Re: df and du don't seem to agree ?
On Tue, Aug 21, 2012 at 04:07:54PM +0100, Karl E. Jorgensen wrote:
> Hi
>
> On Tue, Aug 21, 2012 at 03:45:35PM +0100, David Cho-Lerat wrote:
> > Hi list,
> >
> > this might be a newbie question, but can anyone tell me
> > why "du" and "df" don't seem to agree :
> >
> > server:~# df -h /var
> > Filesystem Size Used Avail Use% Mounted on
> > /dev/mapper/vg00-var 5.0G 4.1G 624M 87% /var
> > server:~# du -h -s /var
> > 1.6G /var
> >
> > ("/var" is on a partition of its own.)
>
> FYI: I always use the "-x" flag on du too, as this will not recurse down
> other mounted file systems - e.g. if you have /var/cache on a separate
> logical volume.
>
> > "du" says 1.6G are used, while "df" reports 4.1G. Any idea why ?
>
> "du" will only be reporting disk usage by files and directories it can
> find. It will not report overhead by the filesystem itself.
>
> In your case, the discrepancy is too big (1.6G vs 4.1G) to be
> explained by this...
>
> A couple of possibilities:
>
> - Deleted files which are open: When a file is deleted, the space is
> usually freed immediately. UNLESS the file is open, in which case
> the space will not be freed until whatever-has-it-open closes it.
>
> - Other mountpoints: If you have lots of files in a subdirectory
> (e.g. /var/cache) and then mount another file system on /var/cache,
> you cannot reach the original contents of /var/cache - and this will
> then be invisible to "du"...
>
> >
> > I know some amount of space is supposed to be "reserved for the
> > super-user", but that's typically around 5%, right ?
>
> Around that percentage, yes. But neither du nor df takes this into
> account.
>
> > By the way, is there a command to see how big this reserved space
> > actually is on a given partition/disk ?
Correction: To find out the reserved-for-root space: I don't know.
Unfortunately, I completely misread your question previously....
--
Karl E. Jorgensen
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