Ora-01034: Oracle not available AND Ora-27101:Shared memory realm does not exist

Check to see that the Oracle service & listeners are running.
What platform are you using (Windows, Unix, etc)? Make sure the user you're logged in as has the appropriate rights.

Oracle service and listeners are running. I am on a Windows platform. I am logged in a administrator.

Is the ORACLE_SID set to the same value (including capitalization) as in tnsnames.ora?

gatorvip nailed it; you may check your variable by getting to the command prompt, then run SET.

What is the syntax to set the Oracle_SID from the command prompt?

set ORACLE_SID= <sid>

although you should probably add ORACLE_SID to your environment variables:

XP:
- right click on My Computer, then select Properties
- select the Advanced tab
- click on Environment Variables
- under System variables, click New
- use variable name ORACLE_SID and variable value your oracle_sid
- OK your way out.

I set the ORACLE_SID=CLReProcs, stop and started the Oracles services. But I still get the same error
ORA-01034:Oracle Not Available
ORA-27101:Shared Memory realm does not exist

I also stopped and started the db after the change took place.

Hi,

  I set the new variable ORACLE_SID=CLRExtProc via the variable environment.

Then I started the command prompt and typed SQLPLUS and got the following error:
ORA-12560:TNS:protocol adapter error
Enter user-name:

Oracle Express\SQLPLus was working until I installed Oracle client software I need for another project. Please advise
Thanks, MissyMadi

What are the full contents of your tnsnames.ora file? What is the name of your instance?

TNSNames.ora listed below.

XE =
  (DESCRIPTION =
    (ADDRESS = (PROTOCOL = TCP)(HOST = Psoras.aaicorp.com)(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)
    )
  )

ORACLR_CONNECTION_DATA =
  (DESCRIPTION =
    (ADDRESS_LIST =
      (ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC_FOR_XE))
    )
    (CONNECT_DATA =
      (SID = CLRExtProc)
      (PRESENTATION = RO)
    )
  )

Where do I find the instance name?

>>XE =
  (DESCRIPTION =
    (ADDRESS = (PROTOCOL = TCP)(HOST = Psoras.aaicorp.com)(PORT = 1521))
    (CONNECT_DATA =
      (SERVER = DEDICATED)
      (SERVICE_NAME = XE)
    )
  )
<<

Then you probably want to use XE as your ORACLE_SID value. After you do that, and restart, ping from the command line: tnsping XE

I did the above, restarted my PC and pinged: tnsping XE
result: "Used TNSNAMES adapter to resolve the alias Attempting to contact .....<Service_Name = XE>> OK<30 Sec>

Got the following error when trying to connect to sqlplus
ORA-01034: ORACLE not available
ORA-27101:shared memory realm does not exist?

Please advise,
Thanks, Missymadi

What happens if you run

>lsnrctl services

from the command line?

Connecting to <DESCRIPTION=<ADDRESS=<PROTOCOL=IPC<KEY=EXTPROC_FOR_XE>>>
Services Summary...
Serive CLRExtProc has 1 instance...
         Instance CLRExtProc status UNKNOWN

Dedicated established 0 refused 0
local server
service PLSExtProc has 1 instance
...
The command completed successfully.

Here is the listener.ora file - where do I add the missing info. (I tried to add but had syntax errors and the listener wouldn't start)

SID_LIST_LISTENER =
  (SID_LIST =
    (SID_DESC =
      (SID_NAME = PLSExtProc)
      (ORACLE_HOME = C:\oraclexe\app\oracle\product\10.2.0\server)
      (PROGRAM = extproc)
    )
    (SID_DESC =
      (SID_NAME = CLRExtProc)
      (ORACLE_HOME = C:\oraclexe\app\oracle\product\10.2.0\server)
      (PROGRAM = extproc)
    )
   
  )

LISTENER =
  (DESCRIPTION_LIST =
    (DESCRIPTION =
      (ADDRESS = (PROTOCOL = IPC)(KEY = EXTPROC_FOR_XE))
      (ADDRESS = (PROTOCOL = TCP)(HOST = name.company.com)(PORT = 1521))
    )
  )

DEFAULT_SERVICE_LISTENER = (XE)