up.