Part of system management is making sure there is enough disk space for the users and the system. If disk space gets too low, Unix will fail and will often do so in a rather perplexing and possibly ugly way (like bouncing mail or scrambling files). As described already in § 2.6, the df command reports the amount of ``disk free'' for each file system, while the du command reports the ``disk usage.'' You correspondingly use df to see if you have a problem and then du to see who is causing it.