[ale] configuring getty for dialOUT logins

Joe jknapka at mindspring.com
Fri Aug 2 18:36:22 EDT 1996

> I'm trying to connect two linux computers via a serial cable and a null
> modem.  I haven't a clue what's wrong, but it worked one time...then never
> again.  The problem is simple...nothing happens.   I run minicom, and
> thwap the enter key like a madman, but nothing shows up.  Sending a break
> doesn't help, sending a hangup does nothing.  I have no idea what's wrong.
> I know the server is fine because it works flawlessly in DOS/Windows, and
> I had a login prompt one time in linux, but since then, nothing.  Can
> someone send me a checklist of common problems or things I may have
> overlooked?

This sounds like an interrupt conflict or some such. I have just
managed to get a Wyse 60 hooked up to COM4 (ttyS3) on my machine, and
I initially saw symptoms similar to this - then I realized that (a) My
ppp connection was up, and (b) my modem (on ttyS1) was sharing
interrupt 5 with ttyS3. Killed off ppp, everything worked. I can even
leave a getty on that terminal while ppp is up, as long as I don't
actually try to log in :-)

In general, look at the following:

(1) Do you need a null-modem adapter? (probably)

(2) Ensure that the two machines agree about such issues as
transmission speed, flow control (XON/XOFF vs RTS/CTS vs none), byte
size, stop bits, and parity. You can find all these things out by
using stty and setserial, but _read the man pages_ for those things,
because the output is rather cryptic, and need not mean what you
naively assume it does.

(3) Make really sure that you are talking on the ports you think you
are. I've done a lot of work on troubleshooting serial line troubles,
and I have been known to religiously believe I had my software talking
to comX, but found out through some weird circumstance that it was
really configured for some different com port. (D'oh)

(4) If you have access to a protocol analyzer or a "blinky-box"
(serial breakout box), stick it in the loop to make sure you're data
is getting out of the serial port. A blinky box costs about $10 at
Radio Shack; it has LEDs on it that show you when the xmt and rcv and
flow control signals are active.

Good luck,

-- Joe

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> Much thanks,
> Michael

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