[Nagiosplug-help] check_disk plugin reporting incorrect values

[Marc Powell]

On Aug 3, 2009, at 8:31 AM, Andrew Hall wrote:

> Hi there.
>
> One of our servers has its MySQL data directory symlinked from /var/ 
> lib/mysql to a mounted filesystem under /mnt
>
> The check_disk plugin is reporting that this /var partition is 85%  
> full and the output of the df command shows this too - but upon  
> running du this clearly isn't the case.
>
> I can only assume that by default the df and check_disk commands are  
> following these symlinks (although oddly even after choosing to  
> follow symlinks with the du command it still doesn't tally up) so I'm
> wondering how I can stop this ?

I'm sure that's not the case. Much more likely is that you have one or  
more large files that are deleted, but still open by a running  
application. The space really is still in use and df/check_disk are  
reporting correctly. The space used will be invisible to du but seen  
by df and check_disk since they calculate disk usage differently.

Use 'lsof | grep deleted' and see if you see them. If you restart the  
process that's holding the lock on them, the space will be freed.

--
Marc