Unable to mount oracle instance

oracleoracle-11g

I am trying to shutdown the system, then I want to mount it. I have tried this:

SQL> shutdown immediate;
Database closed.
Database dismounted.
ORACLE instance shut down.
SQL> startup mount;
ORA-12514: TNS:listener does not currently know of service requested in connect descriptor
SQL> startup mount;
ORA-24324: service handle not initialized
ORA-01041: internal error. hostdef extension doesn't exist

I have googled for solution but I can't found the exact reason that causes it to go wrong.

Best Answer

Exit sqlplus.

Make sure your os user is part of the DBA group (ORA_DBA in Windows).

Make sure ORACLE_SID is set to the SID of the database and unset TWO_TASK:

Windows:

set ORACLE_SID=ORCL
set TWO_TASK=

or

Unix/Linux

ORACLE_SID=ORCL
TWO_TASK=
export TWO_TASK

Now, connect as sysdba:

sqlplus / as sysdba

Now, startup the database:

SQL> startup mount;

SQL> alter database open;
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