relevant software:
Red Hat Enterprise Linux Server release 6.3 (Santiago)
cpanel installed 11.34.0 (build 7)

background and problem:
I was getting a disk usage warning (via cpanel) because /var seemed to be filling up on my server. The assumption would be that there was a log file growing too large and filling up the partition. I recently removed a large log file and changed my syslog config to rotate the log files more regularly. I removed something like /var/log/somefile and edited /etc/rsyslog.conf. This is the reason I was suspicious of the disk usage report warning issued by cpanel that I was getting because it didn't seem right.

This is what df was reporting for the partitions:

$ [/var]# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda2             9.9G  511M  8.9G   6% /
tmpfs                 5.9G     0  5.9G   0% /dev/shm
/dev/sda1              99M   53M   42M  56% /boot
/dev/sda8             883G  384G  455G  46% /home
/dev/sdb1             9.9G  151M  9.3G   2% /tmp
/dev/sda3             9.9G  7.8G  1.6G  84% /usr
/dev/sda5             9.9G  9.3G  108M  99% /var

This is what du was reporting for /var mount point:

$ [/var]# du -sh
528M    .

clearly something funky was going on. I had a similar kind of reporting inconsistency in the past and I restarted the server and df reporting seemed to be correct after that. I decided to reboot the server to see if the same thing would happpen.

This is what df reports now:

$ [~]# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda2             9.9G  511M  8.9G   6% /
tmpfs                 5.9G     0  5.9G   0% /dev/shm
/dev/sda1              99M   53M   42M  56% /boot
/dev/sda8             883G  384G  455G  46% /home
/dev/sdb1             9.9G  151M  9.3G   2% /tmp
/dev/sda3             9.9G  7.8G  1.6G  84% /usr
/dev/sda5             9.9G  697M  8.7G   8% /var

This looks more like what I'd expect to get.

For consistency this is what du reports for /var:

$ [/var]# du -sh
638M    .

question:
This is a nuisance. I'm not sure where the disk usage reports issued by cpanel get their info but it clearly isn't correct. How can I avoid this inaccurate reporting in the future? It seems like df reporting wrong disk usage is a strong indicator of the source problem but I'm not sure. Is there a way to 'refresh' the filesystem somehow so that the df report is accurate without restarting the server? Any other ideas for resolving this issue?