ORA-01034: ORACLE not available in oracle 11g I installed oracle 11g on ubuntu 14.04 and i started lister and the message is as below.

LSNRCTL for Linux: Version 11.2.0.2.0 - Production on 10-OCT-2014 14:20:02

Copyright (c) 1991, 2011, Oracle.  All rights reserved.

Starting /u01/app/oracle/product/11.2.0/xe/bin/tnslsnr: please wait...

TNSLSNR for Linux: Version 11.2.0.2.0 - Production
System parameter file is /u01/app/oracle/product/11.2.0/xe/network/admin/listener.ora
Log messages written to /u01/app/oracle/diag/tnslsnr/TSDC/listener/alert/log.xml
Listening on: (DESCRIPTION=(ADDRESS=(PROTOCOL=ipc)(KEY=EXTPROC_FOR_XE)))
Listening on: (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=TSDC)(PORT=1521)))

Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=IPC)(KEY=EXTPROC_FOR_XE)))
STATUS of the LISTENER
------------------------
Alias                     LISTENER
Version                   TNSLSNR for Linux: Version 11.2.0.2.0 - Production
Start Date                10-OCT-2014 14:20:02
Uptime                    0 days 0 hr. 0 min. 0 sec
Trace Level               off
Security                  ON: Local OS Authentication
SNMP                      OFF
Default Service           XE
Listener Parameter File   /u01/app/oracle/product/11.2.0/xe/network/admin/listener.ora
Listener Log File         /u01/app/oracle/diag/tnslsnr/TSDC/listener/alert/log.xml
Listening Endpoints Summary...
  (DESCRIPTION=(ADDRESS=(PROTOCOL=ipc)(KEY=EXTPROC_FOR_XE)))
  (DESCRIPTION=(ADDRESS=(PROTOCOL=tcp)(HOST=TSDC)(PORT=1521)))
Services Summary...
Service "XE" has 1 instance(s).
  Instance "XE", status UNKNOWN, has 1 handler(s) for this service...
The command completed successfully


Then I started the server by oracle-xe start and it was started successfully.

When I was trying to connect to sql*plus following error was getting..

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


Please suggest me what to do with this?
Run sqlplus / as sysdba then issue command startup; to start the database.

Also on Linux with this error, you can check first if Oracle background processes are up with ps aux | grep pmon. Pmon is process monitor, or check some other background process. If they are not running then the database is not running.