2-user systems

[David Dawes]

In article <PCG.90Nov27172113 at odin.cs.aber.ac.uk> pcg at cs.aber.ac.uk (Piercarlo Grandi) writes:
>On 26 Nov 90 11:30:40 GMT, dawes at suphys.physics.su.OZ.AU (David Dawes) said:
>dawes> Nntp-Posting-Host: suphys.physics.su.oz.au
>
>dawes> For what its worth: On DEC's Ultrix with a 2 user license, a max
>dawes> of 2 users may be logged in at a time.  These 2 users may however
>dawes> be logged in any number of times (from ethernet, serial lines,
>dawes> console or wherever).  root is also able to login when two other
>dawes> users are logged in.  This to me seems the most logical way of
>dawes> implementing a 2-user system.
>
>No, it's a famous and catastrophic bug of some old release of Ultrix.
>It is catastrophic because the limit is not two logins, but two UIDs, as
>you say; so it can be easily circumvented by using the same uid for
>multiple users, and more nastily, if you have something like uucp or the
>printer spooler or other daemon running under its own UID, the number od
>UIDs is reduced even if nobody is logged in.

As I recall, with Ultrix 2.2, the limit was two UIDs logged in.  It worked
on entries in /etc/utmp.  Sure this can be overcome by people sharing UIDs,
but (at least with this version of Ultrix) the number of UIDs was not
reduced by any background or daemon processes that might be running.

David
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 David Dawes (dawes at suphys.physics.su.oz.au) DoD#210   | Phone: +612 692 2639
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