[comp.sources.d] Unusual behavior in "screen"

dhesi@bsu-cs.UUCP (Rahul Dhesi) (08/25/87)

Summary:
     Torture-testing the "screen" program, which allows multiple
     virtual terminals to be created, I found that it is possible
     to get spurious entries in /etc/utmp.
Software:
     4.3BSD straight from Berkeley, obtained around September 1986.
Hardware:
     VAX-11/785.
Symptoms:
     After a user logs out from a new login session that was running under
     control of "screen", the user's name is still in /etc/utmp and
     the "who" command will show the user still logged in.
Repeat-By:
     1.   Invoke "screen".
     2.   Execute /bin/login by typing "/bin/login".
     3.   Log normally at the login prompt.
     4.   Log out normally.
     5.   Use the "who" or "w" command and observe that you are shown
	  logged in twice.
Comments:
     It's a bit disconcerting to be able to create an entry in
     /etc/utmp that doesn't seem to get removed.  This confuses my
     timeout program, because it examines /etc/utmp to look for idle
     users.
-- 
Rahul Dhesi         UUCP:  {ihnp4,seismo}!{iuvax,pur-ee}!bsu-cs!dhesi

net@tub.UUCP (08/26/87)

> Symptoms:
>      After a user logs out from a new login session that was running under
>      control of "screen", the user's name is still in /etc/utmp and
>      the "who" command will show the user still logged in.

You didn't install "screen" with set-uid and owner root as explained
in the README-file, the Makefile, and the BUGS-section of the manual page.
If "screen" isn't granted write access to /etc/utmp it cannot remove
the utmp-entry inserted by /bin/login.  You can reproduce this ``bug in
screen'' even without the help of "screen": Just run /bin/login on a
random pseudo-tty without the help of friendly set-uid programs like
"rlogind" or "screen" that clean up after you.

--
    Oliver Laumann, Technical University of Berlin, Germany.
    ...!pyramid!tub!net   or   net@TUB.BITNET

"I have yet to see anything posted by Dhesi that was correct."
       --Doug Gwyn

dhesi@bsu-cs.UUCP (Rahul Dhesi) (09/01/87)

In article <49100001@tub.UUCP> net@tub.UUCP writes about my report
that "screen" can leave behind ghosts in /etc/utmp:

>You didn't install "screen" with set-uid and owner root as explained
>in the README-file, the Makefile, and the BUGS-section of the manual page.

>    Oliver Laumann, Technical University of Berlin, Germany.
>    ...!pyramid!tub!net   or   net@TUB.BITNET

But I did.
-- 
Rahul Dhesi         UUCP:  {ihnp4,seismo}!{iuvax,pur-ee}!bsu-cs!dhesi