Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!csd4.milw.wisc.edu!uxc!uxc.cso.uiuc.edu!kailand!pwolfe
From: pwolfe@kailand.KAI.COM
Newsgroups: comp.sys.sequent
Subject: Re: why does who not show rlogin-users
Message-ID: <2400057@kailand>
Date: 10 Jun 89 15:54:00 GMT
References: <964@maestro.htsa.aha.nl>
Lines: 51
Nf-ID: #R:maestro.htsa.aha.nl:964:kailand:2400057:000:2817
Nf-From: kailand.KAI.COM!pwolfe    Jun 10 10:54:00 1989


> /* Written by phil@sequent.UUCP in kailand:comp.sys.sequent */
> In article <964@maestro.htsa.aha.nl> jand@maestro.htsa.aha.nl (Jan Derriks) writes:
> | Is this bug is a way of getting over the 32 user limit ?
> Nope!

Yep!  Since /bin/login counts users by counting entries in /etc/utmp, if you
are missing entries for some real or pseudo terminals in /etc/ttys, those
logins don't get counted.

I asked Sequent to find a better way to count logins back in early 1988, when I
installed Screen V2.0, which had a new feature of adding entries to /etc/utmp
for each window it created.  Screen didn't count the existing /etc/utmp entries
to make sure we didn't go over our limited user limit (and it shouldn't have
to, since I don't think each window of a virtual terminal manager should be
considered a separate login), and the next person to really login caused the
system to panic "illegal number of users".

Sequent Customer Service's official responce was "this will not be changed",
and now that I understand the next release of Dynix will be based on System V
(release 2? 3?), I guess I understand why they are reluctant to spend any time
fixing non-serious bugs in the current release.  I've since fixed Screen to
(among other things) count logins (like /bin/login does) before adding any
entries to utmp, and to allow each user to selectively "login" or "unlogin"
windows at will.

How does BSD 4.3 count logins?  I've seen the quota checks in 4.3 tahoe's
/bin/login (anonymously ftp'able from uunet.uu.net), but don't know where/how
the data is actually stored and modified.

We've run into problems when someone's session gets killed, but the entry in
utmp doesn't get removed.  They don't have any processes running, but they
still show up in "w" or "who", and they also take up one of those precious user
slots (one of our machines has only a 16 user license, and we have approx 20
people that want to use it).  I've written a program to zero out specified
entries from the utmp file, which I use to fix this problem (since the only
other workaround is to reboot).

While I only use my program to fix problems, a dishonest system administrator
might use something similar to it in /etc/.login, so their site would never
have to upgrade their user license (which is pretty cheap anyway).

Also, if someone wanted to port that BSD 4.3 Tahoe /bin/login program, or
install the one that passed through the source newsgroups earlier this year,
they wouldn't run into user license limit problems (except possibly problems
of the legal type, of course).

Patrick Wolfe	(pat@kai.com, {uunet,uiucuxc,alliant,sequent}!kailand!pat)
System Manager, Kuck and Associates, Inc.
"The opinions expressed here are strictly my own, and not neccessarily
those of the company I work for.  Please don't call my boss (again)."