df and du don't seem to agree ?

[David Cho-Lerat <david.lerat@asterion.fr>]

Hi list,

this might be a newbie question, but can anyone tell me
why "du" and "df" don't seem to agree :

server:~# df -h /var
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/vg00-var  5.0G  4.1G  624M  87% /var
server:~# du -h -s /var
1.6G    /var

("/var" is on a partition of its own.)

"du" says 1.6G are used, while "df" reports 4.1G. Any idea why ?

I know some amount of space is supposed to be "reserved for the
super-user", but that's typically around 5%, right ?

By the way, is there a command to see how big this reserved space
actually is on a given partition/disk ?

Thanks,
David.