Marist,
To free up the space ,to terminate that process is one way, but not the only one.
Look:
oracle@dwdb udump]$ df -k /oracle
Filesystem 1k-blocks Used Available Use% Mounted on
/dev/sda8 10080488 7721256 1847164 81% /oracle
[oracle@dwdb udump]$ ls -lt largefile
-rw-r--r-- 1 oracle dba 1048576000 Dec 12 20:32 largefile
In another session telnet terminal, i open that file via:
[oracle@dwdb udump]$ more largefile





Here, I wait here.

And in the first session, i clear the file with:
[oracle@dwdb udump]$ echo ''>largefile
[oracle@dwdb udump]$ df -k /oracle
Filesystem 1k-blocks Used Available Use% Mounted on
/dev/sda8 10080488 6696256 2872164 70% /oracle

Now the space is released, but that session opening the file is still active.

This is useful if you really cannot terminate that process(like a bg process or shared server process).