Discovery fails with Oracle

Reason 1: Service is not running.

Solution: The oracle server is down or the oracle server is not accessible from the applications manager machine.
Try to open a socket to the oracle machine by executing the following command from the machine in which Applications Manager server is running,

telnet oracle_hostname oracle_portnumber.

Reason 2: Unable to connect to Oracle Server.
Error Message:
Io exception:
Connection refused (DESCRIPTION=(TMP=)(VSNNUM=135294976)(ERR=12505)(ERROR_STACK=(ERROR =(CODE=12505)(EMFI=4))))

Solution: The Instance Name (Service Name) specified in Applications Manager is wrong or this instance is not running. Try to connect to oracle using SQL plus and the "Connect String/Service Name" given when you are connecting through the SQLPlus, should be given as Instance Name in Applications Manager.

The instance name can also be found out from the <oracle-installation directory\network\admin\listener.ora>. In <listener.ora> file, you will have an entry <SID_NAME = orcl>, where orcl is the Instance name.

The instance name can also be found out from the<oracle-installation directory\network\admin\tnsnames.ora>. In <tnsnames.ora> file, you will have an entry <SERVICE_NAME = orcl>, where orcl is the Instance name.

Reason 3: Unable to connect to Oracle Server. Error Message: 7

 ? Authentication details are correct

Solution: Download the latest Oracle 12c database JDBC driver (ojdbc6.jar file), rename it as classes12.zip and copy it to <AppManager_Home>\working\classes directory. Then restart Applications manager and try to add Oracle DB server again.

Reason 4: The user does not have proper privileges. Enter a user with DBA privileges.

Solution: A user with CONNECT and SELECT_CATALOG_ROLE roles is required for monitoring by Applications Manager. So configure a user with these permissions and try with that user in Applications Manager

Reason 5: ORA-28040: No matching authentication protocol

Solution 1: In the Oracle DB server installation directory, edit the sqlnet.ora file (present under <oracle home>\network\admin directory) and remove the entry SQLNET.ALLOWED_LOGON_VERSION=10 in that file or set to lower version. Then restart Oracle DB server and try to add it in Applications Manager.

Solution 2: Download the latest Oracle 12c database JDBC driver (ojdbc6.jar file), rename it as classes12.zip and copy it to <AppManager_Home>\working\classes directory. Then restart Applications manager and try to add Oracle DB server again.

Reason 6: Io exception: Got minus one from a read call

Solution 1: Make sure you are connecting to the correct port, wrong port can also give the error above. Also check the SID used to connect in tnsnames.ora and Listener.ora are correct.

Solution 2: It seems you have enabled ACL on the listener. You can follow these steps to avoid the error:

a. Modify $ORACLE_HOME/network/admin/sqlnet.ora file with following parameter: 
tcp.validnode_checking = no

b. If you don't want to disable this, you can put the machine names (provide appmanager hostname) as follows and restart the listener
tcp.invited_nodes=(machine1, machine2)

Solution 3: Check the number of process and shared pool size.

Show parameter SHARED_POOL_SIZE;
Show parameter Processes;

If the values are insufficient, increase the size using

Alter system set SHARED_POOL_SIZE=<size the environment demands>M;
Alter system set PROCESSES=<Size the environment demands> SCOPE=SPFILE;

NOTE: If none of the above fixes the problem, execute the file OracleDebug.bat under <AppManager_Home>\bin\troubleshooting and send the result to appmanager-support@manageengine.com