Incorrect df -k output??

[Oliver Fromme]

Newtunes Support <ntstaff at gmail.com> wrote:
 > I have resolved this issue using forsed unmount (umount -f /var)

Not a good idea.  It breaks all sorts of things.

 > And after I mounted /var again df -k shows me correct value.

The value was correct before, too.  There probably were
some files that were removed, but some processes still
had them open.  du(1) doesn't see those files, so they're
not included in the sum.  df(1) sees the allocated space,
of course.

It can happen on the /var file system if an error occurs
during log file rotation, so the programs writing to the
log files (e.g. syslogd) are not properly informed about
the rotation, so they keep the old files open.

A good way to view such files/processes is to use the
command "lsof +L1" (lsof can be installed from the ports
collection: /usr/ports/sysutils/lsof).  It lists all
file descriptors in use that have a link count of zero.

The correct way to resolve the issue is to find those
processes and tell them to close the files (usually a
"kill -HUP" will do that).  If everything else fails,
kill the processes (use "kill -KILL" if necessary).
Do not use "umount -f".

 > But I have new problem.
 > fsck -y does not fix anything.

That only works when the file system is not mounted (or
only mounted read-only).  It's usually done in single-
user mode.

(However, I assume that your file system doesn't need
fsck, but it certainly wouldn't hurt either.)

Best regards
   Oliver

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