Why doesn't Oracle release file space when you drop a tablespace?

Sometimes when you drop a tablespace within Oracle, then remove (rm) the underlying data files, Oracle will not release filesystem space until you shut it down. This can be confirmed with the "df -k" command.

This is normal behaviour on Unix machines. If a process has a file open for use, the file will be removed, but the space it occupies will remain in place until all processes referencing it are closed.

Use the "fuser" command before deleting Oracle datafiles. If any processes are touching them, you will not get the space back when you rm the file. If SMON is
locking your file, just wait a few minutes until it releases it.