[PLUG] Busted computer

John Jason Jordan johnxj at comcast.net
Wed Oct 17 05:13:20 UTC 2007


This time it seems to be a bad superblock. Googling on "superblock"
yields a lot, but the more I google the confuseder I get. Here is what
led up to the problem:

A couple days ago at PSU the computer would not boot. The error message
seemed to have something to do with being unable to find the Realtek
ethernet port. I carry a phillips head screwdriver with me, and I used
it to disassemble the part of the case over the ethernet plug. Then I
tapped on it a lot, loosened and tightened the screws holding the
housing over it, and reassembled it. It booted normally. But later at
home it exhibited the same symptoms. I got it to boot just by banging
it lightly on the corner where the ethernet plug is located. Since then
I have rebooted half a dozen times without incident.

Today, upon returning home from PSU, I got 

Grub loading 1.5
Please wait
Error 2

All the usual disassembly/banging on things/reassembly failed to remedy
the problem. "Error 2" appears to be a Grub error that means (loosely
translated) "dude, sumpin' bad happened to your filesystem." Further
googling and trying various things at the command line after booting to
a Gutsy Release Candidate live CD reveals that evidently I have a bad
superblock on /dev/hda2.

Aside: Although they are scattered all over the place and would be a
PITA to reassemble, I have backup copies of everything on /dev/hda2
that would be bad to lose, except a couple of recent documents and the
last couple of weeks worth of financial data in Quickbooks (restorable
from paper copies). 

Aside 2: On the outside of the case this appears to be a Compaq R3240
laptop. In reality is is a rebadged Piece-O-Shit (tm) laptop assembled
from parts supplied by the lowest bidder by lead-poisoned Chinese
laborers. And yes, I have begun shopping for its replacement.

Returning to the topic at hand, at

http://www.cyberciti.biz/tips/understanding-unixlinux-filesystem-superblock.html

I gathered that Linux keeps copies of the superblock data which you can
get with "dumpe2fs /dev/hda3 | grep -i superblock." Unfortunately, that
doesn't work on a filesystem that cannot be mounted (already tried
that). The site also suggests "e2fsck -f /dev/hda2," but that also
fails if the superblock can't be read. Finally, the site suggests "sudo
e2fsck -f /dev/hda2" to get the data. This resulted in:

Block size = 4896 (log=2)
7325696 inodes, 14651288 blocks
732564 blocks 5.88% reserved for the super user
First data block = 0
Maximum filesystem blocks = 4294967296
448 block groups
32768 blocs per group, 32768 fragments per group
16352 inodes per group
Superblock backups stored on blocks:
   32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632,
2654208, 4896000, 7962624, 11239424

And evidently I can repair the superblock with a command like "e2fsck
-f -b 8193 /dev/hda2," except the site let me down by failing to tell
me what the "8193" or the -f and -b mean. I am guessing that the "8193"
should be one of the numbers of where the superblock backups are stored
above, and that any of them will do.

I am about to run:

e2fsck -f -b 32768 /dev/hda2

But before I do it and end up destroying western civilization, I
thought I might ask here first to see if my thinking is correct. 



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