Login into Oracle Database Error

Question

I had installed Oracle 12 to my Linux box. I tried to login using sqlplus but it prompt out this error at below. How to solve it?

Enter user-name: SYSDBA

Enter 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

Additional information: 3701

Additional information: 542678011

Process ID: 0 Session ID: 0 Serial number: 0

EDIT: How to find out default ORACLE_SID?

Answer 1

There could be various reason for this error.

You are using wrong ORACLE_SID and ORACLE_HOME.

The instance that you are trying to connect isn't up and running.

When you have wrong ORACLE SID and HOME.

I could reproduce the error by changing my SID to something else. My SID is oracdb.

[oracle@myserver ~]$ ps -ef | grep pmon
oracle 29336 1 0 Apr27 ? 00:00:22 ora_pmon_oracdb

But I changed it to orcl.

[oracle@myserver Desktop]$ export ORACLE_SID=orcl

Then I tried to connect to the database using SQL*PLUS.

[oracle@myserver Desktop]$ sqlplus sys
SQL*Plus: Release 12.2.0.1.0 Production on Tue May 2 00:23:50 2017
Copyright (c) 1982, 2016, Oracle. All rights reserved.
Enter 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
Additional information: 3701
Additional information: -923528497
Process ID: 0
Session ID: 0 Serial number: 0

Then I changed it to original SID.

[oracle@myserver ~]$ export ORACLE_SID=oracdb
[oracle@myserver ~]$ sqlplus / as sysdba
SQL*Plus: Release 12.2.0.1.0 Production on Tue May 2 00:28:40 2017
Copyright (c) 1982, 2016, Oracle. All rights reserved.
Connected to:
Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production

When your instance is down and connected as a non-sys user

Use the following linux command to check whether some of the important background processes are running or not such PMON or SMON.

[oracle@myserver ~]$ ps -ef| grep pmon
oracle 57587 57044 2 00:52 pts/3 00:00:00 grep pmon

My oracle instance is down.

Now, as you have tried, I attempt to connect to the database using non-sys user, sysdba is a privilege not a database user.

[oracle@myserver ~]$ sqlplus sysdba
SQL*Plus: Release 12.2.0.1.0 Production on Tue May 2 00:53:04 2017
Copyright (c) 1982, 2016, Oracle. All rights reserved.
Enter 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
Additional information: 3701
Additional information: -688980181
Process ID: 0
Session ID: 0 Serial number: 0
Enter user-name: 

I got the same error as you have got.

Now, connect as sysdba/sysoper and start the database instance.

[oracle@myserver ~]$ sqlplus / as sysdba
SQL*Plus: Release 12.2.0.1.0 Production on Tue May 2 00:53:36 2017
Copyright (c) 1982, 2016, Oracle. All rights reserved.
Connected to an idle instance.
SQL> startup

• Ivan: How to find out my default ORACLE_SID?
• atokpas: You can go to $ORACLE_HOME/dbs directory and find initialization parameter files such as spfile<SID>.ora or init<SID>.ora.
• atokpas: @peterwkc: Or if your instance is up and running then $ ps -ef | grep pmon shows instance name at the end of the process name.
• Md Haidar Ali Khan: @peterwkc, For linux & Solaris , you can also find ORACLE_SID from "pgrep -lf pmon" . And In linux you can also find from this query" select distinct sid from v$mystat;"
• Ivan: I"m issue this command ps -ef | grep pmon root 31688 30893 0 19:19 pts/0 00:00:00 grep --color=auto pmon. Is my oracle instance is up? How to start the oracle instance?