connect to Oracle 11g instance

check the ports and see if you have a firewall blocking your connection and that the remote system is running the listener.

How do I check that in Linux? I

Try this
https://localhost:1158/em/

But before this check if the instance is registered by the Listener:

lsnrctl status
lsnrctl services

Also the OEM should be up

emctl start dbconsole

I'm in as root and typed lsnrctl status, and got:

TNS:no listener
TNS:12560:TNS protocol adapter error
TNS-00511: No listener
Linux ERRor 111: Connection refused

Why is the connection refused?

Then start the Listener:

lsnrctl start
emctl start dbconsole

Possibly the Oracle instance is also not startted

% sqlplus /nolog
SQL>connect sys/password@your_instance as sysdba
SQL>startup

I entered lsnrctl start (as root)
I got the error:
Error listening on (DESCRIPTION=(ADDRESS=(PROTOCOL=IPC)(KEY=EXTPROC1521)))
TNS-12555:TNS:permission denied
TNS-12560: TNS:protocol adaptor error
TNS-00525 Insufficient privelige for operation
Linux ERROR: Operation not permitted.

Listener failed to start

How do I fix this error?
Also, it seems that when I changed the HOSTNAME all the problems started. I changed the hostname back to localhost.localdomain and now I have these errors. I do need to change the hostname to mission-rh2 to bind to the IP address when this db goes into prduction. The files that I changed are: /etc/sysconfig network and /etc/hosts. I also made a change to the listener.ora file: I added listener.ora location=/u01/app/oracle/product/11.1.0/db_1/network/admin

Thanks!

Root can not start the Listener!
Listener should be started from 'oracle' user account.
If you have changed the hostname then go to LISTENER.ORA
file and change the HOST_NAME there appropriatelly.
After that start the Listener.

I changed the listener file. The listener started, the orcl database mounted and is up. However I still cannot access the db through Oracle Enterprise Manager. The error is failed to connect using the url
https://mission-2:1158

https://mission-2:1158/em

But before this check if the instance is registered by the Listener:

lsnrctl services

If it is not mentioned do static registration of the instance:

Backup LISTENER.ORA file!!!!!!!

In ...\network\admin open listener.ora

see

SID_LIST_LISTENER =
  (SID_LIST =
    (SID_DESC =
      (SID_NAME = PLSExtProc)
      (ORACLE_HOME = D:\Ora10g)
      (PROGRAM = extproc)
    )
    (SID_DESC =
      (SID_NAME = test)
      (ORACLE_HOME = D:\Ora10g)
    )
  )

Add the entry
    (SID_DESC =
      (SID_NAME = test)
      (ORACLE_HOME = D:\Ora10g)
    )
with regard to the particular Oracle Home and SID Name.


In Oracle 11g you have to create from scratch in the listener.ora file the section

SID_LIST_LISTENER =
&..

mentioned above.

Restart the listener:
c:>lsnrctl stop
c:>lsnctl start

Here is what my listener.ora looks like:
#
#
#
LISTENER =
   (DESCRIPTION LIST =
      (DESCRIPTION =
         (ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC1))
         (ADDRESS = (PROTOCOL =TCP)(HOST=missionrh2)(PORT= 1521))
)
)
     SID_LIST_LISTENER =
         (SID_LIST =
               (SID_DESC =
               (SID_NAME = PLSExtProc
               (ORACLE_HOME = /u01/app/oracle/product/11.1.0/db_1)
               (PROGRAM=extproc)
           )
            (SID_DESC=
            (SID_NAME=orcl
            (ORACLE_HOME=/u01/app/oracle/product/11.1.0/db_1)
       )

I go to the $ORACLE_HOME/bin directory and run lsnrctl stop and an error is returned bash: "lsnrctl:command not found

Seems you use an user that is not the Oracle user (DBA group)
and it has not rights to execute lsnrctl. I am sure it exists there
and you also can see it.

Clarify the name of the 'oracle' user - the same that has installed Oracle
After that give him rights over /u01 and subdirectories:

% chown oracle /u01 -R

I am using the oracle account. I also entered SU to change to root to see if I could get to the listener service but could not.
What is the exact syntax to give oracle acct rights over the oracle home directory?

I set my environment variables and found the listener.
Anyway - I ran lsnrctl stop and get the following error
Connecting to (DESCRIPTION..address...protocol ipc...key..extproc1))
TNS-12541 TNS no listener
TNS-12560 TNS protocol adapter error
tNS 00511 no listener
Connecting to desc..address..protocol=tcp...host missionrh2 port=1521

TNS 12541 - tns no listener
tns 12560 TNS protocol adapter error
tns 00511 no listener
linux error 111 connection refused.


why isnt this working?

listener is now working, I guess I just needed to wait for the settings to take place. Anyway, I started the listener and it is working now. I entered emctl start dbconsole and it returns:
https://localhost.localdomain://1158/em/console/aboutApplication  - An instance of OEM 11g....already running.
However my host name is mission-2? I changed the hostname to mission-2. I still cannot connect to Oracle enterprise manager through Firefox

Good!

The next step is to try to recreate the repository (see snppet).

Before this try to use the IP of the host instead the name.

To recreate the configuration files and repository for Database Console, run: 
$ emca -config dbcontrol db -repos recreate
 
STARTED EMCA at Jul 24, 2006 10:08:20 PM
EM Configuration Assistant, Version 10.2.0.1.0 Production
Copyright (c) 2003, 2005, Oracle.  All rights reserved.
 
Enter the following information:
Database SID: TESTDB
Database Control is already configured for the database TESTDB
You have chosen to configure Database Control for managing the database TESTDB
This will remove the existing configuration and the default settings and perform a fresh configuration
Do you wish to continue? [yes(Y)/no(N)]: Y
Listener port number: 1521
Password for SYS user: change_on_install
Password for DBSNMP user: manager
Password for SYSMAN user: manager
Email address for notifications (optional):
Outgoing Mail (SMTP) server for notifications (optional):
-----------------------------------------------------------------
 
You have specified the following settings
 
Database ORACLE_HOME ................ /u01/app/oracle/product/10.2.0/db_1
 
Database hostname ................ linux3
Listener port number ................ 1521
Database SID ................ TESTDB
Email address for notifications ...............
Outgoing Mail (SMTP) server for notifications ...............
 
-----------------------------------------------------------------
Do you wish to continue? [yes(Y)/no(N)]: Y
Jul 24, 2006 10:08:50 PM oracle.sysman.emcp.EMConfig perform
INFO: This operation is being logged at /u01/app/oracle/product/10.2.0/db_1/cfgtoollogs/emca/TESTDB/emca_2006-07-24_10-08-20-PM.log.
Jul 24, 2006 10:08:53 PM oracle.sysman.emcp.util.DBControlUtil stopOMS
INFO: Stopping Database Control (this may take a while) ...
Jul 24, 2006 10:09:29 PM oracle.sysman.emcp.EMReposConfig dropRepository
INFO: Dropping the EM repository (this may take a while) ...
Jul 24, 2006 10:11:23 PM oracle.sysman.emcp.EMReposConfig invoke
INFO: Repository successfully dropped
Jul 24, 2006 10:11:23 PM oracle.sysman.emcp.EMReposConfig createRepository
INFO: Creating the EM repository (this may take a while) ...
Jul 24, 2006 10:15:09 PM oracle.sysman.emcp.EMReposConfig invoke
INFO: Repository successfully created
Jul 24, 2006 10:15:18 PM oracle.sysman.emcp.util.DBControlUtil startOMS
INFO: Starting Database Control (this may take a while) ...
Jul 24, 2006 10:17:21 PM oracle.sysman.emcp.EMDBPostConfig performConfiguration
INFO: Database Control started successfully
Jul 24, 2006 10:17:22 PM oracle.sysman.emcp.EMDBPostConfig performConfiguration
INFO: >>>>>>>>>>> The Database Control URL is http://linux3:1158/em <<<<<<<<<<<
Enterprise Manager configuration completed successfully
FINISHED EMCA at Jul 24, 2006 10:17:22 PM

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Things were going good until I got to an error:
SEVERE: Error starting Database Control
Could not complete the configuration. From the logs : WARNING: Error executing /u01/app/oracle/product/11.1.0/db_1/bin/emctl start dbconsole....Error starting db control ...at oracle.sysman.emcp.EMconfigAssistant.main(EMConfigAssistant.java:467)

Look here and repeat the steps.

GREAT! I repeated the emca process and it finally finished! I connected to OEM! Thanks for your help.

One question, mission-rh is on port 5500. Where is the port number set? I thought it would be on 1158?

I will also so say GREAT!
Good luck!