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000098_news@watsun.cc.columbia.edu _Wed May 26 13:22:52 1999.msg
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From: jaltman@watsun.cc.columbia.edu (Jeffrey Altman)
Subject: Re: kermit process hangs around after terminal disconnect
Date: 26 May 1999 16:54:48 GMT
Organization: Columbia University
Message-ID: <7ih90o$fe2$1@newsmaster.cc.columbia.edu>
To: kermit.misc@watsun.cc.columbia.edu
In article <7ih1du$rfg$1@nnrp1.deja.com>,
Mr. Scott <scott_davis@my-dejanews.com> wrote:
:
: > Which indicates that your Telnet connection was no longer valid
: because
: > the AIX box did not recognize that the connection was terminated. If
: the
: > AIX box received the connection closure it would have terminated the
: > shell, the kermit process, and anything else that you were running.
:
: Okay, now it's your turn to explain a bit more.
:
: Are you saying that my Procomm session disconnected without realizing
: it was disconnected and without sending some sort of message to UNIX
: saying "hey, i have disconnected", and therefore UNIX didn't clean up.
: Wouldn't UNIX sense a broken connection even though a nice, neat, "hey,
: I'm disconnected" message didn't arrive?
:
: One thing I can see clearly now, and thanks in advance for leading me
: to think it out myself. That is, I understand why kermit is hanging
: around. Obviously, if UNIX thinks I'm still running my shell, there's
: no reason to send a HUP to kill kermit. But why does it still think
: I'm running my shell when my session terminated? I know this goes back
: to the previous paragraph's question, and I await what I'm sure will be
: a very interesting answer.
>From the standpoint of the Unix side of the connection everything is
perfectly fine. It has not received any data in a long time but there
is no requirement that it ever receive any data. Nor has it tried
to send any data therefore as far as it is concerned everything
is ok.
>From the Procomm side, it looks to me that Procomm is not checking the
error code of attempts to write to the socket. If it did it would
eventually determine that the route between the PC and AIX is no
longer functioning. The problem could be caused by extremely high
packet loss rates over the Internet or a router which has been
restarted.
What Kermit 95 would do in this situation would be to check the error
condition of each attempt to write data. The first attempt to send
data on a broken connection would not report an error but all future
attempts would fail. Once a failure was detected K95 would close
the connection. However, this might not help you. If the cause of
your problem is a router that is no longer functioning, there is no
way for the PC to indicate to the AIX box that this particular
TCP/IP connection is being closed.
If you want the host to detect that the connection is no longer
valid, the telnetd will have to be modified to attempt to send some
message on a periodic basis to test the connection. This could be
a telnet go ahead or a telnet data mark message. Anything that the
client will process and not respond with real data.
Jeffrey Altman * Sr.Software Designer * Kermit-95 for Win32 and OS/2
The Kermit Project * Columbia University
612 West 115th St #716 * New York, NY * 10025
http://www.kermit-project.org/k95.html * kermit-support@kermit-project.org