ORA-00027 Cannot kill current session
Cause: Attempted to use ALTER SYSTEM KILL SESSION to kill the current session. Action: None.
ORA-00026 Missing or invalid session ID
Cause: Missing or invalid session ID string for ALTER SYSTEM KILL SESSION. Action: Retry with a valid session ID.
ORA-00025 Failed to allocate %s
Cause: Out of memory. Action: Restart with larger sga heap.
ORA-00024 Logins from more than one process not allowed in single-process mode
Cause: Trying to login more than once from different processes for ORACLE started in single-process mode. Action: Log off from the other process.
ORA-00023 Session references process private memory; cannot detach session
Cause: An attempt was made to detach the current session when it contains references to process private memory. Action: A session may contain references to process memory (PGA) if it has an open network connection, a very large context area, or operating system privileges. To allow the detach, it may be necessary to close the…
ORA-00022 Invalid session ID; access denied
Cause: Either the session specified does not exist or the caller does not have the privilege to access it. Action: Specify a valid session ID that you have privilege to access, that is either you own it or you have the CHANGE_USER privilege.
ORA-00021 Session attached to some other process; cannot switch session
Cause: The user session is currently used by others. Action: Do not switch to a session attached to some other process.
ORA-00020 Maximum number of processes (%s) exceeded
Cause: All process state objects are in use. Action: Increase the value of the PROCESSES initialization parameter.
ORA-00018 Maximum number of sessions exceeded
Cause: All session state objects are in use. Action: Increase the value of the SESSIONS initialization parameter.
ORA-00017 Session requested to set trace event
Cause: The current session was requested to set a trace event by another session. Action: This is used internally; no action is required.
Oracle Database Internal Mechanism 