I have recently learned that ext3 (or some other filesystems) reserve some space of a drive by default for previliged processes. One can change this by doing the following:
# tune2fs -m 4 /dev/sdXY
where 4 in this case is the percentage to reserve. If I run df -h before and after that command I see the impact on the output of df. I was wondering if there was a way to see the actual usage of the partitions. Something like df -h gives but without taking the reserved bits into account.
I think the idea of the reserved blocks is that once the filesystem is filled up to capacity sans the reserved blocks, only root processes will be able to write to disk. So the space functions like a buffer zone once the disk is otherwise full -- it is not a pre-existing area. Hence, there is no separate usage statistic for that space, because it is (normally) theoretical.
In short, it's in case of emergency. Keep in mind that filling a general purpose disk to 100% (or 95%) is a big mistake; realistically, a 100 GB hard drive shouldn't be used to store more than 90-95 GB (and perhaps ideally, even less than that). So those "reserved blocks" are not a real issue.
If you already understand all this and just want a way to get a usage % exclusive of the reserved blocks, the answer is probably: arithmetic ;)
