[Posted and mailed]
> i try to connect an old macintosh over a nullmodemcable with my suse
> linux 6.4 pc on ttyS0. i veryfied the connection under msdos.
> q1: how to setup atalk to use ttyS0 instead of eth0
> q2: how to setup tcp/ip to use ttyS0
For TCP/IP networking, your best solution is probably to use PPP. You
can run pppd in daemon mode on the Linux box, so that it accepts PPP
connections, by editing /etc/inittab. The Linux PPP HOWTO document
(http://www.linuxdoc.org/HOWTO/PPP-HOWTO/index.html) has more details.
I don't know precisely how you'd configure the Mac to handle PPP without
the usual modem dialing and whatnot, but it's probably possible. If
nothing else, you could write a custom Linux shell script that simulates
the dialing and whatnot for the Mac's benefit.
A better solution is to bypass the serial port altogether and go for
Ethernet networking. If the Mac's old enough, it may not have Ethernet
support, and some particularly ancient models may not even allow you to
add an Ethernet card. If that's the case, there are (or were; I don't
know if they're still made) a few LocalTalk cards for x86 computers,
and at least two or three of these do have Linux driver support. Check
the Linux kernel configuration options for details. Alternatively,
there are some Ethernet/LocalTalk bridges available, like the
(http://www.asante.com/product/adapters/MicroAP.html). Either way, you
can then use normal Linux TCP/IP networking tools and a TCP/IP stack on
the Macintosh (which you may need to add, if the version of MacOS is as
old as it sounds like the hardware is).
Author of books on Linux & multi-OS configuration