[oracle] How can I kill all sessions connecting to my oracle database?

I need to quickly (and forcibly) kill off all external sessions connecting to my oracle database without the supervision of and administrator.

I don't want to just lock the database and let the users quit gracefully.

How would I script this?

If Oracle is running in Unix /Linux then we can grep for all client connections and kill it

grep all oracle client process:

ps -ef | grep LOCAL=NO | grep -v grep | awk '{print $2}' | wc -l

Kill all oracle client process :

kill -9 ps -ef | grep LOCAL=NO | grep -v grep | awk '{print $2}'

To answer the question asked, here is the most accurate SQL to accomplish the job, you can combine it with PL/SQL loop to actually run kill statements:

select ses.USERNAME,
    substr(MACHINE,1,10) as MACHINE, 
    substr(module,1,25) as module,
    status, 
    'alter system kill session '''||SID||','||ses.SERIAL#||''';' as kill
from v$session ses LEFT OUTER JOIN v$process p ON (ses.paddr=p.addr)
where schemaname <> 'SYS'
    and not exists
    (select 1 
        from DBA_ROLE_PRIVS 
        where GRANTED_ROLE='DBA' 
            and schemaname=grantee)
    and machine!='yourlocalhostname' 
order by LAST_CALL_ET desc;

I've been using something like this for a while to kill my sessions on a shared server. The first line of the 'where' can be removed to kill all non 'sys' sessions:

BEGIN
  FOR c IN (
      SELECT s.sid, s.serial#
      FROM v$session s
      WHERE (s.Osuser = 'MyUser' or s.MACHINE = 'MyNtDomain\MyMachineName')
      AND s.USERNAME <> 'SYS'
      AND s.STATUS <> 'KILLED'
  )
  LOOP
      EXECUTE IMMEDIATE 'alter system kill session ''' || c.sid || ',' || c.serial# || '''';
  END LOOP;
END;

If you want to stop new users from connecting, but allow current sessions to continue until they are inactive, you can put the database in QUIESCE mode:

ALTER SYSTEM QUIESCE RESTRICTED;

From the Oracle Database Administrator's Guide:

Non-DBA active sessions will continue until they become inactive. An active session is one that is currently inside of a transaction, a query, a fetch, or a PL/SQL statement; or a session that is currently holding any shared resources (for example, enqueues). No inactive sessions are allowed to become active...Once all non-DBA sessions become inactive, the ALTER SYSTEM QUIESCE RESTRICTED statement completes, and the database is in a quiesced state

Try trigger on logon

Insted of trying disconnect users you should not allow them to connect.

There is and example of such trigger.

CREATE OR REPLACE TRIGGER rds_logon_trigger
AFTER LOGON ON DATABASE
BEGIN
  IF SYS_CONTEXT('USERENV','IP_ADDRESS') not in ('192.168.2.121','192.168.2.123','192.168.2.233') THEN
    RAISE_APPLICATION_ERROR(-20003,'You are not allowed to connect to the database');
  END IF;

  IF (to_number(to_char(sysdate,'HH24'))< 6) and (to_number(to_char(sysdate,'HH24')) >18) THEN
    RAISE_APPLICATION_ERROR(-20005,'Logon only allowed during business hours');
  END IF;

END;

I found the below snippet helpful. Taken from: http://jeromeblog-jerome.blogspot.com/2007/10/how-to-unlock-record-on-oracle.html

select
owner||'.'||object_name obj ,
oracle_username||' ('||s.status||')' oruser ,
os_user_name osuser ,
machine computer ,
l.process unix ,
s.sid||','||s.serial# ss ,
r.name rs ,
to_char(s.logon_time,'yyyy/mm/dd hh24:mi:ss') time
from v$locked_object l ,
dba_objects o ,
v$session s ,
v$transaction t ,
v$rollname r
where l.object_id = o.object_id
and s.sid=l.session_id
and s.taddr=t.addr
and t.xidusn=r.usn
order by osuser, ss, obj
;

Then ran:

Alter System Kill Session '<value from ss above>'
;

To kill individual sessions.

As SYS:

startup force;

Brutal, yet elegant.

Before killing sessions, if possible do

ALTER SYSTEM ENABLE RESTRICTED SESSION;

to stop new sessions from connecting.

Additional info

Important Oracle 11g changes to alter session kill session

Oracle author Mladen Gogala notes that an @ sign is now required to kill a session when using the inst_id column:

alter system kill session '130,620,@1';

http://www.dba-oracle.com/tips_killing_oracle_sessions.htm