挂载硬盘报错无法挂载：# mount /dev/sdb1 /mnt/sdb1
mount:wrong fs type, bad option, bad superblock on /dev/sdb1,
missingcodepage or other error
Insome cases useful info is found in syslog - try
dmesg| tail or so
解决方案：这种情况一般为superblock损坏的概率很大。
superblock是什么？
分区的第一块superblock位于分区的第二块block。
如果分区的blocksize是1024，则superblock位于[1024,204之间。
ext2文件系统的结构请参考这个网站，写的非常清楚：
http://homepage.smc.edu/morgan_david/cs40/analyze-ext2.htm
这个是superblock的结构，摘自：
http://homepage.smc.edu/morgan_david/cs40/analyze-ext2.htm
继续刚才的话题。我/dev/sdb1挂载不上了。
所以我做了如下操作：
[root@dhcp-0-142~]# dumpe2fs /dev/sdb1
dumpe2fs1.39 (29-May-2006)
Filesystemvolume name:
Lastmounted on:
FilesystemUUID: c3800df3-5c34-4b53-8144-94029b5736d8
Filesystemmagic number: 0xEF53
Filesystemrevision #: 1 (dynamic)
Filesystemfeatures: has_journal resize_inode dir_index filetypesparse_super
Defaultmount options: (none)
Filesystemstate: clean with errors
Errorsbehavior: Continue
FilesystemOS type: Linux
Inodecount: 0
Blockcount: 0
Reservedblock count: 0
Freeblocks: 20926971
Freeinodes: 4705752
Firstblock: 1
Blocksize: 1024
Fragmentsize: 1024
ReservedGDT blocks: 256
Blocksper group: 8192
Fragmentsper group: 8192
Inodesper group: 2008
Inodeblocks per group: 251
Filesystemcreated: Tue Oct 7 19:18:08 2008
Lastmount time: n/a
Lastwrite time: Tue Oct 7 19:29:39 2008
Mountcount: 0
Maximummount count: 20
Lastchecked: Tue Oct 7 19:18:08 2008
Checkinterval: 15552000 (6 months)
Nextcheck after: Sun Apr 5 19:18:08 2009
Reservedblocks uid: 0 (user root)
Reservedblocks gid: 0 (group root)
Firstinode: 11
Inodesize: 128
Journalinode: 8
Defaultdirectory hash: tea
DirectoryHash Seed: 7f7e1c41-5cae-4f23-9873-877991751ccb
Journalbackup: inode blocks
dumpe2fs:Illegal inode number while reading journal inode
[root@dhcp-0-142~]#
根据Blocksper group: 8192的信息，我定位了第一个备份superblock的位置为8193。
所以我做如下操作：
[root@dhcp-0-142~]# fsck -b 8193 /dev/sdb1
fsck1.39 (29-May-2006)
e2fsck1.39 (29-May-2006)
/dev/sdb1was not cleanly unmounted, check forced.
Pass1: Checking inodes, blocks, and sizes
Pass2: Checking directory structure
Pass3: Checking directory connectivity
Pass4: Checking reference counts
Pass5: Checking group summary information
/dev/sdb1:***** FILE SYSTEM WAS MODIFIED *****
/dev/sdb1:11/26104 files (9.1% non-contiguous), 8966/104388 blocks
[root@dhcp-0-142~]# mount /dev/sdb1 /mnt/sdb1
[root@dhcp-0-142~]# ls /mnt/sdb1
lost+found
[root@dhcp-0-142~]#
superblock已经修复，文件系统挂载正常。
之所以这么做，是有依据的。
ext2/3文件系统在创建文件系统的时候会创建若干个superblock的备份存放于特定位置。
[root@dhcp-0-142~]# dumpe2fs /dev/sdb1 | grep --before-context=1 superblock
dumpe2fs1.39 (29-May-2006)
Group0: (Blocks 1-8192)
Primarysuperblock at 1, Group descriptors at 2-2
--
Group1: (Blocks 8193-16384)
Backupsuperblock at 8193, Group descriptors at 8194-8194
--
Group3: (Blocks 24577-3276
Backupsuperblock at 24577, Group descriptors at 24578-24578
--
Group5: (Blocks 40961-49152)
Backupsuperblock at 40961, Group descriptors at 40962-40962
--
Group7: (Blocks 57345-65536)
Backupsuperblock at 57345, Group descriptors at 57346-57346
--
Group9: (Blocks 73729-81920)
Backupsuperblock at 73729, Group descriptors at 73730-73730
[root@dhcp-0-142~]#
从上面操作可以看出，在第1、3、4、7、9这几个BlockGroup上存放有superblock备份。
什么是BlockGroup？ext2/3文件系统为了提高磁盘寻道效率，把inodetable等信息按照Inodesper group分成若干组存放，而没有全部放在一起。
此图摘自：http://homepage.smc.edu/morgan_david/cs40/analyze-ext2.htm
Inodesper group信息相见命令：
[root@dhcp-0-142~]# dumpe2fs /dev/sdb1 | grep 'Inodes per group'
dumpe2fs1.39 (29-May-2006)
Inodesper group: 2008
[root@dhcp-0-142~]#
有些文件系统superblock损坏的很厉害。连dumpe2fs和tune2fs都看不到信息。[root@dhcp-0-175~]# dd if=/dev/zero of=/dev/sdb1 bs=1 count=1024 seek=1024
1024+0records in
1024+0records out
1024bytes (1.0 kB) copied, 0.0228272 seconds, 44.9 kB/s
[root@dhcp-0-175~]# dumpe2fs /dev/sdb1
dumpe2fs1.39 (29-May-2006)
dumpe2fs:Bad magic number in super-block while trying to open /dev/sdb1
Couldn'tfind valid filesystem superblock.
[root@dhcp-0-175~]# tune2fs -l /dev/sdb1
tune2fs1.39 (29-May-2006)
tune2fs:Bad magic number in super-block while trying to open /dev/sdb1
Couldn'tfind valid filesystem superblock.
[root@dhcp-0-175~]#
这时候我们根本无法从dumpe2fs和tune2fs看到Backupsuperblock的位置。
我们可以尝试从superblock的结构来猜测superblock的位置（superblock结构见上图）。
我们从superblock结构可以知道，卷标volumename存放于superblock中。所以如果文件系统有设置卷标，那么我们可以尝试从卷标来定位superblock。
我们用hexdump把文件系统dump出来：
[root@dhcp-0-175~]# hexdump -C /dev/sdb1 > /var/sdb1.hexdump
[root@dhcp-0-175~]#
我们已知/dev/sdb1的卷标是sdb1(如果不知道卷标或者没有设置卷标，那么我就没办法了)。
我们搜索sdb1，搜到结果如下：
我们猜测这里就是备份superblock的位置。
卷标起始位置是0x18000078。由于superblock结构里volumename位于0x78的位置，所以我们可以猜测备份superblock的起始位置是0x18000078– 0x78 = 0x18000000。
由于blocksize位于superblock的[0x18,0x22)的位置，这里的值是0x0002，得出blocksize是0x0400x ( 0x00020x0002 ) = 0x1000 = 4096
( [0x18, 0x22) 处值n和blocksize的关系是blocksize = 0x0400 x 0x0002n，此公式感谢得新倾情赞助)
而备份superblock的偏移量为offset/ blocksize，即0x18000000/ 0x1000 = 0x00018000 = 98304。
因此我们执行：
[root@dhcp-0-175~]# fsck.ext3 -b 98304 /dev/sdb1
e2fsck1.39 (29-May-2006)
sdb1was not cleanly unmounted, check forced.
Pass1: Checking inodes, blocks, and sizes
Pass2: Checking directory structure
Pass3: Checking directory connectivity
Pass4: Checking reference counts
Pass5: Checking group summary information
sdb1:***** FILE SYSTEM WAS MODIFIED *****
sdb1:11/123648 files (9.1% non-contiguous), 8298/246991 blocks
[root@dhcp-0-175~]#
这样文件系统就有给修复的可能性了。
测试一下：
[root@dhcp-0-175~]# dumpe2fs /dev/sdb1
dumpe2fs1.39 (29-May-2006)
Filesystemvolume name: sdb1
Lastmounted on:
FilesystemUUID: 0293bd85-b911-43bf-853e-6588b3eaaf39
Filesystemmagic number: 0xEF53
Filesystemrevision #: 1 (dynamic)
Filesystemfeatures: has_journal resize_inode dir_index filetypesparse_super large_file
Defaultmount options: (none)
Filesystemstate: clean
Errorsbehavior: Continue
FilesystemOS type: Linux
Inodecount: 123648
Blockcount: 246991
Reservedblock count: 12349
Freeblocks: 238693
Freeinodes: 123637
Firstblock: 0
Blocksize: 4096
Fragmentsize: 4096
ReservedGDT blocks: 60
Blocksper group: 32768
Fragmentsper group: 32768
Inodesper group: 15456
Inodeblocks per group: 483
Filesystemcreated: Wed Oct 8 12:49:09 2008
Lastmount time: n/a
Lastwrite time: Wed Oct 8 12:52:10 2008
Mountcount: 0
Maximummount count: 28
Lastchecked: Wed Oct 8 12:52:10 2008
Checkinterval: 15552000 (6 months)
Nextcheck after: Mon Apr 6 12:52:10 2009
Reservedblocks uid: 0 (user root)
Reservedblocks gid: 0 (group root)
Firstinode: 11
Inodesize: 128
Journalinode: 8
Defaultdirectory hash: tea
DirectoryHash Seed: 2efa124c-dde6-4046-9181-a05b7e6d182a
Journalbackup: inode blocks
Journalsize: 16M
Group0: (Blocks 0-32767)
Primarysuperblock at 0, Group descriptors at 1-1
ReservedGDT blocks at 2-61
Blockbitmap at 62 (+62), Inode bitmap at 63 (+63)
Inodetable at 64-546 (+64)
28113free blocks, 15445 free inodes, 2 directories
Freeblocks: 4655-32767
Freeinodes: 12-15456
Group1: (Blocks 32768-65535)
Backupsuperblock at 32768, Group descriptors at 32769-32769
ReservedGDT blocks at 32770-32829
Blockbitmap at 32830 (+62), Inode bitmap at 32831 (+63)
Inodetable at 32832-33314 (+64)
32221free blocks, 15456 free inodes, 0 directories
Freeblocks: 33315-65535
Freeinodes: 15457-30912
Group2: (Blocks 65536-98303)
Blockbitmap at 65536 (+0), Inode bitmap at 65537 (+1)
Inodetable at 65538-66020 (+2)
32283free blocks, 15456 free inodes, 0 directories
Freeblocks: 66021-98303
Freeinodes: 30913-46368
Group3: (Blocks 98304-131071)
Backupsuperblock at 98304, Group descriptors at 98305-98305
ReservedGDT blocks at 98306-98365
Blockbitmap at 98366 (+62), Inode bitmap at 98367 (+63)
Inodetable at 98368-98850 (+64)
32221free blocks, 15456 free inodes, 0 directories
Freeblocks: 98851-131071
Freeinodes: 46369-61824
Group4: (Blocks 131072-163839)
Blockbitmap at 131072 (+0), Inode bitmap at 131073 (+1)
Inodetable at 131074-131556 (+2)
32283free blocks, 15456 free inodes, 0 directories
Freeblocks: 131557-163839
Freeinodes: 61825-77280
Group5: (Blocks 163840-196607)
Backupsuperblock at 163840, Group descriptors at 163841-163841
ReservedGDT blocks at 163842-163901
Blockbitmap at 163902 (+62), Inode bitmap at 163903 (+63)
Inodetable at 163904-164386 (+64)
32221free blocks, 15456 free inodes, 0 directories
Freeblocks: 164387-196607
Freeinodes: 77281-92736
Group6: (Blocks 196608-229375)
Blockbitmap at 196608 (+0), Inode bitmap at 196609 (+1)
Inodetable at 196610-197092 (+2)
32283free blocks, 15456 free inodes, 0 directories
Freeblocks: 197093-229375
Freeinodes: 92737-108192
Group7: (Blocks 229376-246990)
Backupsuperblock at 229376, Group descriptors at 229377-229377
ReservedGDT blocks at 229378-229437
Blockbitmap at 229438 (+62), Inode bitmap at 229439 (+63)
Inodetable at 229440-229922 (+64)
17068free blocks, 15456 free inodes, 0 directories
Freeblocks: 229923-246990
Freeinodes: 108193-123648
[root@dhcp-0-175~]# mount /dev/sdb1 /mnt
[root@dhcp-0-175~]# ls /mnt
lost+found
[root@dhcp-0-175~]#