Ever wanted to know why, on Ubuntu, the available disk space and the free disk space are not the same ?
By default, Ubuntu keeps 5% of partition space for root user, to avoid users to fill up all the disk space: this makes for the difference between available and free space disk.
Although this is a good solution in the case of a single partition, that might not be interesting with many partitions in particular with big ones. In that case, you might want to drop the space reserved to root to zero.
Here is how: run the following command,
sudo tune2fs -m 0 /dev/MyPartition