kill specific connection on Oracle Database

Once we figure out who is on the system, we will probably want to know what they are doing. In this case, we will join the v$session view we just queried with another view, the V$SQL view. This alter statement kill the selected session

ALTER SYSTEM DISCONNECT SESSION 'sid,serial#' IMMEDIATE;
ALTER SYSTEM KILL SESSION '26,6764' IMMEDIATE;

How to list active / open connections in Oracle

There are times that you may need to issue a “SHUTDOWN IMMEDIATE” command to an Oracle Database. It is critical that you should consider checking who are the users that are currently running sessions on that Database. You don’t want to shutdown on your Boss or VP on Finance. Here’s a simple SQL to find all Active sessions in your Oracle Database:

select
       substr(a.spid,1,9) pid,
       substr(b.sid,1,5) sid,
       substr(b.serial#,1,5) ser#,
       substr(b.machine,1,6) box,
       substr(b.username,1,10) username,
       b.server,
       substr(b.osuser,1,8) os_user,
       substr(b.program,1,30) program
from v$session b, v$process a
where b.paddr = a.addr
  and type='USER'
order by spid;