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	Mon, 29 Sep 1997 15:33:04 +0930 (CST)
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Date: Mon, 29 Sep 1997 15:33:03 +0930
From: Greg Lehey <grog@lemis.com>
To: Donn Miller <dmm125@bellatlantic.net>
Cc: freebsd-questions@FreeBSD.ORG
Subject: Re: "df" estimates are off
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In-Reply-To: <Pine.NEB.3.96.970929011000.28104B-100000@myname.my.domain>; from Donn Miller on Mon, Sep 29, 1997 at 01:13:06AM +0000
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On Mon, Sep 29, 1997 at 01:13:06AM +0000, Donn Miller wrote:
> Hello,
>
> Recently, I've noticed that the df command has been showing negative disk
> space, and was wondering how far negative it could go until the /usr
> partition was full:
>
> Filesystem  1K-blocks     Used    Avail Capacity  Mounted on
> /dev/wd0a       48431    39551     5006    89%    /
> /dev/wd0s1     423072   392984    30088    93%    /dos
> /dev/wd0s4e    548911   526867   -21868   104%    /usr
> procfs              4        4        0   100%    /proc
>
> But then I noticed that, for /usr, it shows -21868 avail, but when doing
> the math, 22044 is actually available.  For /, shows 5006, but act. free
> space is 8880.

ufs allows users access to only 90% of the total space on disk.  The
rest is reserved for root.  To make it more confusing, the 90% mark
can be changed with tunefs(8), so the designers chose to refer to
whatever this mark is as 100%.  Under normal circumstances, this means
that root can pump the file system up to 111% of its nominal
capacity.  This is *bad*, especially on /usr, since no normal user can
write to the disk any more.

> The disk usage for /dos is right on target.

This suggests that /dos is not ufs.

> Is it because df is allowing for a 'safety margin' of free space, or do I
> need to reboot or rebuild some database or something?

You need to remove some data, or you'll run into trouble.

Greg