Oracle listener errors : Troubleshooting Oracle Net Services :ORA-12541 TNS :no listener:ORA-01034: ORA-27101

Oracle listener errors :

you may get following type of error for listener :

C:\Users\Administrator>lsnrctl status
Connecting to (DESCRIPTION=(ADDRESS=(PROTOCOL=TCP)(HOST=WIN-JSJDDUESQH9)(PORT=1521)))
TNS-12541: TNS:no listener
TNS-12560: TNS:protocol adapter error
TNS-00511: No listener
64-bit Windows Error: 61: Unknown error

When you get the error "TNS no listener errors", that the Windows listener service is not accepting connections or the service is not running.As recommended need to re-start the listener by using the command "lsnrctl start" or lsnrctl reload  

 

 Once the listener started using "LNSRCTL START or LSNRCTL RELOAD" listener will start and you can observe the status of current listener by run the following command "LSNRCTL STATUS"

Most of the cases once the listener will start then your are able to connect the oracle and issue got resolved.Even though listener was running some time you may get another type of errors like "ORA-01034: ORA-27101:  "as following :

C:\Users\Administrator>sqlplus

SQL*Plus: Release 11.2.0.1.0 Production on Mon Jul 25 17:44:31 2016

Copyright (c) 1982, 2010, Oracle.  All rights reserved.

Enter user-name: system
Enter password:
ERROR:
ORA-01034: ORACLE not available
ORA-27101: shared memory realm does not exist
Process ID: 0
Session ID: 0 Serial number: 0

For these kind of errors even listener was running, we have to run the following commands to resolve the issue. We have to connect the oracle by using /nolog first and then run the below commands.

set oracle_sid=orcl
sqlplus /nolog
conn sys/sys as sysdba
shutdown abort
startup

check the below image :

now the oracle has started successfully and you are able to see the ORCL instance in listener status also.