Alzheimer's Syndrome

[Albert Hybl Dept of Biophysics SM]

In Message-ID: <8520 at smoke.ARPA> at Organization: Ballistic Research
Lab (BRL), APG, MD. writes:
# In article <406 at amyerg.UUCP> appleton at amyerg.UUCP (Ewan Grantham) writes:
# >In Mr. Hybl's article, he mentions his /usr4 file system losing it's
# >"memory" and suddenly running out of inodes.
# 
# That sounds like the kernel bug in the UFS code that was thoroughly
# dicussed on comp.bugs.sys5 a few months ago.  I suggest nagging AT&T
# for a fix.  Someone there MUST have heard about the problem and its
# solution by now...
#                 Reply-To: gwyn at brl.arpa (Doug Gwyn (VLD/VMB) <gwyn>)

Message-ID: <10611 at ulysses.homer.nj.att.com> from Organization:
AT&T Bell Laboratories, Murray Hill contained the following suggestion:

> Check /usr/spool/news/.rnews for zillions of 0-length files....
                                         (Steven Bellovin[jsw])

In my original posting, I stated that I used the wc command to
count the number of lines produced by the du -a /usr4 command.
One line is equivalent to one inode.  Since this number was
almost 3000 inodes short of full, I concluded that the file system
had lost its inodes.  "marbles :-)"

===============Summary of E-mail responses================

AS TO THE PROBABLE CAUSE:

"This is an OLD problem common to System V implementations of UNIX.
The problem resides within the kernel's inode allocation and release
mechanism."
                 From: uunet!cooper.cooper.EDU!mayer (Mayer Ilovitz)

He also gave an excellent description of the problem,
provided details to demonstrate it in a repeatable manner
and a hint on how to fix it if you have access to the kernel sources.
				Paraphrased from	Mayer Ilovitz
						mayer at cooper.cooper.edu
HOW TO FIX THE PROBLEM

a)  Fix the source, if you have it.
b)  Hack (using umount, fsck and mount).
      The suggestions I received are essentially similar
      to the example posted in Message-ID: <536 at happym.UUCP>
      From: kent at happym.UUCP (Kent Forschmiedt)
c)  Nag AT&T for a fix.

SOME CLOSING COMMENTS

First, let me thank all those individuals who replied to my
plea for assistance.  I will probably adopt a hacked solution.
It will be specific to news2.11 and not address the basic
problem in the kernel.  The best solution would be for AT&T
to fix the kernel code and issue a "recall" to all sysV UNIX
users.  Until there is a general fix, the Alzheimer's syndrome
will reappear every month or two as new usenet sites rediscover
it.  Based upon the number of "me too" messages and postings, it
is not an isolated problem.  In our case, only the posting of new
news is affected; the average reader is not likely to know of the
problem unless he/she is waiting for a lost posting.  More
disruption will occur if the news directories are on the
same file system as general user $HOME directories.

Surely the sysV bug is a disaster waiting to happen.  As the
number UNIX systems continue to grow, the scope of applications
will broaden.  We can live with an occasional loss of news.
However, there will be an application that will experience
the sudden unanticipated disappearance of inodes with tragic
consequences.  This could be at DOD, NSA, CPHA, NASA, SSA or
your local bank--who knows.

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Albert Hybl, PhD.              Office UUCP: uunet!mimsy!mbph!hybl
Department of Biophysics       Home   UUCP: uunet!mimsy!mbph!hybl!ah
University of Maryland                Cosy: ahybl
School of Medicine
Baltimore, MD  21201                 Phone: (301) 328-7940 (Office)
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