Listening directory:
cd $ORACLE_HOME/network/admin
(cd /u01/app/oracle/product/11.2.0/dbhome_1/network/admin)
Stop listening: lsnrctl stop
Start listening: lsnrctl start
Listening status: lsnrctl status
The Status command shows whether the listener is active, the location of the log and trace files, how long the listener has been running, and what tasks the listener is listening for.
SQL> alter system register;
System altered
(Forcibly register, urge the pmon process, start listening)