Subject: Re: 'df' not reporting correct disk usage
To: Brian C. Grayson <email@example.com>
From: Chris Foote <firstname.lastname@example.org>
Date: 07/18/1998 14:13:43
On Fri, 17 Jul 1998, Brian C. Grayson wrote:
> > i.e. df reports an additional 47MB of disk space in use than there
> > really is.
> Have you recently deleted a bunch of stuff on this partition?
Sure did - I moved a stack of files to the /usr partition in order to free
up some room because /var/log & /var/spool/mqueue were chewing up a bit.
One of the things I did was to link /var/account to /usr/var/account.
Looks like kernel process accounting was the culprit.
> particular, did you delete files (i.e. binaries) that were open
> at the time, like a make install? If so, the kernel doesn't
> _actually_ delete them until they are finally
> closed/not-being-used. Thus, one could fill up one's root
> partition by doing something like the following, I believe:
> ## Assume / has 10MB free, and
> ## netscape is a 10MB executable.
> cp /usr/local/bin/netscape /
> /netscape &
> rm /netscape
> At this point, du will say you still have 10MB free, but df
> will say you are at 100%. If you now try to use any disk space
> on /, it'll fail, until you kill the running netscape,
> at which point the disk _really_ no longer needs to hold the
> backing store for /netscape, so the blocks are deallocated.
> Make sense? I'd bet that if you rebooted, df and du would
> agree. If not, then maybe there _really is_ a bug, but I'm
> skeptical.... :)
Yes, the space was reclaimed after a reboot:
Filesystem 1K-blocks Used Avail Capacity Mounted on
/dev/wd0a 84327 27220 52890 34% /
/dev/wd0e 1782683 954568 738980 56% /usr
kernfs 1 1 0 100% /kern
Thanks for the help :-)
Chris Foote SE Net
Technical Manager 222 Grote Street
SE Network Access Adelaide SA 5000
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