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From: kre@cs.mu.oz.au (Robert Elz)
Newsgroups: comp.unix.wizards,alt.security
Subject: Re: BSD tty security, part 3: How to Fix It
Message-ID: <kre.673801266@mundamutti.cs.mu.OZ.AU>
Date: 9 May 91 15:01:06 GMT
References: <12535@dog.ee.lbl.gov> <15896: Apr2714:35:3991@kramden.acf.nyu.edu> <kre.672866069@mundamutti.cs.mu.OZ.AU> <1991May8.050005.26963@cbnewsh.att.com>
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wcs@cbnewsh.att.com (Bill Stewart 908-949-0705 erebus.att.com!wcs) writes:

>I disagree - you have to remember what "write" is supposed to be for:

I'm quite aware what its supposed to be for ...

>* "mail" is for sending people messgaes with potentially structured
(and is irrelevant here)

>* "talk" is for coordinated real-time conversations between people,
>* "write" is for rudely interrupting people who haven't pre-arranged 

I disagree with this .. both initiate conversations, both rudely
interrupt, the sole difference there is that with talk I cannot
see any hint of the other person's message until I respond, and
both have a very fixed interface style, that I can't alter.

The interface we have does not require any pre-arrangement in order
for someone to write to you, a user who does nothing at all will
see nothing different from current practice.  No users need to more
than put a shell script in their login directory to be able to
selectively permit selected users to "rudely interrupt", while
totally ignoring others, and directing others to a less intrusive
communication mechanism.

Unless you have operated in an academic environment with lots of
moronic undergrad students you may not appreciate the usefulness of
selective message control - I don't want to prevent messages from
colleagues, nor necessarily from all but a few known people, but
I do want to be able to make messages from known obnoxious twerps
vanish into a bit bucket.   "Mesg n" simply isn't enough.

It also allows that want to take the effort (which need not be very
great) to create any kind of interface they desire - there is no
particularly good reason why just because someone chooses to use
"write" to initiate a conversation I can't use an interface that
looks like talk, with his message appearing in one window, and
my replies being typed in another - I will still see his lines one
at a time, as he types them, rather than character by character,
as that's te interface he has chosen - he will get my reply lines
line by line as well.  My "talk" interface may be an X application,
or it may just be on a regular terminal using curses.   If the guy
at the other end is using an intelligent interface too, that may
buffer my reply lines until he types 'o' along the typical lines
of a traditional write type conversation.

>The other aspect to this problem is that sometimes root really does
>need to interrupt you, and that can easily get lost in a window system
>or an editing or graphics session.  Any suggestions here?

The same one - obviously how easy it is to provide an unambiguous
but not overly intrusive interrupt mechanism depends on the details
of your particular situation.  On a typical 80x24 terminal there isn't
much possible beyond blatting characters onto the terminal, but given
that its your terminal, so you know its characteristics, you could
make an interface that clears the screen and puts the message in the
middle.   If you have a slightly smarter terminal, it may have switched
to analternate memory page, or something, then restore your work when
you have seen the message - in any case, the point is that its up to
the user to decide just how, and when, if at all, he wants to be interrupted.

kre