Check the following pre-requisites before starting Dbvisit Replicate. If these are not correct, then the replication will NOT function.

1. Connect to the source server as oracle.

su - oracle

2. The database XE on both the source and target server should be started and available. To check if the database XE is running, check the pmon process (on both source and target)

ps -ef | grep pmon
oracle    2467     1  0 13:31 ?        00:00:00 xe_pmon_XE
oracle    2974  2933  0 13:35 pts/1    00:00:00 grep pmon

If the xe_pmon_XE process is running, that is a good indication that the Oracle database is running.

3. On the source server, check the TNS connection to the source database

tnsping SOURCE
 
TNS Ping Utility for Linux: Version 11.2.0.2.0 - Production on 24-MAY-2017 23:30:30
Copyright (c) 1997, 2011, Oracle.  All rights reserved.
Used parameter files:


Used TNSNAMES adapter to resolve the alias
Attempting to contact (DESCRIPTION = (ADDRESS = (PROTOCOL = TCP)(HOST = source)(PORT = 1521)) (CONNECT_DATA = (SERVER = DEDICATED) (SERVICE_NAME = XE)))
OK (10 msec)

4. On the source server, check the TNS connection to the target database

tnsping TARGET

TNS Ping Utility for Linux: Version 11.2.0.2.0 - Production on 24-MAY-2017 23:30:58
Copyright (c) 1997, 2011, Oracle.  All rights reserved.
Used parameter files:

Used TNSNAMES adapter to resolve the alias
Attempting to contact (DESCRIPTION = (ADDRESS = (PROTOCOL = TCP)(HOST = target)(PORT = 1521)) (CONNECT_DATA = (SERVER = DEDICATED) (SERVICE_NAME = XE)))
OK (60 msec)

5. Connect to the target server as oracle.

su - oracle

6. On the target server, check the TNS connection to the source database.

tnsping SOURCE

TNS Ping Utility for Linux: Version 11.2.0.2.0 - Production on 24-MAY-2017 23:31:55
Copyright (c) 1997, 2011, Oracle.  All rights reserved.
Used parameter files:

Used TNSNAMES adapter to resolve the alias
Attempting to contact (DESCRIPTION = (ADDRESS = (PROTOCOL = TCP)(HOST = source)(PORT = 1521)) (CONNECT_DATA = (SERVER = DEDICATED) (SERVICE_NAME = XE)))
OK (20 msec)

7. On the target server, check the TNS connection to the target database.

tnsping TARGET

TNS Ping Utility for Linux: Version 11.2.0.2.0 - Production on 24-MAY-2017 23:32:00
Copyright (c) 1997, 2011, Oracle.  All rights reserved.
Used parameter files:

Used TNSNAMES adapter to resolve the alias
Attempting to contact (DESCRIPTION = (ADDRESS = (PROTOCOL = TCP)(HOST = target)(PORT = 1521)) (CONNECT_DATA = (SERVER = DEDICATED) (SERVICE_NAME = XE)))
OK (0 msec)

8. On the source server, check the database connection to the source database.

sqlplus system/manager@SOURCE

SQL*Plus: Release 11.2.0.2.0 Production on Wed May 24 23:35:47 2017
Copyright (c) 1982, 2011, Oracle.  All rights reserved.


Connected to:
Oracle Database 11g Express Edition Release 11.2.0.2.0 - 64bit Production


SQL>

Then select the hostname from v$instance.

SQL> SELECT host_name FROM v$instance;
HOST_NAME
----------------------------------------------------------------
source

Type exit to exit out of SQL*Plus.

SQL> exit

9. On the source server, check the database connection to the target database.

sqlplus system/manager@TARGET

SQL*Plus: Release 11.2.0.2.0 Production on Wed May 24 23:37:35 2017
Copyright (c) 1982, 2011, Oracle.  All rights reserved.


Connected to:
Oracle Database 11g Express Edition Release 11.2.0.2.0 - 64bit Production

SQL>

Then select the hostname from v$instance.

SQL> SELECT host_name FROM v$instance;
HOST_NAME
----------------------------------------------------------------
target

Type exit to exit out of SQL*Plus.

SQL> exit

10. On the target server, check the database connection to the source database.

sqlplus system/manager@SOURCE

SQL*Plus: Release 11.2.0.2.0 Production on Wed May 24 23:39:51 2017
Copyright (c) 1982, 2011, Oracle.  All rights reserved.


Connected to:
Oracle Database 11g Express Edition Release 11.2.0.2.0 - 64bit Production

SQL>

Then select the hostname from v$instance.

SQL> SELECT host_name FROM v$instance;
HOST_NAME
----------------------------------------------------------------
source

Type exit to exit out of SQL*Plus.

SQL> exit

11. On the target server, check the database connection to the target database.

sqlplus system/manager@TARGET

SQL*Plus: Release 11.2.0.2.0 Production on Wed May 24 23:40:39 2017
Copyright (c) 1982, 2011, Oracle.  All rights reserved.

Connected to:
Oracle Database 11g Express Edition Release 11.2.0.2.0 - 64bit Production

SQL>

Then select the hostname from v$instance.

SQL> SELECT host_name FROM v$instance;
HOST_NAME
----------------------------------------------------------------
target

Type exit to exit out of SQL*Plus.

SQL> exit

If any of the pre-requisites fail, then verify if all the previous steps have been done correctly before continuing.