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Date:      Wed, 30 Jul 2014 17:32:24 +0200
From:      Nils Effenberger <effenberger@work.de>
To:        freebsd-questions@freebsd.org
Subject:   Re: huge difference between du and df  - no open file descriptors
Message-ID:  <20140730173224.76007499@azubix.tec.work>
In-Reply-To: <20140730142609.1ac2bdc9@azubix.tec.work>
References:  <20140730142609.1ac2bdc9@azubix.tec.work>

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> One other way of using up space in a partition without it showing up
> in du(1) is to have files hidden underneath the mount points for other
> filesystems.  So you've got a 5GB UFS partition and a ZFS pool
> somewhere -- if you have (say) a file /mnt/big-file on the root and
> then you mount another filesystem (eg. ZFS) on top of /mnt you'll
> hide that file from du(1), but it will still be using space on the
> root partition and show up in df(1) output.
> 
> The only way to find this sort of thing is to unmount those other
> filesystems and look at what exists under the mount point.
> 
> You can also use up space invisibly by creating snapshots -- see
> mksnap_ffs(8) and snapinfo(8).
> 
> 	Cheers,
> 
> 	Matthew

Thank you for your answer Matthew. Strangely enough I didn't receive
the mail, I found it in the archives. Anyway... I unmounted the zpool
(the only thing that was mounted except the root partition) to make
sure I've nothing mounted on top of something, which brought me to this
state:

root@zhoernchen:~ # zfs unmount /zpool0
root@zhoernchen:~ # mount
/dev/mirror/root on / (ufs, local)
devfs on /dev (devfs, local, multilabel)
root@zhoernchen:~ # df -h
Filesystem          Size    Used   Avail Capacity  Mounted on
/dev/mirror/root    4.8G    4.5G    -15M   100%    /
devfs               1.0K    1.0K      0B   100%    /dev
root@zhoernchen:~ # du -shx /
2.2G    /

I don't have noch snapshots either:
root@zhoernchen:~ # snapinfo /
root@zhoernchen:~ # snapinfo -a
root@zhoernchen:~ # 

Then I tried to create another (big) file which lead to the
following:


root@zhoernchen:~ # dd if=/dev/zero of=/root/test bs=1024 count=3500000

/: write failed, filesystem is full
dd: /root/test: No space left on device
38849+0 records in
38848+0 records out
39780352 bytes transferred in 0.422187 secs (94224517 bytes/sec)
root@zhoernchen:~ # df -h
Filesystem          Size    Used   Avail Capacity  Mounted on
/dev/mirror/root    4.8G    4.8G   -395M   109%    /
devfs               1.0K    1.0K      0B   100%    /dev
root@zhoernchen:~ # rm test
root@zhoernchen:~ # df -h
Filesystem          Size    Used   Avail Capacity  Mounted on
/dev/mirror/root    4.8G    4.8G   -395M   109%    /
devfs               1.0K    1.0K      0B   100%    /dev

(Note that I deleted the 'test' file without effect.)

du(1) still shows 2.2G:

root@zhoernchen:~ # du -shx /
2.2G    /

When I now try to create files I get ENOSPC :(


Regards,

Nils
--
Nils Effenberger
Junior UNIX-Administration

n@work Internet Informationssysteme GmbH Wandalenweg 5, 20097 Hamburg,
http://www.work.de E-Mail: effenberger@work.de, Tel: +49 40 2388090 -
Fax: +49 40 23880929

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