Bug?Be hackered? Or I am foolish? Help me please

[781120]

There is a very strange question with my RedHat 7.2 linux--NO disk space with /usr
[root@server01 etc]# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/sda1 3.9G 114M 3.6G 3% /
/dev/sda6 1011M 633M 327M 66% /data01
/dev/sda7 1011M 508M 452M 53% /home
none 251M 0 250M 0% /dev/shm
/dev/sda3 3.0G 3.0G 0 100% /usr
/dev/sda5 2.4G 356M 1.9G 16% /var
/dev/sda2 4.9G 253M 4.4G 6% /data02
[root@server01 etc]# cp hosts.allow /usr
cp: writing `/usr/hosts.allow': No space left on device
[root@server01 etc]#
But when I run the following command:
[root@server01 etc]# du -sh /usr
1.2G /usr
[root@server01 etc]#

Why? And how can I resolve it?
Tks a lot!!!

 

[bluedevils]

This can ocur when a process is holding space for a file that is no longer there. You must restart the process and the space should reappear