Path: utzoo!attcan!uunet!dino!ux1.cso.uiuc.edu!usenet
From: bruner@sp15.csrd.uiuc.edu (John Bruner)
Newsgroups: comp.sys.mac.comm
Subject: Re: mesg status under Ultr*x MacLayers
Keywords: MacLayers Ultr*x mesg
Message-ID: <1990Jul12.143751.3365@ux1.cso.uiuc.edu>
Date: 12 Jul 90 14:37:51 GMT
References: <8562@uhccux.uhcc.Hawaii.Edu>
Sender: usenet@ux1.cso.uiuc.edu (News)
Reply-To: bruner@sp15.csrd.uiuc.edu (John Bruner)
Organization: CSRD, University of Illinois
Lines: 31
In-Reply-To: mah@uhccux.uhcc.Hawaii.Edu (Michael Hoffhines)

Your inability to use "talk" probably is caused by a non-writable
"/etc/utmp" file on your Ultrix system.  This file, used by programs
such as "who" and "w", records the current users on the system.  It
normally is written by "login" when you log in and cleared by a system
daemon (either "init" for devices directly attached to the machine or
the rlogin/telnet daemon for network connections).  Many Unix machines
do not allow write access to this file because of the confusion that
it could cause.

If MacLayers (or UW, or xterm, etc.) can't write "/etc/utmp", then you
won't appear in a "who" listing and "talk" can't find you.

If I recall correctly, MacLayers is cognizant of the responsibilities
of running setuid or setgid.  Therefore, it is possible to make the
"/etc/utmp" file group writable for some owner/group "foo" and make
MacLayers setuid/setgid-foo.  That is a subject which you must discuss
with your system administrator.

You may also have discovered that you can't change your message
permission with "mesg".  The reason for this is related -- you don't
own the pseudo terminal (MacLayers can't change the owner to you);
therefore, the chmod() call in the "mesg" program will fail.  I don't
know if MacLayers has the code to do this.  It would require making it
setuid-root.

It might appear that you can work around this by running "login" in
the window; however, *don't do it*.  It will write the "/etc/utmp"
entry and will change the owner of the pseudo-terminal to you, but
when the shell terminates nothing will clean it up.  This will make it
appear that you are still logged in, and the pseudo-terminal will be
unusable by anyone else.