The situation specific to old and tight number of Oracle Products used Oracle Universal Installer for lifetime maintenance.
orabase binary executable is used by Oracle products to set ORACLE_BASE environmental variable in the shell session. Contemporary Oracle products have a file $ORACLE_HOME/install/orabasetab which is read by orabase executable to set ORACLE_BASE for current ORACLE_HOME. Some older orabase (32-bit) executables read the file $ORACLE_HOME/inventory/ContentsXML/oraclehomeproperties.xml in order to set ORACLE_BASE.
The issue can be a result of an accident when sometimes (and somehow) the Oracle installer (via installation of the patches or performing a deinstallation (even being operating on another ORACLE_HOME)) corrupts oraclehomeproperties.xml file (located in $ORACLE_HOME/inventory/ContentsXML) cutting out property ORACLE_BASE from it. The fix is to restore it from backup or modify manually.
The following example is an example of corrupted xml file :
<?xml version="1.0" encoding="UTF-8"?>
<!-- Copyright (c) 1999, 2015, Oracle and/or its affiliates.
All rights reserved. -->
<!-- Do not modify the contents of this file by hand. -->
<ORACLEHOME_INFO>
<GUID>113393302.#259383652</GUID>
<HOME/>
<ARU_PLATFORM_INFO>
<ARU_ID>226</ARU_ID>
<ARU_ID_DESCRIPTION>Linux x86-64</ARU_ID_DESCRIPTION>
</ARU_PLATFORM_INFO>
</ORACLEHOME_INFO>
The following example is an example of restored xml file :
<?xml version="1.0" encoding="UTF-8"?>
<!-- Copyright (c) 1999, 2015, Oracle and/or its affiliates.
All rights reserved. -->
<!-- Do not modify the contents of this file by hand. -->
<ORACLEHOME_INFO>
<GUID>113393302.#259383652</GUID>
<HOME/>
<ARU_PLATFORM_INFO>
<ARU_ID>226</ARU_ID>
<ARU_ID_DESCRIPTION>Linux x86-64</ARU_ID_DESCRIPTION>
</ARU_PLATFORM_INFO>
<PROPERTY_LIST>
<PROPERTY NAME="ORACLE_BASE" VAL="/u01/app/oracle"/>
</PROPERTY_LIST>
</ORACLEHOME_INFO>
After modification you should relogin to the server because the contents of corrupted xml for the current session is mapped into the memory (by mmap syscall).
Good Luck !
