I had a DB2 V8.1 fixpack 2 installation on one of my FC5 systems which I upgraded to the (currently) latest fixpack 12. After completing the upgrade and running the post install tasks (iupdate) I found I couldn't run any of the utils such as db2cc:
[db2inst1@medusa ~]$ db2cc
Writing Java core file ....
Written Java core to /tmp/javacore11599.1151439455.txt
DB2JAVIT : RC = 11
Oops! Something was clearly very wrong here. It turns out that the Java SDK (1.31) originally installed with DB2 doesn't work with FC5 or my kernel (2.6.17). My problem was resolved by downloading and installing the Java 1.42 SDK rpm from IBM, and running the following command as user db2inst1:
db2 update dbm cfg using JDK_PATH /opt/IBMJava2-142