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From: jkp@cs.HUT.FI (Jyrki Kuoppala)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: How to get an urgent message to an arbitrary system
Message-ID: <24344@santra.UUCP>
Date: 11 Aug 89 23:15:49 GMT
References: <681@east.East.Sun.COM>
Sender: news@santra.UUCP
Reply-To: jkp@cs.HUT.FI (Jyrki Kuoppala)
Organization: Helsinki University of Technology, Finland
Lines: 88
In-reply-to: geoff@hinode.East.Sun.COM (Geoff Arnold @ Sun BOS - R.H. coast near the top)

In article <681@east.East.Sun.COM>, geoff@hinode (Geoff Arnold @ Sun BOS - R.H. coast near the top) writes:
>My reaction was to say "let's ask the NIC for a UDP port so that
>we can use it to send unsolicited messages to PCs running PC-NFS."
>That would certainly do the trick. However, a moment's thought
>reveals that the problem is bigger than just PC-NFS. Surprisingly,
>there is at present no simple ubiquitous message protocol to fulfil this
>function. rwall is fine for SunOS and other ONC licensees, but
>what about other systems? Do I have to rely upon SMTP? That's
>incompatible with the idea of broadcasting a simple message
>such as "The backbone will be down for five minutes at 12:00
>to replace a bridge." 

Not exactly what you need, but to get experience with SunRPC, I wrote
a program called `rmsg' which can be used to send short (a few lines)
messages to users on other machines.  The program works quite like the
bitnet send / tell feature, except that it directly contacts the
remote machine with tcp/ip instead of using user-mode links as it's
done on bitnet.

Rmsg is available for anonymous ftp on sauna.hut.fi (128.214.3.119) in
the directory pub/tcpip.  Due to disk malfunctioning, anon ftp is not
in use currently, but hopefully will be again in a few days.

I haven't yet looked at zephyr, but I suppose it has more features and
solves the problem of inter-user communications well.  However, rmsg
might be simpler to install.  I hope it's useful to someone; we've
been using it locally for some time, and it's nice because it's not as
much a hassle as a full-screen application like talk is.

Enjoy,

//Jyrki

Here's a README file from rmsg:

This directory contains a messaging system which can be used to send
write-like messages to logged-on users.  The system can cross machine
boundaries, so if another machine has the rmsgd program running, you can
send messages to users on it.

The system also allows bitnet virtual machine-like 'virtual users'
to whom any user can send messages and they can answer the messages.
The rmsgd server makes this possible by allowing a command 'exec' in a users
.msgconf file, and whenever the user receives a message this command is
executed and the message is piped to it.

It is also possible to log incoming and outgoing messages and resend previous
sent message.  You can specify a file to which the last (or every) incoming
message will be stored.

Using the programs:
-------------------

Rmsgd:

Rmsgd is the server program for the system.  It should be started by root,
but for now it works even if started by ordinary users, even though
some capabilities are disabled for security reasons (that is, exec and 
logging of incoming messages, since that would be done by the user-id
who started rmsgd and not the receiver).

At any time, there should be only one rmsgd running.  It doesn't do any harm
to have several rmsgds other than the newly-started servers unmap the
previous and thus the previous servers are unusable.

The server should be named 'rmsgd' to have it start as a daemon.


Rmsg:

Rmsg is the client end of the system.  Rmsg is used by ordinary users
to send messages.  For example, rmsg foo@bar hello there !  ^D would
send a message 'hello there !' to user foo at machine bar.  By
default, rmsg stores the last outgoing message in the user's home
directory in the file .msgout.  Then msg -r user@machine can be used
to resend the message.  Message is normally read from standard input
until EOF.

Configuration:
--------------

The messages system has many options which the user can set by making
a file '.msgconf' in her home directory and placing various command in it.
Read the manual page for rmsg for more information.
-- 
Jyrki Kuoppala    Helsinki University of Technology, Finland.
Internet :        jkp@cs.hut.fi           [128.214.3.119]
BITNET :          jkp@fingate.bitnet      Gravity is a myth, the Earth sucks!