SQL> startup
ORACLE instance started.
Total System Global Area 1.7103E+10 bytes
Fixed Size                  2243608 bytes
Variable Size            8455717864 bytes
Database Buffers         8623489024 bytes
Redo Buffers               21712896 bytes
ORA-01102: cannot mount database in EXCLUSIVE mode

[oracle@zmotm003 dbs]$ oerr ora 01102
01102, 00000, "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.

1、在ORACLE_HOME/dbs/存在 "orcl.dbf" 文件或者lk 文件。这两个文件是用来用于锁内存的。
2、oracle的 pmon, smon, lgwr and dbwr等进程未正常关闭。
3、数据库关闭后，共享内存或者信号量依然被占用。
lk说明DATABASE 已经是MOUNT状态了,不用再次MOUNT.当 DATABASE 被UNMOUNT 后会被自动删除,如果DATABASE没有MOUNT,却依然存在这个问题，只有手工将其删除。

Verify that the database was shutdown cleanly by doing the following: 
1. Verify that there is not a "orcl.dbf" file in the directory 
"ORACLE_HOME/dbs". 
% ls $ORACLE_HOME/dbs/orcl.dbf 
If this file does exist, remove it. 
% rm $ORACLE_HOME/dbs/orcl.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  
3. 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  

and remove the semaphores 
% ipcrm -s  
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. 
4. Verify that the "$ORACLE_HOME/dbs/lk" file does not exist 
5. Startup the instance