ORA-00030: User Session ID Does Not Exist

The Oracle error ORA-00030: user session ID does not exist occurs when you try to perform an action on a session that no longer exists or isn’t valid.

What It Means

Oracle tried to reference a session using its SID and serial number, but the session was already terminated or never existed in the first place.

Common Causes

1. Killing a non-existent session ALTER SYSTEM KILL SESSION 'sid,serial#'; If the session has already ended, Oracle returns ORA-00030.
2. Invalid session references in PL/SQL or scripts
   A script might be using old or cached session IDs.
3. After database restart
   Session IDs change after restarts, so previously saved IDs are no longer valid.
4. RAC environments
   The session might belong to a different instance.

How to Check Sessions

Before acting on a session, verify it exists:

SELECT sid, serial#, username, status
FROM v$session
WHERE username IS NOT NULL;

If it’s not listed, it’s already gone.

How to Fix ORA-00030

• Validate session before killing SELECT sid, serial# FROM v$session WHERE sid = <SID>;
• For RAC systems, specify the instance: ALTER SYSTEM KILL SESSION 'sid,serial#,@inst_id';
• Avoid hard-coded session IDs in scripts; always query them dynamically.
• Handle gracefully in PL/SQL: BEGIN EXECUTE IMMEDIATE 'ALTER SYSTEM KILL SESSION ''123,456'''; EXCEPTION WHEN OTHERS THEN IF SQLCODE = -30 THEN DBMS_OUTPUT.PUT_LINE('Session already terminated.'); END IF; END;

Summary

Key Takeaway

ORA-00030 is harmless—it simply means the target session no longer exists. Always confirm the session is active before running session-level commands.