du, disk usage, is to calculate the size of each file by searching for the file and then accumulate, du can see the file just some currently exists
is not deleted . ( -S: the Summarize display only totals, listed only the last aggregated value)
df, disk free, quick access to information via the file system space, when we delete a file, the file does not
It is soon to disappear among the file system, but temporarily disappeared, when all programs do not have, would have been freed under the rules of the OS
by deleted files, df record is the size of the file acquired by the file system he is able to see deleted du stronger than local
file , and calculate the size of the time, this part of space added, more accurate.
When the file system is also OK to delete the file, this time on du and df agreement.
