I bet your database files are not upgraded to 8.1.7.0.

I can't get how you could open the DB from one or another release without errors. I wonder that since this is a patch release upgrade (http://docs.oracle.com/cd/A84870_01/doc/server.816/a76957/migintro.htm#10138), and the COMPATIBLE parameter in init file its in 8.1.5, when you start the DB from 8.1.7 it builds compatible memory and disk structures with 8.1.5 version and "works" (at least, it opens. But I wouldnt go with this even in TEST environment)

To check the DB version You can also use the DBMS_UTILITY.DB_VERSION procedure. I don't know if it will return the instance or the database files version. You can run something like this in sqlplus:

SQL> set serveroutput on
SQL> DECLARE
       v_version varchar2(10);
       v_comp varchar2(10);
     BEGIN
       DBMS_UTILITY.DB_VERSION ( v_version, v_comp);
       DBMS_OUTPUT.PUT_LINE ('DB Version: ' || v_version);
       DBMS_OUTPUT.PUT_LINE ('Compatibility: ' || v_comp);
     END;
     /

Another option is the hardway. In linux if I use strings with my SYSTEM TABLESPACE datafile I can grep the release version from them. But ... I cannot claim this is a reliable method :\

$ strings o1_mf_system_91ck66x1_.dbf | grep "[0-9]\{1,2\}\.[0-9]\{1\}" | grep -i "Catalog Views" | head
 Oracle Database Catalog Views Re Oracle XML Database Version 11.2
COracle Database Catalog Views Release 11.2.0.3.0 - 64bit Production"DBMS_REGISTRY_SYS.VALIDATE_CATALOG
COracle Database Catalog Views Release 11.2.0.3.0 - 64bit Production"DBMS_REGISTRY_SYS.VALIDATE_CATALOG
COracle Database Catalog Views Release 11.2.0.3.0 - 64bit Production"DBMS_REGISTRY_SYS.VALIDATE_CATALOG

Anyway, In a mess like this I'll go for export-import migration, and forget about what has been done in the past. You said you can perform export with no problems, right? If the database its now open with 8.1.5, and the application has been hard tested with no errors, let's assume it's on 8.1.5 and migrate. Perform a new fresh 8.1.7 install, stop the application, export every application related schema from the production DB, and import into the new 8.1.7. Done.

Now, me and everyone will tell you that this is ridiculous. Why this? I'll try to migrate to a new server and DB version at any cost precisely because the elderly nature of your environment will make it only harder and harder in the future, not to mention the lack of security and new features of having a 13 years old software release running in a server powerless that your cellphone.

I cant imagine a good reason to not migrate that server entirely, even more when (based on what you said) no one knows what kind of mess did in the past. Fix the problem, not the symptom =)

Regards

When it comes to software downloads for production use, the Oracle sites, thankfully, are a little less of a maze - provided that you are familiar with the entrance.

You can find the latest media packs for production use on the Oracle Software Delivery Cloud.

After logging in and accepting terms and export restrictions, select Oracle Database and Linux x86-64. After hitting Go, you should be able to find Oracle Database 11g Release 2 (11.2.0) Media Pack for Linux x86-64 and within; the Oracle Database 11g Release 2 Client (11.2.0.1.0) for Linux x86-64.

You can find Oracle Database 12c Release 1 (12.1.0.2.0) Media Pack for Linux x86-64 and the associated Oracle Database 12c Release 1 Client (12.1.0.2.0) for Linux x86-64 (64-bit) in much the same way.

The patch from 11.2.0.1.0 to 11.2.0.2.0 should be downloaded from Metalink / My Oracle Support.

Starting with 11.2.0.2.0, any subsequent updates can be downloaded from with the installer itself, either as an integrated part of the installation process, or in advance (useful when destined server is restricted from accessing the Internet) by running the installer with the option -downloadUpdates.

I guess you have already considered just running the datapump tools from the actual Oracle home of the database in question?

These days, you may also be offered to try out a new and enhanced version of the software delivery cloud. Look for a big link on the landing page/login page.

On a final note, lots of additional information can be found in the Client Installation Guides available in the Oracle Database Online Documentation 11g Release 2 (11.2) or Oracle Database Online Documentation 12c Release 1 (12.1).