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From: vanni@mit-caf.UUCP (Giovanni Berti)
Newsgroups: comp.unix.wizards
Subject: A synchronization problem with 4.3BSD MAIL ??
Message-ID: <375@mit-caf.UUCP>
Date: Thu, 18-Jun-87 18:13:17 EDT
Article-I.D.: mit-caf.375
Posted: Thu Jun 18 18:13:17 1987
Date-Received: Sun, 21-Jun-87 16:17:43 EDT
Organization: Microsystems Technology Laboratory, MIT
Lines: 50
Keywords: mail bug  4.3bsd ??


	We run the standard MAIL and sendmail under 4.3BSD.

	>>>> You might actually be loosing mail too <<<<
	
	The only reason why we saw the problem is because the
	user has biff set (biff yes) and stays loged on for several
	days at the same terminal.   Therefore whenever sendmail deliver
	new mail to him, a message will remail on his screen.
	
SYMPTOM
	User gets message (via comsat) that there is new mail,
	user enters mail, but no new message exists.
	Sometimes upto 2 successive messages have disappeared.

BEHIND the SCENE
	Sendmail did actually attempt to deliver the mail.  In some cases
	if /usr/spool/mail/$user was examined, prior to invoking mail to
	read the massage, a partial new message was found.  In most cases
	new message had no header and only a portion of it was in the file.

	Note that if user had invoked mail, seen no message and quit, there
	would be actually NO TRACE of the message, except via the sendmail
	log file.   Because of this one would typically think that it was
	user errror ... but it was NOT.


	This is not a reproduceable bug, and have been unable to reproduce it.
	But we have seen it occur an average of of several times a month for
	user which get an average of 10 message per day.
	
	NOTE also that the system and filesystem have been in very stable
	condition, so this has nothing to do with corrupted file or filesys.


POSSIBLE EXPLANATION
	The user could have been loged on 2 terminals and actually
	running mail from at least one of the terminals.  This could
	potentially cause the situation were 3 different programs are
	operating on the same file (/usr/spool/mail/$user).

>>	For example sendmail would be writing to the file, while 
>>	the user could be closing the file.

	Does anyone know how MAIL handles these situations ???

Any suggestion will be apreciated.
thanks in advance.

-vanni