Oracle 11g on OL 6 - Listener not working.

Is the process running?  Can you do a ps and see?

Depending on which version of ps is in your path, I believe this should work:

ps -fu oracle | grep lsnr | grep -v grep

Seems that the process is starting and then stopping after a few seconds. I guess that seems to be the issue.

Please help.

what happens if you launch :
lsnrctl start
and then
lsnrctl status

can you also post the result of the following command (after having launched the command above) :
lsof -i:1521

also can you post your listener.ora file ?

COMMAND   PID   USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
tnslsnr 12542 oracle    8u  IPv4  45565      0t0  TCP flexdb.xx.com:ncube-lm (LISTEN) "This exists for about 5 seconds after that goes off"

Linstener.ora

SID_LIST_LISTENER =
  (SID_LIST =
    (SID_DESC =
      (GLOBAL_DBNAME = fctestdb)
      (ORACLE_HOME = /oracle/app/product/11.2.0/db_1)
      (SID_NAME = fctestdb)
    )
  )

LISTENER =
  (DESCRIPTION =
    (ADDRESS = (PROTOCOL = TCP)(HOST = 192.168.156.139)(PORT = 1521))
  )

ADR_BASE_LISTENER = /oracle/app

is  192.168.156.139 correct address ?
can you try using localhost in place of this address just for testing ?
Also could you post your listener.log ?

Is this a new Oracle install on a new server?  Or, was this working but now it has stopped working?
Is there possibly something else running on this server that uses the same TCP/IP port (1521)?

Did you try changing this port number to a different port number (1522, 1530, 1540, etc.) then re-starting the listener?  Of course if you change this, and that works, you will need to change any/all tnsnames.ora files on your network to this new port number also.

Done