[nSLUG] Re: Multiply-claimed blocks?

Mike Spencer mspencer at tallships.ca
Wed Aug 31 16:25:15 ADT 2011

Dop Ganger <nslug at fop.ns.ca> wrote:

dop> No reason a magnetic bit on a hard drive can't be flipped as well
dop> as a bit in a RAM chip.

I'm not so sure that's true, at least not if you read "as easily" for
"as well".

A bit in RAM is (correct me if I'm wrong here) a very tiny pile of
electrons.  A bit on a HD is a magnetic region, a very small one for
sure but, AFAIK, nowhere near as susceptible to destruction/reversal
as a RAM bit.

In the usual course or operation, many files are written or re-written
on new blocks at times invisible to the user. The current or canonical
versions of some such files may be notionally "stable" of "static" but
nevertheless reside in RAM at different times. I *think/infer* that
this is true. If true, notionally static files could get silently
munged in RAM and written invisibly to disk.

In my case, AFAIK, libc really is static and is never re-written in
normal operation.

dop> I also vaguely recall hearing about a prof who ran a daily md5 of
dop> all the files in his ~, and regularly found checksum errors.

I should try that as a cron job, only in /lib and/or /bin.  I started
to set that up once as a security check but never finished it.

dop> Boot the Debian rescue disk (or any that take your fancy - I find
dop> Recovery Is Possible has a nice choice of tools), fix the disk,
dop> mount it on /mnt, then chroot /mnt and you are back in your
dop> Slackware environment to finish repairs.

In this case "fix the disk" required a good copy of the correct
version of libc and (possibly) running ldconfig in the ROOT=/mnt.
I tried various ways to get a copy of libc onto the HD but none of
them worked.  I was afraid to try ldconfig, with or without chroot,
because I don't fully understand it in detail. Reinstalling the entire
glibc package did work.

Until libc was fixed, chroot /mnt would have had me trying to load the
corrupt libc. (I did manage to get emacs-no-X working in the rescue
environment by doing some elisp twiddling of load-path but it was

Daniel Morrison <draker at gmail.com> wrote:

dm> I'm sure there's a live Slackware out there
dm> (http://www.google.ca/search?q=slackware+live and there seems to
dm> be a dozen, including "Making my own Slackware Live CD").

Oh, good.  I'll have a look.

dm> I haven't used the DVD to boot in... must be years and years. I
dm> decided to stop wasting plastic and do everything with network
dm> boot instead.

I suspect you compute in a much more sophisticated environment that I
do.  I have two machines more or less up to date with Slack 11.0 (main
one) and Slack 12.1 (the other one) but no organized management setup
that I would need if I were supporting numerous other users/boxen.
Nice, tangible read-only chunks of plastic make me feel secure,
however speciously. :-)

- Mike

Michael Spencer                  Nova Scotia, Canada       .~. 
mspencer at tallships.ca                                     /( )\
http://home.tallships.ca/mspencer/                        ^^-^^

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