strange behaviour of df command

[Atul Tyagi]

Thanks but do u have explaination for dummies. This sounded greek to me :-)

On 10/10/06, Manuel Arostegui Ramirez <manuel at todo-linux.com> wrote:
>
> El Martes, 10 de Octubre de 2006 15:58, Atul Tyagi escribió:
> > Hi All,
> >
> > I am facing a little problem. I guess its more of a conceptual problem
> > rather than a OS issue.
> >
> > One of my software raid partiton /dev/md4 is about 30 GB. I had put a
> file
> > of about 18GB in that jus for few mins and then deleted that. Now even
> > after about 6 hrs. My RHEL4 system gives me weird output. following are
> the
> > outputs that might help you understand.
> >
> > df -h
> > ===
> >
> > [root at pingu ~]# df -h
> > Filesystem            Size  Used Avail Use% Mounted on
> > /dev/md0              5.0G  2.7G  2.1G  56% /
> > /dev/md1               99M   17M   78M  18% /boot
> > none                 1014M     0 1014M   0% /dev/shm
> > /dev/md2              5.0G  190M  4.5G   4% /var
> > /dev/md4               30G   22G  5.9G  79% /usr/local/test
> >
> > du -hs
> > =====
> > [root at pingu ~]# du -hs /usr/local/test
> > 2.7G    /usr/local/test
> >
> > Can some one please clear my doubt and explain why there is a such a
> hugh
> > difference in both the commands. Disk usage shown by df -h is 22G where
> as
> > du shows 2.7G.
> >
> > Would appriciate any pointer to this problem.
> >
> > Thanks,
> >
> > Atul
>
> quote from: http://www.acersupport.com/ess/articles/articles/14.cfm
>
> You may often see a difference in the output of the two commands "du" and
> "df". For example, a df -t is executed on a system and it comes back with
> the
> following:
>
>        (/dev/root ):     216000 blocks      41950 i-nodes
>               total:     260460 blocks      43392 i-nodes
>
> If you subtract the total blocks free from the total available you get:
> 44460.
> The command du -s (from the root directory) shows: 39130. This is a
> discrepancy of 5300 blocks. However, there is a big difference in how
> these
> two utilities work. The df command takes a look at the freelist and gives
> a
> picture of how many blocks are available for use. The du command takes a
> snapshot of the blocks in use by a file or directory, BUT, neither does it
> count the blocks used by the directory entries themselves, nor does it
> count
> the blocks used by special files (ie. device files, named pipes, etc.).
>
> So, if you want to get an approximation of what is in use from looking at
> the
> df -t output you need to perform one more step.
>
> Perform the subtraction to determine the number of i-nodes in use and then
> multiply that by 4. When you add that value to the one you got previously
> you
> will get an approximation of the total blocks in use. This will still not
> match exactly!
>
> The general point is that things aren't always as they seem at first
> glance.
> There are many utilities in UNIX. Determine what it is that you really
> want
> to know and then use the appropriate tool.
>
> --
> Manuel Arostegui Ramirez.
>
> Electronic Mail is not secure, may not be read every day, and should not
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>
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