From: justin.bleistein@SUNGARD.COM
Date: Fri Oct 25 2002 - 11:05:07 EDT
I agree with fsck but the thing is, fsck only see's filesystem erors it
would not pick up anything if it's a logical volume error. FSDB only
repairs partition level errors this could very well be one. This filesystem
could very well not be mounted it coule still just have the mount flag on
in the super block. Below is an exercise I did on my test system as you can
see it's the other way around. I first unmounted the filesystem then
corrupted the magic number by setting it to "0" which wiped out the
superblock and magic number then I tried to mount it "no", maybe it's the
same the other way. If fsck doesn't work replacing the magic number could
repair this. I've seem weirder things. Unless this is JFS2 because in JFS
it's in the first 4 bits of the filesystem/partition that the magic number
resides that's why I know to start at logical address: 0x1000 for JFS
filesystems which is in hex.
File System Size: 8192 (512 byte blocks)
Disk Map Size: 2 (4K blocks)
Inode Map Size: 2 (4K blocks)
Fragment Size: 4096 (bytes)
Allocation Group Size: 1024 (fragments)
Inodes per Allocation Group: 1024
Total Inodes: 1024
Total Fragments: 1024
01000
0x0000000200.D: 0x00000000 (0)
0x1000
0x0000001000.D: 0x43218765 (1126270821)
=0
0x0000001000.D: 0x00000000 (0)
1b.p10x
0x0000001000: 0000 0000 0000 0000 0000 0400 0000 0000
0x0000001010: 0000 2000
q
# mount /fsdb
mount: 0506-324 Cannot mount /dev/lv00 on /fsdb: A system call received a
parame
ter that is not valid.
#
"Green, Simon"
<SGreen@KRAFTEURO To: aix-l@Princeton.EDU
PE.COM> cc:
Sent by: IBM AIX Subject: Re: Problem unmounting a fs
Discussion List
<aix-l@Princeton.
EDU>
10/25/2002 06:02
AM
Please respond to
IBM AIX
Discussion List
All this is going to do is display a block of data in a filesystem. Unless
one knows what's supposed to be there, it's not going to mean anything.
Presumably, Justin thinks that there's some specific value which should be
there and could get corrupted. (He may be right; I don't know off hand.)
Personally, I don't think it's a good idea to do this sort of thing
routinely. Sure: if a filesystem is broken and fsdb is the only way to fix
it, but not otherwise. Unless one understands the JFS structure and is
up-to-date on any changes IBM may have made, it may do more harm than good.
If there is a persistent problem, start by ensuring that you always run
fsck.
Simon Green
Philip Morris ITSC Europe
AIX-L Archive at http://marc.theaimsgroup.com/?l=aix-l&r=1&w=2
AIX FAQ at http://www.faqs.org/faqs/aix-faq/
N.B. Unsolicited email from vendors will seldom be appreciated.
> -----Original Message-----
> From: Holger.VanKoll@SWISSCOM.COM [mailto:Holger.VanKoll@SWISSCOM.COM]
> Sent: 24 October 2002 18:00
> To: aix-l@Princeton.EDU
> Subject: Re: Problem unmounting a fs
>
>
> >To prevent this sort of thing from happening in the future always run
> an "fsdb" on a logical volume before mounting it to a filesystem, and
> type in 0440000 to make sure your magic number of that partition isn't
> corrupted.
>
> I dont understand what this does and what I gain here.
>
> Can anybody comment on it?
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