strange behaviour of df command

[Atul Tyagi]

Thanks a lot dag. Your trick worked. There was process which was holding the
file. One the process finished its execution whole space was recovered.

Thanks a ton to everyone in the thread for sharing your views on this.

I Appriciate your efforts.

Atul

On 10/10/06, Dag Wieers <dag at wieers.com> wrote:
>
> On Tue, 10 Oct 2006, Atul Tyagi wrote:
>
> > 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.
>
> Is it possible that something still has this 18GB file open ?
>
> It is not unsual that when removing a file, the diskspace is not freed
> because something is still using the file. Either has it still open, or in
> case of a loop-mount, has it still mounted.
>
> If this is the case, the difference can be explained as follows: df is
> giving the information stored in the filesystem, du is giving the
> information deduced from traversing the filesystem and collecting the
> metadata.
>
> If you delete a file that is still in use, the inode is still allocated
> (since something is using it), but the directory entry (what we humans
> work with) has been deleted. Since du is traversing the directories, it
> finds no reference and doesn't count it as being 'used'.
>
> One way to make sure is by using lsof (ls of open files). Something like:
>
>         lsof | grep <filename>
>
> lsof is great as it both displays the files being in use and that are
> deleted. (As it checks whether the reference in the filesystems exists or
> not).
>
> If you then stop the program that is using the file, the diskspace that
> was allocated will be freed instantly.
>
> Let me know whether this was going on or not.
>
> PS A reboot will help as well, but then you don't know what was going on
> :)
>
> Kind regards,
> --   dag wieers,  dag at wieers.com,  http://dag.wieers.com/   --
> [all I want is a warm bed and a kind word and unlimited power]
>
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