I used the following procedures to enable core dumps in RHEL6.

# vi /etc/security/limits.conf

#* soft core 0
* soft core unlimited

# vi /etc/sysctl.conf

kernel.core_pattern = /tmp/core-%e-%s-%u-%g-%p-%t
fs.suid_dumpable = 2

%e is the filename
%g is the gid the processs was running under
%p is the pid of the process
%s is the signal that caused the dump
%t is the time the dump occurred
%u is the uid the process was running under

# vi /etc/sysconfig/init


# sysctl -p