Date:	Mon, 19 Nov 2012 16:57:43 +0000
From:	Drew Reusser <dreusser@...il.com>
To:	George Spelvin <linux@...izon.com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: Issue with bad file system

On Mon, Nov 19, 2012 at 8:32 AM, George Spelvin <linux@...izon.com> wrote:
>> I am running this on Linux Mint 12 .. I don't know the kernel version
>> as I cannot boot so I am booting of whatever I downloaded from Mint's
>> website (13 rc I think) off a pen drive to try and save my data.
>>
>> mint mnt # uname -a
>> Linux mint 3.5.0-17-generic #28-Ubuntu SMP Tue Oct 9 19:31:23 UTC 2012
>> x86_64 x86_64 x86_64 GNU/Linux
>
> For the benefit of other ext4 hackers, Mint 12 is based on Ubuntu 11.10
> and runs a 3.0 kernel.
>
>> I ran the cat of /proc/partitions and copied the data from previous
>> emails to the linux-raid DL (which forwarded me onto this one).  Must
>> have gotten it before the raid was working.  Here is an updated one.
>
> Okay, no problem.  The failure to show up just conflicted with your
> statement that the RAID worked fine, and I was wondering if there wa a
> problem there.  It appears that's not the issue.
>
>> as for the last command you asked .. can you give me more info on it?
>> if you meant dumpe2fs ... here is the output.
>
> I did; my fingers got confused; sorry about the typo.  Doubly sorry
> because it is a plausible command name.
>
>> mint mnt # dumpe2fs -h /dev/md0
>> dumpe2fs 1.42.5 (29-Jul-2012)
>> dumpe2fs: Bad magic number in super-block while trying to open /dev/md0
>> Couldn't find valid filesystem superblock.
>
> Well, that explains the immediate problem.
>
> Does "dumpe2fs -h -o superblock=32768" produce anything more useful?
> (That checks the first backup superblock.  There are additional backups at
> 98304, 163840, 229376, 294912, ...)
>


mint mnt # dumpe2fs -h -o superblock=32768 /dev/md0
dumpe2fs 1.42.5 (29-Jul-2012)
dumpe2fs: Filesystem has unexpected block size while trying to open /dev/md0
Couldn't find valid filesystem superblock.
mint mnt # dumpe2fs -h -o superblock=98304 /dev/md0
dumpe2fs 1.42.5 (29-Jul-2012)
dumpe2fs: Filesystem has unexpected block size while trying to open /dev/md0
Couldn't find valid filesystem superblock.
mint mnt # dumpe2fs -h -o superblock=163840 /dev/md0
dumpe2fs 1.42.5 (29-Jul-2012)
dumpe2fs: Bad magic number in super-block while trying to open /dev/md0
Couldn't find valid filesystem superblock.
mint mnt # dumpe2fs -h -o superblock=229376 /dev/md0
dumpe2fs 1.42.5 (29-Jul-2012)
dumpe2fs: Bad magic number in super-block while trying to open /dev/md0
Couldn't find valid filesystem superblock.
mint mnt # dumpe2fs -h -o superblock=294912 /dev/md0
dumpe2fs 1.42.5 (29-Jul-2012)
dumpe2fs: Bad magic number in super-block while trying to open /dev/md0
Couldn't find valid filesystem superblock.




>> Can you give me specific e2fsck commands to run which will not ruin my
>> disks and data?  I have seen people online recommending re-writing the
>> super blocks but I am now sure I want to write anything until I know
>> it will not damage something and erase my data.
>
> "e2fsck -n" will only print errors and not change anything.  It's
> always safe.
>


mint mnt # e2fsck -n -v /dev/md0
e2fsck 1.42.5 (29-Jul-2012)
ext2fs_open2: Bad magic number in super-block
e2fsck: Superblock invalid, trying backup blocks...
e2fsck: Bad magic number in super-block while trying to open /dev/md0

The superblock could not be read or does not describe a correct ext2
filesystem.  If the device is valid and it really contains an ext2
filesystem (and not swap or ufs or something else), then the superblock
is corrupt, and you might try running e2fsck with an alternate superblock:
    e2fsck -b 8193 <device>




> Try "e2fsck -n -v /dev/md0" (given the dumpe2fs failure, I expect that
> will not work) and then try "e2fsck -n -v -b 32768 /dev/md0".
>

mint mnt # e2fsck -n -v -b 32768 /dev/md0
e2fsck 1.42.5 (29-Jul-2012)
e2fsck: Filesystem has unexpected block size while trying to open /dev/md0

The superblock could not be read or does not describe a correct ext2
filesystem.  If the device is valid and it really contains an ext2
filesystem (and not swap or ufs or something else), then the superblock
is corrupt, and you might try running e2fsck with an alternate superblock:
    e2fsck -b 8193 <device>



> I don't know what happened to your superblock, but if that's all that
> got trashed, recovery is actually quite straightforward and there's no
> risk of data loss.  e2fsck will just print a huge number of "free blocks
> count wrong" messages as it fixes them.
>
> (However, that's a pretty big "if".)
>
>
> Another thing that would be useful is "dd if=/dev/md0 skip=2 count=2 | xxd"
> (or od -x if you don't have xxd).  That will give a hex dump of the
> primary superblock, which might show the extent of the damage.
>
>


mint mnt # dd if=/dev/md0 skip=2 count=2 | xxd
0000000: 3a3a 6b4e fd9b a66c 6467 f7a6 9fb0 9183  ::kN...ldg......
2+0 records in
2+0 records out
0000010: 3fc6 11aa 0cec 0441 6bc8 6b55 ff4d f2ba  ?......Ak.kU.M..
0000020: a475 15d9 ea5d 6833 5608 df95 60cd 4f76  .u...]h3V...`.Ov
1024 bytes (1.0 kB) copied0000030: 5490 5c22 e564 c91b 1913 a519 807a
8986  T.\".d.......z..
0000040: f3ba 3c8a 6c11 f78a bc94 5947 b55d d83f  ..<.l.....YG.].?
0000050: 2eac 0f3c ab20 d88d 1820 d5bc 0f97 aaf6  ...<. ... ......
0000060: 81f5 63cc 6eff 8e2e 54ad 50fe 291f 17f8  ..c.n...T.P.)...
0000070: be01 67ad b9ec 49f7 fa60 953b 7348 9730  ..g...I..`.;sH.0
, 0.0122559 s, 83.6 kB/s
0000080: 6105 8f4d da9c 3ef3 e90e c190 6471 a766  a..M..>.....dq.f
0000090: c90a 77f6 1196 3b74 9121 e89c 19bd 29f4  ..w...;t.!....).
00000a0: 808c 3342 16e7 0c80 e8c3 3a6a 5560 78eb  ..3B......:jU`x.
00000b0: c0d9 c6d5 b386 a3a9 5275 7f5a f572 218b  ........Ru.Z.r!.
00000c0: 63d5 28f8 71aa 4f6f e716 060a 4a50 70cb  c.(.q.Oo....JPp.
00000d0: a740 8c5f e2df 2e65 11cd a88f c4ed c9bb  .@.....e........
00000e0: d444 2da5 7e5d 7bb4 38f6 5fd0 60a8 d2cf  .D-.~]{.8._.`...
00000f0: 813f 9afd 26b8 8cc0 6e6a 59a2 e1f6 32ce  .?..&...njY...2.
0000100: 8c01 5928 5661 9687 fb9c b07d b412 4a57  ..Y(Va.....}..JW
0000110: 2626 7099 c350 a893 3f76 1953 c34b 7ddf  &&p..P..?v.S.K}.
0000120: d73d 5e7f 9d3c f4fe dac9 e2d7 8eaf da94  .=^..<..........
0000130: 86fb cbfe 7866 45fa 72c9 a687 ea83 3b71  ....xfE.r.....;q
0000140: 80cc 3320 59c3 c653 977d b6e3 79c4 5c3b  ..3 Y..S.}..y.\;
0000150: b36b c978 6824 d4b9 9252 04dd 39de 4c05  .k.xh$...R..9.L.
0000160: d331 951b 3dff 8974 4ac1 1950 f6bd 5586  .1..=..tJ..P..U.
0000170: 1095 f62c e7b3 d9d6 fbee 8cfb 5bd0 959e  ...,........[...
0000180: f6ae f551 1b41 a8cf ae40 435a ff05 c38e  ...Q.A...@......
0000190: 903d 2258 689e b64c f49d b7b3 593d f55c  .="Xh..L....Y=.\
00001a0: fd4f f395 4ecd 6653 e46d 66b6 a046 a9cb  .O..N.fS.mf..F..
00001b0: ee90 58d8 e876 5f63 5014 cbfe b0e1 cd53  ..X..v_cP......S
00001c0: 12ac 43c5 2996 4a15 014e 3c7d a5c2 5842  ..C.).J..N<}..XB
00001d0: 2e00 f2ea 3e12 fbe6 1403 e240 0e01 80d0  ....>......@....
00001e0: 1a03 c0c0 37fb 3cae df51 1818 987f e03b  ....7.<..Q.....;
00001f0: 718f b339 63e7 8495 56b4 045a 0091 7382  q..9c...V..Z..s.
0000200: 9828 187e 5eab e288 a4c6 fd95 3950 f868  .(.~^.......9P.h
0000210: 3ee5 5fe0 4943 8e1d 2315 41a7 0989 c97c  >._.IC..#.A....|
0000220: 992a c47b 9ccd e08a cfea 4603 2f51 e5e3  .*.{......F./Q..
0000230: 04c3 3224 bfaa f0fa 79ae 13db d774 8c87  ..2$....y....t..
0000240: fad8 93b1 ddc6 ce8c 90f3 e754 c6a4 ece3  ...........T....
0000250: 13ab 59e8 b5cc f5d1 c9ab 297f ba63 84a7  ..Y.......)..c..
0000260: c8ed bff6 9e55 a191 cfef c79e 6cd0 8ccd  .....U......l...
0000270: 83b1 de5a 3c26 1f81 e1fa b2ed 503a 2445  ...Z<&......P:$E
0000280: 7212 2b2e 1242 18fb cac7 c3e5 73de fb2a  r.+..B......s..*
0000290: c0ed 2318 01ba 1f04 22f1 fb3d f356 c0a0  ..#....."..=.V..
00002a0: 258f 0184 6653 7814 e3ff b4ab 3276 7b9d  %...fSx.....2v{.
00002b0: 6c68 0b00 8024 68f0 47e6 2aad e447 674b  lh...$h.G.*..GgK
00002c0: 1a0c 0f85 e11d 5275 6d58 9940 e738 a3a8  ......RumX.@....
00002d0: 490f cdbc e710 9099 9dbd a688 00d8 a530  I..............0
00002e0: 843c 6665 a912 abdb 6c95 9e96 70dc f409  .<fe....l...p...
00002f0: f27a 3c12 15b0 c168 29a7 c190 f9ac 90c0  .z<....h).......
0000300: cd58 20ff 0461 ddcf 6617 9764 c352 a0de  .X ..a..f..d.R..
0000310: 3818 e5e0 a168 49aa 8b98 2e6d 92f9 b575  8....hI....m...u
0000320: d7dd 4651 1c54 c5e9 f96a d0f0 14c0 240a  ..FQ.T...j....$.
0000330: 3193 00e1 f895 6aba 0780 37c1 0f3a 3b3e  1.....j...7..:;>
0000340: a8bb c25f 8148 0140 1825 7814 0a68 8e5e  ..._.H.@.....h.^
0000350: 237b db47 9e5f 573c acbd 5d54 a1ae ce9c  #{.G._W<..]T....
0000360: b498 c8cd e0dd 4c34 ee8a bf32 b7cf 0cca  ......L4...2....
0000370: ba69 e0a7 e9ef 09c6 7c20 5007 7662 9c36  .i......| P.vb.6
0000380: f053 fda0 41f6 e560 1f2b ffbc 5344 407c  .S..A..`.+..SD@|
0000390: 9801 ee74 a1ef 236f 6b6c 50c0 2acf 8ebf  ...t..#oklP.*...
00003a0: f6ec 5049 7633 d215 1b35 af46 44e0 a7db  ..PIv3...5.FD...
00003b0: fd01 43ef c03d 2d44 7c21 d12c 75a3 f1f2  ..C..=-D|!.,u...
00003c0: a459 e196 ce0f 6de0 19f1 d086 2504 2f09  .Y....m.....%./.
00003d0: 6abe 5f04 4277 86c9 6b20 a054 bf82 0b5d  j._.Bw..k .T...]
00003e0: 3525 32b4 051a af5e 34af 1b29 0083 4987  5%2....^4..)..I.
00003f0: c071 ab38 2567 0dff 54bc 2f8e 130e 33e2  .q.8%g..T./...3.



> If "e2fsck -n -b 32768" works, the way to repair it is to run it again
> without the "-n", but the -n output will say how bad it is.
>
> As a general rule of thumb, the more phases e2fsck gets through before
> complaining, the less the damage.  Errors in the bitmaps found in phase 5
> are not a serious problem; they only indicate things that would rapidly
> *become* serious problems if you mounted the file system and tried to
> write to it.
>
> One thing I strongly recommend when e2fsck is fixing a lot of problems is
> to save a log (I usually use the "script" program, but you can also use
> "<command> 2>&1 | tee output") of the e2fsck run so you can refer back
> to it later.


Okay .. So basically I just have to find the right superblock and get
that back.  Is there a way to find the list of backup superblocks on
the raid array so i can test each one and see which one will work?

-Drew
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