ORA-01102: cannot mount database in EXCLUSIVE mode

Error happened when try open database :

    SQL> startup
    ORACLE instance started.

    Total System Global Area 267227136 bytes
    Fixed Size 2212496 bytes
    Variable Size 205524336 bytes
    Database Buffers 54525952 bytes
    Redo Buffers 4964352 bytes
    ORA-01102: cannot mount database in EXCLUSIVE mode



 In alert.log

    sculkget: lock held by PID: 12359
    ORA-09968: unable to lock file
    Linux-x86_64 Error: 11: Resource temporarily unavailable
    Additional information: 12359
    ORA-1102 signalled during: ALTER DATABASE MOUNT...


On OS level :

    [oracle@localhost trace]$ ps -ef | grep pmon

    oracle 10222 1 0 10:27 ? 00:00:00 ora_pmon_ORCL
    oracle 2522 1 0 Nov09 ? 00:00:06 ora_pmon_orcl

Use :

 Kill -9 10222 2522

Then
1-After that fire export ORACLE_SID= (watch case sensitive )
2-sqlplus / as sysdba
3-startup ;

Thanks.
NJ