If you are like me, you had some trouble getting apache to dump core on a RHEL5 system. The following steps have produced positive results for me:

echo "ulimit -c unlimited >/dev/null 2>&1" >> /etc/profile
echo "DAEMON_COREFILE_LIMIT='unlimited'" >> /etc/sysconfig/init
echo 1 > /proc/sys/fs/suid_dumpable
echo "core.%p" > /proc/sys/kernel/core_pattern
echo "CoreDumpDirectory /var/apache-core-dumps" > \
/etc/httpd/conf.d/core_dumps.conf
mkdir /var/apache-core-dumps
chown apache: /var/apache-core-dumps
source /etc/profile
/etc/init.d/httpd restart

Now you can test it by sending a SIGSEGV to a random apache child process:

# tail -f /var/log/httpd/error_log | grep -i seg &
# ps auxwww |grep httpd (pick a random pid not owned by root)
# kill -11 2014
# [Mon Jul 06 21:05:39 2009] [notice] child pid 2014 exit signal
Segmentation fault (11), possible coredump in /var/apache-core-dumps
# cd /var/apache-core-dumps
# ls
core.2014

You can then get a backtrace using gdb:

# gdb /usr/sbin/httpd core.2014
(gdb) > bt full

I hope this helps someone. Please feel free to comment.