Problems with DU and DF

[Randy]

Hi

I have a Linux RH5.2 server running and I am having a slight problem 
understanding the results of du and df commands. Disk space is at a premium 
for us at the moment so I check periodically via df to determine whether I 
need to go in an trim a few web accounts of stray "carts" or the various 
server logs.

While df will show the disks getting full, I use du to determine which 
files need truncating. Once located I will either truncate them or just 
remove them via the rm command. However, after removing 150 - 200 megs of 
log files a df command does not show the correct free space on the filesystem.

If, for example, I have a filesystem mounted as /var with log files being 
written on it and a df shows 95% used and I delete 200 megs of files the df 
will still show 95% full for many days. Is there anyway to force it to 
'reset' or 'reread' the filesystem and get the correct numbers? If I add a 
file, no matter what size, a df will show it immediately.. the problem is 
only with removing them. Or am I just removing them incorrectly?

Running du -s /var  always seems to show what I would consider the correct 
space used and changes proportionately with the sizes of the files removed.

Thank you for your time...
Randy Coleman