[root@dell1 /]# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda9             1.9G  652M  1.1G  37% /
/dev/sda2             221M   33M  176M  16% /boot
none                 1014M     0 1014M   0% /dev/shm
/dev/sda3             250G  7.8G  230G   4% /home
/dev/sda7             2.5G   44M  2.3G   2% /tmp
/dev/sda5             9.7G  2.7G  6.5G  30% /usr
/dev/sda6             3.2G  3.1G     0 100% /var

[root@dell1 /]# du -hcs /var
719M    /var
719M    total

[root@dell1 /]#  mount -l
/dev/sda9 on / type ext3 (rw) [/]
none on /proc type proc (rw)
none on /sys type sysfs (rw)
none on /dev/pts type devpts (rw,gid=5,mode=620)
usbfs on /proc/bus/usb type usbfs (rw)
/dev/sda2 on /boot type ext3 (rw) [/boot]
none on /dev/shm type tmpfs (rw)
/dev/sda3 on /home type ext3 (rw) [/home]
/dev/sda7 on /tmp type ext3 (rw) [/tmp]
/dev/sda5 on /usr type ext3 (rw) [/usr]
/dev/sda6 on /var type ext3 (rw) [/var]
none on /proc/sys/fs/binfmt_misc type binfmt_misc (rw)
sunrpc on /var/lib/nfs/rpc_pipefs type rpc_pipefs (rw)

Q: 'df' command says partition is full, while 'du' reports free space
 
Theodore Ts'o, the ext2 developer, said:
 
The standard cause for this is some user process keeping a deleted file open. When this happens, the space is not visible via 'du', since the file is no longer visible in the directory tree. However, the space is still used by the file until it is deallocated, and that can only happen once the last process which has the file open either closes its file descriptor to the file, or the process exits. You can use the lsof program to try to find which process is keeping an open file. Usually it's some log file, or some large data base file which gets rotated out, but some older process are still keeping the log file open.