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Author Topic: Ext3 Journal  (Read 6764 times)

Offline mohit.saha

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Ext3 Journal
« on: May 07, 2008, 05:35:30 AM »
Hi Everybody,

Can anyone tell me how to view the journal file in an ext3 file system?
Or how to see its size?

Thank you in advance..:)

Offline gauravbajaj

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Re: Ext3 Journal
« Reply #1 on: May 07, 2008, 08:26:26 AM »
I m not sure wheather  u can able to see journilising file................., Anyways ext3 is a filesysytem and u cn see the partotions from /etc/fstab file

/etc/fstab contains all the partitions with the file system type information...........

you can see the size of any ext3 type partions, from df -h commad

Offline mohit.saha

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Re: Ext3 Journal
« Reply #2 on: May 07, 2008, 09:15:35 AM »
I m not sure wheather  u can able to see journilising file................., Anyways ext3 is a filesysytem and u cn see the partotions from /etc/fstab file

/etc/fstab contains all the partitions with the file system type information...........

you can see the size of any ext3 type partions, from df -h commad

I was not asking about the ext3 filesystems information. I was asking about the .journal file and how to view its contents..

Anyways, What i have done is

Code: [Select]
$tune2fs -l /dev/hda2            (This is where i have my ext3 partition)

and through that i found out the inode number of the journal file i.e 8. The following is the output of tune2fs

Code: [Select]
tune2fs 1.39 (29-May-2006)
Filesystem volume name:   /ext3fs1
Last mounted on:          <not available>
Filesystem UUID:          18f47a23-d12e-4206-8a0c-e15e1abf5936
Filesystem magic number:  0xEF53
Filesystem revision #:    1 (dynamic)
Filesystem features:      has_journal ext_attr resize_inode dir_index filetype needs_recovery sparse_super large_file
Default mount options:    user_xattr acl
Filesystem state:         clean
Errors behavior:          Continue
Filesystem OS type:       Linux
Inode count:              6469056
Block count:              6468170
Reserved block count:     323408
Free blocks:              6221533
Free inodes:              6469045
First block:              0
Block size:               4096
Fragment size:            4096
Reserved GDT blocks:      1022
Blocks per group:         32768
Fragments per group:      32768
Inodes per group:         32672
Inode blocks per group:   1021
Filesystem created:       Wed May  7 10:02:02 2008
Last mount time:          Wed May  7 10:43:34 2008
Last write time:          Wed May  7 10:43:34 2008
Mount count:              5
Maximum mount count:      -1
Last checked:             Wed May  7 10:02:02 2008
Check interval:           0 (<none>)
Reserved blocks uid:      0 (user root)
Reserved blocks gid:      0 (group root)
First inode:              11
Inode size:               128
Journal inode:            8
Default directory hash:   tea
Directory Hash Seed:      79e25347-d41b-4f7b-9de4-7966af814566
Journal backup:           inode blocks


as can be seen from the output the inode of the journal is given as 8. So then i used debug and stat command

Code: [Select]
$debugfs /dev/hda2
debugfs 1.39 (29-May-2006)
debugfs:  stat <8>
Inode: 8   Type: regular    Mode:  0600   Flags: 0x0   Generation: 0
User:     0   Group:     0   Size: 134217728
File ACL: 0    Directory ACL: 0
Links: 1   Blockcount: 262416
Fragment:  Address: 0    Number: 0    Size: 0
ctime: 0x482139b0 -- Wed May  7 10:40:08 2008
atime: 0x00000000 -- Thu Jan  1 05:30:00 1970
mtime: 0x482139b0 -- Wed May  7 10:40:08 2008
BLOCKS:
(0-11):2054-2065, (IND):2066, (12-1035):2067-3090, (DIND):3091, (IND):3092, (1036-2059):3093-4116, (IND):4117, (2060-3083):4118-5141, (IND):5142, (3084-4107)
:5143-6166, (IND):6167, (4108-5131):6168-7191, (IND):7192, (5132-6155):7193-8216, (IND):8217, (6156-7179):8218-9241, (IND):9242, (7180-8203):9243-10266, (IND
):10267, (8204-9227):10268-11291, (IND):11292, (9228-10251):11293-12316, (IND):12317, (10252-11275):12318-13341, (IND):13342, (11276-12299):13343-14366, (IND
):14367, (12300-13323):14368-15391, (IND):15392, (13324-14347):15393-16416, (IND):16417, (14348-15371):16418-17441, (IND):17442, (15372-16395):17443-18466, (
IND):18467, (16396-17419):18468-19491, (IND):19492, (17420-18443):19493-20516, (IND):20517, (18444-19467):20518-21541, (IND):21542, (19468-20491):21543-22566
, (IND):22567, (20492-21515):22568-23591, (IND):23592, (21516-22539):23593-24616, (IND):24617, (22540-23563):24618-25641, (IND):25642, (23564-24587):25643-26
666, (IND):26667, (24588-25611):26668-27691, (IND):27692, (25612-26635):27693-28716, (IND):28717, (26636-27659):28718-29741, (IND):29742, (27660-28683):29743
-30766, (IND):30767, (28684-29707):30768-31791, (IND):31792, (29708-30682):31793-32767, (30683-30731):34816-34864, (IND):34865, (30732-31755):34866-35889, (I
ND):35890, (31756-32768):35891-36903
TOTAL: 32802

from here i get the size in bytes i.e. 134217728 which comes out to be 128MB...

1st Question: Is there any way to see the contents of the blocks directly?

Now comes the dumping of journal... I dumped it using logdump inside debugfs and following is the output..

Code: [Select]
debugfs 1.39 (29-May-2006)
debugfs:  logdump
Journal starts at block 1, transaction 2
Found expected sequence 2, type 1 (descriptor block) at block 1
Found expected sequence 2, type 2 (commit block) at block 3
Found expected sequence 3, type 1 (descriptor block) at block 4
Found expected sequence 3, type 2 (commit block) at block 6
Found expected sequence 4, type 1 (descriptor block) at block 7
Found expected sequence 4, type 2 (commit block) at block 9
Found expected sequence 5, type 1 (descriptor block) at block 10
Found expected sequence 5, type 2 (commit block) at block 12
Found expected sequence 6, type 1 (descriptor block) at block 13
Found expected sequence 6, type 2 (commit block) at block 15
Found expected sequence 7, type 1 (descriptor block) at block 16
Found expected sequence 7, type 2 (commit block) at block 18
Found expected sequence 8, type 1 (descriptor block) at block 19
Found expected sequence 8, type 2 (commit block) at block 21
Found expected sequence 9, type 1 (descriptor block) at block 22
Found expected sequence 9, type 2 (commit block) at block 24
Found expected sequence 10, type 1 (descriptor block) at block 25
Found expected sequence 10, type 2 (commit block) at block 35
Found expected sequence 11, type 1 (descriptor block) at block 36
Found expected sequence 11, type 2 (commit block) at block 44
Found expected sequence 12, type 1 (descriptor block) at block 45
Found expected sequence 12, type 2 (commit block) at block 47
Found expected sequence 13, type 2 (commit block) at block 48
Found expected sequence 14, type 1 (descriptor block) at block 49
Found expected sequence 14, type 2 (commit block) at block 51
Found expected sequence 15, type 1 (descriptor block) at block 52
Found expected sequence 15, type 2 (commit block) at block 54
Found expected sequence 16, type 1 (descriptor block) at block 55
Found expected sequence 16, type 2 (commit block) at block 57
Found expected sequence 17, type 1 (descriptor block) at block 58
Found expected sequence 17, type 2 (commit block) at block 61
Found expected sequence 18, type 1 (descriptor block) at block 62
Found expected sequence 18, type 2 (commit block) at block 65
No magic number at block 66: end of journal.

Now the 2nd question: How to interpret the journal dump? :):):):)

Offline dragoncity99

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Re: Ext3 Journal
« Reply #3 on: June 13, 2008, 08:50:33 AM »
You cant basically see this ext3 journal "files" as if it is a file.

It's not a file, but a metadata (stored in a defined data structure) in binary format which only the ext3 module itself can understand. Simply to say, if u want to know inside the meaning of it as equivalent to ur first 512bytes in the bootsector MBR, sorry to say that, it's quite tough, unless u have gone through the code and documentation of ext3 specs.

For 512bytes in MBR, we will need to refer to the documentation and specs right? :)

Same goes here for ext3 file system. I looked at the partimage.org sourced before which uses ext3 and other filesystems code and datastructure and how it is implemented. Probably u can take a look there too.

Hope that helps. Cheers.