ORA-01102: cannot mount database in EXCLUSIVE mode


SQL> startup mount
ORACLE instance started.

Total System Global Area 1068937216 bytes
Fixed Size 2260088 bytes
Variable Size 331350920 bytes
Database Buffers 729808896 bytes
Redo Buffers 5517312 bytes
ORA-01102: cannot mount database in EXCLUSIVE mode




Problem Description:


You are trying to startup the database and you receive the following error:

ORA-01102: cannot mount database in EXCLUSIVE mode

Cause: Some other instance has the database mounted exclusive or shared.

Action: Shutdown other instance or mount in a compatible mode.

Problem Explanation:


A database is started in EXCLUSIVE mode by default. Therefore, the ORA-01102 error is misleading and may have occurred due to one of the following reasons:

  • there is still an “sgadef.dbf” file in the “ORACLE_HOME/dbs” directory
  • the processes for Oracle (pmon, smon, lgwr and dbwr) still exist
  • shared memory segments and semaphores still exist even though the

database has been shutdown

  • there is a “ORACLE_HOME/dbs/lk” file

Search Words:


ORA-1102, crash, immediate, abort, fail, fails, migration

Solution Description:


Verify that the database was shutdown cleanly by doing the following:

  1. Verify that there is not a “sgadef.dbf” file in the directory “ORACLE_HOME/dbs”. % ls $ORACLE_HOME/dbs/sgadef<sid>.dbf If this file does exist, remove it. % rm $ORACLE_HOME/dbs/sgadef<sid>.dbf
  2. Verify that there are no background processes owned by “oracle” % ps -ef | grep ora_ | grep $ORACLE_SID

If background processes exist, remove them by using the Unix

command “kill”. For example:

 % kill -9 <rocess_ID_Number>
  1. Verify that no shared memory segments and semaphores that are owned by “oracle” still exist

% ipcs -b

If there are shared memory segments and semaphores owned by “oracle”, remove the shared memory segments

    % ipcrm -m <Shared_Memory_ID_Number>

and remove the semaphores

   % ipcrm -s <Semaphore_ID_Number>

NOTE: The example shown above assumes that you only have one

database on this machine. If you have more than one

database, you will need to shutdown all other databases

before proceeding with Step 4.

  1. Verify that the “$ORACLE_HOME/dbs/lk” file does not exist
  2. Startup the instance

Solution Explanation:


The “lk” and “sgadef.dbf” files are used for locking shared memory. It seems that even though no memory is allocated, Oracle thinks memory is still locked. By removing the “sgadef” and “lk” files you remove any knowledge oracle has of shared memory that is in use. Now the database can start.