recovering FC3 from a bad superblock

[Ben Scott]

On 5/18/05, Derek Martin <invalid at pizzashack.org> wrote:
> > First, it's just asking for data loss to run window$ and linux on the
> > same machine.
> 
> I really have to strongly disagree there... 

  I gotta go with Derek on this one.  Doze and Nix can co-exist just
fine.  Heck, I've had Linux, MS-DOS 5.0, Windows 95, and OS/2 all on
the same disk without problems.  Today, I've got Linux, Windows 98,
and Windows XP, all on the same disk, without problems.

  This is not to say you can't destroy things with Doze.  Despite all
the GUI dressing, Windoze is still a computer operating system, which
makes it a complex, cryptic, complicated, and potentially dangerous
beast.  The same applies to Linux, of course.  I recall a story about
a time when Linus tried to dial his hard drive...

  Of course, the mess that the PC partition table format has become
doesn't help.  If you ask three different OSes about the same
partition table, you'll usually get at least five different answers. 
:-(

>> The fact that *this* happens is important.  If mounting with the
>> rescue disk works without complaint, your superblock is probably *in
>> tact*.  Instead, it may be mount and/or e2fsck which have somehow
>> become corrupt....
> 
> That's just crazy talk.

  While I agree that if mount or e2fsck were corrupt, you'd likely see
different behavior (especially "mount", which is mostly a front-end to
a kernel syscall), the OP has a point.  One is that if you can mount
the filesystem read-only, and it appears intact, you're often in good
shape.  (Of course, file contents might be scrambled while leaving
directories intact...)  The fact that e2fsk otherwise gave a ton of
errors makes me wonder.  Is there something wrong with the installed
kernel or kernel config that is making the disk subsystem unreliable
when booting from HD, but which the rescue disc is bypassing?

>> <to those who have advised not to>: Can it hurt to repair a filesystem
>> while it's mounted read-only?
> 
> Can it hurt?  That depends on your perspective.  If it's already
> broken, then it probably can't hurt much worse...

  It is worth cautioning that, while rare, one can get into other
situations where running e2fsck can make things worse.  This is
especially true if you've got a scrambled filesystem and you want/need
to pay big bucks for professional data recovery.  In that case, it's
best *not* to make *any* changes to the filesystem at all.  Leave it
"as is" so the pros can work their magic unhindered.