ORACLE ERROR: Connected to an idle instance.

[root@ssl Desktop]# source /u01/app/oracle/product/11.2.0/xe/bin/oracle_env.sh

[root@ssl Desktop]# sqlplus /nolog

SQL*Plus: Release 11.2.0.2.0 Production on Mon Oct 7 08:35:04 2013

Copyright (c) 1982, 2011, Oracle.  All rights reserved.

SQL> connect sys / as sysdba
Enter password:
Connected to an idle instance.


SQL> connect sys/password
ERROR:
ORA-01034: ORACLE not available
ORA-27101: shared memory realm does not exist
Linux-x86_64 Error: 2: No such file or directory
Process ID: 0
Session ID: 0 Serial number: 0


Warning: You are no longer connected to ORACLE.





SQL> connect sys/password as sysdba

Connected to an idle instance.


>>>if u face above problem then you apply below command:

SQL> startup
ORACLE instance started.

Total System Global Area 1068937216 bytes
Fixed Size            2233344 bytes
Variable Size          654314496 bytes
Database Buffers      406847488 bytes
Redo Buffers            5541888 bytes
Database mounted.
Database opened.