I'm trying to get Oracle Database 11g Express set up on my server so that it is accessible from the outside. I can talk to the DB locally using SQLPlus, so the database is definitely running. I think my issue is with the listener.

Here's what I'm getting:

$ lsnrctl start

LSNRCTL for Linux: Version 11.2.0.2.0 - Production on 27-AUG-2012 16:14:38

Copyright (c) 1991, 2011, Oracle.  All rights reserved.

Starting /u01/app/oracle/product/11.2.0/xe/bin/tnslsnr: please wait...

TNS-12537: TNS:connection closed
 TNS-12560: TNS:protocol adapter error
  TNS-00507: Connection closed
   Linux Error: 29: Illegal seek

I've tried two solutions I found online, and neither seemed to work. The first, from dba-oracle.com, suggests changing tcp.validcode_checking=yes to tcp.validnode_checking=no in sqlnet.ora. There was no such line, so I added it, and no luck. My sqlnet.ora is otherwise unchanged from when I installed. Note that this referred to version 10.2.

The second suggested adding 127.0.0.1 localhost.localdomain localhost to /etc/hosts, which I did, again with no change. No processes are listening on port 1521 (netstat -aopn | grep 1521 returns nothing).

Any suggestions would be most welcome.

Update

It seems I misunderstood what I was looking at. The sqlnet.ora file is in the samples directory, so it's not actually being read by the listener. Instead it is using the listener.ora file, which looks like this:

SID_LIST_LISTENER =
  (SID_LIST =
    (SID_DESC =
      (SID_NAME = PLSExtProc)
      (ORACLE_HOME = /u01/app/oracle/product/11.2.0/xe)
      (PROGRAM = extproc)
    )
  )

LISTENER =
  (DESCRIPTION_LIST =
    (DESCRIPTION =
      (ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC_FOR_XE))
      (ADDRESS = (PROTOCOL = TCP)(HOST = localhost)(PORT = 1521))
    )
  )

DEFAULT_SERVICE_LISTENER = (XE)

The tnsnames.ora file looks like this:

XE =
  (DESCRIPTION =
    (ADDRESS = (PROTOCOL = TCP)(HOST = localhost)(PORT = 1521))
    (CONNECT_DATA =
      (SERVER = DEDICATED)
      (SERVICE_NAME = XE)
    )
  )

EXTPROC_CONNECTION_DATA =
  (DESCRIPTION =
    (ADDRESS_LIST =
      (ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC_FOR_XE))
    )
    (CONNECT_DATA =
      (SID = PLSExtProc)
      (PRESENTATION = RO)
    )
  )

These are again the files that came with the application. Is there something I need to change here?