@ as kill on login

[Chris Torek]

In article <570004 at hpsemc.HP.COM> bd at hpsemc.HP.COM (bob desinger) writes:
>[It and #-as-erase are] the only characters guaranteed to work while
>logging in on nearly any version of Unix.

But not any version:  `@' does not work on University of Maryland
Computer Science Department machines, for the reason that it is
needed for something else:

	login: guest at timbuktu
	Sorry guest, but timbuktu isn't in the local cluster of machines.
	Send mail to staff at timbuktu to inquire as to the best way to
	connect.

	This login attempt has been recorded.

Believe it or not, the only part of this that is a special case
is that `@host' tells login to log in as user `Rlogin' with shell
`rsh <host> -l <login> -enone' (-enone is another local hack).
The restriction comes from a more general mechanism:  If the
file /etc/restrict/login/<username> exists, it is run after
deciding the password is correct.  If this file exits with a
nonzero status, login rejects the login attempt.  Hence we can
have a `halt' account with no password (it only works from the
console), or temporarily disable a wayward student's account
with a message:

	#! /bin/sh
	cat << eom
	J.Q. Public, talk to Dr. Staff about those 10,000
	pages you printed on the Imagen yesterday....
	eom
	exit 1
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain:	chris at mimsy.umd.edu	Path:	uunet!mimsy!chris