Oracle client ORA-12541: TNS:no listener [closed]

Answer 1

Check out your TNS Names, this must not have spaces at the left side of the ALIAS

Best regards

Answer 2

I also faced the same problem but I resolved the issue by starting the TNS listener in control panel -> administrative tools -> services ->oracle TNS listener start.I am using windows Xp and Toad to connect to Oracle.

Answer 3

According to oracle online documentation

ORA-12541: TNS:no listener

Cause: The connection request could not be completed because the listener is not running.

Action: Ensure that the supplied destination address matches one of the addresses used by 
the listener - compare the TNSNAMES.ORA entry with the appropriate LISTENER.ORA file (or  
TNSNAV.ORA if the connection is to go by way of an Interchange). Start the listener on 
the remote machine.

Answer 4

You need to set oracle to listen on all ip addresses (by default, it listens only to localhost connections.)

Step 1 - Edit listener.ora

This file is located in:

• Windows: %ORACLE_HOME%\network\admin\listener.ora.
• Linux: $ORACLE_HOME/network/admin/listener.ora

Replace localhost with 0.0.0.0

# ...

LISTENER =
  (DESCRIPTION_LIST =
    (DESCRIPTION =
      (ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC1521))
      (ADDRESS = (PROTOCOL = TCP)(HOST = 0.0.0.0)(PORT = 1521))
    )
  )

# ...

Step 2 - Restart Oracle services

• Windows: WinKey + r

  services.msc
  

• Linux (CentOs):

  sudo systemctl restart oracle-xe