Query to see all oracle sessions

Here is a query to see all oracle sessions. You should be logged in as system administrator:

SELECT s.inst_id,
       s.sid,
       s.serial#,
       p.spid,
       s.username,
       s.program
FROM   gv$session s
       JOIN gv$process p ON p.addr = s.paddr AND p.inst_id = s.inst_id
WHERE  s.type != 'BACKGROUND';

   INST_ID        SID    SERIAL# SPID       USERNAME   PROGRAM
---------- ---------- ---------- ---------- ---------- ---------------------------------------------
         1         30         15 3859       TEST       sqlplus@oel5-11gr2.domainname (TNS V1-V3)
         1         23        287 3834       SYS        sqlplus@oel5-11gr2.domainname (TNS V1-V3)

Now if you want to kill any session:

SQL> ALTER SYSTEM KILL SESSION 'sid,serial#';